Chapter 24 - The Digestive System

What is digestion.

Food broken down into molecules small enough to be absorbed by body cells.

What is embedded in the lamina propria of the villi?

- Arterioles - venules - blood capillary network - lacteal.

What are the layers of the GI Tract?

- Mucosa - Submucosa - Muscularis - Serosa

What is the physiology of the esophagus?

- Secretes mucus - transports food into stomach. Does not: - produce digestive enzymes - perform absorption.

What stimulates HCl secretion by parietal cells?

1) Acetylcholine: - Released by parasympathetic nervous system neurons 2) Gastrin: - Secreted by G cells 3) Histamine: - Paracrine substance - released by mast cells - in nearby lamina propria. Acetylcholine and Gastrin: - Stimulate parietal cells to secrete more HCl - in the presence of histamine. Histamine: - synergistic by enhancing the effects of - acetylcholine and gastrin. Receptors - Present in plasma membrane of parietal cells. Histamine H2 Receptors: - on parietal cells - mediate different responses than H1 receptors (involved in allergic reactions).

Absorption of amino acids and dipeptides, tripeptides in the small intestine.

1) Amino acids - absorbed via active transport in duodenum and jejunum - Half amino acids absorbed are present in food - other half absorbed from dead cells that come off mucosal surface and in digestive juices - 95-98% of protein in small intestine digested and absorbed Amino Acid Transporters: - Na+-dependent active transport - or by themselves. 2) Dipeptides and Tripeptides Symporter brings in: - dipeptides and tripeptides with H+ - peptides hydrolyzed to single amino acids inside absorptive cells - move out of absorptive cells via diffusion - enter villus capillaries - transported through hepatic portal system to liver - hepatocytes remove some - the rest enter general circulation.

Absorption of Electrolytes by the Small Intestine.

1) Electrolytes - Come from GI tract secretions - Are compounds that separate into ions and water and conduct electricity. 2) Sodium Ions - Move into absorptive cells - via diffusion and secondary active transport Once in cells: - they are actively transported out of absorptive cells - via basolateral sodium-potassium pumps - Na+/K+ ATPases - most sodium ions in GI tract reabsorbed - not lost in feces. 3) Negatively charged: - bicarbonate - chloride - iodide - nitrate ions -Passively follow sodium or actively transported. 4) Calcium Ions: - Absorbed actively - with help of calcitriol. 5) Iron, Potassium, Magnesium, Phosphate: - Absorbed via active transport mechanisms

Absorption of Vitamins by the Small Intestine.

1) Fat-soluble Vitamins - A, D, E, K - are ingested with dietary lipids in micelles - absorbed via simple diffusion. 2) Water-Soluble Vitamins - B & C - absorbed via simple diffusion 3) Vitamin B12 - combines with intrinsic factor - produced by stomach Combination of B12 and intrinsic factor: - absorbed in ileum of small intestine - via an active transport mechanism.

Table 24.8: Major Hormones that Control Digestion.

1) Gastrin - released by enteroendocrine G cells - located mostly in mucosa of pyloric antrum of stomach Stimulated by: - Distention of stomach - partially digested proteins - caffeine in stomach - high pH of stomach chyme Actions Major Effects: - Promotes secretion of gastric juice - increases gastric motility - promotes growth of gastric mucosa. Minor Effects: - Constricts lower esophageal sphincter - relaxes pyloric sphincter. 2) Secretin - released by enteroendocrine S cells - in mucosa of duodenum Stimulated By: - Acidic (high H+ level) chyme - that enters small intestine Actions Major Effects: - Stimulates release of pancreatic juice and bile - high in bicarbonate ions (HCO3-). Minor Effects: - Inhibits gastric juice secretion - promotes normal growth and maintenance of pancreas - enhances effects of CCK. 3) Cholecystokinin (CCK) - released by enteroendocrine CCK cells - in mucosa of small intestine - released by the brain Stimulated By: - Partially digested amino acids (proteins) - triglycerides - fatty acids - that enter the small intestine Actions Major Effects: - Stimulates secretion of pancreatic juice rich in digestive enzymes - causes ejection of bile from gallbladder - opens sphincter of hepatopancreatic ampulla (sphincter of Oddi) - induces satiety. Minor Effects: - Inhibits gastric emptying - promotes normal growth and maintenance of pancreas - enhances effects of secretin.

Describe the Histology of the Liver.

1) Hepatocytes: - Major functional cells of liver. - Specialized epithelial cells - 5-12 sides - 80% of volume of liver. Functions: - Metabolic - secretory - endocrine. Hepatic Laminae: - Three-dimensional arrangements - Plates of hepatocytes - one cell, thick bordered - on either side of hepatic sinusoids (endothelial-lined vascular spaces) - Highly branched - irregular structures. Grooves between hepatocytes: - space for canaliculi - where hepatocytes secrete bile. 2) Bile Canaliculi: - Small ducts between hepatocytes - collect bile from hepatocytes. Bile canaliculi to - bile ductules to - bile ducts to - merge to form right and left hepatic ducts to - unite to form common hepatic duct that exits the liver. Common hepatic duct - joins cystic duct from gallbladder to - form common bile duct - bile enters small intestine to - participate in digestive functions. 3) Hepatic Sinusoids - Highly permeable blood capillaries - between rows of hepatocytes Receive oxygenated blood from: - hepatic artery Nutrient rich deoxygenated blood from: - hepatic portal vein Hepatic Portal Vein: - brings venous blood from - GI organs and spleen to - liver. Hepatic Sinusoids: - merge to deliver blood into central vein to - hepatic veins to - inferior vena cava. Stellate Reticuloendothelial (Kupffer) Cells: - Fixed Phagocytes - destroy worn out white and red blood cells, bacteria, other foreign matter in venous blood draining form GI tract.

Review: What are the functions of the Digestive System?

1) Ingestion: - taking food in mouth 2) Secretion: Into lumen of GI tract - release of water - acid - buffers - enzymes 3) Mixing and Propulsion: Through GI tract - churning - propulsion of food 4) Digestion: - mechanical and chemical breakdown of food 5) Absorption: - passage of digested products from GI tract into blood and lymph. 6) Defecation: - elimination of feces from GI tract.

Describe chemical digestion of the stomach

1) Parietal cells secrete: - into stomach lumen - hydrogen ions and chloride ions = hydrochloric acid. 2) Proton Pumps powered by: H+/K+ ATPases - actively transport H+ into lumen of stomach - while K+ is brought into the cell (out of stomach lumen). 3) Cl- and K+: - diffuse into lumen through K+ and Cl channels - in the apical membrane. 4) Enzyme carbonic anhydrase (plentiful in parietal cells): - catalyze formation of carbonic acid (H2CO3) - from water (H2O) and carbon dioxide (CO2). 5) Carbonic acid dissociates: - provides a lot of H+ for proton pumps - generates bicarbonate ions (HCO3-). 6) HCO3- build up in cytosol: - it exits through parietal cells - in exchange for Cl- - via the Cl-/HCO3- antiporters - in the basolateral membrane (next to lamina propria). 7) Alkaline Tide: - HCO3- diffuses into nearby capillaries - Elevates pH slightly - more alkaline urine.

How does pepsin not eat away at the stomach lining?

1) Pepsin: - secreted in inactive form pepsinogen by chief cells - where it cannot digest proteins in chief cells - must come in contact with HCl secreted by parietal cells - to be converted to pepsin. 2) Stomach epithelial cells: - protected from gastric juice by a 1-3 mm thick layer of alkaline mucus which is - secreted by mucous cells and mucous neck cells.

Describe the substances involved in digestion.

1) Strong acidity in stomach: - kills microbes in food 2) HCl: Secreted by parietal cells - partially unfolds proteins in food - stimulates secretion of hormones - promotes flow of bile and pancreatic juice. 3) Enzymatic digestion of proteins: - begins in stomach. 4) Pepsin: Secreted by chief cells - proteolytic (protein digesting) enzyme in stomach - severs peptide bonds between amino acids - breaking protein chain of amino acids into - smaller peptide fragments - Most effective in acidic environment (pH 2) - becomes inactive at high pH levels. 5) Gastric Lipase - splits short chain triglycerides (fats and oils) in fat molecules (found in milk) into - fatty acids and monoglycerides Monoglyceride: - glycerol molecule - attached to one fatty acid molecule - Limited role in adult stomach - functions at a pH 5-6. 6) Pancreatic Lipase: - enzyme secreted by pancreas into small intestine.

Figure 24.22: Daily Volumes of fluid ingested, secreted, absorbed, excreted from GI tract.

All water absorption in GI tract occurs - via osmosis. Fluid Balance in GI Tract: Ingested and Secreted. a) Saliva - 1 liter b) Ingestion of Liquids - 2.3 liters c) Gastric Juice - 2 liters d) Bile - 1 liter e) Pancreatic Juice - 2 liters f) Intestinal Juice - 1 liter Total Ingested and Secreted = 9.3 liters. Absorbed. a) Small Intestine - 8.3 liters b) Large Intestine - 0.9 liters Total Absorbed = 9.2 liters Excreted in Feces - 0.1 liter

Functions of the Stomach

1. Mixes: - saliva - food - gastric juice - to form chyme 2. Serves as: - reservoir for food - before released into small intestine 3. Secretes gastric juice: - which contains HCL (kills bacteria and denatures protein) - pepsin (begins the digestion of proteins) - intrinsic factor (aids absorption of vitamin B12) - gastric lipase (aids digestion of triglycerides) 4. Secretes gastrin: - into blood.

What is the neural innervation of the Enteric Nervous System?

100 million neurons: - extend from esophagus to anus. Types of Neurons: - Motor neurons - interneurons - sensory neurons Interneurons: - Connect the neurons of the myenteric - and submucosal plexuses. Sensory Neurons - Supply mucosal epithelium As chemoreceptors: - activated by a presence of a certain chemical in food - located in lumen of GI tract As stretch receptors - activated when food distends the wall of the GI organ Two Plexuses: 1) Myenteric Plexus (Plexus of Auerbach): - Located between longitudinal - and circular smooth muscle layers - of muscularis. Motor Neurons: - Supply smooth muscle of muscularis - mostly control motility of GI tract - frequency, strength of contraction of muscularis. 2) Submucosal Plexus (Plexus of Meissner): - Found within submucosa. Motor Neurons: - Supply secretory cells of mucosal epithelium - controlling secretions of the organs of GI tract.

Describe the development of the Digestive System.

4th Week 1) Cells of endoderm form cavity called primitive gut (forerunner of GI tract). 2) Mesoderm forms and splits into two layers (somatic and splanchnic). 3) Splanchnic mesoderm associates with endoderm of primitive gut - forming a double layer wall in primitive gut. 4) Endodermal layer - gives rise to epithelial lining and glands of most of GI tract. 5) Mesodermal layer - produces smooth muscle and connective tissue of the GI tract. 6) Primitive gut elongates and differentiates into an anterior foregut, intermediate midgut. 5th Week 1) Midgut opens into yolk sac 2) Yolk sac constricts - detaches from midgut - midgut seals. 3) Stomodeum appears - in region of forgut - is depression consisting of ectoderm - develops into oral cavity. 4) Oropharyngeal Membrane - depression of fused ectoderm and endoderm on surface of embryo - separates foregut from stomodeum. 5) Proctodeum - depression consisting of ectoderm - forms hindgut and develops into anus. 6) Cloacal Membrane - fused membrane of ectoderm and endoderm - separates hindgut from proctodeum. 7th Week 1) Proctodeum ruptures 2) Hindgut is continuous with outside of embryo through the anus 3) GI tract forms continuous tube from mouth to anus. ** Foregut develops into: - pharynx, esophagus, stomach, part of duodenum. ** Midgut develops into: - remainder of duodenum, jejunum, ileum, portions of large intestine (cecum, appendix, ascending colon, most of transverse colon). ** Hindgut develops into: - remainder of large intestine, except portion of anal canal that is derived from proctodeum. Development Progresses: Endoderm along foregut develop into hollow buds of mesoderm - develop into salivary glands, liver, gallbladder, pancreas - all retain connection with GI tract through these ducts.

Figure 24.21: Absorption of digested nutrients in the small intestine - Movement of Absorbed Nutrients into Blood and Lymph.

A) Monosaccharides, Small short-chain fatty acids, Amino Acids - travel in the hepatic portal circulation to - liver - via the hepatic portal vein. B) Large-short chain fatty acids and monoglycerides - travel in chylomicrons - via the lymphatic circulation to - thoracic duct to - enter blood at left subclavian vein.

What are pylorospasm and pyloric stenosis?

Abnormalities that occur in infants. Pylorospasm: - Smooth muscle fibers of the pyloric sphincter - don't relax properly - prevents food from entering small intestine - stomach becomes too full - infant throws up to relieve pressure - treated by drugs that relax muscle fibers in the pyloric sphincter. Pyloric Stenosis: - Narrowing of pyloric sphincter - corrected surgically - projectile vomiting.

Describe Absorption in the Small Intestine.

Absorption - Passing of digested nutrients from GI tract to the blood. Occurs via: - diffusion - facilitated diffusion - osmosis - active transport 90% in small intestine 10% in stomach and large intestine Undigested or unabsorbed material TO - large intestine. Chemical and mechanical phases of digestion from mouth to small intestine - changing food to forms that pass through absorptive cells that line mucosa - underlying blood and lymphatic vessels. Carbohydrates: glucose, fructose, galactose to - monosaccharides Proteins: to - single amino acids, dipeptides, tripeptides. Triglycerides: to - fatty acids, glycerol, monoglycerides.

What is the histology of the pancreas?

Acini: - Small clusters of glandular epithelial cells - Exocrine portion of pancreas. Pancreatic Juice: - Secreted by acini Cells - mixture of fluid and digestive enzymes Pancreatic Islets - Remaining 1% of clusters - Endocrine portion of pancreas Secretes hormones: - glucagon - insulin - somatostatin - pancreatic polypeptide.

Describe Peritonitis.

Acute inflammation of the peritoneum - contamination of peritoneum by infectious microbes. Cause: - accidental or surgical wounds puncturing abdominal wall - perforation or rupture of abdominal organs. Example: Bacteria enters peritoneal cavity through - intestinal perforation or rupture of appendix - produce acute, life-threatening form of peritonitis. Less Serious: - Rubbing together of the peritoneal surfaces - causing inflammation. Using peritoneal wall for filtering kidneys are at high risk.

How is alcohol absorbed?

Alcohol: Lipid-soluble - Begins absorption in stomach - more surface area in small intestine - alcohol passes into duodenum - absorbed more rapidly. Slows alcohol absorption: Fatty foods (hamburgers, nachos, pizza) - fatty acids in chyme slows gastric emptying. Gastric mucosa cells contain: - dehydrogenase (60% less in females than males) - breaks down some alcohol into acetaldehyde - not so intoxicating.

What is appendicitis?

Appendicitis: - Inflammation of appendix - precedes obstruction of lumen of appendix by chyme - inflammation or foreign body - carcinoma of cecum - stenosis - kinking of organ. Symptoms: - High fever - high WBC count - neutrophil count higher than 75%. - Referred pain in the umbilical region - anorexia (loss of appetite for food) - nausea - vomiting Following infection: - Result in edema, ischemia - may progress to gangrene and perforation within 24 hours. Pain localizes in: - right lower quadrant - continues as dull or severe pain - intensified by coughing, sneezing or body movements. Appendectomy: - safer to operate than risk of rupture, peritonitis, gangrene - Now performed laparoscopically.

Describe the Submucosa Layer of the GI tract.

Areolar connective tissue: - binds mucosa to muscularis Contains: - blood and lymph vessels - receive absorbed food molecules. Submucosal plexus: - Extensive network of neurons. - May contain glands and lymphatic tissue.

What are liver function tests?

Blood tests used to determine certain chemicals released by liver cells - monitor and evaluate certain liver diseases and damage. Chemicals Detected: - Albumin globulinase - alanine aminotransferase (ALT) - aspartate aminotransferase (AST) - alkaline phosphate (ALP) - gamma-glutamyl-transpeptidase (GGT) biliruben. Common Causes of elevated liver enzymes: - Non-steroidal anti-inflammatory drugs - cholesterol-lowering medications - some antibiotics - alcohol - diabetes - infections (viral hepatitis and mononucleosis) - gallstones - tumors of the liver - excessive use of herbal supplements - kava, comfrey, pennyroyal, dandelion root, skullcap, ephedra.

Describe the Cephalic phase of digestion.

CEPHALIC PHASE 1) Smell, sight, thought, initial taste of food Activates neural centers in: - cerebral cortex - hypothalamus - brain stem. 2) Brain stem activates - facial (VII) - glossopharyngeal (IX) - vagus (X) nerves 3) Facial and glossopharyngeal nerves: - stimulate salivary glands - to secrete saliva 4) Vagus nerve: - stimulates gastric glands - secrete gastric juice. Purpose: - Prepare mouth and stomach for food - that is about to be eaten.

What is vomiting?

Called Emesis: - Forcible expelling of contents from stomach - sometimes duodenum through mouth. Stimuli: - Distention and irritation of stomach - Unpleasant sights or smells - general anesthesia - dizziness - certain drugs such as morphine and derivatives digitalis. Nerve Impulses: - Sent to vomiting center in medulla oblongata - returning impulses sent to GI tract organs, diaphragm, abdominal muscles. Squeezing of stomach between diaphragm and abdominal muscles: - stomach sends contents into open esophageal sphincter Prolonged vomiting: - especially in infants and elderly - serious - loss of gastric juice - lead to alkalosis (higher than normal pH) - dehydration - damage to esophagus and teeth.

Describe the Anatomy of the Liver

Completely covered by: - visceral peritoneum Almost completely covered by: - dense irregular connective tissue - lies deep to peritoneum. Two Lobes: - Large right lobe - smaller left lobe - connected by falciform ligament (fold of mesentary). Inferior quadrate lobe and posterior caudate lobe - belongs in left lobe. Ligaments Falciform Ligament: - Suspends liver in abdominal cavity - extends from under-surface of diaphragm to superior surface of liver. Ligamentum Teres (Round Ligament): Fibrous cord - in free border of falciform ligament - remnant of umbilical vein in fetus - extends from liver to umbilicus. Right and Left Coronary Ligament: Narrow extensions of parietal peritoneum - suspends liver from diaphragm.

Table 24.1: Summary of Digestive Activities of Mouth

Cheek and Lips: - Keep food between teeth - foods uniformly chewed during mastication. Salivary Glands: - Secrete saliva - keeps lining of mouth and pharynx, moistened and lubricated - softens, moistens, dissolves food, cleanses mouth and teeth. Salivary amylase - splits starch into maltose, maltotriose, a-dextrins. Tongue Extrinsic Tongue Muscles: - Move tongue side to side, in and out - maneuvers food during mastication, shapes bolus, maneuvers food during swallowing. Intrinsic Tongue Muscles: Alter shape of tongue - swallowing and speech. Taste Buds: - Receptors for gustation and taste - sense food in mouth - secrete saliva stimulated by nerve impulses from taste buds to - salivary nuclei in brain stem to - salivary glands. Lingual Glands: - Secrete lingual lipase - break down triglycerides into fatty acids and diglycerides. Teeth: - Cut, tear, pulverize food - reduce foods into smaller pieces for swallowing.

Figure 24.19: Histology of the Small Intestine.

Circular folds, villi, microvilli: - increase surface area of the small intestine for digestion and absorption. Mucosa Cells: - Blood capillary - lacteal - lamina propria - intestinal gland - muscularis mucosae. Microvilli: - absorptive Cell - absorbs nutrients Goblet Cell: - Secretes mucus Enteroendocrine Cell Secretes Hormones: - secretin - cholecystokinin - or glucose-dependent insulinotropic peptide (GIP) Paneth Cell Secretes: - lysozyme - capable of phagocytosis Submucosa Contains: - arteriole - venule - lymphatic vessel.

Describe the Defecation Reflex.

DEFECATION REFLEX - Pushing of feces from sigmoid colon to rectum - triggers this reflex. 1) Response to distention of rectal wall: - receptors send sensory nerve impulses to - sacral spinal cord - Motor impulses from sacral spinal cord travel - along parasympathetic nerves back to- descending colon, sigmoid colon, rectum, anus. 2) Contraction of longitudinal smooth muscle fibers: - causes rectum to shorten - increasing pressure in the rectal cavity 3) Pressure within rectum: - contraction of diaphragm - contraction of abdominal muscles - parasympathetic stimulation leads to - internal anal sphincter opening 4) External anal sphincter (voluntarily controlled) Relaxed: - defecation occurs through anus External anal sphincter not relaxed: - defecation is postponed. Bowel Movements: - Vary between 2-3 per day - or 3-4 per week - Depends on diet, stress, exercise. DIARRHEA - Increase in fluid, frequency and volume of feces - increased motility - decreased absorption of water in the intestines - can lead to dehydration - electrolyte imbalance. Caused by: - lactose intolerance - stress - microbes that irritate the GI mucosa. CONSTIPATION - Infrequent - difficult defecation - due to decreased motility of intestines - Excessive water absorption - feces become hard and dry. Caused by: - poor habits (delaying defecation) - spasms of colon - inadequate fluid intake - insufficient fiber diet - lack of exercise - emotional stress - certain drugs.

Describe Deglutition.

Deglutition or Swallowing: - Movement of food from mouth to stomach. Facilitated By: - Saliva and mucus Involves: - mouth - pharynx - esophagus. Three Stages of Swallowing - Takes approximately 4-8 seconds (solid or semisolid food) - 1 second for liquid or soft food 1) Voluntary stage: - bolus passes from mouth to oropharynx - by movement of tongue upward and backward against palate. 2) Pharyngeal stage: - involuntary passing of bolus - from pharynx -esophagus Deglutition Center: - Bolus stimulates receptors in the oropharynx - send impulses to medulla oblongata and lower pons in brain stem - impulses return to soft palate and uvula - close off nasopharynx - prevent food and liquid from entering nasal cavity. Epiglottis closes opening to larynx: - prevent food from entering respiratory tract. Bolus moves from oropharynx - laryngopharynx - upper esophageal sphincter relaxes - bolus moves into esophagus. 3) Esophageal stage: - involuntary passing of bolus from esophagus - stomach. - Bolus enters esophagus - peristalsis - lower esophageal sphincter relaxes - bolus enters stomach. - Mucus secreted by esophageal glands moisten bolus - reduces friction. Peristalsis Alternating contraction and relaxation of: - longitudinal and circular smooth muscle in esophagus - pushes bolus down Circular muscles above bolus contract: - push bolus down Longitudinal muscles contract: - widening area below bolus - allowing bolus to move towards stomach.

What is dietary fiber?

Dietary Fiber Indigestible plant carbohydrates: - cellulose - lignin - pectin - found in fruits, vegetables, grains, beans. Insoluble Fiber - Does not dissolve in water - woody or structural parts of plants - such as skins of fruits, vegetables and bran coating around wheat and corn kernels - passes through GI tract unchanged - quickly moves other materials through the GI tract. Soluble Fiber - Dissolves in water - forms gel that slows material through tract - in beans, oats, barley, broccoli, prunes, apples, citrus fruits. Fiber-rich Diet Reduce risk of: - obesity - diabetes - atherosclerosis - gallstones - hemorrhoids - diverticulitis - appendicitis - colorectal cancer. Soluble fiber - may lower blood cholesterol - liver uses cholesterol to make bile salts which helps break down triglycerides - soluble fiber binds to the bile salts and is defecated - liver then has to make more bile salts using more cholesterol = reduced cholesterol levels.

Absorption of Lipids by the Small Intestine.

Dietary Lipids - Absorbed via simple diffusion - 95% of lipids in adults absorbed. 1) Triglycerides: - Broken down into fatty acids and monoglycerides. 2) Small Short-chain Fatty Acids: - Are small - contain 10-20 carbon atoms - water soluble - easily dissolved in watery intestinal chyme - pass through absorptive cells via simple diffusion - enter villus capillaries - transported through hepatic portal system - those not removed by hepatocytes in the liver enter general circulation. 3) Large short-chain Fatty Acids: - Contain more than 10-20 carbon atoms. 4) Hydrophobic Triglycerides - Large short-chain fatty acids - Long-chain fatty acids Monoglycerides: - Larger, hydrophobic - not water soluble Bile salts surround: - large short chain fatty acids - long-chain fatty acids - monoglycerides - forming micelles. Micelles - Tiny spheres 10-20 um in diameter - 20-50 bile salts that surround the hydrophobic triglycerides. Formed because of the: - amphipathic (hydrophilic and hydrophobic) nature of bile salts Also solubilizes: - hydrophobic molecules such as - fat-soluble vitamins (A, D, E, K) - and cholesterol that may be present in chyme - aids in their absorption. Once micelles formed - move from interior of lumen of small intestine to brush-border of absorptive cells - where the large short-chain fatty acids, long-chain fatty acids and monoglycerides diffuse out of micelles - absorptive cells - leave micelles behind in chyme - micelles continue the process by picking up more of the triglycerides. Hydrophobic region of bile salts - interact with: - large short-chain fatty acids - long-chain fatty acids - monoglycerides. Hydrophilic region of bile salts: - interact with the watery intestinal chyme. Chylomicrons - Large spherical masses of aggregated globules - coated with proteins (prevents chylomicrons from bonding to each other, helps suspend them in blood) Contains: - monoglycerides - long-chain fatty acids - combined to form triglycerides and phospholipids and cholesterol Located: - inside the absorptive cells. Chylomicrons - leave absorptive cells via exocytosis - cannot enter blood capillaries due to size - enter lacteals instead (larger pores than capillaries) - chylomicrons transported through lymphatic vessels to - thoracic duct to - enter blood stream via left subclavian vein. Lipoprotein Lipase - Removes the chylomicrons from the blood as it passes from blood - liver and adipose tissue Breaks down: - trigylcerides in chylomicrons, other lipoproteins to - fatty acids and glycerol Fatty acids diffuse: - into hepatocytes and adipose cells - combine with glycerol - during resynthesis of triglycerides. Enterohepatic Circulation - Reabsorption of bile salts by active transport in final segment of small intestine - returned by blood to the liver through the hepatic portal system for recycling. Bile salt secretion by hepatocytes into bile -reabsorption of bile salts by ileum - resecretion into bile by hepatocytes = enterohepatic circulation. Insufficient Bile Salts: - Obstruction of bile ducts or removal of gallbladder - results in 40% loss of lipids in feces - diminished lipid absorption - fat-soluble vitamins not adequately absorbed.

Figure 24.10: Deglutition (swallowing).

During pharyngeal stage: - tongue rises against the palate - nasopharynx is closed off - larynx rises - epiglottis seals off larynx - bolus passed into esophagus. During Esophageal Stage: - Food moves through esophagus - into stomach via peristalsis. Deglutition: - is a mechanism that moves food - from mouth into the stomach. c) Anterior view of frontal sections of peristalsis in esophagus. Esophagus: - relaxed muscularis - circular muscles contract moves - bolus - longitudinal muscles contract - relaxed muscularis - lower esophageal sphincter relaxing bolus moves - stomach.

Figure 24.3: Organization of the Enteric Nervous System.

Enteric Nervous System 1) Myenteric Plexus From Myenteric Plexus to - Motor Neuron to - Longitudinal and circular muscles of the muscularis layers 2) Myenteric Plexus From Myenteric Plexus to - Interneuron to - Submucosal Plexus to - Motor Neuron to - Mucosal Epithelium 3) Myenteric Plexus / ANS and CNS neurons From Myenteric Plexus / ANS and CNS neurons to - Sensory Neuron to - Mucosal Epithelium

Describe the Esophagus.

Esophagus: - 25 cm long - collapsible muscular tube - lies posterior to trachea Begins at: - Inferior end of laryngopharynx - inferior aspect of neck Enters mediastinum: - anterior to vertebral column - esophageal hiatus (opening in diaphragm) Ends at: - superior portion of stomach. Hiatus Hernia: - Portion of stomach protrudes above diaphragm - through esophageal hiatus.

Describe the absorption and feces formation in large intestine.

Feces: - Solid or semisolid chyme - has remained in large intestine - for 3-10 hours. Consists of: - water - inorganic salts - sloughed off epithelial cells from mucosa of GI tract - bacteria - products of bacterial decomposition - unabsorbed digested materials - indigestible parts of food. Water Balance: - Large intestine absorbs a large amount of water - leaving only 100-200 mL of water - out of .5-1 liters of water that enters large intestine. Absorption: - Water - ions - sodium and chloride - some vitamins.

Describe the Chemical Digestion in the Large Intestine.

Final Stage of Digestion: - Occurs in colon - through activity of bacteria that inhabit the lumen. Mucus secreted by glands: - no enzymes secreted. Bacteria - Prepares chyme for elimination Ferment: - any remaining carbohydrates Release: - hydrogen - carbon dioxide - methane gases = flatulence Converts remaining proteins: - amino acids Break down amino acids: - simpler substances - indole - skatole - hydrogen sulfide - fatty acids Indole, skatole: - eliminated in feces - contributes to its odor - rest is transported to liver - compounds converted to less toxic compounds and excreted in urine. Bacteria decompose bilirubin: - simpler pigments - including stercobilin - gives feces its brown color. Some Bacterial products absorbed by Colon: - Vitamins needed for metabolism - B and K vitamins.

Figure 24.25: Neural negative feedback regulation of the pH of gastric juice and gastric motility during the gastric phase of digestion.

Food entering the stomach stimulates: - secretion of gastric juice - causes vigorous waves of peristalsis. Food entering stomach disrupts homeostasis: Increasing 1) pH of gastric juice 2) Distention (stretching) of stomach walls Chemoreceptors and stretch receptors in stomach detect: - pH increase - distention Input - Nerve impulses to - Control Center to - Submucosal Plexus Output - Nerve impulses (parasympathetic) To Effectors: - parietal cells secrete HCl - smooth muscle in stomach wall contracts more vigorously Increase in: - acidity of stomach chyme - mixing of stomach contents - emptying of stomach Return to homeostasis when: - response brings pH of gastric juice - distention of stomach walls - back to normal (pre-eating status).

What is the histology of the small intestine?

Four Layers - mucosa - submucosa - muscularis - serosa 1) Mucosa of Duodenum - Layer epithelium containing many cells - lamina propria muscularis mucosae. a) Epithelium: Simple columnar Contains Cells Absorptive Cells: - Digest - absorb nutrients in small intestine chyme. Goblet Cells: - Secrete mucus. Intestinal Glands (crypts of Lieberkuhn): - The glandular epithelium - lining the crevices of the small intestine - secrete intestinal juice. Paneth Cells: - Secrete lysozyme - bactericidal enzyme - capable of phagocytosis - Regulate microbial population in small intestine. Enteroendocrine Cells: - S cells - CCK cells - K cells - secrete hormones secretin - cholecystokinin (CCK) - glucose-dependent insulinotropic peptide (GIP). b) Lamina Propria - Areolar connective tissue - mucosa associated lymphatic tissue (MALT). Solitary Lymphatic Nodules: - Mostly in distal part of ileum. Aggregated lymphatic nodules or Peyers patches: - Present in ileum. c) Muscularis Mucosae - Consists of smooth muscle. 2) Submucosa of Duodenum Duodenal Glands (Brunners glands): - Secrete alkaline mucus - helps neutralize gastric acid in chyme. 3) Muscularis of Small Intestine Two layers of smooth muscle Outer Layer: - Longitudinal smooth muscle fibers. Inner Layer: - Thicker layer of circular smooth muscle fibers. 4) Serosa or Visceral Peritoneum - Completely surrounds small intestine - except for major portion of duodenum. Structural Features aid in absorption and Digestion Circular folds or plicae circulares: - folds of mucosa and submucosa Permanent ridges: - 10 mm long - begin near proximal portion of duodenum - end midpoint of ileum - Enhance absorption - increases surface area - causes chyme to spiral through small intestine. Villi - Fingerlike projections of mucosa - increases surface area of epithelium available for absorption and digestion - intestinal mucosa appears velvety Covered by: - epithelium - core of lamina propria Embedded in lamina propria are: - arterioles - venules - blood capillary network - lacteal (lymphatic capillary). Nutrients absorbed by epithelial cells covering the villus: - pass through wall of capillary or lacteal to - blood or lymph. Microvilli - Projections of apical (free) membrane of absorptive cells. Each microvillus: - 1 um long cylinder shaped membrane-covered projection - contains bundles of 20-30 actin filaments. Brush Border - Microvilli as seen on a light microscope - 200 million microvilli per sq inch - increases surface area of plasma membrane Contains: - brush border enzymes - role in digestive functions.

What is the histology of the Large Intestine.

Four Layers: Mucosa, submucosa, muscularis, serosa. 1) Mucosa - Epithelium - Lamina Propria (Areolar Connective Tissue) - Muscularis Mucosae (Smooth Muscle). Epithelium: - simple columnar epithelium Absorptive cells: - Absorb water - contain some microvilli Goblet cells: - Secrete mucus - lubricates passage of colonic contents. Crypts of Lieberkuhn: - Long, straight tubular glands - contain absorptive and goblet cells - extend full length of mucosa - may extend into submucosa and muscularis mucosae. 2) Submucosa - Areolar connective tissue. 3) Muscularis - External layer of longitudinal smooth muscle - internal layer of circular smooth muscle. Teniae Coli: - Three bands of thickened longitudinal smooth muscle - single layer of circular smooth muscle lying between the teniae coli. Haustra: - Series of pouches - created by tonic contractions of the large intestine - give colon a puckered appearance. 4) Serosa - Part of visceral peritoneum. Omental (fatty) Appendices: - Small pouches of visceral peritoneum filled with fat - attached to the teniae coli.

What is the anatomy of the stomach?

Four Main Regions: - Cardia - Fundus - Body - Pyloric Part (3 regions) 1) Cardia: - surrounds opening of stomach. 2) Fundus: - rounded portion superior and to left of cardia. 3) Body: - inferior to fundus - large central portion of stomach. 4) Pyloric Part - 3 regions a) Pyloric Antrum: - connects to body of the stomach b) Pyloric Canal: - leads to third region c) Pylorus: - connects to the duodenum (first part of small intestine) Pyloric Sphincter: - smooth muscle sphincter - connects pylorus to duodenum. Mucosa Rugae (wrinkles): - large folds - more noticeable when stomach empty. Lesser Curvature: - concave - medial border of stomach. Greater Curvature: - convex - lateral border of stomach.

Describe the Anatomy of the Gallbladder.

Fundus: - Broad - projects inferiorly beyond inferior border of liver. Body: - Central portion. Neck: - Tapered portion. Body and Neck project superiorly.

Describe the Gallbladder

GALLBLADDER - Pear-shaped sac. Location: - In depression of posterior surface of liver - 7-10 cm long - typically hangs from anterior, inferior margin of liver.

Digestion of nucleic acids.

NUCLEASES Ribonuclease: - digests RNA Deoxyribonuclease: - digests DNA Nucleosidases and Phosphatases: - Brush border enzymes - further digest the nucleotides TO - pentoses, phosphates, nitrogenous bases - products absorbed via active transport.

Describe the Gastric Phase of Digestion

GASTRIC PHASE - Neural - hormonal - mechanisms that regulate gastric phase. Neural Regulation 1) Activation of Stretch and Chemoreceptors: - Food distends stomach - stimulates stretch receptors in its walls Chemoreceptors in stomach: - monitor pH of stomach chyme - pH goes up from protein digestion - neural negative feedback loop initiated. 2) From stretch receptors and chemoreceptors: - nerve impulses propagate to submucosal plexus - activate parasympathetic and enteric neurons - cause waves of peristalsis - continue to stimulate flow of gastric juice and gastric glands. 3) Peristaltic waves: - mix food with gastric juice as the waves get bigger - some chyme pushed into the small intestine. 4) pH of stomach chyme: - decreases (becomes more acidic) - distention of stomach wall lessens - because chyme passed into the small intestine - suppressing release of gastric juice. Hormonal Regulation 1) Hormone Gastrin: - Released from G cells of gastric glands. Responds to stimuli: - distention of stomach by chyme - partially digested proteins in chyme - high pH of chyme due to presence of food in stomach - caffeine in gastric chyme - acetylcholine released by parasympathetic neurons. 2) Gastrin enters bloodstream: - reaches target organs in digestive system. 3) Gastrin: - stimulates release of gastric juice - strengthens contraction of lower esophageal sphincter to - prevent acid reflux of acid into esophagus - increases stomach motility - relaxes pyloric sphincter to - promote gastric emptying. Negative Feedback Mechanism Provides optimal low pH for: - functioning pepsin - killing microbes - denaturing proteins in stomach a) Gastrin inhibited when: - pH of gastric juice drops below 2.0 b) Gastrin stimulated when: - pH rises.

Other hormones of the digestive system.

GI secretes 10 other hormones. - Motilin, substance P, bombesin - stimulate motility of intestines. Vasoacative intestinal polypeptide (VIP): - stimulates secretion of ions and water by intestines - inhibits gastric acid secretion. Gastrin-releasing peptide: - stimulates release of gastrin. Somatostatin: - inhibits gastrin release.

Describe Aging and the Digestive System.

GI tract and Aging: - Decreased secretory mechanisms - Decreased motility of the digestive organs -Loss of strength and tone of muscular tissue and tone of muscular tissue and its supporting structures - Changes in neurosensory feedback regarding enzyme and hormone release. - Diminished response to pain and internal sensations. Upper Portion of GI Tract: - Reduced sensitivity to mouth irritations and sores - Loss of taste - Periodontal disease - Difficulty in swallowing - Hiatal hernia - Gastritis - Peptic ulcer disease. Changes in Small Intestine - Duodenal ulcers - Malabsorption - Maldigestion Pathologies - Appendicitis - Gallbladder problems - Jaundice - Cirrhosis - Acute pancreatitis Large Intestinal Changes - Constipation - Hemorrhoids - Diverticulitis disease - Cancer of colon or rectum - Bowel obstructions and impactions

Describe the histology of the gallbladder.

Gallbladder: - Simple columnar epithelium - arranged in rugae resembling the stomach. Layers Wall: - lacks submucosa. Middle, muscular coat of wall: - smooth muscle fibers. Cystic Duct: - Contents ejected into duct from contraction of the smooth muscle fibers. Outer: - Visceral peritoneum. Functions of Gallbladder: - Store, and concentrate bile produced by liver (10 fold) - until needed in small intestine. Concentration process - water and ions absorbed by gallbladder mucosa.

Figure 24.12: Histology of the Stomach

Gastric juice is the combined secretions of: - mucous cells - parietal cells - chief cells. Gastric Pit Secretions Surface Mucous Cell: - secretes mucus Mucous Neck Cell: - secretes mucus Parietal Cell: - secretes hydrochloric acid - intrinsic factor Chief Cell: - secretes pepsinogen and gastric lipase G Cell: - secretes hormone gastrin Cells - Superficial to Deep: Superficial - Chief cells - Lumen of gastric gland - G cells - Parietal Cell - Mucous Neck Cell - Lumen of gastric gland - Surface mucous cell - Lamina Propria - Gastric pit Deep

Figure 24.14: Regulation of HCl secretion.

HCl secretion by parietal cells Can be stimulated by several sources: - Acetylcholine (ACh) - gastrin - histamine.

Describe the preferred structural and functional unit of the liver - Hepatic Acinus.

Hepatic Acinus: - Approximately oval mass - includes portions of two neighboring hepatic lobules - Smallest structural and functional units of liver. Short Axis: - Defined by branches of the hepatic portal triad - runs along border of hepatic lobules. Hepatic Portal Triad: Branches of hepatic artery, vein and bile ducts. Hepatocytes: - Arranged in three zones - around short axis - no sharp boundaries between them. Zone 1 Cells - Closest to branches of portal triad - Last ones to die if circulation impaired. First to: - receive incoming oxygen, nutrients, toxins from blood. - take up glucose and store it as glycogen after a meal - break down glycogen to glucose during fasting. - show morphological changes following bile duct obstruction or exposure to toxic substances. - regenerate. Zone 2 Cells: - Structure and functional characteristics intermediate - between Zone 1 and Zone 3. Zone 3 Cells - Farthest from portal triad. Last to: - show changes from obstruction or toxins - regenerate. First to: - show effects of impaired circulation.

Figure 24.16: Histology of Liver

Histologically, the liver is composed of: - hepatocytes - bile canaliculi - hepatic sinusoids. Portal Triad: - Bile duct - branch of hepatic artery - branch of hepatic portal vein.

What is the role of intestinal juice and brush-border enzymes?

INTESTINAL JUICE - Clear, yellow fluid - 1-2 liters secreted each day Contains: - water and mucus - slightly alkaline pH 7.6 Function: - With pancreatic and intestinal juices - aid in absorption of substances in chyme in the small intestine. Brush-Border Enzymes: Several digestive enzymes - synthesized by small intestine - which inserts the enzymes in plasma membrane of microvilli. Some digestion occurs in the absorptive cells of villi: - rather than the lumen exclusively - unlike other parts of GI tract. 4 Carbohydrate Digesting Enzymes: - a-dextrinase - maltase - sucrase - lactase. Protein Digesting Enzymes: Peptidases - aminopeptidase - dipeptidase 2 Types of Nucleotide-digesting Enzymes: - nucleosidases - phosphatases. Sloughing of absorptive cells: - break them apart - releasing more digestive enzymes - help digest nutrients in chyme.

Describe the Intestinal Phase of Digestion.

INTESTINAL PHASE - Begins once food enters the small intestine Inhibitory effects: - slow release of chyme from the stomach - prevents duodenum form being overloaded with chyme. Promotes: - continued digestion of foods that have reached small intestine. Regulated by: - Neural and Hormonal Mechanisms. Neural Regulation 1) Enterogastric reflex: - caused by distention of the duodenum by chyme 2) Stretch receptors in: - duodenal wall - send nerve impulses to medulla oblongata Medulla Oblongata: - inhibit parasympathetic stimulation - stimulate sympathetic nerves in stomach 3) Gastric motility inhibited: - increases contraction of pyloric sphincter - decreases gastric emptying. Hormonal Regulation: - cholecystokinin - secretin. Cholecystokinin 1) Cholecystokinin (CCK): - secreted by CCK cells of small intestinal crypts of Lieberkuhn - in response to chyme - containing amino acids - from partially digested proteins and fatty acids - from partially digested trigylcerides 2) CCK stimulates: - secretion of pancreatic juice - rich in digestive enzymes 3) CCK causes: - contraction of wall of gallbladder - squeezes stored bile out of gallbladder - into cystic duct - through common bile duct 4) CCK causes: - relaxation of sphincter of hepatopancreatic ampulla (sphincter of Oddi) - allows pancreatic juice and bile to flow into duodenum 5) CCK slows: - gastric emptying - promoting contraction of pyloric sphincter - produces satiety (feeling of fullness) - by acting on hypothalamus in brain 6) CCK promotes: - normal growth and maintenance of pancreas 7) CCK enhances: - effects of secretin. Secretin 1) S Cells of small intestinal crypts of Lieberkuhn: - release secretin - in response to acidic chyme entering duodenum 2) Secretin stimulates: - release of pancreatic juice - high in bicarbonate (HCO3-) - which buffers the acidic chyme - that enters duodenum from stomach 3) Secretin inhibits: - secretion of gastric juice - promotes normal growth and maintentance of pancreas - enhances effects of CCK 4) Overall, secretin: - buffers acid chyme that reaches duodenum - slows production of acid in stomach.

Mechanical Digestion in the Large Intestine.

Ileocecal Sphincter - Usually partially closed Opened by: - Gastroileal reflex - gastrin (relaxes ileocecal sphincter) Gastroileal Reflex: - Occurs immediately after a meal - intensifies peristalsis in the ileum - forces any chyme into cecum through the ileocecal sphincter. - Gastrin relaxes the ileocecal sphincter. Movements of Colon: - Begins when substances move past the ileocecal sphincter - chyme fills cecum - accumulates in ascending colon - haustral churning and peristalsis push contents quickly to rectum. Haustral Churning: - Haustra relax - become distended as they fill with chyme - walls contract and squeeze contents into next haustrum. Peristalsis: - Occurs at a slower rate than earlier parts of GI tract. Mass Peristalsis: - Strong peristaltic wave - begins at middle of transverse colon - drives contents of colon to- rectum. Gastrocolic Reflex: - Food in stomach initiates a reflex in the colon - peristalsis occurs during or immediately after a meal - 3-4 times a day.

Describe the Mucosa Layer of the GI tract.

Inner lining of GI tract: - mucous membrane. Two layers: 1) Epithelium: a) Non-keratinized Epithelium: Serves as Protective Function - mouth - pharynx - esophagus - anal canal b) Simple columnar epithelium: - functions in secretion and absorption - in stomach, and intestines Tight junctions prevent leakage between cells Renewal of GI tract epithelial cells: - 5 to 7 days - slough off - new cells beneath Exocrine cells located among: - epithelial cells - secrete mucous and fluid into lumen of tract Enteroendocrine Cells: - type of endocrine cells - secrete hormones. 2) Lamina Propria: - areolar connective tissue - contains blood and lymphatic vessels, are routes for nutrients absorbed by GI tract to other tissues of body - Binds to muscularis mucosae. Mucosa-associated Lymphatic Tissue (MALT): - lymphatic nodules - contain immune system cells - protect against disease - all along GI tract - especially in tonsils, small intestine, appendix, large intestine. 3) Muscular Mucosae - thin layer - gives stomach and small intestine many folds - increases surface area for absorption and digestion - movements of muscularis mucosae - absorptive cells are fully exposed to contents of GI tract

Figure 24.24: Histology of the Large Intestine.

Intestinal glands formed by: - simple columnar epithelial cells - goblet cells - extend the full thickness of the mucosa.

Anatomy of the Large Intestine.

LARGE INTESTINE - 1.5 m long - 6.5 cm in diameter - extends from ileum to anus. Mesocolon: - Attaches large intestine to posterior abdominal wall - double layer of peritoneum. Ileocecal Sphincter: - Opening from ileum to large intestine - fold of mucous membrane - allows materials to enter large intestine from small intestine. Consists of Four Structures: - Cecum - colon - rectum - anal canal. 1) Cecum - Hangs inferior to ileocecal valve - small 6 cm long pouch. Appendix or Verniform Appendix: - Attached to cecum - twisted, coiled tube - measures 8 cm in length Mesoappendix: - Mesentery of appendix - attaches appendix to inferior part of mesentary ileum. 2) Colon - Open end of cecum - long tube Divided into: - ascending colon - transverse colon - descending colon - sigmoid portions Ascending and Descending Colon: - Retroperitoneal Transverse and Sigmoid Colon: - Not retroperitoneal. Ascending Colon: - Ascends on right side of abdomen - reaches inferior surface of abdomen - turns left - forms right colic (hepatic) flexure. Transverse Colon: - Across abdomen to left side - curves underneath the spleen on left side as the left colic (splenic) flexure - passes inferiorly. Descending Colon: - Travels inferior to spleen - level with iliac crest. Sigmoid Colon: - Near left of iliac crest - projects medially to midline - terminates as rectum - level of S3 vertebra. 3) Rectum - Last 20 cm of GI tract - lies anterior to sacrum and coccyx. 4) Anal Canal - Last 2-3 cm of rectum. Anal Columns: - Longitudinal folds of mucous membrane - contains arteries and veins. Anus: - Opens anal canal to the exterior Sphincters Internal anal sphincter: - smooth muscle - involuntary External anal sphincter: - of skeletal muscle - voluntary - keeps anus closed - except during defecation.

Describe the Liver

LIVER - Heaviest gland in body, weighs approximately 1.4 kg (3 lbs) in average adult. Location: - Inferior to diaphragm - occupies most of right hypochondriac space - and part of epigastric region of abdominopelvic cavity.

What is lactose intolerance?

Lactose intolerance: - Small intestine absorptive cells don't produce enough lactase. - Undigested lactose in chyme causes buildup in feces - bacterial fermentation of undigested lactose causes gas. Symptoms: - Gas - bloating - diarrhea - abdominal cramps - Symptoms minor to serous and needing medical attention. Diagnosis: - Hydrogen breath test - checks for lactose fermented by bacteria showing up on the breath.

Describe the Periotoneum

Largest serous membrane of the body. Layers: A) Simple squamous epithelium: - supporting layer of areolar connective tissue. B) Parietal Peritoneum: - lines wall of abdominopelvic cavity. c) Visceral Peritoneum: - is the serosa and covering of the organs in the cavity. Peritoneal Cavity: - space between parietal and visceral peritoneum - contains serous fluid (lubrication). Ascites: - Certain diseases can distend the peritoneal cavity - accumulates liters of fluid. Retroperitoneal: NOT INSIDE PERITONEAL CAVITY - Kidneys - ascending and descending colons - large intestine - duodenum of small intestine - pancreas - lie on posterior abdominal wall - only covered by peritoneum on anterior surface. Five Peritoneal Folds: - bind organs together - weave through viscera - contain blood vessels - lymphatic vessels - nerves that supply abdominal organs. 1) Greater Omentum: - Largest Drapes over: - transverse colon Coils around: - small intestine like a fatty apron Attaches along: - stomach - duodenum Extends downward: - anterior to small intestine Turns upward and attaches to: - transverse colon Contains: - large amounts of adipose tissue - seen in weight gain Lymph nodes: - macrophages - antibody producing plasma cells - help fight infection of GI tract 2) Falciform Ligament: - Attaches liver to anterior abdominal wall and diaphragm Liver only digestive organ attached to anterior abdominal wall. 3) Lesser Omentum: - Anterior fold in serosa of stomach and duodenum Suspends: - stomach and duodenum from liver Pathway for: - blood vessels entering liver Contains: - hepatic portal vein - common hepatic artery - common bile duct - some lymph nodes 4) Mesentery: Binds: - jejunum and ilium of small intestine to - posterior abdominal wall Largest peritoneal fold: - laden with fat - large abdomen in obese. Posterior abdominal wall: - wrap around small intestine - returns to posterior abdominal wall - forms double layered structure Contains: - blood and lymphatic vessels - between the two layers. 5) Mesocolon: - Two separate folds Binds: - transverse colon and sigmoid colon of large intestine - to posterior abdominal wall Carries: - blood vessels and lymphatic vessels to - intestines Mesentary and Mesocolon: - Hold the intestines loosely in place - allow for muscular contractions to mix and move GI tract contents.

What does the sacral spinal cord parasympathetic fibers supply in the Digestive System?

Last half of the large intestine.

What are the functions of the liver and gallbladder?

Liver Functions 1) Bile - 800-1000 mL secreted by hepatocytes per day - Yellowish, brownish, olive green color - pH of 7.6-8.6 - Partially secretive product and digestive product - More is released in response to increases digestion and absorption in the small intestine Hepatopancreatic sphincter (surrounds the hepatopancreatic ampulla) closes: - bile stored in gallbladder. Consists of: -Water - bile salts - cholesterol - phospholipid - lecithin, bile pigments, several ions. Bilirubin: - Principal pigment in bile. - secreted into bile - broken down in intestine - once broken down forms stercobilin Phagocytosis of RBC: - produces iron, globin and biliruben (derived from heme) - Iron and globin recycled Stercobilin: - Product left after bilirubin is broken down in intestines - Gives feces brown color. Bile Salts - Sodium salts - potassium salts of bile acids (mostly chenodeoxycholic acid and cholic acid) Aid in: - absorption of lipids - following their digestion by pancreatic lipase. Emulsification - Bile salts play role - Breakdown of large lipid globules into smaller lipid globule suspensions Small lipid globules: - large surface areas - allows for pancreatic lipase to digest triglycerides quickly. 2) Carbohydrate Metabolism - Liver maintains glucose levels. Blood Glucose low: - liver breaks down glycogen to glucose into bloodstream. - Convert amino acids and lactic acid - glucose. - Convert sugars to - fructose and galactose to - glucose. Blood glucose high: - converts glucose to - glycogen and triglycerides for storage. 3) Lipid Metabolism Hepatocytes: - store some triglycerides - breakdown fatty acids to generate ATP - synthesize lipoproteins - transport fatty acids, triglycerides, cholesterol to and from body cells - synthesize cholesterol - use cholesterol to make bile salts. 4) Protein Metabolism Hepatocytes - deaminate (remove amino group, NH2) from amino acids Synthesize: - most plasma proteins - alpha and beta globulins - albumin - prothrombin - fibrinogen Amino acids: - can be used for ATP production - or converted to carbohydrates and fasts Toxic ammonia (NH3): - converted to less toxic urea - excreted in urine 5) Processing of Drugs and Hormones Liver - detoxifies alcohol Excrete drugs such as: - penicillin - erythromycin - sulfonamides - into bile. Chemically alter or excrete: - thyroid hormones - steroid hormones - estrogen and aldosterone. 6) Excretion of bilirubin Formed by: - breakdown of heme in RBC Absorbed: - into liver Secreted: - in bile Metabolized in: - small intestine by bacteria Eliminated in: - feces. 7) Synthesis of Bile Salts - Used in small intestine - for emulsification and absorption of lipids. 8) Storage - Stores glycogen - vitamins A, B12, D, E, K - minerals copper and iron - released into liver to be used elsewhere. 9) Phagocytosis - Stellate reticuloendothelial cells (Kupffer) cells - destroy worn out RBC, WBC and some bacteria. 10) Activation of Vitamin D - Skin - liver - kidneys - synthesize active form of vitamin D. Gallbladder Functions: - Stores bile when the hepatopancreatic ampulla sphincter closes - shutting off access to the duodenum - triggered when the digestion and absorption in small intestines slows

Describe the muscularis layer of the GI tract.

Located in: - mouth - pharynx - superior and middle parts of esophagus Contains skeletal muscle: - produces swallowing Skeletal muscle: - external anal sphincter - voluntary control of defecation Smooth muscle: - found in two sheets - inner sheet of circular fibers - outer sheet of longitudinal fibers Involuntary contractions: - break down food - mix with digestive secretions - propel food along GI tract Myenteric Plexus: - Neurons between layers of muscularis

What is gastroenterology?

Medical specialty that deals the stomach and intestines - disease - structure - function - diagnosis

Figure 24.20: Histology of the Duodenum and Ileum.

Microvilli in the small intestine contains: - several brush-border enzymes - help digest nutrients.

Figure 24.1: Organs of Digestive System.

Organs of GI tract are: - mouth - pharynx - esophagus - stomach - small intestine - large intestine. Accessory Digestive Organs are: - teeth - tongue - salivary glands - liver - pancreas - gallbladder A) Right lateral view of head and neck and anterior view of trunk. Parotid Gland (salivary gland) Submandibular Gland (salivary gland) Sublingual Gland (salivary gland) Mouth (Oral cavity) contains: teeth, tongue. Pharynx Esophagus Liver Stomach Duodenum Gallbladder Pancreas Appendix Jejunum From Jejunum to - Ilium to - Ascending Colon to - Cecum to - Transverse Colon to - Descending Colon to - Sigmoid Colon to - Rectum to - Anal Canal to - Anus

Figure 24.21: Absorption of digested nutrients in the small intestine - Mechanisms for Movement of Nutrients through Absorptive Epithelial Cells of Villi.

Long-chain fatty acids and monoglycerides - are absorbed into lacteals - other products of digestion enter blood capillaries. a) Glucose and Galactose Lumen of Small Intestine via - Secondary Active Transport with Na+ through - Microvilli (brush border) on Apical Surface Monosaccharides: - via Facilitated Diffusion - To blood capillary of villus. b) Fructose: Lumen of Small Intestine via - Facilitated Diffusion through - Microvilli (brush border) on Apical Surface to - Epithelial Cells of Villus via - Facilitated Diffusion - To blood capillary of a Villus. c) Amino Acids: Lumen of Small Intestine via - Active Transport or Secondary Active Transport with Na+ through - Microvilli (brush border) on Apical Surface with - Amino Acids through - Epithelial Cells of Villus via- Diffusion - To blood capillary of Villus. d) Dipeptides and Tripeptides: Lumen of Small Intestine via - Secondary Active Transport with H+ through - Microvilli (brush border) on Apical Surface with - Amino Acids through - Epithelial Cells of Villus via - Diffusion - To blood capillary of Villus. e) Small Short-Chain Fatty Acids: Lumen of Small Intestine via - Simple Diffusion through - Microvilli (brush border) on Apical Surface to - Epithelial Cells of Villus via - Diffusion - To blood capillary of Villus. f) Micelle of Large short-chain fatty acid and Long-chain fatty acid and Monoglycerides: Lumen of Small Intestine via - Simple Diffusion through - Microvilli (brush border) on Apical Surface through - Epithelial cells of Villus with - Triglyceride via - Chylomicron through - Basolateral Surface of epithelial cell of Villus to - Lacteal of Villus.

What is gastroesophageal reflux disease?

Lower esophageal sphincter doesn't close properly - stomach contents enter esophagus - hydrochloric acid burns esophagus - causing heart burn. Causes - drinking alcohol - smoking. Controlled by: - avoiding foods that stimulate stomach secretion (coffee, chocolate, tomatoes, fatty foods, orange juice, peppermint, spearmint, onions). Treatment: - Over counter histamine-2 - pepcid - tums - maalox.

Figure 24.6: Summary of digestive activities in the large intestine.

Lumen: - Bacterial activity Breaks down: - carbohydrates - proteins - amino acids - into products expelled in feces or absorbed by liver - synthesizes B and K vitamins. Mucosa: a) Secrete mucus: - lubricates colon - protects mucosa. b) Absorption: - water absorption solidifies feces - contributes to water balance - absorbed solutes - ions and some vitamins. Muscularis: a) Haustral Churning: - moves contents form haustrum to haustrum - by muscular contractions. b) Peristalsis: - moves contents along length of colon - by contraction of circular and longitudinal muscles c) Mass Peristalsis: - forces contents into sigmoid colon and rectum d) Defecation Reflex: - eliminates feces by contraction in sigmoid colon and rectum.

Describe the steps in mechanical and chemical digestion in the mouth.

MECHANICAL DIGESTION Mastication: - Chewing - food manipulated by tongue - ground by teeth - mixed with saliva. CHEMICAL DIGESTION Bolus: - Food turned into a soft ball ready for swallowing. Food molecules dissolve in saliva: - enzymes begin breakdown of food Enzymes: Salivary amylase and lingual lipase. a) Salivary amylase: - secreted by the salivary glands Breakdown starch: - dietary carbohydrates - monosaccharides - disaccharide - sugars - complex polysaccharides Monosaccharides: - absorbed in blood stream Digested disaccharides and polysaccharides: - must be broken into monosaccharides. Breaks down: - disaccharide maltose - trisaccharide maltotriose - short-chain glucose polymers called a-dextrins. * Stomach acids inactivate it. b) Lingual Lipase: - Secreted by lingual glands in tongue - begins after swallowing. * Activated in acidity of stomach Breaks Down: - Dietary triglycerides (fats and oils) - fatty acids - diglycerides (glycerol molecules attached to fatty acids).

Absorption of Monosaccharides by Small Intestine.

MONOSACCHARIDES - Absorbed 120 mL per hour by small intestine - almost all absorbed besides cellulose and fiber which pass on to the large intestine. Pass from lumen TO - apical membrane - via facilitated diffusion or active transport. a) Fructose Monosaccharide: - Transported via facilitated diffusion. b) Glycose and Galactose - Transported into absorptive cells - via secondary active transport. Active transporter: - has room for one glucose molecule and two Na+ ions - if all sites are filled neither substance transported Galactose: - competes for a spot on the active transporter - with glucose Glycose (Galactose) and Na+ are symporters: - move move in the same direction. Monosaccharides: - move out of absorptive cells - through their basolateral surfaces - via facilitated diffusion - enter villus capillaries - transported to liver through hepatic portal circulation - if not removed by hepatocytes - goes to general circulation.

What is the histology of the esophagus?

MUCOSA - Non-keratinized stratified squamous epithelium - lamina propria (areolar connective tissue) - contains mucous glands near stomach. Muscularis mucosae: - smooth muscle Non-keratinized stratified squamous epithelium Protects: - lips - tongue - oropharynx - laryngopharynx - esophagus - wear and tear - abrasion from food particles. Submucosa: - Areolar connective tissue - blood vessels - mucous glands MUSCULARIS Superior 1/3 of esophagus: - skeletal muscle Middle 1/3 of esophagus: - skeletal and smooth muscle Inferior 1/3 of esophagus: - smooth muscle. Two Sphincters - Upper esophageal sphincter or valve, - lower esophageal sphincter or valve a) Upper esophageal sphincter: - skeletal muscle - regulates movement of food from pharynx - esophagus b) Lower esophageal sphincter: - smooth muscle - regulates movement of food from esophagus - stomach. ADVENTITIA - Superficial (outer) layer of esophagus - attaches esophagus to surrounding structures - contains areolar connective tissue - not covered by mesothelium - merges with connective tissue of surrounding structures

Table 24.3: Summary of digestive activities of the stomach.

MUCOSA a) Surface mucous cells and mucous neck cells: - Secrete mucus - forms protective barrier that prevents digestion of stomach wall. Absorption: - small quantities of water - ions - short-chain fatty acids - some drugs enter bloodstream. b) Parietal Cells Secrete intrinsic factor: - needed for absorption of vitamin B12 - Vitamin B12 - used in RBC formation, or erythropoiesis Secrete hydrochloric acid: - kills microbes in food - denatures some proteins - converts pepsinogen to pepsin. c) Chief Cells Secrete pepsinogen: - pepsin is the activated form - breaks down proteins into peptides. Secrete gastric lipase: - splits triglycerides - into fatty acids and monoglycerides. MUSCULARIS Mixing waves (gentle peristalsis): - churns and physically breaks down food - mixes food with gastric juice - forming chyme - Forces chyme through pyloric sphincter. Pyloric Sphincter: - Opens to permit passage of chyme into duodenum - regulates passage of chyme from stomach to duodenum - prevents back flow of chyme from duodenum into stomach

Describe Mechanical Digestion in the Small Intestine.

Migrating-motility Complexes: Two types of movements - segmentations and type of peristalsis. SEGMENTATIONS - Localized mixing contractions - in areas of intestine distended with chyme - does not propel food - mix chyme with digestive juices - bring particles of food in contact with mucosa for absorption - Occur rapidly in duodenum (12 x min) - slower in ileum (8 x min) 1) Starts with: - contractions of circular muscle fibers in portion of small intestine - constricts intestine into segments 2) Muscle fibers that circle middle of each segment contract: - dividing each segment again 3) Circular muscles relax: - each small segment joins with the other small segment - creates large segment - chyme sloshes back and forth 4) Repeats again. MIGRATING MOTILITY COMPLEX (MMC) - Type of peristalsis - begins after most food absorbed - segmentation has slowed 1) MMC begins in lower portion of stomach: - pushes chyme forward along short part of small intestine - dying down 2) MMC migrates down small intestine: - reaching end of ileum - in 90-120 minutes 3) Another MMC begins: - in the stomach Chyme remains in small intestine for: - 3-5 hours.

Describe the Mechanical Digestion in the Stomach.

Mixing Waves: - After food enters stomach - Gentle, rippling waves of peristalsis - occur every 15-25 seconds - macerate food - mix it with gastric secretions from gastric glands - reduce food to soup (chyme). Chyme: - Soupy fluid that food is reduced too. Gastric Emptying: - Digestion in stomach - mixing waves begin at body of stomach - more vigorous as reaches pyloris - pyloris sphincter slightly open - 3 mL of chyme squeezes through pyloris sphincter - into duodenum. Food remains in fundus without mixing for some time: - salivary amylase continues to break down carbohydrates (starch) - churning action of stomach mixes chyme with gastric juice then - salivary amylase inactivated then - lingual lipase activated begin - break down of triglycerides into - fatty acids and diglycerides begins. 2-4 hours after eating meal: - stomach empties into duodenum - carbohydrates released first - high-protein foods stay a bit longer - fat-laden meals rich in triglycerides stay the longest in the stomach.

Figure 24.18: Anatomy of the small Intestine.

Most digestion and absorption occur in the small intestine. Functions of the Small Intestine. 1. Segmentations: - mix chyme with digestive juices - bring food into contact with mucosa for absorption - peristalsis propels chyme through small intestine. 2. Completes Digestion Of: - carbohydrates - proteins - lipids - begins and completes digestion of nucleic acids. 3. Absorbs about: - 90% of nutrients and water that pass through digestive system.

Describe the components of the mouth.

Mouth: - Oral cavity - formed by cheeks, hard and soft palate, tongue. Cheeks - Lateral walls of the oral cavity Covered by: skin externally - internally by a nonkeratinized stratified squamous epithelium mucous membrane Buccinator muscles and connective tissue: - lie between skin and epithelium Anterior portion of cheeks - end at lips. Lips or labia: - Fleshy folds - surrounds opening of mouth - contain orbicularis oris muscle - covered by skin externally and mucous membrane internally. Labia Frenulum: - Midline fold of mucous membrane - attaching the inner part of lips to the their corresponding gum. Orbicularis and Buccinator Muscles: - function to keep food between upper and lower teeth. Oral Vestibule: - Oral cavity bound externally by cheeks and lips - internally by teeth and gums. Oral Cavity Proper: - Space extending from gums and teeth to fauces - opening between oral cavity and oropharynx - throat Palate: - Wall or septum - between oral cavity and nasal cavity - forms roof of mouth - helps with chewing, breathing at same time. Hard Palate: - Anterior portion of floor of mouth - formed by maxillae and palatine bones - covered by mucous membrane - Forms bony partition between oral cavity and nasal cavity. Soft Palate: - Forms posterior portion of roof of mouth - partition between nasopharynx and oropharynx - arch-shaped - lined with mucous membrane. Uvula: - Hanging from border of soft palate - muscular cone process - soft palate and uvula drawn superiorly during swallowing - closing off the nasopharynx from oropharynx - prevents food and liquid from entering the nose. Two muscular folds lateral to base of uvula: a) Palatoglossal Arch: Anteriorly - extends from base of tongue b) Palatopharyngeal Arch: Posteriorly - extends to side of pharynx. Tonsils: a) Palatine Tonsils: - Located between the palatoglossal arch - and palatopharyngeal arch. b) Lingual Tonsils: - Located at base of tongue. Oropharynx: - Posterior border of soft palate.

What is a root canal?

Multi-step procedure - remove traces of pulp from pulp cavity and root canals from badly diseased tooth Hole in teeth: - root canals filed - irrigated to remove bacteria - canals treated with medication - sealed tightly - damaged crown repaired.

Describe the ANS of the Digestive System.

Neurons of ENS regulated by ANS. Parasympathetic Nerves: - increase motility and GI secretions - by increasing activity of the ENS. 1) Vagus (X) nerve: - supplies the parasympathetic fibers of most parts of GI tract, except last half of large intestine - forms connection with ENS Large Intestine: - supplied by parasympathetic fibers of sacral spinal cord 2) Parasympathetic preganglionic neurons of Vagus and Pelvic Splanchnic Nerves: - synapse with parasympathetic postganglionic neurons - in myenteric and submucosal plexus. Postganglionic neurons: - synapse with neurons of ENS - or innervate smooth muscle and glands within the walls of the GI tract. Sympathetic Nerves: - Decrease in secretion and motility - stimulate sympathetic nerves that supply the GI tract - Respond to emotions of fear, anxiety, anger. 3) Thoracic and Lumbar regions of spinal cord: - neural connections with ENS - synapse with neurons in myenteric plexus and submucosal plexus.

What are the GI tract Reflex Pathways?

Neurons regulate GI secretion and motility - respond to stimuli present in lumen of GI tract. Sensory receptors: - chemoreceptors or stretch receptors - associated with sensory neurons of ENS - synapse with neurons in the ENS, CNS, ANS - send information about contents of GI tract, distention ENS, CNS, ANS: - activate or inhibit GI glands and smooth muscle - alter GI secretion and motility.

What is ocult blood?

Ocult Blood: - Blood that is hidden. Tests: - Done at home - to test urine and feces for hidden blood.

Describe the term - digestive system

Organs involved with breakdown of food Extends from: - mouth to anus - tubular system Forms extensive surface area of contact with: - external environment - cardiovascular system.

Describe the Pancreas

PANCREAS - Retroperitoneal gland Consists of: - head - body - tail Attached to duodenum: - by two ducts Size: - 2.5 cm wide - 12-15 cm long Location: - Posterior to greater curvature of stomach. Ducts 1) Pancreatic Duct (duct of Wirsung): Larger of two ducts. Hepatopancreatic Ampulla (ampulla of Vater): - Connecting the two ducts - Opens at elevation of duodenal mucosa. Major Duodenal Papilla: - 10 cm inferior to pyloric sphincter of stomach Sphincter of the Hepatopancreatic Ampulla (sphincter of Oddi) - Mass of smooth muscle Regulates passage of bile and pancreatic juice: - from hepatopancreatic ampulla - to small intestine 2) Accessory Duct (duct of Santorini): - Goes from pancreas - empties into duodenum - about 2.5 cm superior to hepatopancreatic ampulla.

What is pancreatitis and pancreatic cancer?

PANCREATITIS - Inflammation of pancreas - associated with alcohol abuse (70% of people) - or gallstones. Acute Pancreatitis: - More serious - associated with heavy alcohol intake - biliary tract obstruction - pancreatic cells release trypsin instead of trypsinogen - release less trypsin inhibitor - trypsin breaks down pancreas cells Treatment: - Respond well - re-attacks common - some idiopathic Other causes: - Cystic fibrosis - autoimmune conditions - high calcium levels in blood - high fat levels in blood - some drugs. PANCREATIC CANCER - Affects people over 50 years - mostly males - not recognized until advanced stages - usually metastasized to lymph nodes, liver, lungs and usually fatal. Risk: - High alcohol intake - fatty foods - genetic factors - chronic pancreatitis.

Table 24.4: Summary of Digestive Activities in the Pancreas, Liver, Gallbladder, Small Intestine

Pancreas: - Delivers pancreatic juice to duodenum via pancreatic duct - assist in absorption. Liver: - Produces bile (bile salts) - for emulsification and absorption of lipids. Gallbladder: - Stores - concentrates - delivers bile to duodenum - via common bile duct. Small Intestine: - Major site of digestion and absorption of nutrients and water in GI tract. MUCOSA AND SUBMUCOSA a) Intestinal Glands: - Secrete intestinal juice to assist absorption. b) Absorptive Cells: - Digest and absorb nutrients. c) Goblets Cells: - Secrete mucus. d) Enteroendocrine Cells (S, CCK, K): Secrete - secretin - cholecystokinin (Vitamin B absorption) - glucose-dependent insulinotropic peptide. e) Paneth Cells: - Secrete lysozyme (bactericidal enzyme) and phagocytosis. f) Duodenal (Brunner's) Glands: - Secrete alkaline fluid to buffer stomach acids - mucus for protection and lubrication. g) Circular Folds: - Folds of mucosa and submucosa - increase surface area for digestion and absorption. h) Villi: - Finger-like projections of mucosa - sites of absorption of digested food - increase surface area for digestion and absorption. i) Microvilli: - Microscopic - membrane-covered projections of absorptive epithelial cells - contain brush border enzymes - increase surface area for digestion and absorption. MUSCULARIS a) Segmentation: - Type of peristalsis - alternating contractions of circular smooth muscle fibers - produce segmentation and resegmentation of sections of the small intestine - mixes chyme with digestive juices - brings food into contact with mucosa for absorption. b) Migrating Motility Complex (MMC): - Type of peristalsis - waves of contraction and relaxation of circular smooth muscle fibers - passing along entire length of small intestine - moves chyme toward ileocecal sphincter.

What is the composition and functions of pancreatic juice?

Pancreatic Juice - Pancreas produces 1200-1500 mL of clear, colorless liquid Contains: - water - salts - sodium bicarbonate - several enzymes. Sodium Bicarbonate: - Slightly alkaline (pH 7.1-8.2) - acts as buffer for acidic gastric juice in chyme - stops action of pepsin from stomach - creates proper pH for digestive enzymes in small intestines. Pancreatic Amylase: - Starch digesting enzyme. Protein Digesting Enzymes Include In active form: - trypsin - chymotripsin - carboxypeptidase - elastase Produced in inactive form: - to avoid ingesting pancreatic wall - tripsinogen - chymotripsinogen - procarboxypeptidase - proelastase Trypsin Inhibitor: - Deactivates any trypsinogen formed by accident in the pancreas or pancreatic juice - blocks enzymatic activity. Trypsinogen (inactive form of trypsin) - Travels to beginning of small intestine - meets activating brush border enzyme enterokinase Enterokinase: - splits off part of the trypsinogen molecule - to form trypsin (active form) Trypsin Acts on precursor cells: - chymotrypsinogen - procarboxypeptidase - proelastase To produce active: - chymotrypsin - carboxypeptidase - elastase. Pancreatic Lipase: - Digests triglycerides. Nucleic Acid-Digesting Enzymes Include: - ribonuclease - deoxyribonuclease Digest: - ribonucleic acid (RNA) - deoxyribonucleic acid (DNA) - into nucleotides

Figure 24.15: Relation of the pancreas to the liver, gallbladder, duodenum.

Pancreatic enzymes digest: - starches (polysaccharides) - proteins - triglycerides - nucleic acids Right Hepatic Duct + Left Hepatic Duct - Common Hepatic Duct - Cystic Duct from Gallbladder - Common Hepatic Duct from Liver - Common Bile Duct - Pancreatic Duct - Sphincter - Duodenum. Duodenum - Sphincter - Common Bile Duct - Cystic Duct from Gallbladder

What are mumps?

Paramyxovirus: - attacks parotid glands. Mumps: - Inflammation and enlargement of parotid glands Symptoms: - Fever - malaise (general discomfort) - extreme pain in throat - especially when swallowing sour foods or acidic juices Testes may become inflamed in: - 30% of males (after puberty) - only unilateral - sterility not normal. Swelling occurs: - one or both sides of face - anterior to ramus of mandible. Vaccine available.

Describe digestion of proteins.

Pepsin - Protein digestion starts in stomach - proteins broken into peptide fragments. Pancreatic Enzymes - Break down proteins into peptides. a) Trypsin, Chymotrypsin, Elastase: - cleave bond between amino acid and its neighbor. b) Carboxypeptidase: - Splits off amino acid at the carboxyl end of a peptide. Peptidases - Completes protein digestion - located in the brush border - aminopeptidase and dipeptidase. a) Aminopeptidase: - Cleaves off the amino acid at the amino end of a peptide. b) Dipeptidase: - Splits dipeptides (two amino acids joined by a peptide bond) - into single amino acids.

What is the pharynx?

Pharynx: - Funnel shaped tube - Extends from internal nares to - esophagus posteriorly and larynx anteriorly. Skeletal muscles: - lined with mucous membrane - contract and propel food into esophagus to - stomach. Divided in three parts: 1) Nasopharynx: - respiration. 2) Oropharynx: - digestive and respiratory - swallowed food passes from mouth to - oropharynx and laryngopharynx 3) Laryngopharynx: - digestive and respiratory

Table 24.2: Summary of Digestive Activities in the Pharynx and Esophagus.

Pharynx: - Pharyngeal stage of deglutition - moves bolus from oropharynx into laryngopharynx - esophagus - closes air passages. Esophagus: Relaxation of upper esophageal sphincter - permits entry of bolus from laryngopharynx - esophagus. Esophageal stage of deglutition (peristalsis) - pushes bolus down esophagus. Relaxation of lower esophageal sphincter - permits entry of bolus into stomach. Secretion of mucus - lubricates esophagus - smooth passage of bolus - reduces friction.

What are polyps in the colon?

Polyps: - Slow developing - benign growths - arise from the mucosa of the large intestine. Symptoms: - Generally none - may cause diarrhea - blood in feces - mucus discharged from anus. Colonoscopy or surgery - to remove, some may be cancerous.

What structures make up the hepatic Portal Triad.

Portal Triad Include: - Bile duct - branch of hepatic artery - branch of hepatic vein.

What is the medical specialty that deals with diagnosis and treatment of disorders of the rectum and anus.

Proctology.

Figure 24.13: Secretion of HCl (hydrochloric acid) by parietal cells in the stomach.

Proton pumps: - powered by ATP - secrete H+ Cl- diffuses into stomach lumen - through Cl- channels.

Table 24.5: Summary of Digestive Enzymes

SALIVA a) Salivary Amylase: - Salivary glands - Starches (polysaccharides) - Maltose (disaccharide) - maltotriose (trisaccharide) - a-dextrins. b) Lingual Lipase: - Lingual glands in tongue - Triglycerides (fats and oils) and other lipids - Fatty acids and diglycerides. GASTRIC JUICE a) Pepsin: - activated from pepsinogen by pepsin and hydrochloric acid - Stomach chief cells - Proteins to - Peptides. b) Gastric Lipase: - Stomach chief cells - Triglycerides (fats and oils) to - Fatty acids and monoglycerides. PANCREATIC JUICE a) Pancreatic Amylase to - Pancreatic acinar cells - Starches (polysaccharides) to - Maltose (disaccharide) - maltotriose (trisaccharide) - a-dextrins. b) Trypsin: - activated from trypsinogen by enterokinase - Pancreatic acinar cells - Proteins to - Peptides. c) Chymotrypsin: - activated from chymotrypsinogen by trypsin - Pancreatic acinar cells - Proteins to - Peptides. d) Elastase: - activated from proelastase by trypsin - Pancreatic acinar cells - Proteins to - Peptides. e) Carboxypeptidase: - activated from procarboxypeptidase by trypsin - Pancreatic acinar cells - Amino acids at carboxyl end of peptides to - Amino acids and peptides. f) Pancreatic Lipase: - Pancreatic acinar cells - Triglycerides (fats and oils) that have been emulsified by bile salts to - Fatty acids and monoglycerides. NUCLEASES - Pancreas a) Ribonuclease: - Pancreatic acinar cells - Ribonucleic acid to - Nucleotides. b) Deoxyribonuclease: - Pancreatic acinar cells - Deoxyribonucleic acid to - Nucleotides. BRUSH BORDER ENZYMES - in Microvilli Plasma Membrane of Small Intestine a) a-Dextrinase: - Small intestine - a-dextrins to - Glucose. b) Maltase: - Small Intestine - Maltose to - Glucose. c) Sucrase: - Small Intestine - Sucrose to - Glucose and Fructose. d) Lactase: - Small Intestine - Lactose to - Glucose and Galactose. e) Enterokinase: - Small Intestine - Trypsinogen to - Trypsin. f) Peptidases Aminopeptidase: - Small Intestine - Amino acid at amino end of peptides to - Amino acids and peptides. Dipeptidase - Small Intestine - Dipeptides to - Amino acids. g) Nucleosidases and Phosphatases: - Small Intestine - Nucleotides to - Nitrogenous bases, pentoses, and phosphates.

Describe the Small Intestine.

Small Intestine: - 3 m Long tube - 2.5 cm diameter - most of nutrients are absorbed and digested Large surface area for: - digestion and absorption Circular folds, villi, microvilli: - increase surface area. Begins at pyloric sphincter of stomach - coils through central and inferior part of abdominal cavity - opens into large intestine.

What is the histology of the stomach?

SURFACE MUCOSA - Layer of simple columnar epithelial cells. Contains: - Lamina Propria - areolar connective tissue - muscularis mucosae (smooth muscle). Gastric Glands - Exocrine gland Epithelial cells project into: - the lamina propria - creating gastric glands Open into: - bottom narrow channels - gastric pits Secretions flow from: - gastric glands to - gastric pits to - lumen of stomach. Gastric Glands - 3 types of exocrine gland cells 1) Mucus Neck Cells / Surface Cells: Secrete - mucus. 2) Chief Cells: Secrete - pepsinogen - gastric lipase 3) Parietal Cells: Secrete - intrinsic factor (absorption of B12) - hydrochloric acid. Gastric Juice Secretions of: - mucus neck cells - chief cells - parietal cells - Totals 2000-3000 mL (2-3 qt) per day. G Cell: - In gastric glands - Enteroendocrine cell - Located in pyloric antrum - secretes gastrin into blood stream. LAYERS THAT LIE DEEP TO MUCOSA 1) Submucosa of Stomach: - composed of areolar connective tissue 2) Muscularis: - 3 layers of smooth muscle - outer longitudinal layer - middle circular layer - inner oblique layer (limited to body of stomach) 3) Serosa - simple squamous epithelium (mesothelium) - areolar connective tissue. Visceral peritoneum serosa - covers stomach Extends upward to liver: - as lesser omentum At greater curvature of stomach: - continues downward as greater omentum - drape over intestines.

What is the composition and function of saliva?

Saliva - 99.5% water - 0.5% solutes - ions, sodium, chloride, bicarbonate, phosphate - Dissolved gases Various organic substances: - urea - uric acid - mucus - immunoglobulin A - lysozyme (the bacteriolytic enzyme) - salivary amylase - digestive enzyme acts on starch. Parotid Gland: - Secretes watery liquid - containing only salivary amylase. Submandibular Gland: - Secretes salivary amylase - and mucous mixture. Sublingual Gland: - Secretes thick fluid filled with mucous - and little salivary amylase. Salivary Amylase: - Activated by chloride ions - It is an enzyme that starts breakdown of starch - maltose, maltotriose, a-dextrin. Bicarbonate and Phosphate Ions: - buffer acidic foods that enter mouth - saliva only slightly acidic (pH 6.35-6.85). Salivary Glands: - like sweat glands of skin - removed waste molecules from body - accounts for small amounts of urea and uric acid in saliva. Mucus: - lubricates food - forms food into ball - enables food to move in mouth easier - can be swallowed. Microbes and Bacteria Killed by: - Immunoglobulin A - prevents attachment of microbes - to prevent penetration into epithelium Enzyme Lysozyme: - kills bacteria - Both not enough to kill all bacteria.

Figure 24.6: Major salivary glands - parotid, submandibular, sublingual

Saliva lubricates and dissolves foods Begins chemical breakdown of: - carbohydrates - lipids.

How are carbohydrates digested by the small intestine?

Salivary Amylase - Action still continues in stomach for a bit Destroyed by: - acidity in gastric juice - only some starches broken down into maltose, maltotriose, a-dextrins. Pancreatic Amylase - Enzyme in pancreatic juice - acts on glycogen and starches in the small intestine - no effect on cellulose (plant starch). A-dextrinase - Brush-border enzyme Breaks down left over a-dextrins: - not broken apart by pancreatic or salivary amylase - in small intestine. Three Brush-border Enzymes - break apart disaccharides TO - monosaccharides. 1) Sucrase: - Breaks down sucrose into - a molecule of glucose and a molecule of fructose. 2) Lactase: Breaks down lactose into - a molecules of glucose and galactose. 3) Maltase: - Breaks down maltose and maltotriose into - 2 or 3 molecules of glucose.

Describe the absorption of the stomach.

Small amounts absorbed - most impermeable because of epithelial cells. Mucous cells absorb some: - water - ions - short-chain fatty acids - certain drugs (aspirin, alcohol).

Describe the chemical digestion of the small intestine.

Salivary Amylase in the Mouth Converts: - starch (a polysaccharide) to maltose (a disaccharide) - maltotriose (a trisaccharide) - a-dextrins (short-chain, branched fragments of starch 5-10 glucose units). Pepsin in the Stomach Converts: - proteins to peptides (small fragment proteins) Lingual and gastric lipase converts: - some triglycerides into - fatty acids - diglycerides - monoglycerides. Chyme in Small Intestine - Partially digested carbohydrates - proteins - lipids. Pancreatic Juice, Bile, Intestinal Juice: - Collectively complete the remaining digestion in small intestine of - carbohydrates - proteins - lipids.

Describe the Salivary Glands

Salivary Gland: - releases saliva - increases when food enters mouth - lubricates mouth, and pharynx - cleanses teeth and mouth - lubricates - dissolves, begins chemical break down food. Location: - Mucous membrane of mouth and tongue - open directly, or indirectly through short ducts - into oral cavity. Types: - Labial - buccal - palatal glands (lips, cheeks, palate) - lingual glands (tongue) - all make small contribution to saliva. Three Major Salivary Glands: - Most of saliva comes from them - parotid, sublingual, submandibular. 1) Parotid Glands: - Inferior and anterior to ears - between skin and masseter muscle - secrete saliva into parotid duct. Parotid Duct: - Pierces buccinator muscle - vestibule - opposite second maxillary (upper) molar tooth. 2) Submandibular Glands: - Floor of mouth - inferior and slightly lateral to body of mandible Submandibular Duct: - Run under mucosa - on either side of floor of - oral cavity proper - lingual frenulum. 3) Sublingual Glands: - Beneath tongue - superior to submandibular glands. Lesser Sublingual Ducts: - Open into floor of mouth - into oral cavity proper.

What is salivation?

Salivation: - Controlled by ANS. Parasympathetic Stimulation: - promotes salivary production - moistens food and esophagus - moistens mucous membranes - lubricates movement of tongue and lips during speech. Most components of saliva reabsorbed: - prevents fluid loss. Sympathetic Stimulation: - during stress - dryness of mouth. Dehydration: - salivary glands stop producing saliva to conserve water - dryness of mouth contributes to sensation of thirst Drinking restores homeostasis of body water: - also moistens mouth. Stimulators of Salivary Gland Secretions - feel and taste of food -Smell - sight - sound - thought of food - stimulation of secretion of saliva. Superior and Inferior Salivary Nuclei in Brain Stem - Chemicals in food stimulate receptors on tongue - send impulses from taste buds to the salivary nuclei. Returning parasympathetic impulses in the facial (VII) and glossopharyngeal (IX) nerves: - stimulate secretion of saliva - saliva secreted heavily after food swallowed - to dilute and buffer remnants of irritating chemicals left in mouth.

Describe the stomach.

Stomach: - J-shaped enlargement - inferior to diaphragm in abdomen. Connects esophagus - duodenum (first part of small intestine). Function: - Mixing chamber - holding reservoir - moves small quantities of material into small intestine. Diaphragm pushes stomach inferiorly: - inhalation Diaphragm Pulls stomach superiorly: - exhalation. Digestion: - Starch and triglycerides continue - digestion of proteins begin - semisolid bolus converted to liquid - certain substances absorbed.

Describe the Serosa Layer of the GI Tract.

Superficial layer - on Suspended organs in abdominopelvic cavity Serous membrane to - areolar connective tissue - simple squamous epithelium (mesothelium) Visceral Peritoneum: - forms portion of peritoneum Esophagus: - lacks serosa - only has a single layer of areolar connective tissue called adventitia - forms superficial layer of the esophagus.

Describe the Teeth.

Teeth or dentes: - Accessory organ of digestion - in sockets of alveolar processes of mandible and maxillae. Gingivae or gums: - Extend into every socket slightly Periodontal Ligament: - Lines sockets. Membrane: - Dense fibrous connective tissue - anchors teeth to socket walls - shock absorber during chewing. Tooth: Crown, root and neck a) Crown: - Visible portion above level of gums. b) Root: Embedded in socket - usually 1-3 c) Neck: Constricted junction of gum and root and gum line. Dentin: - Within the tooth - calcified connective tissue - basic structure and rigidity of a tooth - has high calcium salts (70% of dry weight) - stronger than bone. Enamel: - Covers dentin of crown - primarily calcium phosphate and calcium carbonate - harder than bone with high level of calcium salts (95% of dry weight) with calcium salts - hardest substance in body - protect tooth from chewing - protect tooth from acids that can easily dissolve dentin. Cementum: - Covers dentin of the root - bone like substance - attaches root to periodontal ligament. Pulp Cavity - Lies within crown Contains: - connective tissue - lymphatic vessels - nerves - blood vessels. Root Canals: - Narrow extensions of pulp cavity - run through root of tooth. Apical Foramen: - Opening in base of root canal - blood vessels (nourishment) - lymphatic vessels (protection) - nerves (sensation) Endodontics - Treat - diagnose Prevent diseases affecting: - root - pulp - periodontal ligament - alveolar bone. Orthodontics: - Branch of dentistry - involved with prevention and correction of abnormally aligned teeth. Periodontics: - Treatment of abnormal conditions in tissues surrounding teeth - gingivitis. Dentitions: Deciduous Teeth, Permanent Teeth a) Deciduous: - baby teeth - primary teeth - milk teeth - erupt 6 months of age - up to 20 teeth Incisors (central and lateral): - closest to midline - adapted to cut food Cuspids (posterior, next to incisors): - pointed surface (cusp) - tear and shred food - only one root First and second molars: - four cusps Maxillary upper molars: - 3 cusps Mandibular lower molars: - 2 cusps - grind and crush food. - Lost between 6-12 years. b) Permanent (secondary) Teeth - 32 teeth - between age 6 and adulthood - Deciduous molars replaced by permanent teeth 1st and 2nd premolars (bicuspids): - 2 cusps, 1 root - upper 1st premolars - 2 roots - crushing and grinding First molars: - age 6 Second molars: - age 12 Third molars (wisdom teeth): - age 17 or not at all.

Figure 24.9: Histology of the Esophagus.

The esophagus secretes mucus and transports food to the stomach.

Figure 24.2: Layers of the GI tract.

The four layers of the GI tract: from deep to superficial - mucosa - submucosa - muscularis - serosa

Figure 24.11: External and Internal Anatomy of the Stomach.

The four regions of the stomach are the: - cardia - fundus - body - pyloric part.

Figure 24.17: Hepatic Blood Flow: Sources, path through the liver, and return to heart.

The liver receives: - oxygenated blood via the hepatic artery - nutrient-rich deoxygenated blood via the hepatic portal vein. 1) Oxygenated Blood from Hepatic Artery Nutrient-rich deoxygenated blood from hepatic portal vein 2) Liver Sinusoids 3) Central Vein 4) Hepatic Vein 5) Inferior Vena Cava 6) Right Atrium of Heart

What organ is the only organ that attaches to the anterior abdominal wall?

The liver.

Figure 24.5: Structures of the mouth (oral cavity)

The mouth is formed by the: - cheeks - hard and soft palates - tongue.

Figure 24.4: Relationship of the peritoneal folds to one another and to organs of the digestive system.

The peritoneum is the largest serous membrane of the body.

Figure 24.23: Anatomy of the Large Intestine.

The regions of the large intestine are the: - cecum - colon - rectum - anal canal. Functions of Large Intestine: 1) Haustral churning, peristalsis, mass peristalsis: - drive contents of colon into rectum. 2) Bacteria in large intestine: - convert proteins to amino acids - break down amino acids - produce some B vitamins and Vitamin K. 3) Absorbing some water, ions, and vitamins. 4) Forming feces. 5) Defecating (emptying rectum).

Figure 24.8: Dentitions and times of eruptions.

There are 20 teeth in a complete deciduous set and 32 teeth in a complete permanent set. a) Deciduous (primary) dentition Lower Central Incisor: 6-8 months Upper Central Incisor: 8-12 months Lower Lateral Incisor: 12-15 months Upper Lateral Incisor: 12-24 months Lower Cuspid or Canine: 16-24 months Upper Cuspid or Canine: 16-24 months Lower First Molar: 12-16 months Upper First Molar: 12-16 months Lower Second Molar: 24-32 months Upper Second Molar: 24-32 months b) Permanent (secondary) dentition Lower Central Incisors: 7-8 years Upper Central Incisors: 7-8 years Lower Lateral Incisor: 7-8 years Upper Lateral Incisor: 8-9 years Lower Cuspid: 9-10 years Upper Cuspid: 11-12 years Lower First Premolar or Bicuspid: 9-10 years Upper First Premolar or Bicuspid: 9-10 years Lower Second Premolar or Bicuspid: 11-12 years Upper Second Premolar or Bicuspid: 10-12 years Lower First Molar: 6-7 years Upper First Molar: 6-7 years Lower Second Molar: 11-13 years Upper Second Molar: 12-13 years Lower Third Molar (Wisdom Tooth): 17-21 years Upper Third Molar (Wisdom Tooth): 17-21 years

Describe the Tongue.

Tongue: - Accessory digestive organ - skeletal muscle covered with mucous membrane - Forms floor of mouth with associated muscles - divided into symmetrical right and left halves by a median septum Median Septum: - Divides tongue into symmetrical lateral halves. Attachments: - Inferiorly to hyoid bone - mandible - styloid process of temporal bone. Extrinsic Muscles of Tongue - Originate outside tongue - insert into connective tissue in tongue. Include: - hyoglossus - genioglossus - styloglossus muscles Movements: - side to side, in and out - chewing - shape food into rounded mass - force food to back of throat for swallowing - Form floor of mouth - hold tongue in position. Intrinsic Muscles of Tongue - Originate inside tongue - insert into connective tissue within tongue. Include: - longitudinalis superior - longitudinalis Inferior - transversus linguae - verticalis linguae Movements: - Alter shape and size of tongue - speech and swallowing. Lingual Frenulum: - Fold of mucous membrane under tongue - floor of mouth - prevents tongue from slipping posteriorly. Ankyloglossia: - Short lingual frenulum - tongue tied - impairment of speech. Papillae: - On dorsum of tongue - projections of lamina propria - covered with stratified squamous epithelium - many contain taste buds - Some lack taste buds - contain receptors for touch - increase friction between tongue and food - moves food easier around oral cavity. Lingual Glands: - Located in lamina propria - secrete both mucous and water serous fluid - contains lingual lipase enzyme - acts on 30% of dietary triglycerides - converts to simpler fatty acids and diglycerides.

Describe the Anatomy of the Small Intestine.

Three Regions: - Duodenum - Jejunum - Ileum 1) Duodenum - Shortest region - retroperitoneal. Pyloric sphincter of stomach: - extends 25 cm as a C-tubed shape TO - jejunum. 2) Jejunum - 1 m long - extends from ilium. 3) Ileum - 2 m long - joins large intestine at smooth muscle ileocecal sphincter (valve)

Figure 24.7: Summary of the Digestive System and Their Functions.

Tongue: - Maneuvers food for mastication - forms food into a bolus - maneuvers food for deglutition - detects sensations of taste - initiates digestion of triglycerides. Salivary Glands: - Softens, moistens, dissolves food - cleanses mouth and teeth - initiates digestion of starches. Teeth: - Cut - tear - pulverize food - reduce large pieces of food to small particles for swallowing. Pancreas: - Pancreatic juice buffers the acidic gastric juice - maintains normal pH for digestion in small intestine - stops action of pepsin from stomach - participates in digestion of carbohydrates, proteins, triglycerides, nucleic acids. Liver: - Produces bile - required for emulsification and absorption of lipids in small intestine. Gallbladder: - Stores and concentrates bile - releases it into the small intestine. Mouth: - Lips and cheeks keep food between teeth during mastication - buccal glands lining mouth produce saliva. Pharynx: - Receive bolus from oral cavity - passes it into the esophagus. Esophagus: - Receives bolus from pharynx - moves it into the stomach - requires relaxation of the esophageal sphincter and secretion of mucus. Stomach: - Mixing waves combine saliva, food, gastric juice - activates pepsin - initiates protein digestion - kills microbes in food - absorbs vitamin B12 - contracts lower esophageal sphincter - increases stomach motility - relaxes the pyloric sphincter - moves chyme into small intestine. Small Intestine: - Segmentation mixes chyme with digestive juices - peristalsis moves chyme toward ileocecal sphincter - digestive secretions from small intestine, pancreas, liver - complete digestion of carbohydrates, proteins, lipids, nucleic acids - circular folds, villi, and microvilli help absorb 90% of digested nutrients. Large Intestine: - Haustral churning, peristalsis, mass peristalsis drive the colonic contents into the rectum - bacteria produce some B and K vitamins - absorption of water, ions, vitamins - defecation.

Absorption of Water by the Small Intestine.

Total volume of fluid enters small intestine per day: 9.3 liters per day - from ingestion of liquids (2.3 liters) - GI secretions (7.0 liters). Small Intestine Absorbs: - 8.3 liters of fluid - remainder 0.9 liters passes into large intestine - 0.1 liter is excreted in feces each day. Water Absorption: - Via osmosis - from lumen of intestines - through absorptive cells to - blood capillaries Absorbed electrolytes, monosaccharides, amino acids: - establish concentration gradients - to promote water absorption via osmosis. Osmotic Balance in Blood: - Water can pass out of and into small intestine - electrolytes and nutrients maintains blood osmotic balance.

Digestion of Lipids

Triglycerides - Most abundant lipid in diet Consists of: - a molecule of glycerol - bonded to three fatty acid molecules Broken down by Lipases - Enzymes that split triglycerides - Lingual lipase - gastric lipase - pancreatic lipase. a) Lingual and Gastric Lipase: - starts lipid digestion in stomach. b) Pancreatic Lipase - in pancreatic juice - majority of lipid digestion occurs in small intestine with help of pancreatic juice Breaks proteins into: - long chain fatty acids or short-chain fatty acids - with fewer than 10-20 carbons and monoclycerides. Emulsification: - Breaks down large lipid globule - into several small lipid globules. Bile Salts - Contained in bile - are sodium salts and potassium (chenodeoxycholic acid and cholic acid) Amphipathic: - each salt has a hydrophilic and hydrophobic polar region. Hydrophobic Polar Region of Bile Salt: - Interacts with large lipid globule. Hydrophilic Polar Region of Bile Salts: - Interacts with watery intestinal chyme. Large lipid globule TO - small lipid globules: - small lipid globules provides large surface area - pancreatic lipase works more efficiently.

Explain the overview of the digestive system.

Two groups of organs. 1) Gastrointestinal Tract - Continuous tube from mouth to anus - through thoracic and abdominopelvic cavities. Length: - 5-7 meters in living person maintained state of tonus of smooth muscle fibers - 7-9 meters in dead person loss of smooth muscle tone Organs: - Mouth - most of pharynx - esophagus - stomach - small intestine - large intestines. 2) Accessory Digestive Organs - Tongue - teeth - salivary glands - liver - gallbladder - pancreas Teeth aid in: - chewing Tongue aid in: - chewing and swallowing Other accessory organs: - do not come in contact with food - produce and store secretions that flow through GI tract ducts - aid in chemical break down of food. Muscular Contractions: - Aid in break down of food - moving food through the digestive tract - help break down food by mixing it with fluids secreted into the tract. Enzymes: - Secreted by accessory organs and cells lining the digestive tract - aid in break down of food chemically. Six Basic Processes 1) Ingestion: - Process involves taking foods and liquids into the mouth. 2) Secretion: - Cells within walls of GI tract secrete 7 liters of fluid (water, buffer, enzymes) into lumen of tract. 3) Mixing and Propulsion: - Motility - Alternating contract and relax of smooth muscle in walls of GI tract - mix and propel food and secretions toward anus. 4) Digestion: - Mechanical and chemical processes - involved in break down of food into small molecules. a) Mechanical Digestion: - Teeth cut and grind food before swallowed - smooth muscle in stomach and small intestine churn the food - food molecules dissolve -and thoroughly mixed with digestive enzymes. b) Chemical Digestion: - Large carbohydrate - lipid - protein - nucleic acid molecules in food - split into smaller molecules by hydrolysis. Digestive enzymes produced by: - salivary glands - tongue - stomach - pancreas - small intestine - catalyze catabolic reactions Few substances in food absorbed without chemical digestion: - water, vitamins, ions, cholesterol. 5) Absorption: - Entrance of ingested and secreted fluids - ions - products of digestion into epithelial cells lining lumen of GI tract - absorbed substances pass into blood or lymph - circulate to cells in body. 6) Defecation: - Wastes - non digestible substances - bacteria - cells sloughed off in GI tract - digested materials not absorbed in journey through digestive tract - leave body through anus - Eliminated material - feces or stool.

What is the blood supply of the Liver?

Two sources: 1) Hepatic Artery: - receives oxygenated blood. 2) Hepatic Portal Vein: - receives deoxygenated blood, nutrients, toxins, drugs, possibly microbes from GI tract. Branches of hepatic artery and hepatic portal vein: - carry blood to liver sinusoids - oxygen, nutrients, certain toxic substances taken up by hepatocytes. Products manufactured by hepatocytes and nutrient needed by cells: - secreted back to blood - drains into central vein - passes to hepatic vein Metastasis Cancer Site: - Blood travels from GI tract to liver through hepatic portal circulation.

What is jaundice?

Yellowish coloration of sclera (whites of eyes), skin, mucous membranes - buildup of bilirubin - yellow compound. Bilirubin formed by: - breakdown of heme portion of RBC - then sent to liver to be processed and excreted in bile. Three main categories of jaundice. 1) Prehapatic jaundice: - excess production of bilirubin. 2) Hepatic Jaundice: - congenital liver disease - cirrhosis of the liver - hepatitis. 3) Extrahepatic Jaundice: - blockage of bile drainage by gallstones - cancer of bowel or pancreas. Neonatal (physiological) Jaundice - Liver in newborn functions poorly 1st week or so - babies experience mild jaundice - disappears as liver matures. Treatment: - Blue light exposure - converts bilirubin into substances kidneys can excrete.

What is bile?

Yellowish, brownish, olive-green liquid - secreted by hepatocytes - excretory product and digestive function.