Digestive System

Lipid Digestion

Bile salts- liver Lipase- pancreas Both fatty acids and monoglycerides.

Types of teeth

Incisors (8) Canines (4) Premolars (8) Molars (12)

Lipid Digestion

Include triglycerides, phospholipids, steroids, and fat soluble vitamins. Pancreatic lipase in the duodenum performs most of lipid digestion into fatty acids and monoglycerides.

Oral Cavity proper

Lies medial to the alveolar processes.

Which of the following describes the blood in the hepatic portal vein?

Oxygen- poor, nutrient rich

Swallowing

Pharyngeal phase Esophageal phase (peristalsis)

Where do blood vessels, lymphatic vessels, ducts, and nerves enter the liver?

Porta hepatis

During swallowing, the X elevates closing off the nasopharynx and the X closes to prevent food from entering the trachea.

Soft palate; epiglottis.

Absorption of nutrient

movement of nutrients from the GI tract into the blood or lymph

Amino acid transport across the intestinal epithelium

1. An amino acid is absorbed by simper along with Na+ across the intestinal cell membrane. 2. A Na+K+ pump establishes a Na+ concentration gradient from outside to inside the intestinal epithelial cell 3. Amino acids move out of the cell by facilitated diffusion. 4. Amino acids enter the capillary of an intestinal villus and are carried through the hepatic portal vein to the liver.

HCl production by parietal cells in the gastric glands of the stomach

1. Carbon dioxide diffuses into the parietal cells. 2. Carbon dioxide combines with water in an enzymatic reaction that is catalyzed by carbonic anhydrase to form carbonic acid. 3. Carbonic acid dissociates into a bicarbonate ion and a hydrogen ion 4. Bicarbonate ions are transported back into the bloodstream. AN antiproton in the plasma membrane exchanges HCO3 for a chloride ion. 5. A H+ K+ pump moves H+ into the duct of the gastric gland and K+ into the parietal cell. 6. Chloride ions diffuse with the charged H+.

Carbohydrate Digestion Process

1. Pancreatic amylase is produced by the pancreas and secreted into the small intestine 2. Pancreatic amylase continues digestion of starch that began in the oral cavity by salivary amylase 3. Brush border enzymes complete the breakdown of starch to individual glucose molecules, and are responsible for the digestion of disaccharides.

Protein Digestion

1. Proteolytic enzymes are released from pancreas. 2. Enteropeptidase activates trypsinogen to trypsin; trypsin then activates other proteolytic enzymes 3. Activated pancreatic proteolytic enzymes break proteins into peptides and amino acids. 4. Brush border peptidases break peptides into single amino acids to be absorbed through epithelial cell into blood.

Peristalsis

1. a wave of circular smooth muscle relaxation moves ahead of the bolus of food allowing the digestive tract to expand. 2. a wave of contraction of the circular smooth muscles behind the bolus of food propels it through the digestive tract.

Transport of monosaccharides across the intestinal epithelium

1. glucose is absorbed by symport along with Na+ 2. A Na+K+ pump established a Na+ concentration gradient from outside to inside the intestinal epithelial cell 3. Glucose moves out of the cell by facilitated diffusion. 4. glucose enters the capillary of an intestinal villus and is carried through the hepatic portal vein to the liver

Bile

A yellow-green alkaline solution containing bile salts, bile pigments, cholesterol, neutral fats, phospholipids, and electrolytes. Bile salts emulsify fat, facilitate fat and cholesterol absorption, helps make cholesterol soluble.

Saliva

About 1 liter of saliva/ day. Secreted from serous (enzymes, ions, mucin) and mucous (mucus) cells of salivary glands. Composition is 97-99.5% water and contains: digestive enzymes and proteins (mucin, lysozyme)

Functions of Large Intestine

Absorbs water and salts. Secretes mucus. Resident bacteria helps to form the feces from leftover chyme (indigestible ingested material). Stores and eliminates feces.

Accessory digestive organs

Aids in the breakdown of food. Salivary glands, liver, gallbladder,and pancreas.

Peptidases

Are bound to the microvilli of the small intestine and they break down peptides.

Hard palate

Assists the tongue in chewing

What is the function of intrinsic factor in the gastric juices?

Binds with vitamin B12 and helps its absorption in the small intestine.

Oral Cavity or mouth

Bounded by lips, cheeks, palate, and tongue. Has the oral orifice as its anterior opening. Is continuous with the oropharynx posteriorly. 2 regions: vestibule, oral cavity proper Mouth is lined with stratified squamous epithelium.

Pepsin

Break proteins into polypeptide chains in the stomach.

Central vein

Center of each lobule where mixed blood flows towards; former hepatic veins

What phase of gastric secretion is stimulated by the smell and taste of food?

Cephalic phase

Stomach

Chemical breakdown of proteins begins and food is converted from a bolus to chyme.

Which of the following is the correct arrangement of the duodenal epithelium in the order of largest to smallest?

Circular folds, villi, microvilli

Muscularis

Consists of an inner layer of circular smooth muscle and an outer layer of longitudinal smooth muscle. Myenteric plexus (enteric nervous system) is located between two muscle layers: Responsible for GI motility. It causes peristalsis to mix and move food along the GI tract.

Enteric Nervous System

Consists of nerve plexuses within the wall of the digestive tract. Serves the digestive tract and regulates digestive activity. Submucosal nerve plexus and myenteric nerve plexus.

A tooth consists of a crown, a neck, and a root

Crown: exposed part of the tooth. Dentin (living) is covered by enamel (non- living). Enamel is the hardest substance in the body. Root: Contains pulp cavity, blood vessels, and nerves.

Circular Folds

Deep folds of mucosa and submucosa into the lumen

What is the function of pepsin in the gastric juices?

Digests proteins

Lobules

Divisions of liver with portal triads at the corners

Pathological conditions of excess stomach acid production

Dyspepsia or indigestion. Gastroesophageal reflex disease (GERD) Peptic ulcer formationl stress gastritis

Lipid Transport

Fatty acids and monoglycerides are surrounded by bile salts to form micelles which move into small intestine epithelial cells by simple diffusion. Within epithelial cells, free fatty acids are recombined with monoglycerids to form triglycerides. Proteins coat trigycerides, phospholipids, and cholesterol to form chylomicrons. Chylomicrons enter lacteals within intestinal villi and are carried through the lymphatic system to the bloodstream and to the liver. Triglycerides are stored in adipose tissue, converted into other molecules, or used as energy.

Villi

Fingerlike extensions of the mucosa. Each contains a blood capillary network, a lymphatic capillary (lacteal). Important in transporting absorbed nutrients.

Soft Palate

Fold formed from skeletal muscle. Closes the nasopharynx while swallowing.

Serosa or Adventitia

Forms the outermost layer of the digestive tract. Series covering the organs is the same as visceral peritoneum. Consists of epithelial and/ or CT layers.

Peyer's Patches

Found in mucosa and submucosa of the ileum. Initiate immune responses against micro- organisms that enter the mucosa from ingested food.

Proteolytic enzymes

From pancreas into the duodenum, produce small peptide chains including trypsin, chymotrypsin, carboxypeptidase

Which of the stomach hormones increase stomach secretions?

Gastrin and Histamine

Movement in the Large Intestine

Haustra mix the contents and moves them slowly toward the anus. Mass movement are strong peristaltic contractions that occur 2-3 times per day. Local relfexes (ENS) can stimulate mass movements (gastrocolic- initiated by stomach, duodenocolic- initiated by the duodenum). Defacation is the elimination of feces. The distension of rectal walls caused by feces stimulates contraction of the rectal walls and relaxes the internal anal sphincter. Reflex activity moves feces through the internal anal sphincter and produces the urge to defecate. Voluntary activity regulates movement through the external anal sphincter.

Blood flow through the liver

Hepatic arteries provide oxygenated blood to liver cells. Hepatic portal vein formed by the union of large veins that drain the stomach and intestines. Portal veins branch into small veins which bring the nutrients to the hepatocytes for processing. After passing through hepatocytes, venous blood is then collected into larger veins which empty into the IVC.

Bile transport

Hepatocytes produce bile which is collected into small bile canaliculi. The canaliculi join small hepatic ducts which converge to form the right and left hepatic ducts, which exit the liver. Outside the liver, the left and right hepatic ducts join to form the common hepatic duct. The cystic duct from the gallbladder joins the common hepatic duct to form the common bile duct. The common bile duct and pancreatic duct join and opens into the duodenum at the duodenal papilla.

Functions of the Liver

Hepatocytes produce bile. Bile neutralizes acids and contains bile salts that emulsify fats. The liver stores and processes nutrients. The liver detoxifies molecules. Hepatic phagocytic cells phagocytize red blood cells, bacteria, and other debris. Heme molecules from broken down hemoglobin are converted to bile pigments and released as part of bile. Main bile pigment is bilirubin- gives bile its color. The liver produces blood components (albumin, fibrinogen, globulins, and clotting factors- vitamin K is necessary for the liver to make clotting factors)

Which of the following is the correct movement of bile in the liver as it is produced?

Heptocytes, bile canalicui, bile duct

Which of the following is the junction between the small and large intestines?

Ileocecal junction

Stages of Digestion

Ingestion Digestion Absorption Defacation

What other effect does CCK have on the GI tract?

Inhibit stomach secretions.

Gastric Phase

Initiated by distention of the stomach, which stimulates gastrin and histamine secretion and activates CNS and local reflexes that promote secretion. 1.Distention of the stomach stimulates mechanoreceptors and activates a parasympathetic reflex. Action potentials generated by the mechanoreceptors are carried by the vagus nerves to the medulla oblongata. 2. The medulla oblongata increases action potentials in the vagus nerves that stimulate secretions by parietal and chief cells and stimulate gastrin and histamine secretion by endocrine cells. 3. Distention of the stomach also activates local reflexes that increase stomach secretions. 4. Gastrin is carried through the circulation back to the stomach, where along with histamine, it stimulates secretion.

Which of the following sphincters opens to initiate defecation?

Internal anal sphincter

Which of the following are the small glands found at the base of the villi?

Intestinal glands.

Lipoproteins

Lipids are not soluble in water, so they are transported in the blood in combination with proteins. Lipoproteins include chylomicrons, VLDL, LDL, and HDL. Higher amount of protein relative to the lipid determines the density. LDL transport cholesterol to cells, and HDL transports it from cells to the liver for recycling or excretion in bile.

Greater omentum

Mesentary connecting greater curvature of stomach to transverse colon and posterior body wall

Lesser omentum

Mesentary connecting lesser curvature of stomach to liver and diaphragm.

Submucosa

Mostly CT with small glands and blood vessels. Contains the submucosal plexus (enteric nervous system): regulates secretion from the glands and innervates smooth muscle in the mucosa layer to mix the GI contents.

Cephalic Phase

Mouth starts watering. Initiated by the sight, smell, taste, or though of food. Nerve impulses from the medulla stimulate HCl, pepsinogen, gastrin, and histamine secretion. 1. The taste, smell, or thought of food or tactile sensations of food in the mouth stimulate the medulla oblongata. 2. Parasympathetic action potentials are carried by the vagus nerves to the stomach, where enteric plexus neurons are activated. 3. Postganglionic neurons stimulate secretion by parietal and chief cells and stimulate gastrin and histamine secretion by endocrine cells. 4. Gastrin is carried through the circulation back to the stomach, where along with histamine, it stimulates secretion.

Four tunics of the bowel wall

Mucosa Submucosa Muscularis (smooth muscle) Serosa (if covering muscles) or adventitia

Secretions of the small intestine

Mucus protects against digestive enzymes and gastric acids. Digestive enzymes are bound to the intestinal wall. The large surface area of the microvilli brings the enzymes into contact with the intestinal contents. Once broken down, small nutrient molecules are absorbed through microvilli and enter the circulatory or lymphatic system.

Secretions of the Large intestine

Mucus protects the intestinal lining. Bacterial flora of the large intestine consist of bacteria surviving the small intestine that enter the cecum and those entering via the anus. These bacteria colonize the colon, ferment indigestible carbohydrates, release irritating acids and gases, synthesize B complex vitamins and vitamin K, and constitute about 30% of the dry weight of the feces.

Functions of components of gastric juice

Mucus: protects stomach lining Pepsinogen: converted to pepsin to digest proteins HCl promotes pepsin activity and kills microorganisms. Intrinsic factor necessary for vitamin B12 absorption. Gastrin and histamine regulate stomach secretions.

Digestive tract or GI tract

Muscular tube winds through the body. Responsible for the digestion/ absorption of food. Oral cavity, pharynx, esophagus, stomach, small intestine, large intestine, and anus.

A potential side effect of open abdominal operations is decreased movements of the large intestine, resulting in constipation. The digestive tract layer most likely to be involved in producing this outcome would be the:

Muscularis

Pharynx

Nasopharynx, oropharynx, and layrngopharynx.

Which division of the autonomic nervous system has a greater influence on the activity of the digestive system?

PNS (rest and digest) (specifically the vagus nerve, CN X) has more control over the secretions and movements of the digestive system than the SNA (fight or flight)

What is not part of the digestive tract?

Pancreas

Protein Digestion

Pepsin- stomach (polypeptides) Trypsin, chymotrypsin, carboxypeptidase- pancreas (peptides) Peptidases- epithelium of small intestine (amino acids)

Functions of the Digestive System

Processes food Extracts nutrients Eliminates residue

Salivary glands

Produce and secrete saliva. Minor salivary glands are embedded in the palate, cheeks and lips. Major salivary glands are parotid, submandibular, and sublingual.

Epithelium of the mucosa of the small intestines

Produce digestive enzymes; absorb digested food. Produce a protective mucus. Protect the intestinal epithelium from bacteria. Produce regulatory hormones.

Treatment of excess stomach acid

Protein pump inhibitors. Block the H+- K+ exchange proton pump across the surface of the parietal mucosa cell that produces HCl. Drugs include Prilosec, zegerid, Prevacid, Nexium.

Which parts of the stomach contain a sphincter?

Pyloric and cardiac

What are the waves that precede vomiting called?

Reverse peristaltic waves

Carbohydrate digestion

Salivary amylase (polysaccharides, disaccharides)- mouth Pancreatic amylase (disaccharides)- duodenum Disaccharidases (monosaccharides)- epithelium of small intestine

Mucosa

Secretes mucus to protect the digestive tract from self digestion and lubricate food for ease of passage. Consists of the epithelium, lamina propria, and muscular mucosae. Contains cells that absorb nutrients from food; secrete/ contain digestive enzymes and hormones. Intestines have lymphatic tissues (peer's patches) that protect bowel form microbes.

Pancreatic Exocrine Function

Secretes pancreatic juice which breaks down all categories of foodstuff. Divided into lobules that contain acini- clusters of secretory cells that make digestive enzymes and connect to a duct system that eventually forms the pancreatic duct. The pancreatic duct empties at the major duodenal papilla. An accessory pancreatic duct empties into the duodenum at the minor duodenal papilla. Endocrine function: The islets of Langerhans release insulin and glucagon.

Movement of the small intestine

Segmental contractions mix intestinal contents. Peristaltic contractions move materials forward along the GI tract. Distension of the intestinal wall, local reflexes, and the PNS stimulate contractions. Distention of the cecum initiates a reflex that stimulates contraction of the ileocecal sphincter.

Enteric neurons

Sensory neurons: chemo or mechanoreceptors detect changes in the chemical composition of the digestive tract or dissension of the bowel walls. Motor neurons: stimulate or inhibit smooth muscle contraction and glandular secretion. Interneurons: Connect sensory to motor neurons. Regulation involves local reflexes within the ENS, but general responses can be mediated by the autonomic division of CNS.

Peritoneum

Serous epithelial membrane lining abdominopelvic cavity/ organs. Mesenteries are peritoneum that extend from body wall to organs (stomach, gallbladder, liver, small bowel, large bowel). Organs behind peritoneum are called retroperitoneal (pancreas, duodenum, ascending and descending colon, kidneys, rectum, urinary bladder).

Vestibule

Space between the lips or cheeks and the alveolar processes, which contain the teeth.

Small Intestine

Specializations of small intestine wall increase its surface area about 600- fold. Mucosa is simple columnar epithelium between the villi and the intestinal glands.

Secretin

Stimulates the release of the aqueous component, which neutralizes acidic chyme.

Cholecystokinin

Stimulates the secretion of the enzymatic component and relaxation of the sphincters of the pancreatic ducts. PNS stimulation increases enzyme secretion. SNA stimulation decreases enzyme secretion.

Movement of the stomach 2

Stronger peristaltic waves move the chyme through the pyloric sphincter into the duodenum. Other peristaltic movements of the stomach include hunger contraction, reverse peristalsis: contractions that move GI contents backwards. Precedes vomiting which is the ejection of the stomach's contents through the esophagus and out of the mouth. 1. A mixing wave initiated in the body of the stomach progresses toward the pyloric sphincter. 2. The more fluid part of the chyme is pushed toward the pyloric sphincter, whereas the more solid center of the chyme squeezes past the peristaltic constriction back toward the body of the stomach. 3. Peristaltic waves move in the same direction and in the same way as the mixing waves but are stronger. 4. Again, the more fluid part of the chyme is pushed toward the pyloric region, whereas the more solid center of the chyme squeezes past the peristaltic constriction back toward the body of the stomach. 5. Peristaltic contractions force a few milliliters of the mostly fluid chyme through the pyloric opening in to duodenum. Most of the chyme, including the more solid portion, is forced back toward the body of the stomach for further mixing.

Which part of the enteric system will be stimulated in the cephalic phase of stomach secretion?

Submucosal plexus controls gland secretions. Myenteric plexus is the other part of the enteric nervous system that controls muscle movements. It is located within the two layers of the muscular layer, or within the three layers of the muscular layer in the stomach.

Monosaccharide Transport

Taken up by intestinal epithelial cells by cotransport that is powered by a Na+ concentration gradient; or by facilitated diffusion. Carried to the liver, where the non- glucose sugars are converted to glucose. Glucose is transported to cells that require energy. Glucose enters the cells through facilitated diffusion.

Pancreatic Secretions

The aqueous component of pancreatic juice: composed of a water solution of enzymes and electrolytes (neutralizes acidic chyme and provide optimal environment for pancreatic enzymes to work) The enzymatic component of pancreatic juice is produced by the acini (contains enzymes that digest carbohydrates, lipids, and proteins. Enzymes are released in inactive form and activated in the duodenum)

Histology of large intestine

The mucosal lining of the large intestine is a simple columnar epithelium that is lined with mucus- producing crypts (no microvilli)

Regulation of Bile secretion

The presence of acidic, fatty chyme causes the duodenum to release cholecystokinin and secretin into the bloodstream. Cholecystokinin causes the gallbladder to contract and release bile. Secretin increases bile secretion. As a result bile enters the duodenum. Bile salts and secretin transported in blood stimulate liver to produce bile. Vagus nerve stimulation can also cause the gallbladder to contract.

Which is not a part of the colon?

The rectum is not.

How is the muscular tunic of the large intestine different from the muscular tunic of the small intestine?

There are 3 teniae coli bands instead of a complete longitudinal muscular layer.

How is the muscular tunis of the stomach different from either intestine?

There is third muscle layer in addition to the circular and longitudinal layers.

Microvilli

Tiny projections of absorptive mucosal cells plasma membranes. This formed a brush border.

Amino Acid Transport

Tripeptides, dipeptides, and amino acids are absorbed by symport that is powered by a Na gradient. Amino acids are transported to the liver, where the amino acids can be modified or released into the bloodstream. Amino acids are used as building blocks for energy. Amino acids cannot be stored by the body, so excess amino acids are converted to glycogen and fat.

Esophagus

Upper and lower esophageal sphincters regulate movement. 4 tunics: Adventia, muscularis propria, submucosa, mucosa

Movements of the stomach

Weak contractions of smooth muscle in the stomach walls produce mixing waves. These waves mix the stomach contents with stomach secretions and form chyme. 1. A mixing wave initiated in the body of the stomach progresses toward the pyloric sphincter. 2. The more fluid past of the chyme is pushed toward the pyloric sphincter, whereas the more solid center of the chyme squeezes past the peristaltic constriction back toward the body of the stomach. 3.Peristaltic waves move in the same direction and in the same way as the mixing waves but are stronger. 4. Again, the more fluid part of the chyme is pushed toward the pyloric region, whereas the more solid center of the chyme squeezes past the peristaltic constriction back toward the body of the stomach. 5. Peristaltic contractions force a few mililiters of the mostly fluid chyme through the pyloric opening into the duodenum. Most of the chyme, including the more solid portion is forced back toward the body of the stomach for further mixing.

Gastrointestinal Phase

When acidic chyme enters the duodenum, it stimulates the secretion of hormones that inhibit gastric secretions. 1. Chyme in the duodenum with a pH less than 2.0 or containing fat digestion products inhibits gastric secretions by three mechanisms 2. Chemoreceptors in the duodenum are stimulated by H+ or lipids. Action potentials generated by the chemoreceptors are carried by the vagus nerves to the medulla oblongata where they inhibit parasympathetic action potentials, thereby decreasing gastric secretions. 3. Local reflexes activated by H+ or lipids also inhibit gastric secretion 4. Secretin and cholecystokinin produced by the duodenum decrease gastric secretions in the stomach.

Secretions of the stomach

When gastric juice is mixed with ingested food, chyme (semi liquid) is produced.

Hepatic sinusoids

blood channels containing phagocytic cells that remove foreign particles from blood

Tunics of stomach

external series muscularis (longitudinal, circular, oblique) submucosa mucosa (simple columnar epithelium): secrete a thick mucus that protects the stomach from acid, produce gastric juice

Epiploic appendages

fat filled pouches of vessel peritoneum

Hepatic cords

formed by hepatocytes located between margins of each lobule and separated by hepatic sinusoids.

Portal triad

hepatic artery, hepatic portal vein, hepatic duct.

Control of salivation

mostly parasympathetic. Salivary glands secrete serous, enzyme- rich saliva in response to: the thought of food, ingested food which stimulates chemoreceptors and pressoreceptors. Sympathetic stimulation inhibits salvation and increases mucus content of saliva.

What is needed to digest proteins?

pepsin, trypsin, peptidases

What of the following are functions of the liver?

production of bile, storage of glycogen, convert protein to carbohydrate.

Gastric mucosa

secretory cells in the gastric pits of the mucosa combine to form gastric juice, made of: mucosa, HCl, pepsinogen, regulatory hormones (gastrin, histamine, secretin, cholecystokinin)