Digestive System and Nutrition

central vein of liver - where blood drains to the heart

1. CCK and secretin are secreted by duodenal enteroendocrine cells - cck release is stimulated by proteins and fats in chyme - secretin release is stimulated by acidic chyme - cck and secretin enter the circulation and cause the following ... 2. pancreatic secretion: - cck induces secretion by acinar cells of enzyme rich pancreatic juice - secretion causes secretion by duct cells of HCO3 rich pancreatic juice - vagus nerve weakly stimulates during cephalic and gastric phases 3. bile secretion by liver: - bile salts returning from enterohepatic circulation are the most powerful stimulus for bile secretion - secretion is a minor stimulus 4. cck causes gallbladder contraction - vagus nerve stimulus weak gallbladder contraction during cephalic and gastric phases 5. hepatopancreatic sphincter to relax. bile and pancreatic juices enter duodenum cck inhibits stomach when chyme enter duodenum cck excites gallbladder and pancreas secretin causes secretion of HCO3 rich pancreatic juice - stimulates liver to make more bile - stimulates the release of insulin - to lower bp b/c chyme higher bp)

small intestine absorbs nutrients into blood vessels - or lymph (fatty lymph)

1. Mucosa - (surround lumen) Functions: different layers perform one or all three • Secretes mucus, digestive enzymes, and hormones • Absorbs end products of digestion • Protects against infectious disease - Made up of three sublayers • Epithelium • Lamina propria • Muscularis mucosae 2. Submucosa - Consists of areolar connective tissue - Contains blood and lymphatic vessels, lymphoid follicles, and submucosal nerve plexus that supply surrounding GI tract tissues - Has abundant amount of elastic tissues that help organs to regain shape after storing large meal 3. Muscularis externa - Muscle layer responsible for segmentation and peristalsis - Contains inner circular muscle layer and outer longitudinal layers • Circular layer thickens in some areas to form sphincters 4. Serosa - Outermost layer, which is made up of the visceral peritoneum • Formed from areolar connective tissue covered with mesothelium (single layer of squamous epithelium) in most organs • Replaced by fibrous adventitia in esophagus - Dense connective tissue that holds esophagus to surrounding structures • Retroperitoneal organs have both an adventitia and a serosa

Oxidation reactions: involve the gain of oxygen or loss of hydrogen atoms (and their electrons) • Oxidation-reduction (redox) reactions - Oxidized substances lose electrons and energy - Reduced substances gain electrons and energy - Redox reactions are catalyzed by enzymes that usually require a B vitamin coenzyme - Two important coenzymes act as hydrogen (or electron) acceptors in oxidative pathway • Nicotinamide adenine dinucleotide (NAD+ ) • Flavin adenine dinucleotide (FAD)

1. • Two mechanisms are used to make ATP 1. Substrate-level phosphorylation • High-energy phosphate groups are directly transferred from phosphorylated substrates to ADP • Occurs twice in glycolysis and once in Krebs cycle - Necessary enzymes are in cytosol for glycolysis and in mitochondria for Krebs cycle 2. Oxidative phosphorylation • More complex process, but produces most ATP • Chemiosmotic process: couples movement of substances across membranes to chemical reaction 3. When glucose enters a cell, it is phosphorylated to glucose-6-phosphate - Most cells lack enzymes for reverse reaction, so glucose becomes trapped inside cell • Only cells in intestine, kidney, and liver can reverse reaction and release glucose - Keeps intracellular glucose concentration low, which ensures continued glucose entry

1. Transamination - Many amino acids can transfer their amine group to α-ketoglutaric acid, transforming it into glutamic acid • As a result, original amino acid becomes a keto acid • Glutamic acid is an intermediate keto acid of the citric acid cycle • Reaction is reversible

2. Oxidative deamination - In liver, amine group of glutamic acid is removed as ammonia (NH3 ) - α-ketoglutaric acid is regenerated - NH3 then combines with CO2 to form urea and water • Urea is released to blood and excreted in urine - This urea cycle helps rid body of toxic ammonia Keto acid modification - Keto acids formed from transamination are altered to produce metabolites that can enter citric acid cycle • Major metabolites produced: pyruvic acid, acetyl CoA, α-ketoglutaric acid, oxaloacetic acid - Glycolysis reactions are reversible, so pyruvic acid metabolites formed can be reconverted to glucose • Contributes to gluconeogenesis

mesentery It provides a route for blood vessels, lymphatics, and nerves to reach the digestive viscera.

A burst appendix is the most common cause of peritonitis.

Most of the ATP produced during cellular respiration is produced by oxidative phosphorylation during the chemiosmotic process

A function of the liver during the postabsorptive state is The liver mobilizes glucose reserves quickly and efficiently to maintain blood sugar levels for about four hours during the postabsorptive state.

A kilocalorie is the amount of energy

A kilocalorie is the amount of energy needed to heat 1 kilogram of water 1 degree Celsius.

Alimentary canal (gastrointestinal or GI tract or gut) - Continuous muscular tube that runs from the mouth to anus - Digests food: breaks down into smaller fragments - Absorbs fragments through lining into blood - Organs: mouth, pharynx, esophagus, stomach, small intestine, large intestine, anus

Accessory digestive organs - Teeth - Tongue - Gallbladder - Digestive glands • Salivary glands • Liver • Pancreas

Which of the following is the amount of energy the body needs to maintain life?

BMR

The Pancreas • Location: mostly retroperitoneal, deep to greater curvature of stomach • Exocrine function: produce pancreatic juice - Acini: clusters of secretory cells that produce zymogen granules containing proenzymes - Ducts: secrete to duodenum via main pancreatic duct; smaller duct cells produce water and bicarbonate • Endocrine function: secretion of insulin and glucagon by pancreatic islet cells Composition of pancreatic juice - 1200-1500 ml/day is produced containing: • Watery, alkaline solution (pH 8) to neutralize acidic chyme coming from stomach • Electrolytes, primarily HCO3 − • Digestive enzymes - Proteases (for proteins): secreted in inactive form to prevent self-digestion - Amylase (for carbohydrates) - Lipases (for lipids) - Nucleases (for nucleic acids)

Bile and Pancreatic Secretion into the Small Intestine (cont.) • Regulation of bile and pancreatic secretions - Hormonal controls include: • Cholecystokinin (CCK) • Secretin - Bile secretion is increased when: • Enterohepatic circulation returns large amounts of bile salts • Secretin, from intestinal cells exposed to HCl and fatty chyme, stimulates gallbladder to release bile • Hepatopancreatic sphincter is closed, unless digestion is active

Gastrin is the major stomach hormone. Both the stomach and the small intestine produce this chemical.

Bile and pancreatic enzymes mix at the hepatopancreatic ampulla.

• Digestion - Breakdown of food molecules for absorption into circulation • Mechanical: breaks large food particles to small • Chemical: breaking of covalent bonds by digestive enzymes • Absorption and transport - Molecules are moved out of digestive tract and into circulation for distribution throughout body

Carbohydrates • Types - Simple: • Monosaccharides: Glucose, Fructose, Galactose • Disaccharides: Sucrose, Lactose, Maltose - Complex (all are made of glucose): • Starch, Fiber, Glycogen fructose - makes you hungry sucrose = glucose + fructose Lactose = glucose + galactose maltose = glucose + glucose

Three stages in processing nutrients Stage 1: Digestion, absorption, and transport to tissues Stage 2: Cellular processing (in cytoplasm) • Synthesis of lipids, proteins, and glycogen, or • Catabolism (glycolysis) into pyruvic acid and acetyl CoA Stage 3: Oxidative breakdown of intermediates into CO2 , water, and ATP • Occurs in mitochondria

Cellular respiration: catabolic breakdown of food fuels whereby energy from food is captured to form ATP in cells - Goal of cellular respiration is to trap chemical energy in ATP • Energy can also be stored in glycogen and fats, which can be broken down later • Phosphorylation: enzymes shift high-energy phosphate groups of ATP to other molecules - Phosphorylated molecules become activated to perform cellular functions

duodenum, jejunum, ileum, cecum, ascending colon, transverse colon, descending colon, sigmoid colon, anus

Chemical breakdown - salivary enzymes in mouth --> stomach acid a lot of chemical digestion happens in the duodenum (bile and pancreatic juices)

Which element below is considered a trace mineral?

Chromium is considered a trace mineral. Impaired glucose metabolism occurs without chromium.

Histology of the small intestine wall - Intestinal crypts: tubular glands scattered between villi - Five main types of cells found in villi and crypts 1. Enterocytes: make up bulk of epithelium - Simple columnar absorptive cells bound by tight junctions and contain many microvilli 2. Goblet cells: mucus-secreting cells found in epithelia of villi and crypts 3. Enteroendocrine cells: source of enterogastrones (examples: CCK and secretin) - Found scattered in villi but some in crypts 4. Paneth cells: found deep in crypts, specialized secretory cells that fortify small intestine's defenses - Secrete antimicrobial agents (defensins and lysozyme) that can destroy bacteria 5. Stem cells that continuously divide to produce other cell types - Villus epithelium renewed every 2-4 days

Chyme from stomach contains partially digested carbohydrates and proteins and undigested fats • Takes 3-6 hours in small intestine to absorb all nutrients and most water • Sources of enzymes for digestion - Substances such as bile, bicarbonate, digestive enzymes (not brush border enzymes) are imported from liver and pancreas - Brush border enzymes bound to plasma membrane perform final digestion of chyme

• Citric acid cycle - Also called Krebs cycle - Occurs in mitochondrial matrix - Fueled by pyruvic acid from glucose breakdown and fatty acids from fat breakdown • Pyruvic acid must be actively transported into mitochondria because it is a charged molecule • Once inside mitochondria, pyruvic acid enters transitional phase

Citric acid cycle (cont.) - Transitional phase is where each pyruvic acid is converted to acetyl coenzyme A (acetyl CoA): 1. Decarboxylation: 1 carbon from pyruvic acid is removed, producing CO2 gas, which diffuses into blood to be expelled by lungs 2. Oxidation: remaining 2-C fragment is oxidized to acetic acid by removal of H atoms, which are picked up by NAD+ 3. Formation of acetyl CoA: acetic acid combines with coenzyme A to form acetyl CoA Citric acid cycle (cont.) - For each turn of the cycle, we get: • 2 CO2 from decarboxylation • 4 molecules of reduced enzymes - 3 NADH + H+ and 1 FADH2 • 1 ATP (by substrate level phosphorylation) - Started with 2 pyruvic acid molecules, so amount of final products from 1 glucose is doubled: • 4 CO2 , 6 NADH + H+ , 2 FADH2 , and 2 ATP - Adding products of transitional phase, total final products for breakdown of 1 glucose are: • 6 CO2 , 8 NADH + H+ , 2 FADH2 , and 2 ATP Electron transport chain and oxidative phosphorylation - Oxidative phosphorylation consists of two phases: Phase 1: Electron transport chain creates a proton (H+ ) gradient across mitochondrial membrane using high-energy electrons removed from H from food fuels Phase 2: Chemiosmosis uses the energy of the proton gradient to synthesize ATP

Location: mostly retroperitoneal, deep to greater curvature of stomach • Exocrine function: produce pancreatic juice - Acini: clusters of secretory cells that produce zymogen granules containing proenzymes - Ducts: secrete to duodenum via main pancreatic duct; smaller duct cells produce water and bicarbonate • Endocrine function: secretion of insulin and glucagon by pancreatic islet cells

Composition of pancreatic juice - 1200-1500 ml/day is produced containing: • Watery, alkaline solution (pH 8) to neutralize acidic chyme coming from stomach • Electrolytes, primarily HCO3 − • Digestive enzymes - Proteases (for proteins): secreted in inactive form to prevent self-digestion - Amylase (for carbohydrates) - Lipases (for lipids) - Nucleases (for nucleic acids)

Dietary requirements - Recommended daily intake: 45-65% of total calories • Should consist mostly of complex carbohydrates (whole grains and vegetables) • Added sugars should be less than 10% of total calories

Dietary sources - Triglycerides: most abundant form • Saturated fatty acids found in meat, dairy foods, tropical oils, or hydrogenated oils (trans fats) • Unsaturated fats found in seeds, nuts, olive oil, and most vegetable oils - Cholesterol found in egg yolk, meats, organ meats, shellfish, and milk products • Liver makes ~85% cholesterol - Essential fatty acids = linolenic (omega-3) and linoleic (omega-6) acids

Types of gland cells - Glands in fundus and body produce most gastric juice - Glands include secretory cells: • Mucous neck cells • Parietal cells - HCl - Intrinsic factor • Chief cells - Pepsinogen (activated by HCI into pepsin) - Lipase • Enteroendocrine cells (release hormones) - serotonin and histamine "ogen" - inactive until attached to HCI - positive feedback

Digestive Processes in the Stomach 1. Carries out breakdown of food 2. Serves as holding area for food 3. Delivers chyme to small intestine 4. Denatures proteins by HCl 5. Pepsin carries out enzymatic digestion of proteins 6. Lipid-soluble alcohol and aspirin are absorbed into blood 7. Only stomach function essential to life is secretion of intrinsic factor for vitamin B12 absorption - B12 needed for red blood cells to mature

Cyanide acts as a poison by interfering with the flow of electrons in the electron transport chain.

During fasts lasting several weeks, blood glucose is maintained by gluconeogenesis

Nutrient: substance in food needed for growth, maintenance, repair - Essential nutrients: nutrients that must be eaten because body cannot synthesize these from other nutrients • 45-50 nutrients are considered essential • Macronutrients: three major nutrients that make up the bulk of ingested food - Carbohydrates, lipids, and proteins • Micronutrients: two other nutrients that are required, but only in small amounts - Vitamins and minerals • Water is required, so technically it is a nutrient

Energy value is measured in kilocalories (kcal) - A calorie is the amount of heat needed to raise temperature of 1 kg H2O by 1C • One dietary "Calorie" equals 1 kcal

• Splanchnic circulation includes: - Arteries that branch off aorta to serve digestive organs (supply blood to digestive organs) • Hepatic, splenic, and left gastric arteries • Inferior and superior mesenteric arteries - Hepatic portal circulation • Drains nutrient-rich blood from digestive organs • Delivers blood to liver for processing liver - gatekeeper for venous blood (cleans blood before sent to the body) liver failure - blood will back up into abdominal body organs - causing ascites

Enteric Nervous System • GI tract has its own nervous system, referred to as enteric nervous system - Also called the gut brain - Contains more neurons than spinal cord • Gut brain is made up of enteric neurons that communicate extensively with each other - Major nerve supply to GI tract wall that controls motility

Proteins deteriorate, so they need to be continually broken down and replaced • Amino acids are recycled into new proteins or different compounds • Proteins are not stored in body - When dietary proteins are in excess, amino acids are: • Oxidized for energy or • Converted to fat for storage

First step in amino acid breakdown is deamination, whereby NH2 (amine group) is removed, then converted into: - Pyruvic acid or - One of keto acid intermediates of citric acid cycle • Three events of amino acid degradation 1. Transamination 2. Oxidative deamination 3. Keto acid modification

The Liver • Hepatocytes - Functions: • Produce ~900 ml bile per day - Yellow-green, alkaline solution containing: » Bile salts: cholesterol derivatives that function in fat emulsification and absorption » Bilirubin: pigment formed from heme » Cholesterol, triglycerides, phospholipids, and electrolytes - Enterohepatic circulation » Recycling mechanism that conserves bile salts • Process bloodborne nutrients - Ex: store glucose as glycogen • Store fat-soluble vitamins • Perform detoxification - Ex: converting ammonia to urea Homeostatic imbalance of liver - Hepatitis • Usually viral infection, drug toxicity, wild mushroom poisoning - Cirrhosis • Progressive, chronic inflammation from chronic hepatitis or alcoholism • Liver fatty, fibrous portal hypertension - Liver transplants successful, but livers are scarce • Liver can regenerate to its full size in 6-12 months after 80% removal

Gallbladder is a thin-walled muscular sac on ventral surface of liver - Contains many honeycomb folds that allow it to expand as it fills • Functions: store and concentrate bile - Muscular contractions release bile via cystic duct, which flows into bile duct • Gallstones are precipitated cholesterol, and can block the cystic duct

The Liver • Hepatocytes - Functions: • Produce ~900 ml bile per day - Yellow-green, alkaline solution containing: » Bile salts: cholesterol derivatives that function in fat emulsification and absorption » Bilirubin: pigment formed from heme » Cholesterol, triglycerides, phospholipids, and electrolytes - Enterohepatic circulation » Recycling mechanism that conserves bile salts • Process bloodborne nutrients - Ex: store glucose as glycogen • Store fat-soluble vitamins • Perform detoxification - Ex: converting ammonia to urea Homeostatic imbalance of liver - Hepatitis • Usually viral infection, drug toxicity, wild mushroom poisoning - Cirrhosis • Progressive, chronic inflammation from chronic hepatitis or alcoholism • Liver fatty, fibrous portal hypertension - Liver transplants successful, but livers are scarce • Liver can regenerate to its full size in 6-12 months after 80% removal

Gallbladder is a thin-walled muscular sac on ventral surface of liver - Contains many honeycomb folds that allow it to expand as it fills • Functions: store and concentrate bile - Muscular contractions release bile via cystic duct, which flows into bile duct • Gallstones are precipitated cholesterol, and can block the cystic duct

Regulation of Gastric Secretion • Gastric mucosa secretes >3 L of gastric juice/day and are regulated by: - Neural mechanisms • Vagus nerve stimulation increases secretion • Sympathetic stimulation decreases secretion - Hormonal mechanisms • Gastrin stimulates enzyme and HCl secretion • Gastrin antagonists are secreted by small intestine

Gastric secretions are broken down into three phases 1. Cephalic (reflex) phase • Conditioned reflex triggered by aroma, taste, sight, thought (before ingesting food - thought of food) 2. Gastric phase • Lasts 3-4 hours and provides two-thirds of gastric juice released (food in stomach) 3. Intestinal phase • Begins with a brief stimulatory component followed by inhibition - when small intestine digests chyme it stops the stomach from working

Glycolysis (cont.) - Although 4 total ATPs are made, the 2 ATPs needed to prime system in phase 1 must be subtracted - So, final products of glycolysis are: • 2 pyruvic acids (C3H4O3 ) • 2 reduced NAD+ (NADH + H+ ) • Net gain of 2 ATP - Glycolysis results in faster ATP production than aerobic respiration, but yields far less ATP

Glycolysis (cont.) - Supply of NAD+ is limited • NADH must donate its accepted hydrogen atoms to become NAD+ again to be free to pick up more H+ so glycolysis can continue - If oxygen is present, NADH will transfer its H to proteins in electron transport chain » Occurs in mitochondria - If no oxygen is present, NADH will give hydrogen atoms back to pyruvic acid, reducing it to lactic acid

Esophagus has all four alimentary canal layers Mucosa (stratified squamous epithelium) Submucosa (areolar connective tissue) Muscularis externa (- circular layer, - longitudinal layer) Adventitia (fibrous connective tissue)

Gross Anatomy of the Stomach • Stomach is a temporary storage tank that starts chemical breakdown of protein digestion - Converts bolus of food to paste-like chyme - Empty stomach has ~50 ml volume but can expand to 4 L - When empty, stomach mucosa forms many folds called rugae

The myxovirus causes mumps.

Halitosis is caused by increased activity of anaerobic bacterial activity at the back of the tongue.

Which of the following intestinal hormones is NOT an enterogastrone? gastrin

Hollow muscular organs, like the stomach, that act as reservoirs exhibit plasticity, which is the intrinsic ability of visceral smooth muscle to exhibit the stress-relaxation response.

A major means for conserving heat is vasoconstriction of cutaneous blood vessels

In glycolysis, glucose must be activated with the use of how many ATP molecules? 2 Glucose must be activated with two ATP molecules. Fructose-1,6-bisphosphate is formed when ATP does its job.

Many of the early food allergies seen in infants are caused by __________. absorption of whole proteins Lactase deficiency develops later in life, not in infancy.

Irritable bowel syndrome is not explained by anatomical or biochemical abnormalities.

• Lipogenesis: triglyceride synthesis that occurs when cellular ATP and glucose levels are high • Dietary glycerol and fatty acids not needed for energy are stored as triglycerides - 50% is stored in adipose tissue; other 50% is deposited in other areas • Glucose is easily converted to fat because acetyl CoA is an intermediate in glucose catabolism and the starting point for fatty acid synthesis

Lipolysis: breakdown of stored fats into glycerol and fatty acids; reverse of lipogenesis - Fatty acids are actually preferred by liver, cardiac muscle, resting skeletal muscle for fuel - Lipolysis is accelerated when carbohydrate intake is inadequate • Beta oxidation of the released fatty acids results in production of large amounts of acetyl CoA - Acetyl CoA can enter citric acid cycle only if enough intermediates (oxaloacetic acid) are available • If intermediates are not available, acetyl CoA can accumulate • Accumulated acetyl CoA can be converted by ketogenesis in liver to ketone bodies (ketones)

Examples of uses in body - Calcium, phosphorus, and magnesium salts harden bone - Iron is essential for oxygen binding to hemoglobin - Iodine is necessary for thyroid hormone synthesis - Sodium and chloride are major electrolytes in blood • Mineral-rich foods - Vegetables, legumes, milk, some meats

Metabolism: sum of all biochemical reactions inside a cell involving nutrients - Anabolism: synthesis of large molecules from small ones • Example: synthesis of proteins from amino acids - Catabolism: hydrolysis of complex structures to simpler ones • Example: breakdown of proteins into amino acids

Gross Anatomy of the Stomach • Autonomic nervous system supplies stomach - Sympathetic fibers from thoracic splanchnic nerves are relayed through celiac plexus - Parasympathetic fibers are supplied by vagus nerve • Blood supply - Celiac trunk (gastric and splenic branches) - Veins of hepatic portal system

Microscopic Anatomy of the Stomach • Mucosa layer - Consists of simple columnar epithelium entirely composed of mucous cells • Secrete two-layer coat of alkaline mucus - Surface layer traps bicarbonate-rich fluid layer that is beneath it - Dotted with gastric pits, which lead into gastric glands • Gastric glands produce gastric juice

Liver, gallbladder, and pancreas are accessory organs associated with small intestine • Liver: digestive function is production of bile - Bile: fat emulsifier • Gallbladder: chief function is storage of bile • Pancreas: supplies most of enzymes needed to digest chyme, as well as bicarbonate to neutralize stomach acid

Microscopic anatomy of the liver - Liver lobules • Hexagonal structural and functional units • Composed of plates of hepatocytes (liver cells) that filter and process nutrient-rich blood • Central vein located in longitudinal axis

The Liver • Gross anatomy of the liver - Falciform ligament • Separates larger right and smaller left lobes • Suspends liver from diaphragm & anterior abdominal wall - Round ligament (ligamentum teres)

Microscopic anatomy of the liver - Liver lobules • Hexagonal structural and functional units • Composed of plates of hepatocytes (liver cells) that filter and process nutrient-rich blood • Central vein located in longitudinal axis

Two types of vitamins based on solubility - Water-soluble vitamins • B complex and C are absorbed with water • B12 absorption requires intrinsic factor • Not stored in the body - Any not used within 1 hour are excreted - Fat-soluble vitamins • A, D, E, and K are absorbed with lipid digestion products • Stored in body, except for vitamin K - Excessive consumption can cause health problems

Minerals • Seven minerals are required in moderate amounts: - Calcium, phosphorus, potassium, sulfur, sodium, chlorine, and magnesium • Others are required in trace amounts • Work with nutrients to ensure proper body functioning • Uptake and excretion are balanced to prevent toxic overload

Which lipoprotein contains high levels of cholesterol? LDLs are about 45% cholesterol.

Nutritionally incomplete proteins are low in one or more of the essential amino acids

Most vitamins function as coenzymes or parts of coenzymes in the body. Coenzymes help catalyze chemical reactions.

One function of vitamin A is to _ form visual pigments Retinol in the rods and cones are derived from vitamin A.

Gluconeogenesis - Process of forming new (neo) glucose from noncarbohydrate sources - Occurs in the liver - Glucose can be formed from glycerol and amino acids when blood glucose levels drop - Protects against damaging effects of low blood glucose levels (hypoglycemia) • Especially important for nervous system

Only triglycerides are routinely oxidized for energy • Two building blocks of triglycerides are oxidized separately 1. Glycerol breakdown • Glycerol is broken down into glyceraldehyde 3-phosphate (same as in glycolysis), which then enters citric acid cycle - ATP yield is roughly half that of glucose because glyceraldehyde is only a half glucose - Yields 15 ATP/glycerol 2. Fatty acid breakdown - Fatty acids undergo beta oxidation in mitochondria: • Fatty acid chains are broken into two-carbon acetic acid fragments, and coenzymes (FAD and NAD+ ) are reduced in process • Acetic acid fragment fuses with CoA to form acetyl CoA, which enters citric acid cycle - Reduced coenzymes enter electron transport chain • Referred to as "beta" oxidation because two carbons are broken off fatty acid chain, allowing third-position carbon to be oxidized

Basic Concepts of Regulating GI Activity Three key concepts: 1. Digestive activity is provoked by a range of mechanical and chemical stimuli - Receptors located in walls of GI tract organs - Respond to stretch, changes in osmolarity and pH, and presence of substrate and end products of digestion 2. Effectors of digestive activity are smooth muscle and glands - When stimulated, receptors initiate reflexes that stimulate smooth muscle to mix and move lumen contents - Reflexes can also activate or inhibit digestive glands that secrete digestive juices or hormones 3. Neurons (intrinsic and extrinsic) and hormones control digestive activity - Nervous system control • Intrinsic controls: involve short reflexes (enteric nervous system) • Extrinsic controls: involve long reflexes (autonomic nervous system) - Hormonal controls • Hormones from cells in stomach and small intestine stimulate target cells in same or different organs to secrete or contract

Oral Cavity Associated organs include: - Mouth - Tongue - Salivary glands - Teeth walls of mouth - stratified squamous epithelium

Phase 1: Electron transport chain • ETC: only pathway that directly uses oxygen - Citric acid cycle will not run if oxygen is not present, but does not directly use oxygen • Overview - NADH + H+ and FADH2 (from glycolysis and Krebs cycle) deliver hydrogen atoms taken from glucose to ETC proteins - ETC will use energy harnessed in electrons of hydrogen to pump H+ across membrane to create proton gradient - Some H+ will combine with O2 to produce water

Oxidation of Glucose (cont.) Phase 1: Electron transport chain (cont.) • Three major steps involved in ETC Step 1. Complexes I and II accept hydrogen from NADH and FADH2 » NAD+ and FAD can now return to glycolysis and Krebs cycle Step 2. Hydrogen atoms are split into H+ + electrons (e−) » Electrons are passed down chain » Each complex is reduced when it accepts e−, then oxidized when it passes electron on to next complex Step 3 » At complex IV, electron pairs combine with some H+ and a molecule of oxygen to form w

Wisdom teeth are the most common teeth to become impacted.

Periodontitis is associated with an increased risk for heart disease or stroke.

Processing of food involves six essential activities: 1. Ingestion: eating 2. Propulsion: movement of food through the alimentary canal, which includes: • Swallowing • Peristalsis: major means of propulsion of food that involves alternating waves of contraction and relaxation

Peristalsis Adjacent segments of the alimentary canal organs alternately contract and relax. • Food is moved distally along the tract • Primarily propulsive; some mixing may occur From mouth Segmentation (mixing of food) Nonadjacent segments of the alimentary canal organs contract and relax. • Food is moved forward, then backward • Primarily mixes food and breaks it down mechanically; some propulsion may occur

Mechanical breakdown: includes chewing, mixing food with saliva, churning food in stomach, and segmentation • Segmentation: local constriction of intestine that mixes food with digestive juices 4. Digestion: series of catabolic steps that involves enzymes that break down complex food molecules into chemical building blocks 5. Absorption: passage of digested fragments from lumen of GI tract into blood or lymph 6. Defecation: elimination of indigestible substances via anus in form of feces

Peritoneum: serous membranes of abdominal cavity that consists of: - Visceral peritoneum: on external surface of most digestive organs - Parietal peritoneum: covers interior surface of body wall • Retroperitoneal organs: located outside, or posterior to, the peritoneum - Includes most of pancreas, duodenum, and parts of large intestine most digestive organs are intraperitoneal and are suspended from the body wall by a dorsal mesentery some intraperitoneal digestive organs are suspended from the body wall by ventral mesenteries

Protective collections of lymphocytes and macrophages are found in

Peyer's patches, which contain lymphocytes and macrophages, increase in number toward the end of the ileum.

glucose and galactose are absorbed via contransport with NA+

Proteins • Made up of amino acids - 20 different types • Essential - Must consume in diet • Non-essential - Made by body in sufficient quantity • Amino acids joined together by peptide bonds

The hormone that controls essentially all events of the absorptive state is _

Rising blood glucose levels after a carbohydrate-containing meal act as a humoral stimulus that prods the beta cells of the pancreatic islets to secrete more insulin.

Salivary Glands • Functions of saliva - Cleanses mouth - Dissolves food chemicals for taste - Moistens food; compacts into bolus - Begins chemical breakdown of food • Composition of saliva - Mostly water (97-99.5%), so hypo-osmotic - Slightly acidic (pH 6.75 to 7.00) - Electrolytes: Na+ , K+ , Cl− , PO4 2−, HCO3 − - Salivary amylase and lingual lipase - Proteins: mucin, lysozyme, and IgA - Metabolic wastes: urea and uric acid - Lysozyme, IgA, defensins, and nitric oxide from nitrates in food protect against microorganisms

Salivary glands are composed of two types of secretory cells - Serous cells: produce watery secretion, enzymes, ions, bit of mucin - Mucous c

The secretion of intrinsic factor is the only stomach function that is essential to life.

Some aspects of the cephalic phase of gastric secretion may be considered conditioned reflexes.

Gross Anatomy • Large intestine has three unique features not seen elsewhere: - Teniae coli: three bands of longitudinal smooth muscle in muscularis - Haustra: pocketlike sacs caused by tone of teniae coli - Epiploic appendages: fat-filled pouches of visceral peritoneum

Subdivisions of Large Intestine 1. Cecum: first part of large intestine 2. Appendix: masses of lymphoid tissue 3. Colon: has several regions • Ascending colon: travels up right side of abdominal cavity to level of right kidney • Transverse colon: travels across abdominal cavity • Descending colon: travels down left side of abdominal cavity • Sigmoid colon: S-shaped portion that travels through pelvis 4. Rectum: three rectal valves stop feces from being passed with gas (flatus) 5. Anal canal: last segment of large intestine that opens to body exterior at anus • Has two sphincters - Internal anal sphincter: smooth muscle - External anal sphincter: skeletal muscle

Tooth structure - Each tooth has two major regions: • Crown: exposed part above gingiva (gum) - Covered by enamel, the hardest substance in body » Heavily mineralized with calcium salts and hydroxyapatite crystals » Enamel-producing cells degenerate when tooth erupts, so no healing if tooth decays or cracks; needs artificial repair by filling • Root: portion embedded in jawbone - Connected to crown by neck

The Pharynx • Food passes from mouth into oropharynx and then into laryngopharynx - Allows passage of food, fluids, and air - Stratified squamous epithelium lining with mucus-producing glands The Esophagus • Flat muscular tube that runs from laryngopharynx to stomach - Is collapsed when not involved in food propulsion

The digestive system in a cadaver is longer than that in a living person because there is no muscle tone in a cadaver.

The enteric nerve plexuses stimulate the short reflexes in the digestive system.

HCl, IF, mucous, and pepsinogen (pepsin) are products of the stomach.

The final product of carbohydrate digestion is __________. monosaccharides

The pancreatic duct empties into the duodenum, where activation of proteases occurs. This process occurs to prevent self-digestion of the pancreas.

The gastroesophageal sphincter is the junction between stomach (gastro) and esophagus. A loose gastroesophageal sphincter can cause heartburn or acid reflux.

Which of the following is a characteristic of the large intestine?

The large intestine contains a large number of bacteria. E. coli is the primary bacterial species in the colon.

The only enzyme produced by the stomach is pepsin, which digests protein.

The propulsive function that occurs in the esophagus is called __________. Peristalsis occurs as a wave of contraction.

The hormone responsible for setting the basal metabolic rate is __________ Thyroxine is the body's major controller of metabolism.

The site of electron transport is the mitochondrial inner membrane (cristae) The inner membrane of the mitochondrion contains the integral proteins necessary for electron transport.

Lips and cheeks - Lips (labia): composed of fleshy orbicularis oris muscle - stratified squamous cells Cheeks: composed of buccinator muscles - Labial frenulum: median attachment of each lip to gum • Palate: roof of oral cavity - Hard palate: anterior, supported by maxilla and palatine bone - Soft palate: posterior, consists of skeletal muscle and CT - Uvula: projects from posterior of soft palate

Tongue • Functions include: - Gripping, repositioning, and mixing of food during chewing - Formation of bolus, mixture of food and saliva - Initiation of swallowing, speech, and taste • Intrinsic muscles change shape of tongue • Extrinsic muscles alter tongue's position - Protrude or retract tongue - Move side to side • Lingual frenulum: attachment to floor of mouth

The final product of glycolysis is _

Two molecules of pyruvic acid, two molecules of NAD+, and a net gain of two ATP

Proteins Carbohydrates • Dietary sources - Plants! • Sugars (mono- and disaccharides) in fruits, sugarcane, sugar beets, honey, and milk • Starch & fiber in grains, root vegetables, legumes (beans) - Insoluble fiber: cellulose in vegetables provides roughage - Soluble fiber: pectin in apples and citrus fruits reduces blood cholesterol levels - Small amount in milk sugar, glycogen in meats

Uses in body - Glucose: fuel most used by cells to make ATP • Some cells use fat for energy - Neurons and RBCs rely entirely on glucose » Neurons die quickly without glucose - Excess glucose is converted to glycogen or fat, then stored - Fructose and galactose are converted to glucose by liver before entering circulation

• Dietary sources - Animal products (eggs, milk, fish, most meats), as well as soybeans, are considered complete proteins • Contain all needed essential amino acids - Legumes, nuts, and cereals contain incomplete proteins • Legumes and cereal grains together contain all essential amino acids

Uses in body - Structural materials • Example: keratin (skin), collagen and elastin (connective tissue), and muscle proteins - Functional molecules • Example: enzymes and some hormones - Nitrogen balance • Rate of protein synthesis equals rate of breakdown and loss - Positive nitrogen balance: synthesis exceeds breakdown (normal in children, pregnant women, tissue repair) - Negative nitrogen balance: breakdown exceeds synthesis (example: stress, burns, infection, injury, poor dietary proteins, starvation)

Lipids • Types - Triglycerides • Major source of lipid in our diet • Main storage form of lipid in the body - Phospholipids - Sterols • Cholesterol © 2016 Pearson Education, Inc. • Plant sterols

Vitamin absorption - In small intestine • Fat-soluble vitamins (A, D, E, and K) are carried by micelles; diffuse into absorptive cells • Water-soluble vitamins (C and B) are absorbed by diffusion or by passive or active transporters • Vitamin B12 (large, charged molecule) binds with intrinsic factor and is absorbed by endocytosis - In large intestine: vitamin K and B vitamins from bacterial metabolism are absorbed

Dietary requirements - Needs reflect age, size, metabolic rate, nitrogen balance, exercise level, pregnancy status - Rule of thumb: daily intake of 0.8 g per kg body weight - American diet provides more than needed

Vitamins • Organic compounds that are crucial in helping body use nutrients • Most function as coenzymes • Most must be ingested, except: - Vitamin D (made in skin) - Some B and K synthesized by intestinal bacteria - Beta-carotene (e.g., from carrots) converted in body to vitamin A • No one food group contains all vitamins

In order for amino acids to be oxidized for energy, the amine group (NH2) must be removed.

What is the major role of leptin in the body? promote a feeling of satiety

The thermoregulatory center is located in the hypothalamus

Which coenzyme is reduced in both glycolysis and the Krebs cycle? Reduction is the gain of H. NAD is reduced to NADH in both glycolysis and the Krebs cycle.

Parietal cells make HCl and intrinsic factor.

Which of the following cells produce pepsinogen? Chief cells are the enzyme-producing cells.

Which of the following substances is considered a provitamin? beta-carotene

Which of the following fat-soluble vitamins is NOT stored in the body? VITAMIN K

gastroesophageal sphinter

aka cardiac sphincter - where heart burn is mistaken

Which of the following factors makes it harder for an obese person to lose weight?

an increase in alpha receptors (the kind that favors fat accumulation) in fat cells

lesser curvature

attaches to liver greater curvature attaches to abdominal wall fundus - food is held here

1. Propulsion - peristaltic waves moves from the fundus toward the pylorous 2. grinding - the most vigorous peristalsis and mixing action occur close to the pylorus. The pyloric end of the stomach acts as a pump that delivers small amounts of chyme into the duodenum 3. Retropulsion - the peristaltic wave closes the pyloric valve, forcing most of the contents of the pylorus backwards into the stomach (burping)

carb rich chyme moves quickly through duodenum (ex. bread) fatty chyme remains in duodenum 6 hours or more dumping syndrome - receives nutrients too quickly

bile is yellow- green because of bilirubin

interlobular veins drains into inferior vena cava bile duct receives bile from bile canaliculi portal vein - where digestive system drains nutrient rich oxygen poor blood

a substance secreted by the stomach which enables the body to absorb vitamin B12. It is a glycoprotein.

intrinsic factor

Bile and Pancreatic Secretion into the Small Intestine (cont.) • Regulation of bile and pancreatic secretions - Hormonal controls include: • Cholecystokinin (CCK) • Secretin - Bile secretion is increased when: • Enterohepatic circulation returns large amounts of bile salts • Secretin, from intestinal cells exposed to HCl and fatty chyme, stimulates gallbladder to release bile • Hepatopancreatic sphincter is closed, unless digestion is active

liver uses damaged RBCs to make bile stercobilin - color brown feces

Prolonged high protein intake can lead to

loss of bone mass

Essential nutrients refer to nutrients that are _________

obtained from an outside source because the body cannot make them fast enough to meet the body's needs, so our diet must provide them

A low-density lipoprotein would contain a high lipid content

periodontal - ligament anchors a tooth in the alveolus of the jaw

Which of the following is a physiological response to hypothermia?

shivering

During the intestinal phase of gastric regulation,

the stomach is initially stimulated and later inhibited

Absorption of electrolyte minerals - Iron and calcium are absorbed in duodenum • Iron and calcium absorption is related to need - Ionic iron is stored in mucosal cells with ferritin - When needed, transported in blood by transferrin • Ca2+ absorption is regulated by vitamin D and parathyroid hormone (PTH) - Na+ absorption is coupled with active absorption of glucose and amino acids - Cl− is transported actively - K+ diffuses in response to osmotic gradients; lost if water absorption is poor

• Absorption of water - 9 L water, most from GI tract secretions, enter small intestine • 95% is absorbed in the small intestine by osmosis • Most of rest is absorbed in large intestine - Net osmosis occurs if concentration gradient is established by active transport of solutes - Water uptake is coupled with solute uptake

Major organ of digestion AND absorption • 2-4 m long (7-13 ft) from pyloric sphincter to ileocecal valve, point at which it joins large intestine • Subdivisions - Duodenum: mostly retroperitoneal; ~25.0 cm (10.0 in) long; curves around head of pancreas • Has most features - Jejunum: ~2.5 m (8 ft) long; attached posteriorly by mesentery - Ileum: ~3.6 m (12 ft) long; attached posteriorly by mesentery; joins large intestine at ileocecal valve

• Blood supply: - Superior mesenteric artery brings blood supply - Veins (carrying nutrient-rich blood) drain into superior mesenteric veins, then into hepatic portal vein, and finally into liver • Nerve supply - Parasympathetic innervation via vagus nerve, and sympathetic innervation from thoracic splanchnic nerves

The Teeth • Teeth lie in sockets in gum-covered margins of mandible and maxilla • Dentition - Primary dentition consists of 20 deciduous teeth, or baby teeth, that erupt between 6 and 24 months of age - 32 deep-lying permanent teeth enlarge and develop while roots of milk teeth are resorbed from below, causing them to loosen and fall out • Occurs around 6-12 years of age - All but 3rd molars (wisdom teeth) are in by end of adolescence • Third molars may or may not emerge around 17-25 years of age

• Dentition • Teeth are classified according to shape: - Incisors: chisel shaped for cutting - Canines: fanglike teeth that tear or pierce - Premolars (bicuspids): broad crowns with rounded cusps used to grind or crush - Molars: broad crowns, rounded cusps: best grinders • During chewing, upper and lower molars lock together, creating tremendous crushing force

Uses in body - Adipose tissue offers protection, insulation, fuel storage - Phospholipids essential in myelin sheaths and all cell membranes - Cholesterol stabilizes membranes; precursor of bile salts, steroid hormones - Prostaglandins smooth muscle contraction, BP control, inflammation - Help absorb fat-soluble vitamins - Major fuel of hepatocytes and skeletal muscle

• Dietary requirements - Fats: Less than 30% of total calories - Saturated fats: Less than 10% of total calories - Keep trans fat intake to minimum - Essential fatty acids: • 1.1-1.6 grams/day Omega-3 • 11-17 grams/day Omega-6

Phase 1: Electron transport chain (cont.) Coenzyme-2H + ½ (O2 ) Coenzyme + H2O reduced oxidized coenzyme coenzyme • Energy from electrons is used to pump H+ into inner membrane space, creating an electrochemical proton (H+ ) gradient Phase 2: Chemiosmosis • Proton concentration gradient formed also creates - (1) pH gradient - (2) voltage gradient across membrane

• Glycogenesis - Glycogen can be formed with excess glucose • Catalyzed by glycogen synthase • Glucose is converted to glucose-6-phosphate, then converted to isomer glucose-1-phosphate - Mostly occurs in liver and skeletal muscle cells • Glycogenolysis - Breakdown of glycogen via glycogen phosphorylase in response to low blood glucose • Forms glucose-1-phosphate, which is converted to glucose-6- phosphate, which then can enter glycolysis in that cell - Liver cells, as well as some kidney and intestinal cells, also contain enzyme glucose-6-phosphatase that removes terminal phosphate, producing free glucose • Glucose can enter bloodstream to be used by other cells

Oxidation of Glucose • Glucose is catabolized via following reaction: C6H12O6 + 6O2 6H2O + 6CO2 + 32 ATP + heat glucose oxygen water carbon dioxide • Complete glucose catabolism requires three pathways 1. Glycolysis 2. Krebs cycle 3. Electron transport chain and oxidative phosphorylation

• Glycolysis - Also called glycolytic pathway - Involves 10-step pathway - Anaerobic: occurs despite presence/absence of O2 - Occurs in cytosol - Glucose is broken into two pyruvic acid molecules - Three major phases Phase 1: Sugar activation Phase 2: Sugar cleavage Phase 3: Sugar oxidation and ATP formation

Defecation - Mass movements force feces toward rectum - Distension initiates spinal defecation reflex - Parasympathetic signals • Stimulate contraction of sigmoid colon and rectum • Relax internal anal sphincter - Conscious control allows relaxation of external anal sphincter - Muscles of rectum contract to expel feces - Assisted by Valsalva's maneuver

• Liver, gallbladder, and pancreas are accessory organs associated with small intestine • Liver: digestive function is production of bile - Bile: fat emulsifier • Gallbladder: chief function is storage of bile • Pancreas: supplies most of enzymes needed to digest chyme, as well as bicarbonate to neutralize stomach acid

• Regulating chyme entry - Chyme entering duodenum is usually hypertonic; therefore, chyme delivery has to be slow to prevent osmotic loss of water from blood - Low pH of chyme has to be adjusted upward - Chyme has to be mixed with bile and pancreatic juice to continue digestion - Enterogastric reflex and enterogastrones control movement of food into duodenum to prevent it from being overwhelmed

• Motility of the small intestine - After a meal • Segmentation is most common motion of small intestine - Initiated by intrinsic pacemaker cells - Mixes/moves contents toward ileocecal valve - Between meals • Peristalsis increases, initiated by rise in hormone motilin in late intestinal phase (every 90-120 minutes) • Meal remnants, bacteria, and debris are moved toward large intestine • Complete trip from duodenum to ileum takes ~2 hours

Gut bacteria and health - Mounting evidence supports findings that the kinds and proportions of gut bacteria can influence: • Body weight • Susceptibility to various diseases (including diabetes, atherosclerosis, fatty liver disease) • Our moods - Manipulating gut bacteria may become a routine health-care strategy in future

• Residue remains in large intestine 12-24 hours • No food breakdown occurs except what enteric bacteria digest • Vitamins (made by bacterial flora), water, and electrolytes (especially Na+ and Cl− ) are reclaimed • Major functions of large intestine is propulsion of feces to anus and defecation - Haustral contractions: most contractions of colon • Slow segmenting movements, mostly in ascending and transverse colon - Gastrocolic reflex: initiated by presence of food in stomach • Results in mass movements

• Enterogastric reflex - Duodenum inhibits acid secretion in stomach by: • Enteric nervous system short reflexes • Sympathetic nervous system and vagus nerve long reflexes • Enterogastrones - Duodenal enteroendocrine cells release two important hormones that inhibit gastric secretion • Secretin • Cholecystokinin (CCK) - when chyme contains fat

• Response of the stomach to filling - Stretches to accommodate incoming food - Two factors cause pressure to remain constant until 1.5 L of food is ingested • Receptive relaxation: reflex-mediated relaxation of smooth muscle coordinated by swallowing center of brain stem • Gastric accommodation: intrinsic ability of smooth muscle to exhibit stress-relaxation response, which enables hollow organs to stretch without increasing tension or contractions