Ch 14: Digestive Physiology

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Ch 14: Digestive Physiology The GI tract is a hollow tube ~30 ft, mouth to anus Transports food/liquid/chime Accessory organs (liver, pancreas) & glands outside tubular system secrete substances that aid
Ch 14: Digestive Physiology The GI tract is a hollow tube ~30 ft, mouth to anus Transports food/liquid/chime Accessory organs (liver, pancreas) & glands outside tubular system secrete substances that aid digestion. Allows for absorption of nutrients across intestinal membrane to blood. Packages un-used substances for excretion as solid waste. 2 1 GI tract: Mouth, teeth, salivary glands Pharynx Esophagus Stomach Small intestine - duodenum - Jejunum - ileum Accessory to small Intestine: - Liver - Pancreas Large intestine Rectum Anus 4 basic GI processes Motility- muscles mix & move food through successive compartments Digestion- ingested food broken into small molecules Absorption- molecules move from GI lumen into blood stream Secretion- movement of substances into the lumen, e.g. enzymes, HCO 3-4 2 GI Tract Layers Four layers (a.k.a. tunics): 1. Mucosa: 2. Submucosa: 3. Muscularis: 4. Serosa: 1. Mucosa: - innermost layer with: - mucus-secreting (goblet) cells or other exocrine cells - endocrine cells - absorptive cells - lymph nodes (immune function) - may be folded ( plicae ) to surface area 3 2. Submucosa: - layer with: - blood supply & lymph vessels - nerve supply= Miessner s plexi sensory neurons & motor neurons transmitting vagus nerve commands to muscularis, parasympathetic = sympathetic = 3. Muscularis: - layer with: - 2 muscle layers (circular layer for diameter, & longtitudinal for length) - nerve supply= Auerbach s plexis 4. Serosa: outermost layer of connective tissue, continuous with peritoneum and mesentery. 4 Upper GI tract begins mouth mastication, saliva, amylase Pharynx or throat- common passage for air & food Epiglottis covers opening to trachea (glottis) when swallowing. 9 Saliva is a cocktail produced by several glands HCO 3 - mucus amylase lysozyme: lyses bacteria 10 5 Esophagus is a muscular tube Beginning is skeletal muscle, lower portions all smooth muscle. Each end controlled by circular sphincter muscle Passes thru hole in diaphragm: esophageal hiatus Failure of lower esophageal sphincter allows gastric reflux- backflow of acidic stomach contents = 11 Barrett s esophagus is pre-cancerous condition Chronic acid damage Misplaced glandular cells replace normal squamous epithelium Higher risk of adenocarcinoma (cancer of glandular tissue) 12 6 Barrett s endoscopy Pink- normal esophageal Squamous epithelium Red- Barrett s columnar epithelium Esophageal cancer: On the rise- top 10 most common cancers worldwide Risk factors: alcohol, smoking, acid reflux Very poor 5 yr survival rate for advanced stages ( 40%) 90% of cases diagnosed in advanced stages Therapy- surgery, radiation, chemo 13 Cancer terminology Neoplasm- any new growth, designated by the suffix -oma Carcinoma- cancerous cells arising from epithelial tissue Adenocarcinoma- cancerous cells with glandular (secretory) properties that begin growing in the cells that line some internal organs 14 7 Esophageal cancer On the rise- top 10 most common cancers worldwide Risk factors: alcohol, smoking, reflux Very poor 5 yr survival rate for advanced stages ( 40%) 90% of cases diagnosed in advanced stages Therapy- surgery, radiation, chemo 15 Stomach is J-shaped muscular sac Folded lining (rugae) contains gastric glands Contractile activity mixes gastric juice w/ food chyme pyloric sphincter controls emptying 16 8 Gastric pits, in fundus & body, have gastric cells: Neck cells: make mucus Parietal cells: secret HCl, & intrinsic factor for B12 absorption Chief cells: pepsinogen G-cells: hormone gastrin, stimulates parietal cells 17 Peptic ulcer disease results from erosion of stomach lining Stomach mucus protects against ph~2! Open lower layers to acid & pepsin attack Affects ~10% of US population Many are caused by H. pylori infection Perforated ulcer 18 9 Helicobacter pylori: an acidophile Cause immune response that destroys tissue Treated w/: 1) antibiotics 2) histamine receptor (H 2 ) antagonists 3) proton pump blockers Ex. 19 Sm Intestine - site of digestion for most foods 3 regions: duodenum, jejunum, ileum (Most nutrient absorption completed in first 20%, before reaching ileum) Duodenum receives chyme from stomach, pancreatic enzymes & bicarbonate, & bile from liver. Sm intestine endocrine secretions: (REVIEW!) - secretin - stimulate water and bicarbonate secretion from pancreas - cholecystokinin stimulates gallbladder contraction & stimulates pancreatic enzyme secretion - gastric inhibitory peptide - slows gastric motility (slow down) & stimulates pancreatic enzyme secretion 20 10 Hepatic portal system Substances absorbed into blood from intestine go to liver 1st pass metabolism - orally administered drugs are taken directly to liver 21 Liver produces bile Contains HCO 3-, phospholipids, cholesterol-like bile salts Excess bile stored in gall bladder - bile secreted thru common bile duct to duodenum Gallstones or cholelethiasis Bile salts precipitate out of bile and form stones. 10% of americans TX: - Medication to dissolve stones - Surgical removal of gallbladder (laproscopically) 12 Liver: a most versatile organ Glucose/glycogen metabolism Removal of old RBCs Clears hormones, medications, toxins from body Cori cycle Blood glucose regulation Amino acid metabolism 25 Pancreas has endocrine & exocrine functions Acinar cells exocrine secretions (digestive enzymes) Amylase for starch & glycogen Lipases for fats Proteases for proteins Nucleases for nucleic acids Islet cells endocrine secretion Beta cells - insulin alpha cells - glucagon 26 13 Large intestine removes H 2 O from chyme Lg intestine: - Cecum - colon (ascending, transverse, descending) - rectum Transforms chyme into solid feces (water reabsorbed from chyme) Solid feces stored in rectum - has stretch receptors that signal for defecation Anus has involuntary and voluntary sphincters Blockage/inflammation of vermiform appendix = appendicitis 27 Defecation involves voluntary & involuntary anal sphincters Colon contraction pushes feces into rectum As rectum fills, stretch receptors stimulate urge to defecate. To defecate or not defecate depends on state of the anal sphincters: Internal anal sphincter = smooth muscle (involuntary) parasympathetic - internal sphincter relaxes, allowing feces to pass through anus. sympathetic internal sphincter contract, keep feces in (moves back into colon, more water resorbed) External sphincter Internal sphincter External anal sphincter = skeletal muscle (voluntary) 28 14 Defecation Reflex Stimulus: Rectum stretches Autonomic Response: - Rectum & sigmoid colon contracts (push feces into anus) - Internal anal sphincter relaxes (allow anus to fill) - External anal sphincter contracts (keep it in temporarily) Delay defecation (hold it!): - External anal sphincter contracts (keep feces in) - Puborectalis muscle contracts (keep feces in) Defecation: - External anal sphincter relaxes (allow feces out) - Puborectalis muscle relaxes (allow feces out) - Straining (abdominal) Carbohydrate digestion A. Simple carbohydrates Monosaccharides = single sugar unit. Ex.: Glucose, galactose, fructose Disaccharides = 2 sugar units. Ex.: Sucrose, lactose, maltose B. Complex carbohydrates (polysaccharides) - Made of more than 2 sugar units Ex.: Starch = storage form of sugar in plants (ex. Potatoes) Cellulose = indigestible polysaccharide in plant cell walls. Glycogen = storage form of glucose in muscles & liver Different types of enzymes can break down different nutrients: Amylase enzymes break down starch (polysaccharides) into sugar. (secreted in saliva & by pancreas) Protease enzymes break down proteins into amino acids. (secreted by stomach and pancreas) Lipase enzymes break down fats into fatty acids and glycerol. (secreted by pancreas) BUT lipid digestion 1 st relies on bile to break down to size enzymes can be effective Proteases stored as zymogens Inactive, stored in vesicle: protect cells from proteolytic digestion undergo proteolytic activation in lumen of gut Enterokinase: sm intestine brush boarder enzyme that activates zymogens 32 16
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