66 Digestive Secretion

66 Digestive Secretion - PSL302: Lecture 66, by French!...

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Unformatted text preview: PSL302: Lecture 66, by French! Wed. Mar. 30, 2011 Digestive Secretions Outline - How much is secreted/absorbed in GI tract per day? - How is surface area of the GI tract increased? - Where is saliva produced? - What is secreted from the stomach? - What pancreatic secretions enter the small intestine? - What is secreted from the liver via the gall bladder? - What hormones are released from the small intestine? Textbook reading: 695-699, 702 (5E), 684-689, 692-693 (4E) Recall: Functions of digestive system Recall: Fxns of digestive system! ! Recall: Specialized cells of the mucosa Recall: Specialized cells of the mucosa! Transport cells Goblet cell Enteroendocrine cell CIRCULATION CONTROL Figure modified from Crosnier et al. al (2006) Nature Reviews Genetics 7:349359 Figure 21.2 Single cells Many types release different hormones Hormones released into the blood Regulated by content of GI tract and autonomic nervous system ow much is secreted/absorped in GI tract per day? How much is secreted/absorbed in GI tract per day? - Secretion into lumen or into circulation, i.e. via specialized mucosa - Transport cells: acid into stomach, bicarbonate into duodenum, absorbing nutrients - Enteroendocrine cells (single cells, many types): hormones; regulate GI fxn via ANS Figure 21.3 21 3 Requires large surface area 1 of 9 PSL302: Lecture 66, by French! Wed. Mar. 30, 2011 - Fluid input - Ingestion: 2.0L of food & fluid per day - Secretion: 7.0L of fluid by the GI tract! - Total input: 9.0L! (recall: total blood volume: 5.0L) - We must be able to reabsorb this fluid or else become dehydrate - Fluid removed - Absorption: 7.5L by S intestine + 1.4L from L intestine - Excretion: 0.1L lost in feces - Total removed: 9.0L (what goes in must come out) - Requires large SA in GI tract: mechs to SA How isis surfacearea of the GI tract increased? How surface area increased? Folds 3X 10X Hills/valleys Microscopic Mi i protrusions 20X - In diff parts of the GI tract, these surface area in What increases the features look different What SA in the stomach? the stomach? Rugae Gastric pits - Folds are called rugae - Look microscopically at stomach valleys: gastric pits - On cells microscopic protrusion: microvilli Figure 21.3 2 of 9 PSL302: Lecture 66, by French! Wed. Mar. 30, 2011 What increases the surface What SA in the small intestine? area in the small intestine? Villi and Crypts of Lieberkuhn of Lieberkuhn Plica (also called ( valvulae conniventes) - Folds: plica (valvulae conniventes) - On these folds hills: villi What crypts of Liberkuhn (location area in the - Between villi: increases the surfaceof stem cells) What SA in the large intestine? Figure 21.3 large intestine? Haustra Crypts of Lieberkuhn - Folds: haustra - Surface of L intestine is pitted: intestinal glands - At the base of these: crypts of Lieberkuhn (location of stem cells) Fig 21 31 21.31 3 of 9 PSL302: Lecture 66, by French! Microvilli--throughout the gi tract Wed. Mar. 30, 2011 Microvilli: throughout the GI tract - Image: one villus - Close up of epithelial cell: microvilli on cell plasma membrane - Under microscope: cytoskeleton w/i microvilli = SA of plasma membrane Review - On what layer of the GI tract are the microvilli found? Figure from Martini (2006) Fundamentals of Anatomy and (a) Serosa Physiology ~Fig 21.13 (b) Muscularis (c) Submucosa (d) Mucosa Where is saliva produced? Salivary glands Where is saliva produced? Salivation is under neural control -Saliva: water, electrolytes (salts), buffers, mucous, IgA antibodies, lysozyme (break down bacterial cell Parotid gland walls), enzymes (salivary amylase, lingual lipase) -Not isotonic: quite watery Unconditioned Conditioned -Fxn: protection, lubrication, taste, digestion Sublingual gland -3 types of salivary glands: exocrine -Parotid Submandibular gland -Submandibular Saliva: water, electrolytes, buffers, mucous, IgA antibodies, Salivation is under neural control -Sublingual lysozyme, enzymes (salivary amylase, lingual lipase) Function: Regulation:protection, lubrication,under neural control Salivation is taste, digestion Pearson Figure from Interactive Physiology, salivary center Unconditioned Conditioned salivary center Unconditioned! ! ! ! ! Conditioned Stimulus: food in mouth sensory signal! Stimulus: sight of food is associated w/ taste of food salivary center in medulla! ! ! Visual signal visual cortex medulla ! ! ! ! Trigger motor pathways ! ! ! ! = secretion of saliva 4 of 9 PSL302: Lecture 66, by French! Wed. Mar. 30, 2011 Salivation control cont'd - Involuntary control of salivary pdc via ANS: parasympathetic & sympathetic - Diagram: Both activate salivation by innervating salivary glands: - Parasympathetic = lots of watery saliva - Via CN VII (facial nerve) & CN IX (glossopharyngeal nerve) - Start at medulla & pons (salivary center) - Sympathetic = small amt of thick saliva - Originate from thoracic spinal cord What is secreted from the stomach? What is secreted from the stomach? pons salivary center medulla CN VII CN IX Parasympathetic lots of watery saliva Sympathetic small amount of thick saliva Figure from Interactive Physiology, Pearson Mucous cells Parietal cells HCl, intrinsic factor Chief cells pepsinogen gastric lipase pepsinogen, Enterochromaffin-like cells histamine D cells -- somatostatin G cells gastrin - Close up: gastric pit & gastric gland has variety of cells Modified Figure 21.3 - Mucous cells: produce mucin (protein that makes mucous slippery) - Parietal cells: produce HCl acid, intrinsic factor (binds to vitamin B12 & helps its reabsorption at ileum, at end of S intestine) - Chief cells: produce proenzymes pepsinogen & gastric lipase - Hormone-releasing cells - Enterochromaffin-like cells: produce histamine (locally active) - D cells: produce somatostatin (inhibitory hormone) - G cells: produce gastrin (important for regulation) Mucous and bicarbonate protect the stomach lining - pH of stomach acid: 1-2 - To protect our stomach epithelium = pH at cell surface ~7 - Mucous cells = mucous layer as physical barrier - Epithelial cells = bicarbonate as chemical barrier that neutralizes acid Mucous and bicarbonate protect the stomach lining g Figure 21-27 5 of 9 PSL302: Lecture 66, by French! Wed. Mar. 30, 2011 Parietal cells secrete acid and intrinsic factor Parietal cells secrete acid & intrinsic factor - HCl acid: breaks down plant cell walls, denatures proteins, activates pepsinogen - Secretion of HCl into lumen of stomach - H+-K+ ATPase pumps H+ out in exchange for K+ in (leaks out via K+ channels) - Cl- leaks out via chloride channels + synthesized w/i parietal cell by carbonic anhydrase -H - Takes H2O + CO2 H+ + bicarbonate - Bicarbonate transported out to capillaries in exchange for ClAcid: breakdowns plant cell walls, denatures proteins, - Blood draining from stomach has [bicarbonate] activates pepsinogen - Intrinsic factor: binds to and gastric lipase Chief cells secrete pepsinogen vit B12 & ensures its absorption into ileum (at end of S intestine) Chief Chief cells secrete pepsinogen & gastric lipase - Pepsinogen is inactive when secreted by chief cells cleaved & activated by acid - Pepsin: lg proteins peptides & aas - Can act on pepsinogen convert & activate into pepsin = +ve feedback acid Peptides and amino acids Figure from Interactive Physiology, Pearson Instrinsic factor: binds to vitamin B12, ensures absorption of vitamin B12 in ileum cells secrete pepsinogen and gastric 21-6 Figure lipase Protein G cells secrete gastrin acid - Hormone enters bloodstream: travel to all diff places, incl. cells that secrete other things - I.e. activity of parietal cells = acid pdc - I.e. Enterochromaffin-like cells = histamine (also activates parietal cells) - I.e. Mucous, pepsinogen Protein - Activates stomach digestion by acid secretions, & motility - Stimulus: peptides, PNS Review - Which of the following is NOT released into the lumen of the stomach? (a) HCl (b) Pepsinogen (c) Gastrin (d) Intrinsic factor (e) Mucous Peptides and amino acids Figure from Interactive Physiology, Pearso 6 of 9 PSL302: Lecture 66, by French! Wed. Mar. 30, 2011 What pancreatic secretio small intestine What pancreatic secretions enter the small intestine? - Recall: pancreas has duct system - Two parts: exocrine & endocrine - Pancreatic duct collects all secretions from exocrine pancreas - Two kinds of exocrine cells line these ducts - Acinar cells (top arrow): pancreatic amylase, pancreatic lipase, nucleases, proteases, proenzymes (trypsinogen, chymotrypsinogen, procarboxypeptidase, proelastase), etc. - Duct cells (bottom arrow): sodium bicarbonate & water - Pancreatic secretions enter duodenum (stomach empties acidic secretions here) - Bicarbonates must neutralize stomach acid Pancreatic enzymes activated at neutral pH - Enzymes most active in the small intestine Acinar cells amylase, pan nucleases, nucleases p (trypsinogen procarboxyp etc Duct cells se bicarbonate a Pancreatic enzymes activated in S intestine via enterokinase Enterokinase Figure 21-7 -Enterokinase: TM proteins in plasma membranes of epithelial cells lining duodenum -Main fxn: activate trypsinogen trypsin -Trypsin has proteolytic activity activates other proenzymes -Activation of proenzymes outside of pancreas and inside S intestines = prevents autodigestion Secretion of bicarbonate & water - Bicarbonate secretion of ductal cells - Bicarbonate transported out of cell into lumen of duct, in exchange for Cl- Synthesized by action of carbonic anhydrase - H+ transported out into circulation, in exchange for Na+ - Na+-K+ ATPase exchanges Na+ out for K+ - Co-transporter of Na+-Cl--K+ brings all 3 in - leaks back out via CFTR channel = creates - Cl osmotic & elcal gradient - Ensure that water & salts will be secreted btwn cells into lumen of duct Figure from Interactive Physiology, Pearson Secretion of bicarbonate and water Figure 21-8 21 8 (Note see also Figure 21-9 how water transported into intestinal lumen) Why do individuals with cystic fibrosis have to ingest pancreatic enzymes? ingest pancreatic enzymes? g p y - CFTR channel is reduced or blocked: unable to transport out Cl- = H2O & salt secretion - Thick mucous builds up in pancreatic ducts enzymes cannot travel to the small intestine to help in digestion - Also pbms in lungs: thick mucous builds in lungs Why do individuals with cystic fibrosis have to Figure 21-7 Figure 21 8 21-8 Thick mucous builds up in pancreatic ducts--enzymes cannot travel to the small intestine 7 of 9 PSL302: Lecture 66, by French! What is secreted from the liver intestine Mar. 30,the gall blad via 2011 Wed. What is secreted from liver via the gall bladder? - Bile: bile salts, lecithin, cholesterol, bilirubin, bicarbonate - Bile is synthesized in liver & secreted into common hepatic duct gall bladder - At gall bladder: water is removed = [bile] - After a meal: gall bladder contracts release bile into duodenum - Bile salts used in digestion of fats reabsorbed in S intestine & recycled back to liver - Bile can also contain metabolites of drugs/toxins created by liver excreted in feces Bile: bile lecit l it cho biliru bica What What hormones are released from the small intestine? hormones released from small intestine? See animation of bile salt circulation 0 Interactive Physiolog - At duodenum (1) Secretin - At jejunum (2) Cholecystokinin (3) Motilin: released during fasting generates migrating myoelectric complex (sweeping out of GI tract) (4) Gastrin inhibitory peptide (GIP): release is stimulated by presence of nutrients in GI tract insulin for glucose uptake + gastric emptying & acid pdc = overall gastric activity) - At ileum (5) Glucagon-like peptide-1 (GLP-1) Secretin Cholecystokinin (CCK) Gastric inhibitory peptide (GIP) Figure from Inte + Motilin released during g fasting migrating myoelectric complex Glucagon like peptide 1(GLP 1) Glucagon-like peptide-1(GLP-1) Figure from Interactive Physiology, Pearson glucose/ fatty acids/ amino acids insulin gastric emptying/acid * The following diagrams: on left stimulus, on right purposes of hormone Secretin: secretedSecretin by duodenum! ! Cholecysteokinin (CCK): secreted by jejunum C Cholecystokinin (CCK) contraction of th t ti f the gall bladder C S acid in small intestine S S release of bicarbonate gastric acid/emptying fatty acids and amino acids in small intestine release of pancreatic enzymes gastric acid/emptying C C + + Figure from Interactive Physiology, Pearson Figure from Interactive Physiology, Pearson 8 of 9 PSL302: Lecture 66, by French! Wed. Mar. 30, 2011 Glucagon-like peptide-1 (GLP-1) Glucagon-like peptide (GLP-1): secreted by ileum feeling of satiety insulin i li glucagon cell growth gastric acid/emptying fatty acids and carbohydrates in small intestine GLP1 GLP1 + GLP1 Figure from Interactive Physiology, Pearson Review - What would you expect to observe in someone if he had taken a drug that had inhibited the action of secretin and had eaten a meal 3h earlier in comparison to someone who had eaten the same meal but had not taken the drug? (a) Difficulty emulsifying fat (b) Reduced stomach motility (c) Reduced secretion of gastrin (d) Lower pH in the duodenum 9 of 9 ...
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