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4. Gastrointestinal Tract

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University of Guelph
Human Kinetics
HK 2810
Coral Murrant

upper esophageal sphincter lower esophageal sphincter pyloric sphincter gall bladder sphincter of Oddi ileocecal sphincter anal sphincters From Boron and Boulpaep pg 934 4. Gastrointestinal tract 1 From Bern and Levy pg 590 4. Gastrointestinal tract 2 From Silvethorn pg 607 4. Gastrointestinal tract 3 Enteric nervous system connectivity secretory cells chemo Rc mechano Rc osmo Rc From Guyton pg 721 4. Gastrointestinal tract 4 -10 -40 Stanfiels pg 596 4. Gastrointestinal tract 5 SECRETIONS: 1. salivary glands 2. stomach 3. pancreas 4. liver 5. small intestine 1. Salivary Glands - parotid, submandibular (submaxillary) and sublingual secrete: a) saliva b) serous cells (parotid) - ▯-amylase -ae c) mucous cells (submaxillary and sublingual) - mucin Control of secretion: ISS + lumen ▯cAMP SNS + ▯ Ca++ amylase ▯ IP3 PNS lipase Na+ Na+ ATP 2K+ H 2 3Na+ 4. Gastrointestinal tract 6 2. Gastric secretions (stomach) a) Columnar epithelial cells and mucous cells -muous -HCO 3 b) Pareital cells - HCl -nrsccor c) Cheif cells - pepsinogen d) G cells - gastrin e) D cells - somatostatin f) enterochromaffin-like cells - histamine 4. Gastrointestinal tract 7 Parietal cell ISS lumen HCO - H+ 3 HCO + H + ATP Cl- 3 K+ K+ K+ H 2O 3 ATP 2K+ 3Na+ CA Cl- CO + H O somatostatin Rc 2 2 prostaglandin Rc metabolism histamine Rc gastrin/CCKBRc muscarinic intrinsic cholinergic Rc factor Control of acid secretion somatostatin hyperpolarize driving force out for Cl- prostaglandins - K+ channels on basolateral side - histamine + ▯cAMP ▯ Intrinsic factor ACh ▯ Ca++ + Cl- channels + H+-K+ ATPase on apical side Gastrin 4. Gastrointestinal tract 8 Cheif cells ISS lumen 2K+ ATP 3Na+ PKA secretin Rc pepsinogen cAMP ? VIP Rc acid pH 3 beta adrenergic Rc pepsin pepsinogen Ca++ gastrin/CCK Rc A muscarinic IP3 cholinergic Rc H+ in contact with gastric mucosa stimulates pepsinogen release by local neural reflex 4. Gastrointestinal tract 9 3. Pancreatic secretions A. Pancreatic duct cell - aqueous component ISS lumen HCO 3- H+ H + HCO 3- HCO 3- ATP K+ Cl- H+ H CO H CO Cl- 2 3 Na+ 2 3 CA H O + CO CO + H O 2 2 2 2 K+ metabolism 2K+ ATP 3Na+ secretin Rc gastrin/CCK Rc muscarinic cholinergic Rc number of H+-K+-ATPase secretin + ▯ cAMP open time of Cl- channels CCK + ▯Ca++ activates K+ channels + ACh 4. Gastrointestinal tract 10 B. enzymatic component - enzymes necessary for digestion of all major classes of foodstuff - secreted by acinar cells 1. proteases - cleaves proteins - secreted as inactive zymogens plus trypsin inhibitor enteropeptidase trypsinogen trypsin secreted by duodenum trypsin chymotrypsinogen chymotrypsin trypsin procarboxypeptidase carboxypeptidase trypsin trypsinogen trypsin proelastase trypsin elastase 2. ▯ amalyse - cleaves starch 3. lipases - digests lipids -aygyeoldoae -hlsrlsrydoae -hopoiaeA2 4. ribonuclease - digests RNA 5. deoxyribonclease - digests DNA 4. Gastrointestinal tract 11 Control of Secretion ISS lumen 2K+ ATP 3Na+ enzymes gastrin/CCKA Rc IP3 Ca++ muscarinic cholinergic Rc secretin/VIP Rc cAMP PNS enhances secretion, SNS inhibits secretion 4. Gastrointestinal tract 12 5. Small intestine goblet cells - similar to mucous cells of the stomach - secrete mucous I cells - cholecystekinin (CCK) S cells - secretin D cells - somatostatin K cells - GIP - gastric inhibitory peptide (old name), glucose-dependent insulinotropic peptide (new name) Endocrine cells - motilin -guagnieppdeG L-) -buogsone -etooxnn Secretory cells - enterpeptidase (aka enterokinase) 4. Gastrointestinal tract 13 Carbohydrate digestion -mouth - ▯ amylase - hydrolyzes ▯ 1-4 links of starch -pancreas - ▯ amylase -small intestine - duodenum and jejunum brush border enzymes lactase - lactose to glucose and galactose sucrase - sucrose to glucose and fructose ▯-dextrinase (isomaltase) - break down dextrins glucoamylase - malto-oligosaccharides to glucose Carbohydrate absorption blood ISS lumen glucose or galactose 2 Na+ fructose 4. Gastrointestinal tract 14 Protein digestion -cells of the duodenum and jejunum secrete enteropeptidase which convert zymogens (from pancreatic juice) to proteases. enteropeptidase secreted by duodenum trypsinogen trypsin chymotrypsinogen trypsin chymotrypsin trypsin procarboxypeptidaseA carboxypeptidaseA procarboxypeptidase B trypsin carboxypeptidase B proelastase trypsin elastase
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