64 Digestive System - Fxns & Structures

64 Digestive System - Fxns & Structures - PSL302:...

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Unformatted text preview: PSL302: Lecture 64, by French! Fri. Mar. 25, 2011 Digestive System: Overview of Fxn & Structure Outline - What are the fxns of the digestive system? - What structures make up the digestive system? - What is the structure of the wall of the GI tract? - How is the activity of the digestive system regulated? What are the functions of digestive system? - What vessels bring blood to and from the digestive system? Reading: 687-692, 699-702 (5E), 677-682, 689-693 (4E) supply water, What are the fxns of the digestive system? nutrients to the - Supply water, electrolytes, & nutrients to body body - Defense mechs to prevent both infection & autodigestion provide - Remove waste (indigestible, toxins, metabolic pcts) = feces defenses to - Diagram: schedule of lectures prevent both (1) Food digestion infection and autodigestion (2) Motility: of food through GI system (3) Secretions: hormones, enzymes, bicarbonate remove waste (4) Absorption of nutrients circulation What (5) Control in GI system What structures make up the digestive system? - Tubular GI tract - Esophagus, stomach, S & L intestine, rectum - Accessory organs - Mouth: teeth, tongue - Salivary glands - Liver, gall bladder & pancreas: secrete products into GI tract - Liver: secrete bile salts to digest fats - Gall bladder (under liver): concentrates & stores bile salts = bile - Pancreas (behind stomach): secrete digestive enzymes & bicarbonate electrolytes and CIRCULATION CONTROL structures make up the digestive Figure 21.2 tubular esophag p g stomach small an intestine Mouth (1) Mouth - Receptacle for food - Tongue tastes & guides food - Teeth grind food - Mix food with saliva (from salivary glands) - Minimal digestion of carbohydrates (salivary amylase) & lipids (linguinal lipase) - Lubricates passage of food & buffers food contents accesso organs teeth, to salivary li liver, gal and pan p 1 of 9 recepta tongue guides f teeth gr mix food (from sa glands) minimal of carbo and lipid PSL302: Lecture 64, by French! Fri. Mar. 25, 2011 Pharnyx (2) Pharynx: - Common passage for air & food - Swallowing reflex: - Epiglottis covers larynx during swallowing - Pushes food into esophagus swallowing pushes f h foo esophagus (3) Esophagus: muscular tube - Top: skeletal (striated) muscle; middle: striatal/smooth mix; bottom: smooth - Some voluntary control at early esophagus, then rest moves thru peristalsis - Peristalsis: moves food into stomach - Guarded by 2 sphincters - Upper esophageal sphincter: constricts & keeps food moving dwd - Lower esophageal sphincter: prevents stomach contents from entering esophagus - No digestion - If pbms w/ esophagus: gastric pull-up surgery - Modify stomach into tube, remove esophagus, raise stomach up and reattach - Create esophagus out of stomach = no more stomach! - Most digestion & absorption now occurs in S intestine Esophagus moves stomac no dige (4) Stomach Stomach - Main fxns: - Temporarily stores ingested food - Secretes enzymes & acids for digestion (mainly protein) - 3 layers of muscle: - Outer longitudinal, circular, & inner oblique - Mechanically breaks down food mix w/ secretions - 4 sections: - Cardia (top), fundus, body (main), pylorus - Slowly empties into small intestine - Food converted into chyme (mixed w/ acid) temporarily stores ingested food - Pyloric sphincter: controls how much secretes acid/enzymes for digestion (mainly protein) chyme enters duodenum - Small amounts allow better absorption & digestion of chyme with secretions y mechanically breaks down food / mix slowly empties into small intestine Figure from Martini (2006) Fundamentals of Anatomy and Physiology ~ Fig 21.3 2 of 9 PSL302: Lecture 64, by French! Small intestine Fri. Mar. 25, 2011 (5) Small intestine -3 sections: duodenum, jejunum, ileum -Main fxns: segmentation and -Digestion of all types of nutrients peristalsis -Main site of absorption digestion of all types of nutrients -Diff kinds of mvt: -Segmentation: random contractions of muscles = allow mixing cont'd main site of Small intestine inabsorption region digestion aided by secretions of liver (via g -Peristalsis: sequential contractions in one direction compel bladder) and pancreas chyme thru tract Figure from Martini (2006) Fundamentals of Anatomy and Physiology ~ Fig 21.3 Liver: Bile - Digestion aided by secretions of liver (via gall bladder) & bilirubin bili bi pancreas - Liver: produces bile salts, bilirubin, detoxified drugs Pancreas: - Collected in common hepatic duct & enter bicarbonate gall bladder enzymes - Gall bladder: concentrates & stores bile; water removed - After a meal (esp. fatty one), it constricts - Bile released into common bile duct enter Figure 21.10 duodenum - Pancreas: exocrine portion secrete bicarbonate & digestive enzymes - Empty into pancreatic duct enter stomach just before duodenum - Enzymes digest proteins, lipids & carbohydrates - Bicarbonate neutralizes stomach acid Large intestine (colon) (6) Large intestine (colon) - Sections: cecum, appendix (some lymphoid tissue) - Mvt of chyme thru: ascending transverse descending sigmoid rectum - Diff kinds of mvt: - Segmentation - Mass movement: strong peristalsis, moves all the way thru to force feces into rectum - Main fxns: absorption of water/electrolytes - Synthesis of vitamin B12 by colon bacteria - Storage of fecal matter for expulsion Review - People who have severe ulcerative colitis (inflammation of colon) sometimes need to have all or part of their colon removed. They might be more susceptible to which of the following? (a) Inadequate protein digestion (b) Dehydration (c) Low blood glucose levels (d) Enhanced acid secretion - Two inflammatory Dx of GI system: ulcerative colitis (colon & rectum), Chrohn's - Cause pbms w/ absorption of nutrients & water = diarrhea segmentation g mass moveme absorption of electrolytes storage of fec material for expulsion 3 of 9 PSL302: Lecture 64, by French! What is the structure of the wal GI tract? Fri. Mar. 25, 2011 What is the structure of the wall of the GI tract? Four la - 4 layers to any part of GI tract (diagram: S intestine) - Mucosa mucos - Contains intestinal epithelial cells (exposed to lumen & chyme) submu - Villi: small folds projecting into lumen muscu - Pica: larger folds, incl. submucosa - Submucosa serosa - Contains blood & lymphatic vessels - Lacteal: lymphatic vessel important for absorption of fat - Submucosal plexus: network of neurons; control secretions from mucosa ~ Figure 21.3 - Muscularis - 2 layers of smooth muscle: submucosal plexus - Longitudinal (outer) & circular (iner) from Martini (2006) Fundamentals of Figure network of neurons Anatomy and Physiology ~ Fig 21.3 - Myenteric plexus: network of neurons btwn smooth muscle layers - Contains as many neurons as in spinal cord! - Regulates motility - Serosa - Connective tissue covering outer surface of GT tract - Slippery: prevents parts of tract (i.e. S intestine) from adhering to each other Specialized cells of the mucosa - All are epithelial cells (columnar shaped) - Transport cells: several types - Secrete acid, bicarbonate - Absorption of nutrients, water, vitamins - Transport into lumen or into cells end up in bloodstream (or lymph for fat) - Exocrine cells: secrete enzymes, mucous, etc. - Goblet cells: secrete mucous (protect GI tract from acid) - Paneth cells: secrete antimicrobial compounds from immune system - Enteroendocrine cells: several types - Secrete many types of hormones into bloodstream - Stem cells: located in crypts - Give rise to epithelial cells (constantly replenished) - Continual renewal of epithelium (often sloughed off) Specialized cells of the mucosa - Susceptible to high lvls of radiation: epithelium destroyed GI tract bleeds Specialized ce Transport cells Trans bicarb vitamin Entero hormo Transport cells Goblet cell Transport cells: several types--secrete acid, bicarbonate, absorption of nutrients, water, p vitamins Enteroendocrine cells: several types--secrete hormones into the blood stream Enteroendocrine cell Paneth cell Stem cell Figure modified from Crosnier et al. (2006) N t Nature R i Reviews G Genetics ti 7:349359 4 of 9 Exocr PSL302: Lecture 64, by French! Fri. Mar. 25, 2011 Enteric nervous system Contains 100 million neurons (sensory, interneurons, Enteric nervous system parasympathetic ganglia, - Contains 100mil neurons: sensory, interneurons, sympathetic postganglionic th ti t li i parasympathetic ganglia, sympathetic postfibres) ! ! ! ! ganglionic fibers - Myoenteric plexus (Auerbach's plexus), top arrow Myenteric plexus - Regulates motility ( (Auerbach's p ) - Located btwn smooth muscle layers plexus) regulates - Together, called muscularis externamotility - Submucosal plexus (Meissner's plexus) Submucosal plexus S b l l - Regulates secretion & absorption (Meissner's plexus) - Located btwn submucosa & circular muscle How is the activity of the digestive system regulates secretion and absorption regulated? How is the activity of the digestive system regulated? Heanue and Pachnis (2007) Nature Reviews Neuroscience 8:466-479 Figure 21.11 - Control of GI tract activity by regulating digestive system responses - Muscle contraction/relaxation - Exocrine secretion (enzymes, mucous, acid, bicarbonate), paracrines - Endocrine secretions - Generated by effectors: smooth muscles or secretory cells - Local stimuli may stimulate them to generate digestive system responses - Regulated by ENS (neurons of myenteric & submucosal plexuses) - Include interneurons, sensory receptors & neurons - Local stimuli affect sensory receptors ENS & cephalic brain - Affected by external stimuli (i.e. Cinnabon) sensory receptors - Signals sent to cephalic brain stimulate myenteric & submucosal plexuses 5 of 9 PSL302: Lecture 64, by French! Fri. Mar. 25, 2011 Parasympathetic control Parasympathetic control cranial (vagus) and - Effect: generally gut muscle activity (activation) sacral divisions - Relax sphincters preganglion neurons li - secretion - Nerve cxns: cranial (vagus) & sacral divisions synapse on ganglionic - Preganglion neurons synapse on ganglionic neurons in enteric neurons in ENS (at tissues) nervous system - Postganglionic fibers secrete ACh postganglionic fibres secrete Ach generally increase gut muscle activity l ti it relax sphincters Sympathetic control increase secretion - Comes off the sympathetic chain (near sp.c.) - Preganglionic neurons are shorter & synapse onto prevertebral ganglia - Postganglionic neurons innervate all portions of GI tract - Release noradrenaline - Note: pre-ganglionic release ACh Sympathetic control postganglion neurons inner portions of the release noradrenaline inhibit gut - Effect: gut mvts during flight-or-fight movements response (inhibition) constrict sph - Constrict sphincters - secretions reduce secre Contents/state of the GI tract help to regulate Contents of the GI tract help to regulate activity activity - Mechs regulating digestive activities (1) Neural mechs - Long reflex: CNS can influence myenteric plexus; influenced by receptors - Short reflex: stretch & chemoreceptors influence myenteric plexus - Affect: - Smooth muscle = peristalsis & segmentation mvts - Secretory cells = release of buffers, acids & enzymes - Enteroendocrine cells = hormones released into circulation Figure from Martini (2006) Fundamentals of Anatomy and Physiology ~ Fig 21.3 6 of 9 PSL302: Lecture 64, by French! Fri. Mar. 25, 2011 (2) Hormone mechs - Released by enteroendocrine cells into circulation - Affect: secretory cells & smooth muscle (3) Local mechs - Local factors (i.e. pH, physical & chemical stimulation) - Affect: secretory cells & enteroendocrine cells Example of gut regulation of endocrine secretion - Taste receptors (i.e. for glucose) in mouth & also in small intestine (pink) - Bind to glucose hormone secretion - Enteroendocrine cells secrete hormones: - GIP (gastric inhibitory peptide): release of insulin - GLP-1 (glucagon-like peptide): release of insulin in the presence of glucose - Effect: transport of glucose into enterocytes Example of gut regulation of endoc secretion GIP = Gastric in peptide stimulates the of insulin GLP-1 = Glucag peptide enhances rele insulin in the pre glucose Sclafani A (2007) PNAS;104:14887-14888 Review - What would you expect to observe if you electrically stimulated the vagus nerve in an individual? (a) Enhanced secretion of acid from the stomach (b) Reduced motility of the stomach (c) Reduced levels of ACh in the ENS (d) Enhanced motility of the rectum - Vagus is parasympathetic nerve = gut muscle activity - Enhanced secretion & motility in GI tract (incl. stomach) - NOT enhanced motility in rectum (influenced by sacral PNS) - [ACh] in ENS: released by post-ganglionic neurons What vessels bring blood to and from the digestive system? - Splanchnic circulation: blood flow in viscera - Hepatic artery takes blood to liver - Several arteries supply GI tract enter capillaries exit and... - Returns to liver = hepatic portal vein - Collects absorbed nutrients & water for liver - I.e. glucose stored as glycogen - Portal: takes blood from one capillary bed to another What vessels bring blood to and from the digestive system? Splanchnic circulation i l ti Fig 21.30 7 of 9 PSL302: Lecture 64, by French! Fri. Mar. 25, 2011 Blood supply--arterial Blood supply: renal Stomach celiac artery Small intestine superior mesenteric artery p y Large intestine superior and inferior mesenteric arteries Figure from Martini (2006) Fundamentals of Anatomy and Physiology Circulation in the villi - Capillaries: gas exchange, transport soluble nutrients, water & electrolytes (in red/blue) Circulation in the villi - Collect absorbed material & provide secretions - Central lacteal: fat absorption into lymphatic system (blind-ended vessel, in green) monosacchrides amino acids Blood from gas exchange, heart via soluble capillaries for gut returns to the transportthe liver nutrients, - Blood from intestinal capillaries sup/inf mesenteric veins hepatic portal vein liver water and electrolytes - Main fxns: central lacteal for fat absorption into lymphatic system - Hepatocytes remove potentially harmful agents - H2O & soluble nutrients absorbed Blood from gut returns to the veins inferior vena cava - Blood exits from liver via hepatic heart via the liver hepatic veins inferior vena cava hepatic portal vein superior mesenteric vein inferior mesenteric vein Figure from Martini (2006) Fundamentals of Anatomy and Physiology hepatocytes remove potentially harmful agents H2O and soluble nutrients absorbed 8 of 9 PSL302: Lecture 64, by French! Fri. Mar. 25, 2011 Blood Supply: liver - Blood fromBlood the livervein & hepatic artery pools in the sinusoids hepatic portal - Moves to central veins, which drain into the hepatic veins Trafficking of substances to and from the liver Fig 21.10 blood from hepatic portal vein and hepatic artery pools in the i Trafficking of substances to and from the liver th sinusoids id moves to central veins, which drain into the hepatic veins Review - In which blood vessel would you expect to observe the highest [glucose] following a meal? (a) Hepatic artery (b) Hepatic vein (c) Hepatic portal vein (d) Superior mesenteric artery Fig 21.10 9 of 9 ...
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