AP II-GI Physiology Part 1.pdf

The Gastro-Intestinal System Part 2: Neurologic, Endocrine, and Exocrine Physiology Anatomy & Physiology II BIOL2220 1 Version 01  The Gastro-Intestinal System GI Physiology Enteric Nervous System...

The Gastro-Intestinal System Part 2: Neurologic, Endocrine, and Exocrine Physiology Anatomy & Physiology II BIOL2220 1 Version 01  The Gastro-Intestinal System GI Physiology Enteric Nervous System Basic Activities General Intestinal Histology 1. Motility 2. Secretion 3. Digestion 4. Absorption Basic Histology 1. Epithelium 2. Lamina Propria 3. Muscularis Mucosa 4. Submucosa 5. Submucosal Plexus 6. Circular Muscle 7. Myenteric Plexus 8. Longitudenal Muscle 9. Serosa (Peritoneum) The Enteric Nervous System: Consists of the Submucosal and Myenteric Plexuses. They are both INTRINSIC to the GI Tract 2  The Gastro-Intestinal System Intrinsic Vs Extrinsic GI Physiology Autonomic Nervous System 3  The Gastro-Intestinal System GI Physiology – ANS Review ANS Factoids: ANS Factoids: 1. Mainly A Visceral Motor System. 5. Sympathetic is THORACOLUMBAR! 2. Innervates: a) Cell Bodies Of Origin In T1 – L2 Spinal a) Smooth Muscle. Cord Segments. b) Cardiac Muscle. 6. Parasympathetic is CRANIOSACRAL! c) Glands. a) Cell Bodies Of Origin In Brain Stem (CN 3. Divisions: 3, 7, 9, 10) & S2 – S4. 1. The Sympathetic. 7. Both SNS & PSNS have CNS and PNS 2. The Parasympathetic. Components. 4. Dual Innervation (To Same Organ, Etc.). 8. But, Only Sympathetic To Blood Vessels, Arrector Pili & Sweat Glands. Pre-Ganglionic Ganglion Post-Ganglionic Targets Myelinated Un-Myelinated CNS PNS Epinephrine Sympathetic T1 – L2 Spinal Cord Acetylcholine Norepinephrine 4 Parasympathetic Brain Stem & S2 – S4 Acetylcholine Acetylcholine  The Gastro-Intestinal System Intrinsic Plexuses=Enteric Nervous System Overview – Major Physiologic Mechanisms Parasympathetics (Vagus, Pelvic), and Symnpathetics=Extrinsic Chemoceptor Mechanoceptor Mechanoceptor Chemoceptor Mucosa Exocrine Endocrine Exocrine Cell Cell Cell Muscularis Mucosae Submucosal Plexus Inner Circular Muscle Myenteric Plexus Outer Longitudinal Muscle 5 Pelvic Nerve Vagus Nerve (CN X) Numerous Nameless Sympathetic Postganglionics  The Gastro-Intestinal System Overview – Major Physiologic Mechanisms Reflexes are built into the GI Tract Chemoceptor Mechanoceptor Mechanoceptor Chemoceptor Exocrine Endocrine Exocrine Cell Cell Cell Muscularis Mucosae Submucosal Plexus Inner Circular Muscle Myenteric Plexus Outer Longitudinal Muscle 6 Vagus Nerve (CN X)  The Gastro-Intestinal System 3 Types of Neurologic Reflexes that Govern GI Secretion & Motility Overview – Major Physiologic Mechanisms 1. “Food in yer’ Face” -Actually known as the Cephalic Stage/Phase of Digestion -Chewing, tasting, swallowing excites the Vagus, which then sends impulses to the stomach, pancreas, duodenum, etc to improve secretion & motility, and ready the processes of digestion 2. “Up yer’ Vagus, Down yer’ Vagus” -Actually known as the Vago-Vagal Reflex -Part of the Gastric/Intestinal Stage/Phase of Digestion -Based mainly on mechanosensation, this reflex keeps the Vagus active in secretion & motility once food has passed the mouth. 3. “Local Reflexes” -Another part of the Gastric/Intestinal Stage/Phase of Digestion -Based mainly on chemosensation, these reflexes rely on the intrinsic plexuses of the Enteric Nervous System. 7 The Gastro-Intestinal System GI Physiology – Key GI Hormones Endocrine Stimuli Hormone Effects Dietary Peptides & Amino Acids G-cells in Gastric Antrum Gastric Acid Secretion (HCl) Gastric Distention (Duodenum?) Gastrin Gastric Gland Mucosa Repair Stimulation Of Vagus Dietary Peptides & Amino Acids I-cells in Duodenum Gall Bladder Contraction & Jejunum CCK* Longer Chain Fatty Acids Pancreatic Enzyme HCl & HCO3- Release Repair Of Exocrine Pancreas *Cholecystokinin Acids Pancreatic, Biliary, and Fats S-cells in Duodenum Secretin Brunner’s Gland HCO3-Secretion Growth Of Exocrine Pancreas Pepsin Secretion Glucose K-cells in Duodenum & Insulin Release Amino Acids Jejunum GIP* Fatty Acids Gastric Acid Secretion *Gastric Inhibitory Peptide (aka glucose-dependent insulinotropic peptide) Nervous (vagal) Stimulation M-cells in Duodenum & Gastric & Intestinal Motility Dietary Fat Jejunum Motilin Acid 8 The Gastro-Intestinal System GI Physiology – Key GI Hormones Paracrine Stimuli Hormone Effects Acid D-cells in Gastric Antrum Gastric Acid Secretion (HCl) & Duodenum Somatostatin* Gastric Gland Mucosa Repair *Inhibited by Vagal Stimulation Gastrin ECL-cells in Gastric Mucosa Histamine HCl Vasoactive Intestinal Peptide (VIP) Neurocrine Intestinal Secretion Relaxes Sphincters & Smooth Muscle Bombesin (Gastrin Releasing Peptide) Released From: Nerve Cells In Mucosa & Smooth Muscle Gastrin Release Enkephalins Released From: Nerve Cells In Gastric Mucosa Smooth Muscle Contraction Intestinal Secretion Released From: Nerve Cells In GI Mucosa & Smooth Muscle 9  The Gastro-Intestinal System GI Physiology – Key GI Hormones Composite View Gastrin (E) Gastric Inhibitory Peptide (E) Histamine (P) Somatostatin (P) Bombesin (N) Vasoactive Secretion Intestinal Enkephalins Peptide Contraction HCl GI Tract Motilin Movement Cholecystokinin (CCK) Gall Bladder Contraction Pancreas Enzyme & Bi- Carbonate Release Secretin Pancreatic & Biliary Bi- Carbonate Release Pepsin Secretion 10 (Protealytic Enzyme)  The Gastro-Intestinal System GI Physiology – Key GI Hormones An Integrated Systemic View Taste, Smell, GI Distention Chew, Etc. (Vago-Vagal Reflex) (Cephalic Stage) Production & Inhibition Vagus Nerve Of Gastric Acid GRP ACH Stomach – Duodenum – Pancreas Somatostatin G Cell 1 1 Low pH Digested (-) Duodenum Protein Parietal (+) (-) Gastrin Gastric Acid Secretin Cell Low pH 1 Dueodenum - Jejunum ECL ACH Histamine Gastric Inhibitory Peptide Cell (GIP) Fatty Acids 1 11  The Gastro-Intestinal System GI Physiology – Key GI Hormones An Integrated Systemic View Vagus Nerve Liver Duodenum Bile Gastrin Digestive ACH Controls Pancreas Gall Bladder Duct Acinar Cell Cell Distention Concentrated Bicarbonate + Enzymes Bicarbonate + Bile Duodenum Secretin CCK Secretin CCK Proteins, Fats & H+ S I S I Cell Cell Cell Cell 12 Brunner’s Glands:Bicarbonate  The Gastro-Intestinal System GI Physiology – Exocrine Secretion Salivary Glands Saliva Contains: 1. Water, Bicarbonate (Buffer/Dilute) Enhancing Salivation: 2. Amylase (Carbohydrates) Chewing, Tasting, Smelling, Conditioned 3. Lingual Lipase (Lipids)-Actually from Reflexes, Nausea Tongue 4. Mucous (Lubrication) Inhibiting Salivation: 5. Antibacterial Agents (Lysozyme, Sleep, Fatigue, Dehydration, Fear, SNS Lactoferrin, Etc.) activation 6. Glycoproteins 7. Nerve & Epidermal Growth Factors Important CNʼs: Large Volume CN VII CN IX High Electrolyte Content Ion Fluxes In Salivon 13  The Gastro-Intestinal System GI Physiology – Exocrine Secretion Stomach Parietal Cell Gastric Exocrine Secretion Includes: 1. HCl – Parietal (Oxyntic) Cells 2. Pepsin – Chief Cells (Proteolytic) 3. Lipase – Chief Cells (Lipolytc) 4. Mucous – Mucous Neck Cells & Epitheial Cells 5. Gastric Intrinsic Factor – Parietal Cells (B12 Absorption) Stimulants Of Acid Secretion 1. Gastrin (Gastric Mucosa) 2. Ach (Parasympathetic Nerves) Gastric Pit Parietal Cell 3. Histamine (From ECL Within Mucosa) Enterochromaffin-Like 14 Cell  The Gastro-Intestinal System GI Physiology – Exocrine Secretion Pancreas Functional Unit Of Pancreas Pancreatic Juice: Water Enzymes Electrolytes Gastric/Intestinal Stage 15  The Gastro-Intestinal System GI Physiology – Exocrine Secretion Gall Bladder/Liver Bile Acids, Salts & Other Biliary System and Enterohepatic Circulation 1. Bile Acids of Bile Acids 2. Bile Salts Note Recirculation Of Bile! Gallstones 1. Cholesterol Stones 2. Pigment Stones (Bilirubin) 3. Cholecystectomy How is Bile Made? Bile acids are made in the liver by the oxidation of cholesterol. Microscopic Liver Structure Whatʼs the difference between a bile acid and a bile salt? Bile acid refers to the protonated (-COOH) form. Bile salt refers to the deprotonated or ionized (-COO-) form. Other important Facts: Bile is used to break down fat globules into tiny droplets. Bile is secreted by hepatocytes using an active transport mechanism Synthesis of bile acids is a major route of cholesterol metabolism in most species other than humans. The body produces about 800 mg of cholesterol per day and about half of that is used for bile acid synthesis. In total about 20-30 grams of bile acids are secreted into the intestine daily. About 90% of excreted bile acids are reabsorbed by active transport in the ileum and recycled in what is referred to as the enterohepatic circulation. 16  The Gastro-Intestinal System GI Physiology – Exocrine Secretion The Liver , Bilirubin, and Jaundice Bilirubin The yellow breakdown product of normal heme catabolism. Heme is found in hemoglobin, a principal component of red blood cells. Bilirubin is excreted in bile, and its levels are elevated in certain diseases. It is responsible for the yellow color of bruises and the yellow discoloration in jaundice. RBCʼs are disposed of in the spleen when they get old or damaged. This releases hemoglobin, which is broken down to release heme. The heme is Function of Bilirubin: then turned into unconjugated bilirubin in the macrophages of the spleen. Bilirubin is created by the This unconjugated bilirubin is not soluble in water. It is then bound to activity of biliverdin albumin and sent to the liver. reductase on biliverdin. In the liver it is conjugated to glucuronic acid, making it soluble in water. Bilirubin, when oxidized, Much of it goes into the bile and thus out into the small intestine. Some of reverts to become the conjugated bilirubin remains in the large intestine and is metabolized by biliverdin once again. colonic bacteria to urobilinogen, which is further metabolized to This cycle, in addition to stercobilinogen, and finally oxidised to stercobilin. This stercobilin gives feces the demonstration of the its brown color. Some of the urobilinogen is reabsorbed and excreted in the potent antioxidant activity urine along with an oxidized form, urobilin. of bilirubin, has led to the Normally, a tiny amount of bilirubin is excreted in the urine, accounting for hypothesis that bilirubin's the light yellow color. If the liverʼs function is impaired or when biliary main physiologic role is as a drainage is blocked, some of the conjugated bilirubin leaks out of the cellular antioxidant hepatocytes and appears in the urine, turning it dark amber. 17 The Gastro-Intestinal System Liver GI Physiology – Liver Markers of Function Hepatocellular Leakage Enzymes The hepatocellular leakage enzymes are useful in detecting injury to liver parenchymal cells. Generally, increased serum activity represents enzyme leakage from cells through damaged cell membranes. ALT: Largely liver-specific, but can also increase in severe myopathies (release of muscle enzyme) and hemolysis. AST: Present liver as well as skeletal muscle and erythrocytes. SDH: Liver specific GLDH: Liver specific LDH: Lactic dehydrogenase is seen in both liver and muscle, so like AST it is not liver specific. 18