Physiology Unit 4 DIGESTIVE PHYSIOLOGY

Physiology Unit 4 DIGESTIVE PHYSIOLOGY

Func1ons Mo1lity Inges1on Mas1ca1on Deglu11on Peristalsis Secre1on 7 liters/day! Exocrine/endocrine Diges1on Absorp1on

Diges1on of Carbohydrates Average intake is 250-300 g/day Amylase Salivary, pancrea1c Products: maltose, short chains of glucose Brush border enzymes Products: glucose, galactose, fructose

Absorp1on of Carbohydrates Luminal absorp1on Glucose/galactose cotransport with Na + into enterocytes Fructose facilitated diffusion into enterocytes Basolateral absorp1on Monosaccharides enter blood via facilitated diffusion

Diges1on of Proteins Require 40-50g of protein/day Supply essen1al amino acids We consume 70-90 g/day Stomach Pepsin Products are short chain polypep1des Small intes1nes from pancreas Trypsin, chymotrypsin Products are short chain polypep1des CarboxypepAdase Products are free amino acids Small Intes1nes from brush border enzymes AminopepAdase Products are free amino acids

Absorp1on of Proteins Luminal absorp1on Free amino acids enter enterocytes by counter- transport with Na + Short polypep1des (2 or 3 amino acids) enter enterocytes by counter- transport of H + Basolateral absorp1on Free amino acids enter blood by facilitated diffusion

Diges1on of Fat Daily intake 70-100 g/day (mostly triglycerides) Emulsifica1on by bile salts Pancrea1c lipase Monoglyceride + 2 fa[y acids Forma1on of micelles by bile salts

Absorp1on of Fat Luminal Absorp1on Monoglycerides and fa[y acids enter enterocytes by diffusion Basolateral absorp1on into lacteals Exocytosis of chylomicrons Chylomicrons contain triglycerides, phospholipids, cholesterol, fat- soluble vitamins

Lipid Transport From lympha1cs to thoracic duct Free fa[y acids and glycerol into 1ssues Le]overs to liver Remnant par1cles contain cholesterol Combined with apoproteins (lipid binding protein) to produce VLDL s Deliver triglycerides to other organs

Lipoproteins Lipid & protein complexes Transport cholesterol & triglycerides in blood Protein allows hydrophobic lipids to remain in suspension Five classes: Based on density, molecular weight, size, chemical composi1on Chylomicrons VLDL IDL LDL High levels associated with increased risk CVD HDL Low levels associated with increased risk of CVD Best profile = high HDL, low LDL

Absorp1on of Vitamins Fat- soluble vitamins Vitamins A, D, E, K Exocytosis in chylomicrons Water- soluble vitamins Vitamins B, C Absorbed by diffusion or mediated transport Vitamin B 12 Binds to intrinsic factor Endocytosis (in ileum) into enterocytes

Absorp1on of Water and Minerals Water is most abundant substance in chyme 8 L of ingested and secreted water enter the small intes1ne each day! 1.5 L make it to the large intes1ne 80% absorbed in small intes1ne Minerals Na + HCO 3 - Cl - Small concentra1ons K +, Mg 2+, Ca 2+, Fe 3+, Zn 2+, I -

Regula1on of Gastrointes1nal Processes Regula1on of the condi1ons of the lumen of the tract (the outside of the body) Governed by the volume and composi1on of the luminal contents rather than the nutri1onal state of the body (the inside of the body)

Basic Principles 1. Disten1on of the lumen wall (volume of contents) 2. Chyme osmolarity (solute concentra1on) 3. Chyme acidity 4. Chyme concentra1ons Monosaccharides Fa[y acids Pep1des Amino acids

Neural Regula1on Enteric Nervous System (ENS) Myenteric plexus Influences smooth muscle ac1vity Submucosal plexus Influences secretory ac1vity

Neural Regula1on Neural ac1vity in one plexus influences the ac1vity of the other S1mula1on at one point in the plexus can lead to impulses that are conducted both up and down the tract Neural reflexes independent of CNS CNS can influence mo1lity and secre1on of the tract

Hormonal Regula1on Hormones that control the GI system are secreted by cells sca[ered throughout the epithelium of the stomach and small intes1ne One surface of each endocrine cell is exposed to the lumen of the tract Chemicals in chyme s1mulate the cell to secrete its hormones from the opposite side of the cell into the blood

Hormonal Regula1ons Each hormone par1cipates in a feedback control system that regulates some aspect of the the luminal environment Most GI hormones affect more than one type of target cell Best understood pep1de GI Hormones Gastrin Cholecystokinin (CCK) Secre1n Glucose- dependent insulinotropic pep1de (GIP)

Gastrin Endocrine cell loca1on: G cells of the antrum of stomach S1mulus for release Protein in stomach Parasympathe1c nervous system Ac1ons S1mulates Stomach: (+) acid secre1on and mo1lity Pancreas: (+) enzyme secre1ons Intes1nes: (+) mo1lity in ileum and colon

Cholecystokinin (CCK) Endocrine cell loca1on: small intes1ne S1mulus for release amino acids, fa[y acids in small intes1ne Ac1ons S1mulates Pancreas: (+) enzyme secre1on Gall bladder: (+) contrac1on Poten1ates Pancreas: (+) bicarbonate secre1on Liver: (+) bicarbonate secre1on Inhibits Stomach: (- ) acid secre1on, gastric mo1lity

Secre1n Endocrine cell loca1on: small intes1ne S1mulus for release Acid in small intes1ne Ac1ons S1mulates Pancreas: (+) bicarbonate secre1on Liver: (+) bicarbonate secre1on Inhibits Stomach: acid secre1on, gastric mo1lity

Glucose- Dependent Insulinotropic Pep1de Endocrine cell loca1on: small intes1ne S1mulus for release glucose, fat in the small intes1ne Ac1ons S1mulates Pancreas: (+) insulin secre1on

Stomach Func1on Ini1ates protein diges1on Kills bacteria Intrinsic factor Secreted by parietal cells Needed for Vitamin B 12 absorp1on in ileum Absorp1on Water Alcohol Aspirin 3 func1ons of ph in stomach Denature ingested protein Convert pepsinogen to pepsin Digests proteins Destroy bacteria

Gastric Glands Goblet cells mucus Parietal cells HCl Intrinsic factor Chief cells Pepsinogen Argentaffin cells Serotonin Regulate intes1nal movements G cells Gastrin

Pancrea1c acini Pancrea1c juice water bicarbonate diges1ve enzymes Pancreas Ac1va1on by enterokinase

Pancrea1c Enzymes

Energy Regula1on by Islets of Langerhans Three cell types produce pep1de hormones Beta cells: insulin S1mulates cellular uptake of glucose In liver, ac1vates glycogenesis S1mulates lipid synthesis S1mulates cellular uptake of amino acids Alpha cells: glucagon Encourages libera1on of reserves Prevents glucose uptake by liver, muscle, adipose Delta cells: somatosta1n Not sure

Regula1on of Insulin and Glucagon Secre1on Effects of glucose and amino acids Increase in plasma glucose S1mulates b cells Inhibits a cells Decrease in plasma glucose decreased insulin produc1on increased glucagon produc1on Meals high in protein s1mulates insulin Meals high in protein and low in carbohydrate s1mulates glucagon result: increase in blood glucose and increased incorpora1on of amino acids into 1ssues

Regula1on of Insulin and Glucagon Secre1on Effects of autonomic nerves Parasympathe1c ac1va1on increased insulin Sympathe1c ac1va1on increased glucagon, inhibits insulin stress hyperglycemia = glucagon + epinephrine Goal: Keep blood glucose between 50-170mg/100ml higher = glycosila1on; lower = brain damage

Func1ons of the Liver Exocrine Endocrine Clopng func1ons Synthesizes plasma proteins Organic metabolism Cholesterol metabolism Excretory and degrada1ve func1ons

Exocrine & Endocrine Func1ons Exocrine FuncBons Synthesis and secre1on of bile salts 250-1500ml/day Adds bicarbonate rich solu1on to bile Endocrine FuncBons Secretes IGF- 1 promotes cell division Forms T 3 from T 4 Secretes angiotensinogen Increases BP S1mulates aldosterone secre1on Metabolizes hormones Secretes immune cytokines

Clopng and Plasma Proteins Produces Prothrombin Fibrinogen Plasma albumin Regulates blood volume Acute phase proteins Binding proteins Lipoproteins

Organic Metabolism Converts plasma glucose to glycogen and triglycerides Converts amino acids to fa[y acids Produces triglycerides and secretes them as lipoproteins Gluconeogeneisis and glycogenolysis Converts fa[y acids into ketones Produces urea

Cholesterol Metabolism/Excretory & Degrada1ve Func1ons Synthesizes cholesterol Converts plasma cholesterol into bile salts Bile salts needed for vitamin K absorp1on Excretes toxins via bile Destroys old erythrocytes and lots, lots more!

Absorp1ve State High insulin and low glucagon Insulin cellular uptake of glucose uptake & incorpora1on of amino acids conversion of glucose to glycogen addi1onal glucose to fat incorpora1on of glucose into adipose 1ssue suppression of liver glycogenolysis

Postabsorp1ve State Low insulin, high glucagon low insulin encourages movement of amino acids out of the muscles Cor1sol - - s1mulates produc1on of enzymes to convert pyruvic acid to glucose Glucagon s1mulates glycogenolysis s1mulates gluconeogenesis s1mulates lipolysis s1mulates ketogenesis