Transcript Slide 1
Digestive Physiology The primary function of the digestive system is move nutrients from the external environment into the body Outline 1) 2) 3) 4) Digestion & Absorption of nutrients Secretion of digestive chemicals Regulation of Digestion Regulation of Metabolism Digestion & Absorption of Protiens 1) Proteins digested in stomach & small intestine 2) Proteins are broken into smaller peptides & amino acids by: 1) Pepsin: Stomach 2) Trypsin & chymotrypsin: SI 3) Exopeptidases: SI 3) Peptides/Amino Acids are absorbed in SI by: 1) Cotransport then Antiport with H+ 2) Cotransport then Antiport with Na+ 3) Transcytosis via vesicles Digestion & Absorption of Fats Emulsified fats are digested by Lipase & Colipase 4) End products move into SI wall 1) Monoglycerides & fatty acids: simple diffusion 2) Cholesterol: NPC1L1 transporter 5) End products are re-comined in absoptive cells to form Chylomicrons 6) Chylomicrons travels through lymph to body Digestion & Absorption of Carbohydrates 1) Carbs digested in mouth & SI 2) Complex Carbs are digested into Disaccharides by amalyase & alpha-amylase Maltose, Sucrose, Lactose 3) Disaccharides are digested into Monosacch. By: 1) Maltose by Maltase to glucose 2) Sucrose by Sucrase to glucose + fructose 3) Lactose to Lactase to glucose + galactose Na+Glucose Symporter Glut5 4) Monosaccharides can FINALLY! be absorbed 1) Glucose & Galactose via Na+-glucose Symporter Glut2 2) Fructose via Glut5 & Glut2 transporter Absorption of Vitamins, Ions, Minerals, Water Vitamins: Fat-Soluble (A, D, E, K) – transported with fats Water-Soluble (C, B) – mediated transport Minerals: Ca2+ (hormonally controlled ion channels/Active transport) – used everywhere Iron (???)- needed for RBC Ions: Na+ - active transport, symport, antiport Water: Follows Na+ & other absorbed solutes by Osmosis Secretion: Salivary Glands Parotid, Sublingual, & Submandibular glands secrete Saliva Saliva contains Alpha-amylase (carbs), lingual lipase (fats) Secretion: Stomach Acid Secretion 1) Protein in food activates enteric nervous system Surface Mucosa 2) Gastric enzymes activate a variety of pathways Gastric Glands Vasculature * Muscle 3) Secretion of H+ & Pepsinogen Pepsinogen converted to Pepsin by H+ * Drugs for heartburn & ulcers (Zantac, Pepcid) block Histamine receptors in stomach! Secretion: Pancreas Pancreatic Duct Small Intestine Pancreas Pancreas secretes Trypsin & Trypsinogen Exopeptidases Amylase Lipase Acini Cells Bicarbonate Ions (raise pH) Pancreatic Enzymes work best at higher pH Islet Cells Secretion: Small Intestine Villi Small Intestine Vasculature Crypts with glands Muscle Glands with crypts secrete: Amylase, Maltase, Lactase, Sucrase Peptidase Enterokinase (activates trypsin!) Secretion: Bile Bile is secreted by the LIVER Stored in Gall Bladder Without Bile….fat digestion is very slow Why doesn’t the digestive system digest itself? Digestive tract is made of cells that can be digested by enzymes! Mucus forms a protective barrier between intestinal walls & acids/bases, enzymes Goblet Cell Mucous Cells in Stomach Goblet Cells in Small Intestine Outline 1) 2) 3) 4) Digestion & Absorption of nutrients Secretion of digestive chemicals Regulation of Digestion Regulation of Metabolism Regulation of Digestion: Thinking with your stomach 1) Long Reflexes – CNS Parasympathetic- Increase Digestion Sympathetic – Slow Digestion 2) Short Reflexes – Enteric Nervous System Ingested food and pH trigger selfregulating changes in digestive system Neurons located in walls of digestive system 3) Digestive Peptide (Hormones) Autonomics work with the Enteric System to coordinate Digestive Function Digestive system release several hormones to regulate itself and communicate with brain Digestive Peptides: CCK, Gastrin, Secretin, GIP, Motilin, GLP-1 The Liver 1) Bile Production: Fat Emulsification 2) Processes & Detoxifies Absorbed Products Hepatic Portal System carries products to and from liver 3) Storage: Liver is a major storage site of glucose & some vitamins Cholesterol Metabolism LPL = Lipoprotien Lipase (Endothelial Enzyme) CE = Cholesteryl Esters VLDL = Very Low Density Lipoprotien LDL = Low ‘’ IDL = Intermediate ‘’ HDL = High ‘’ Cholesterol Synthesis ‘Statins’ = Inhibit HMG CoA reductase Reduce Total Cholesterol * Bile Acid Sequestrants Bile Acids with Fats REMAIN in Digestive Tract Acids + Cholesterol + Triglycerides are Excreted via Feces! Amino Acid Metabolism -Some AA are used by body -Excess is metabolized by the liver -End product is NH3 or NH4 = TOXIC -NH3 and NH4 repackaged for transport and excretion 1) Urea Cycle 2) Glutamate-Glutamine Transport Kidney excretes urea and NH4 via urine Amino Acid Metabolism Urea, Glutamate and Glutamine carry Ammonia(ium) (NH3, NH4+) to kidney for excretion Glutamine