KIN 275 2025 Winter Chapter 3 (Digestion and Absorption-Part I) PDF

Chapter 3 DIGESTION, ABSORPTION, AND METABOLISM Digestion and Absorption -Muscle -Nerve -Connective -Epithelial  Key terms : process of breaking food into components small...

Chapter 3 DIGESTION, ABSORPTION, AND METABOLISM Digestion and Absorption -Muscle -Nerve -Connective -Epithelial  Key terms : process of breaking food into components small enough to be absorbed by the body : process of taking substances into the interior of the body : amount of time it takes food to pass the length of the GI tract (24-72 hrs) Fat has the longest transit time, followed by protein Carbohydrates have the shortest transit time Gastrointestinal tract (GI): hollow tube consisting of the mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anus Structure of the GI tract Inside portion of the hollow tube (food in lumen has yet been absorbed) Structure of the GI tract Layer of tissue lining the lumen; mucosal cells provide protection and aid in absorption; have a short life-span of ; require nutrients to survive; produce mucus Structure of the GI tract ; provide structural support & deliver nutrients to mucosa; help with nutrient secretion and muscle contractions Structure of the GI tract Helps Structure of the GI tract Provides strong structural support and Overview of the Digestive System Digestive Secretions Digestion inside the GI tract is assisted by digestive secretions. : viscous material produced by cells in the mucosal lining of the gut; mucus moistens, lubricates and protects the GI tract Enzymes: protein molecules that speed up chemical reactions; enzymes are not changed during reactions Digestive Enzymes TABLE 3.2 Enzyme Functions Where It Is Enzyme Found What It Does Salivary amylase Mouth Breaks starch (a large carbohydrate molecule) into smaller carbohydrate molecules. Rennin Stomach Causes the milk protein casein to curdle. Pepsin Breaks proteins into polypeptides and amino acids. Trypsin Pancreas Breaks proteins and polypeptides into shorter polypeptides. Chymotrypsin Breaks proteins and polypeptides into shorter polypeptides. Carboxypeptidase Breaks polypeptides into amino acids. Pancreatic lipase Breaks triglycerides into monoglycerides, fatty acids, and glycerol. Pancreatic amylase Breaks starch into shorter glucose chains and maltose. Carboxypeptidase, Small intestine Breaks polypeptides into amino acids. aminopeptidase, and dipeptidase Lipase Breaks monoglycerides into fatty acids and glycerol. Sucrase Breaks sucrose into glucose and fructose. Lactase Breaks lactose into glucose and galactose. Maltase Breaks maltose into glucose. Dextrinase Breaks short chains of glucose into individual glucose molecules. Digestive Hormones TABLE 3.3 Digestive Hormone Functions Hormone Where It Comes From What It Does Gastrin Stomach mucosa Stimulates secretion of hydrochloric acid (HCl) and pepsinogen by gastric glands in the stomach and increases gastric motility and emptying. Somatostatin Stomach and duodenal Inhibits the following: stomach secretion, mucosa motility, and emptying; pancreatic secretion; absorption in the small intestine; gallbladder contraction; and bile release. Secretin Duodenal mucosa Inhibits gastric secretion and motility; increases output of water and bicarbonate from the pancreas; increases bile output from the liver. Cholecystokinin Stimulates contraction of the gallbladder to (CCK) expel bile; increases output of enzyme-rich pancreatic juice. Gastric Inhibits gastric secretion and motility. inhibitory peptide The GI Tract and Barrier Function Barrier function: The protective role that gastrointestinal cells have in limiting the absorption of harmful substances (by mucosal cells) and disease-causing organisms (by immune cells which reside under the muscosa and respond to antigens) The GI tract limits the absorption of toxins and disease-causing organisms. The GI Tract and Barrier Function : A foreign substance (almost always a protein) that, when introduced into the body, stimulates an immune response. Some cells of the immune system are present in the GI tract: o Phagocytes o Lymphocytes o Antibodies The GI Tract and Barrier Function Digestion and Absorption  Digestion and Absorption The mouth is the entry point for food into the digestive tract. o in the mouth moistens food and initiates digestion. o Saliva contains (which helps to break down carbohydrates) and lysozymes (which help to inhibit bacterial growth in the mouth- helps prevent tooth decay). o Chewing mechanically breaks food down, increasing the surface area in contact with digestive enzymes. Digestion and Absorption-Swallowing Digestion and Absorption- Swallowing Pharynx (i.e. Throat): opening that is shared with the -when swallowing, allows for the passage of food/liquid to the esophagus Digestion and Absorption- Swallowing Epiglottis: Connective tissue which covers over the passageway to lungs (larynx and trachea) - prevent food/liquid from entering passageway to lungs  Digestion and Absorption Peristalsis  Digestion and Absorption Peristalsis Esophageal sphincter : Acidic contents leak out through esophageal sphincter and travel back to esophagus : ‘Reverse’ peristalsis in response to various ‘abnormal’ situations or factors Figure 3.6  Digestion and Absorption Stomach: Stomach walls are very thick and have the in the GI tract : The mixture of partially digested food stored/held in the stomach. Very little absorption takes place in Stomach walls are lined with mucus and millions of - openings that contain gastric glands and secrete gastric juice Food entering the stomach stimulates the release of - hormone secreted by the stomach muscosa which stimulates the release of gastric juice from the gastric glands  Digestion and Absorption Structure of the stomach  Digestion and Absorption Main Composition of Gastric Juice: 1. HCL (hydrochloric acid) and intrinsic factor (protein) produced by Parietal Cells : helps digest food and inhibit bacterial growth : Involved in the absorption of Vitamin B12 2. Pepsinogen: An inactive protein-digesting enzyme, produced by chief cells, which is activated to pepsin by acid in the stomach. : Responsible for digesting proteins into amino acids - Works best in acidic environment of stomach -If mucoa (and thick, protective mucus layer of stomach is penetrated), Peptic Ulcer  Digestion and Absorption Rate of Stomach Emptying: -Chyme normally leaves stomach by -Duration depends on (1) large vs. small meal, (2) solid vs. liquid meal, and (3) composition of meal - Transit Time: > >  Digestion and Absorption Small intestine : Lumen is covered by millions of ‘Finger- like protrusions’ called villi that participate in the digestion and absorption of nutrients Each villi contains (these are needed to absorb nutrients into the blood) Microvilli or brush border: Extend from ; minute, brush-like projections that in the small intestine. Copyright ©2020 John Wiley & Sons, Inc. 30 Chyme is propelled through the small intestine by peristalsis, which allows it to mix with digestive enzymes. Segmentation (alternating contraction and relaxation) moves chyme back and forth, time of absorption Copyright ©2020 John Wiley & Sons, Inc. 31  Digestion and Absorption Small Intestine needs the assistance of the Pancreas (which secretes pancreatic juice: contains bicarbonate ions and digestive enzymes) and Gall Bladder (which stores bile) Secretin: A hormone released by the duodenum that signals the release of pancreatic juice rich in bicarbonate ions and stimulates the liver to secrete bile ( ) into the gallbladder. Cholecystokinin (CCK): A hormone released by the duodenum that stimulates the release of pancreatic juice rich and causes the gallbladder to contract and release bile into the duodenum. Digestion and Absorption The large intestine contains the colon and the rectum. The large intestine can absorb water and some vitamins and minerals. Water, nutrients and fecal material may spend up to in the large intestine. Absorption Mechanisms Simple Osmosis Facilitated Active Diffusion Diffusion Transport -Movement of compounds from an area of high concentration to low concentration -Requires i.e. Vit E, fatty acids Absorption Mechanisms Simple Osmosis Facilitated Active Diffusion Diffusion Transport -Water moves in a direction to equalize dissolved substances on either side of membrane. - Move in a direction of high concentration to low concentration -Requires energy Absorption Mechanisms Simple Osmosis Facilitated Active Diffusion Diffusion Transport -Some molecules cannot pass freely across cell membranes - help of carrier proteins/molecules - Move in a direction of high concentration to low concentration -Requires energy i.e. fructose Absorption Mechanisms Simple Osmosis Facilitated Active Diffusion Diffusion Transport -Requires carrier protein/molecule AND -movement of substance from a low concentration to high concentration Summary