Digestion Absorption Transport 1 Digestion The Digestive System

Digestion, Absorption, & Transport 1

Digestion & The Digestive System ü Digestion- the process by which food is broken down into absorbable units. ü Digestive system- all the organs and glands associated with the ingestion and digestion of food. ü GI tract- the gastrointestinal tract. Gastro- stomach. Intestinalis- intestine. 2

Anatomy Of The Gastrointestinal Tract Mouth- chews and mixes food with saliva. Salivary glands- secrete saliva. Epiglottis- cartilage in the throat that guards the entrance to the trachea. Protects airway during swallowing. Trachea (windpipe)- allows air to pass to and from the lungs. 3

Anatomy Of The Gastrointestinal Tract {continued} Esophagus (food pipe)- passes food from the mouth to the stomach. Cardiac sphincter (lower esophageal sphincter)allows passage from the esophagus to stomach. Prevents backflow from the stomach. * Sphincter- a circular muscle surrounding, and able to close, a body opening. They are found at specific points along the GI tract and regulate the flow of food particles. 4

Anatomy Of The Gastrointestinal Tract {continued} Stomach- adds acid, enzymes, and fluid. Churns, mixes, and grinds food to a liquid mass. Pyloric sphincter- allows passage from stomach to small intestines. Prevents backflow from small intestines. Liver- manufactures bile salts, detergent-like substances to help digest fats. 5

Anatomy Of The Gastrointestinal Tract {Continued} Gallbladder- stores bile until needed. Bile duct- conducts bile from the gallbladder to the small intestine. Ileocecal valve- allows passage from the small to large intestine. Prevents backflow from the colon. Appendix- stores lymph cells. 6

Anatomy Of The Gastrointestinal Tract {continued} Small intestine- A 10 ft. length of small diameter intestine that is the major site of digestion of food and absorption of nutrients. Its segments include the duodenum, jejunum, and ileum. Pancreas- a gland that secretes digestive enzymes and juices into the duodenum. Pancreatic duct- conducts pancreatic juice from the pancreas to the small intestine. 7

Anatomy Of The Gastrointestinal Tract {continued} Large intestine (colon)- reabsorbs water and minerals. Passes waste along with water to the rectum. Its segments include the ascending, transverse, descending, and sigmoid colon. Rectum- stores waste prior to elimination. Anus- the terminal sphincter of the GI tract. Opens to allow elimination. 8

Muscular Actions Of Digestion ü Peristalsis- wavelike muscular contractions of the GI tract that push its contents along. ü Stomach action- contains circular, longitudinal, and diagonal muscles that contract and relax to force the chyme downward to the pylorus. 9

Muscular Actions Of Digestion {continued} ü Segmentation- periodic squeezing or partitioning of the intestine at intervals along its length by its circular muscles. ü Sphincter contractions- four major sphincter muscles divide the GI tract into its principal divisions. Contraction of these sphincters allows food to pass along the entire length of the GI tract. 10

Secretions of Digestion The five organs which produce secretions during digestion: ü Salivary glands ü Stomach ü Pancreas ü Liver (via gallbladder) ü Small intestine 11

The Salivary Glands ü Secrete saliva into the mouth and begin the digestive process ü Its principal enzyme, amylase, begins carbohydrate metabolism. ü Saliva contains water, salts, and enzymes. 12

The Stomach ü Cells in the stomach produce gastric juice which is a mixture of water, enzymes, and hydrochloric acid. ü Gastric gland are also referred to as exocrine glands. ü The major digestive event of the stomach is the partial breakdown of proteins. ü Gastro = stomach 13

Pancreatic Juice And Intestinal Enzymes ü Pancreatic juice is the exocrine secretion of the pancreas, containing enzymes for the digestion of carbohydrate, fat, and protein. ü The pancreas contributes digestive juices by way of ducts leading to the intestines. ü In addition to enzymes, pancreatic juice also contains sodium bicarbonate to neutralize the acid chyme from the stomach. 14

The Liver ü The liver produces bile which is stored in the gallbladder. ü Bile flows from the gallbladder to the duodenum. ü Bile emulsifies fat for absorption. * an emulsifier is. . . 15

Anatomy Of The Absorptive System ü Absorption- the passage of nutrients from the GI tract into either the blood or lymph. ü Villi- fingerlike projections from the folds of the small intestines. 16

Anatomy Of The Absorptive System {continued} ü Microvilli- tiny, hairlike projections on each cell of every villus that trap nutrient particles and transport them into the cells. ü Crypts- tubular glands that lie between the intestinal villi and secrete intestinal juices into the small intestines. 17

Overview of Macronutrients And Their Digestive Fate Mouth • Carbohydrate digestion begins. Stomach • Carbohydrate digestion continues. • Protein digestion begins. 18

Overview of Macronutrients And Their Digestive Fate Small Intestines • Starch digestion/absorption is completed. Large Intestines • Fluid reabsorbed. • Some fibers continue digestion. • Fat is emulsified and absorbed. • Some fibers pass through the large intestine and get • Protein digestion/ excreted. absorption is completed. 19

Hormones ü Hormones- chemical messengers secreted by a variety of glands in response to altered conditions. ü They travel to target tissues or organs where they elicit a specific response to maintain homeostasis. ü Homeostasis- the maintenance of constant internal conditions by the body’s control systems. ü Homeo = the same. ü Stasis = staying. 20

Gastrointestinal Hormones ü Gastrin- the hormone secreted by the cells of the stomach wall. Gastrin stimulates the stomach glands to secrete the components of hydrochloric acid. ü Hydrochloric acid (HCL)- an acid composed of hydrogen and chloride atoms. 21

Hormones Of The Small Intestines ü Secretin- produced by cells in the duodenum wall. Target organ is the pancreas. Response is the release of bicarbonate-rich pancreatic juice. ü Cholecystokinin (CCK)- produced by cells of the intestinal wall. Target organ is the gallbladder. Response is the release of bile and slowing of GI motility. ü Gastric-inhibitory peptide- produced by the intestine. Target organ is the stomach. Response is slowing 22 the secretion of gastric juice and slowing of GI motility.

Common Digestive Problems ü Choking- when food has slipped into the air passage (trachea) and breathing has been blocked. ü Vomiting- when the waves of peristalsis reverse direction and the stomach contents are propelled up the esophagus and out of the mouth. Arising from a variety of situations. ü Diarrhea- characterized by frequent loose, watery stools. Indicating that the intestinal contents have moved too rapidly through the intestines for fluid absorption to take place. This can be a symptom of 23 a variety of medical conditions.

Common Digestive Problems {continued} ü Constipation- longer than usual time between bowel movements and there is difficulty, pain, or discomfort when having a bowel movement. Each person’s GI tract responds differently to food, digestion, absorption, and transport. ü Heartburn- a painful sensation a person feels when the cardiac sphincter fails to prevent the contents of the stomach from refluxing into the esophagus. 24

Strategies For Prevention Of Common GI Problems Ø Choking Ø Take small bites. Ø Chew thoroughly. Ø Don’t talk with food in your mouth. Ø Diarrhea Ø Rest. Ø Drink plenty of fluids to replace losses. Ø Seek medical attention if problem persists. 25

Strategies For Prevention Of Common GI Problems {continued} ü Constipation ü Eat a high fiber diet. ü Drink plenty of fluids. ü Exercise regularly. ü Do not delay defecation. 26

Strategies For Prevention Of Common GI Problems {continued) ü Heartburn ü Eat small meals ü Follow a low fat diet ü Sit up while eating ü Drink liquids in between meals ü Wait 1 hour after eating before lying down ü Wait 2 hours before exercising ü Refrain from smoking ü Obtain a healthy weight 27