Digestion and absorption

Transcription

1 Digestion and absorption

2 Objectives Understandings: The contraction of circular and longitudinal muscle of the small intestine mixes the food with enzymes and moves it along the gut. The pancreas secretes enzymes into the lumen of the small intestine. Enzymes digest most macromolecules in food into monomers in the small intestine. Villi increase the surface area of epithelium over which absorption is carried out. Villi absorb monomers formed by digestion as well as mineral ions and vitamins. Different methods of membrane transport are required to absorb different nutrients. Applications and skills: Application: Processes occurring in the small intestine that result in the digestion of starch and transport of the products of digestion to the liver. Application: Use of dialysis tubing to model absorption of digested food in the intestine. Skill: Production of an annotated diagram of the digestive system. Skill: Identification of tissue layers in transverse sections of the small intestine viewed with a microscope or in a micrograph.

3 Digestion Metabolism chemical reactions breaking down food and releasing energy from nutrients Digestion mechanical & chemical breakdown of food into nutrients

4 Digestion Prepares food for cellular intake because most food molecules are large polymers and insoluble They must first be digested to smaller soluble molecules before they can be absorbed into the blood

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6 The Digestive Process Mechanical processing and movement: chewing, mixing Secretion: fluid, digestive enzymes and hormones, bile, acid, alkali, mucus Digestion: breaking down food to smallest absorbable units Absorption: through mucosa, into blood or lymph vessels Elimination: undigested eliminated material Ingestion Taking in food through the mouth Propulsion (movement of food) Swallowing Peristalsis propulsion by alternate contraction &relaxation Mechanical digestion Chewing Churning in stomach Mixing by segmentation Chemical digestion By secreted enzymes: see later Absorption Transport of digested end products into blood and lymph in wall of canal Defecation Elimination of indigestible substances from body as feces 6

7 Movement & Control Peristalsis push food along by rhythmic waves of smooth muscle contraction in walls of digestive system Sphincters muscular ring-like valves, regulate the passage of material between sections of digestive system

8 Chemistry of Digestion Amylases Lipases Enzymes are biological catalysts that increase the rate of reaction Hydrolysis of insoluble food molecules to soluble end products Proteases Nucleases

9 The Digestive Enzymes type of enzyme example of enzyme source substrate product optimum ph Amylase salivary amylase saliva starch maltose ph 7 Protease pepsin gastric juice protein shorter polypeptid e chains ph 2 Lipase pancreatic lipase pancreatic juice lipids (triglycerid es) glycerol and fatty acids ph 8

10 The Digestive Enzymes

11 The Digestive Enzymes

12 Digestive System

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14 Digestive System mouth - the first part of the digestive system, where food enters the body. Chewing and salivary enzymes in the mouth are the beginning of the digestive process (breaking down the food). esophagus - the long tube between the mouth and the stomach. It uses rhythmic muscle movements (called peristalsis) to force food from the throat into the stomach. stomach - a sack-like, muscular organ that is attached to the esophagus; food is mixed with acids & enzymes chemical digestion. Food remains for few hours; peristalsis mixes food until almost fluid called chyme; pyloric sphincter opens allowing small amounts of acid chyme into duodenum; repeated until stomach empty Main function: storage; chemical digestion of proteins

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18 Digestive System small intestine - the long, thin tube that food goes through after it leaves the stomach. Main function: chemical digestion of carbs, lipids, proteins & absorption. large intestine - the long, wide tube that food goes through after it goes through the small intestine anus - the opening at the end of the digestive system from which feces exit the body.

19 Digestive System pancreas - enzyme-producing gland located below the stomach and above the intestines. Enzymes help in the digestion of carbohydrates, fats and proteins in the small intestine. liver - a large organ located above and in front of the stomach. It filters toxins from the blood, and secretes bile (which breaks down fats) and some blood proteins. gall bladder - a small, sac-like organ located by the duodenum. It stores and releases bile (digestive chemical produced in liver) into the small intestine

20 Accessory Organs

21 Absorption & Assimilation Absorption The soluble products are first taken up by various mechanisms into the epithelial cells that line the gut. These epithelial cells then load the absorbed molecules into the blood stream. Assimilation The soluble products of digestion are then transported to the various tissues by the circulatory system. The cells of the tissues then absorb the molecules for use within this tissues the broken down molecules actually become part of the body

22 Structure of the Small Intestine Blood supply in the villus which absorb the end products of digestion from the epithelial cells The lacteals (green) that receive the lipoproteins before transporting them to the circulatory system. Muscular walls that maintain the movement of chyme by peristalsis.

23 Structure of the Small Intestine

24 Structure of the Small Intestine

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26 Structure of the villus The structure of the villus (villi) increases the surface are for the absorption of digested food molecules. folds increase SA:VOL ratio by X 3 Villi project into the lumen of the gut increasing the surface area by X 10 Microvilli are outward folds of the plasma membrane increasing the surface area another X10

27 The Process of Digestion A. Mouth 1. teeth begin mechanical digestion (chewing, grinding) 2. saliva (digestive enzyme) begins chemical digestion, breakdown of carbohydrates into smaller sugar molecules (amylase) and breakdown of bacteria cell walls (lysozyme) B. Esophagus food tube 1. peristalsis contractions of smooth muscle toward the stomach

28 The Process of Digestion C. Stomach 1. chemical digestion pepsin breaks down proteins and needs hydrochloric acid to work which stops amylase. Mucus needed to protect stomach 2. mechanical digestion churned stomach contents become chyme. D. Small Intestine 1. most chemical digestion and absorption of food 2. digestive fluids from pancreas, liver and lining of duodenum a. pancreas regulates blood sugar 1. breaks down carbohydrates, proteins, lipids, and nucleic acids 2. produces sodium bicarbonate, neutralizes acids b. liver makes bile for breaking down fats (stored in gall bladder)

29 The Process of Digestion E. Absorption in the Small Intestine 1. villi folded surfaces, increase surface area for absorption a. products of carbohydrates and proteins (undigested fat and some fatty acids absorbed by lymph) F. Large Intestine 1. absorption of water 2. bacteria produce compounds (vitamin K) a. massive antibiotic use can cause vitamin K deficiency 3. undigested material leave body through rectum