6.1 - Digestion

Digestion and Absorption Essential Idea: The structure of the wall of the small intestine allows it to move, digest and absorb food. 6.1 Digestion and Absorption 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: Processes occurring in the small intestine that result in the digestion of starch and transport of the products of digestion to the liver Use of dialysis tubing to model absorption of digested food in the intestine Skills: Produce an annotated diagram of the digestive system Identify tissue layers in transverse sections of the small intestine viewed with a microscope or in a micrograph

Purpose of digestion A. Food is made of cells, and therefore macromolecules (carbs, lipids, proteins, nucleic acids) that your body needs to function B. Macromolecules are too big to cross cell membranes C. Your digestive system breaks polymers down into monomers so that they can get into your cells D. Your cells use the monomers to build macromolecules

4 steps Ingestion – eat Digestion – break down into smaller molecules Absorption – molecules move from digestive tract into blood and lymph Transport – circulatory system delivers molecules to cells

Digestion is an enzyme-driven process A. Digestive enzymes catalyze hydrolysis reactions – hold macromolecules in place and stress bonds until body heat causes them to break

glycerol and fatty acids   Salivary Amylase Pepsin Trypsin Pancreatic Lipase Pancreatic Amylase Source Salivary Glands Stomach cells Pancreas Location of action Mouth stomach Small intestine Small Intestine Substrate Amylose (starch) proteins lipids Product maltose, glucose amino acids glycerol and fatty acids pH 7 2-3 8

Absorption Villi – finger-like projections that line the small intestine – increase surface area! 1. Contain a capillary network for nutrients to pass into the blood (carbs and proteins) and a lacteal for the lymph system (lipids)

Passive Transport 1. Simple diffusion - fatty acids 2. Facilitated diffusion – glucose, amino acids Active Transport Pumps – glucose, amino acids Endocytosis – not fully digested macromolecules

Importance of smooth muscle A. Longitudinal – moves food through B. Circular – mechanical digestion