6.1 - Digestion

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 pH 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