The Digestive System Chapter 45

Animals are heterotrophs Require fuel –Chemical energy is obtained from the oxidation of complex organic molecules Require essential nutrients –Chemicals an animal requires but cannot synthesize – varies from species to species –Essential amino acids – human adults can produce 12 of the 20, making 8 essential –Essential fatty acids – deficiencies are very rare –Vitamins and minerals (required in small amounts)

Food Processing Ingestion –The act of eating Digestion –Breaking down food into smaller molecules –Polymers  monomers –Mechanical digestion: physically breaks food up and increases its surface area –Chemical digestion: enzymatic hydrolysis uses water to break bonds in polymers Absorption –The uptake of small molecules into the body Elimination –Undigested material passes out of the body

The Mammalian Digestive System The oral cavity –Begins both physical and chemical digestion Teeth + saliva produce bolus The pharynx –Epiglottis helps prevent food in trachea The esophagus –Peristalsis – rhythmic contractions that move food; starts as voluntary and changes to involuntary

The Mammalian Digestive System… The stomach –Stores food and performs preliminary digestion Churning to mix food into chyme Gastric juice works mainly on proteins The small intestine –Most enzymatic hydrolysis of food and absorption of nutrients –Also involved: pancreas, liver, gall bladder –Huge surface area provided by villi and microvilli –Nutrients cross into bloodstream by diffusion and active transport The large intestine –Reclaiming water from feces is the major job –Intestinal bacteria live on organic material – produce vitamin K