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Digestive system Body has a structural organization 1 Body is an open system Why? Respiratory, digestive and excretory systems allow for exchange with external environment Circulatory system in charge of transport within the body Blood exchanges materials with each cell via interstitial fluid Since the body is an open system it is sensitive to changes in the surrounding environment Body needs to maintain constant conditions inside “Homeostasis” What needs to be maintain constant? •Concentration of oxygen and carbon dioxide •Concentration of nutrients and waste products •Temperature •Water Systems function together to maintain homeostasis 2 Organ’s form fits Organ’s function As product of natural selection Structure of a body part (aka anatomy) Corresponds With the task it must perform (aka physiology) What is the purpose of Food? Source chemical energy That can be extracted by cellular respiration This process requires participation of Digestive, Respiratory and Circulatory Systems Source of building materials Some need to be consumed already fabricated essential nutrients 8 amino acids 13 Vitamins 12 Minerals Essential fatty acids 3 Why does food need to be broken down? Food processing occurs in four stages Digestive system consists of an alimentary canal and accessory glands 4 Small intestine: example of form fits function Function: Absorption of nutrients Form: Your small intestine is about 4 times your body length Diameter, folds, villi, microvilli Increase the surface area of absorption Digestive Systems in Animals No digestive system: Sponges why? Gastrovascular cavity: Cnidarians and Flatworms (absent in Tape worm) One opening, two way movement of food How is the gastrovascular cavity of flatworms different from that of the cnidarians? 5 Digestive Systems in Animals Digestive tract: two openings, one way movement, advantage? Pharynx: muscular pouch For mechanical digestion Esophagus Crop: moistens and stores food Gizzard: churns food and Usually has grit or gravel Intestine: Earthworm is crescent shape Accessory organs: Pancreas and liver Adaptations In mouth: In intestine the cecum stores food where bacteria are able to break down the cellulose 6 A bear and not a bear Pandas spend up to 14 hours eating Koalas spend about 4.7 h eating 0.3 lbs food/lb body (6x) 0.05 lbs food/lb body 7