Digestion Chapter 41. Homeostatic mechanisms manage an animal s energy budget.

Transcription

1 1 AP Biology March 2008 Digestion Chapter 41 Homeostatic mechanisms manage an animal s energy budget. 1) Four main feeding mechanisms of animals a) Suspension feeders i) animals that sift small food particles from water. (1) Humpback whales b) Substrate feeders i) live in or on their food source, eating their way through the food. (1) Moth larvae c) Fluid feeders i) pull nutrient-rich fluid from a living host. (1) Mosquitoes d) Bulk feeders i) eat relatively large pieces of food. (1) Humans ii) Three types of bulk feeders: (1) Herbivores eat mainly autotrophs. (2) Carnivores eat other animals. (3) Omnivores eat both plants and animals. 2) Glucose regulation is an example of homeostasis. a) Animals store excess calories as glycogen in the liver and muscles and as fat in fat tissues. b) These energy stores can be tapped when an animal is in need of ATP. c) Blood glucose level is maintained within a relatively narrow range by a negative feedback mechanism. d) Diabetes mellitus 3) Calorie imbalance a) result in undernourished animals that have diets deficient in calories, or overnourished animals that consume more calories than they need. Diet must supply carbon skeletons and essential nutrients.

2 2 1) Essential nutrients a) must be obtained in preassembled form because the animal cannot produce them. 2) Essential amino acids a) About half of the 20 amino acids are required by animals b) Must be obtained from food. c) There are also essential fatty acids that animals cannot make and must ingest. 3) Vitamins a) Organic molecules required in small amounts. 4) Minerals a) Simple inorganic nutrients required in small amounts. Four main stages of food processing 1) Ingestion a) Act of taking down food. 2) Digestion a) Breakdown of food into small molecules capable of being absorbed by the cells of the body. b) Enzymatic hydrolysis is the reaction by which macromolecules are broken up. It involves the addition of water. 3) Absorption a) body s cells take up small molecules from the digestive track. 4) Elimination a) passing of undigested material from the digestive track. Types of digestion 1) Intracellular digestion a) Occurs within a cell enclosed by a protective membrane. b) Sponges digest their food this way. 2) Extracellular digestion a) Carried out by most animas b) Food is broken down outside of cells. 3) Gastrovascular cavity a) Simple animals have a single opening through which food enters and waste is eliminated. 4) Complete digestive tracks (alimentary canals)

3 3 a) One-way digestive tubes that begin at the mouth and terminate at the anus. The movement of food through the digestive system. 1) Food in the mouth a) Nervous reflex occurs that causes saliva to be secreted into the mouth. b) Saliva lubricates the food to facilitate swallowing. i) Contains the enzyme salivary amylase, which hydrolyzes starch and glycogen into smaller polysaccharides and the disaccharide maltose. 2) Chewed food is shaped into a ball bolus. a) After swallowing, the bolus enters the pharynx a junction that opens to the esophagus and the trachea. b) During swallowing, the epiglottis (the flap made of cartilage) covers the trachea. This diverts the food down the esophagus. 3) The esophagus moves food from the pharynx down to the stomach through peristalsis. a) Peristalsis is rhythmic waves of contraction by smooth muscle in the walls of the esophagus. 4) The stomach s functions include storing food and secreting gastric juice. a) Gastric juice contains hydrochloric acid, which is very acidic. Breaks down the extracellular matrix of meat and plant materials. Kills most of the bacteria ingested with food. 5) Pepsin is an enzyme in gastric juice that begins to hydrolyze proteins into smaller polypeptides. a) Secreted in an inactive form called pepsinogen, activated by hydrochloric acid in the stomach. 6) The result of stomach digestion is acid chime. 7) Acid chime is shunted from the stomach into the small intestine via the pyloric sphincter. 8) The first section of the small intestine is the duodenum. a) In the duodenum, the acid chime mixes with secretions from the pancreas, the gallbladder, and the intestinal wall itself. b) The rest of the small intestine is responsible for the absorption of nutrients. 9) Particular macromolecules are broken down in the small intestine by the following processes: a) Carbohydrates

4 i) The breakdown of starch and glycogen begins with salivary amylase in the mouth. In the small intestine, pancreatic amylases break starch, glycogen, and small polysaccharides into disaccharides. The breakdown of these disaccharides occurs at the wall of the intestinal epithelium, and the monosaccharides are quickly absorbed. b) Proteins i) Pepsin begins the breakdown of proteins in the stomach, and in the small intestine; trypsin and chymotrypsin break polypeptides into smaller chains. Dipeptidases, carboxypeptdase, and aminopeptidase break apart proteins into amino acids. c) Nucleic acids i) The breakdown of nucleic acids is similar to that of proteins. In the small intestine, nucleases break them down into nucleosides, nitrogenous bases, sugars, and phosphate groups. d) Fats i) Digestion of fats starts in the small intestine. Bile salts coat the fat droplets and keep them from clumping and lipase hydrolyzes them. 10) The epithelial lining of the small intestine has folds called villi, which in turn bear projections called microvilli a) Both of which radically increase the surface area available for absorption. 11) In each villus is a set of tiny blood vessels called capillaries and a lymph vessel called a lacteal, which absorbs small fatty acids. 12) Monosaccharides, such s glucose, cross the lining via passive diffusion, whereas amino acids and dipeptides are pumped across in active transport. 13) The capillaries and veins that drain the nutrients away from the villi all join the hepatic portal vessel, which brings them to the liver. a) The liver metabolizes the organize molecules in various ways. 14) Some other hormones involved in digestion are: a) Gastrin i) Stimulates the secretion of gastric juice b) Enterogastrone i) Slows digestion c) Secretin and cholecystokinin (CCK) 4

5 5 i) Secreted by the walls of the duodenum and that prompt the digestion of various macromolecules. 15) The large intestine, also called the colon, is connected to the small intestine by a sphincter. a) The point of the connection is the site of the cecum, a small pouch with an extension called the appendix. 16) The main function of the large intestine is to compact waste and recover water. a) The wastes become more solid as they travel along and form feces. 17) At the end of the colon is the rectum, where feces are stored until they are eliminated. Adaptations of digestive systems are associated with diet. 1) A mammal s dentition is greatly correlated with its diet. a) Mammals have specialized dentition that best enables them to ingest their usual diet. 2) Herbivores generally have longer alimentary canals than carnivores. Why? a) It reflects the longer time needed to digest vegetation.