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Digestion ch34 Mader p647 #1,2,4,5 7,9, 10 #1 an incomplete digestive tract has a single opening, usually called a mouth. For example the planarians (flatworms that are carnivorous) have a mouth and muscular pharynx, the tract (a gastrovascular cavity) branches throughout the body. They wrap their body around the prey and the pharynx (which extends beyond the mouth) sucks up minute quantities at a time. Digestive enzymes allow some extracellular digestion to occur. Digestion is completed intracellularly by the cells that line the tract. No cell is far from the tract so diffusion is sufficient to distribute nutrients. Earthworms (annelids) have a complete digestive tract and feed mainly on dead organic matter in soil. They have a single opening which is used as both a mouth an entrance for food (mouth) and an exit for wastes (anus).Muscular pharynx draws in food with a sucking action. Food enters crop (storage area with thin expansive walls). Then, food goes to gizzard and there, thick,muscular walls crush and sand grinds the food. Digestion is extracellular within an intestine.The surface area of digestive tracts is often increased for absorption of nutrient molecules, and in earthworms, this is accomplished by an intestinal fold called the typhlosole. Undigested remains pass out the anus. The specialized parts are the pharynx, the crop, the gizzard and the intestine each has a particular function in the digestive process. #2 Clams (continuous feeder which are constantly in the process of digesting whatever they can filter into their bodies) are filter feeders. Water always moves through the mantle cavity by the incurrent siphon (slitlike opening) and depositing particles (algae, protozoans, invertebrates)which adhere on the gills. Ciliary action moves particles that are the right size to the labial palps, which force them through the mouth into the stomach. Digestive enzymes are secreted by a digestive gland but amoeboid cells present throughout the tract are believed to complete the digestive process by intracellular digestion. Squids (discontinuous feeders that have storage areas for food for later digestion) have tentacles with suckers with toothed horny rings that they use to capture prey (fish, shrimp, worms) to bring it to the beak like jaws, which bite off pieces with a radula (a tongue-like structure). The esophagus Digestion ch34 Mader leads to a stomach and a cecum, where digestion occurs. The stomach and cecum retain food until digestion is complete. #4 Digestion ch34 Mader Notes: Saliva contains salivary amylase to begin the break down of starch into maltose The stomach churns and mixes food with mucus and gastric juices to produce chyme. Pepsin begins protein breakdown. Duodenum of small intestine receives bile from the liver and pancreatic juice from the pancreas. Bile emulsifies fat (breaks it into smaller droplets) to ready it for digestion by an enzyme from pancreas. Pancreas also produces enzymes that digest starch and protein (see chart that you were given in class) Small intestine has small fingerlike projections called villi where nutrient molecules are absorbed. Amino acids and glucose enter blood vessels of a villus. Glycerol and fatty acids are packaged as lipoproteins before entering lymphatic vessels called lacteals in a villus. Large intestine has no digestive juices. It absorbs water, salts and some vitamins Liver receives blood from hepatic portal vein. #5 Nutrients are absorbed into the vessels of a villus, which contains blood capillaries and a lymphatic capillary, called a lacteal. Sugars (remnants of digestion of carbohydrates) and amino acids (from protein) enter the blood capillaries of a villus. Glycerol and fatty acids (from fats) enter the epithelial cells of the villi and within these cells, they are joined and packaged as lipoprotein droplets (chylomicrons), which enter a lacteal. After the are absorbed, they are eventually carried to all cells of the body by the bloodstream. #7 Functions of the Accessory organs: Liver, gall bladder and pancreas The liver receives blood from two sources. Freshly oxygenated blood is brought to the liver by the common hepatic artery, a branch of the celiac trunk from the abdominal aorta. Blood that is rich in nutrients from the digestive tract is carried to the liver by the hepatic portal vein.The liver has a wide variety of functions and many of these are vital to life. Digestion ch34 Mader Liver functions include the following: • secretion • synthesis of bile salts • synthesis of plasma protein • storage • detoxification • excretion • carbohyrate metabolism • lipid metabolism • protein metabolism • filtering GALLBLADDER: The principal function of the gallbladder is to serve as a storage reservoir for bile. Bile is a yellowish-green fluid produced by liver cells. The main components of bile are water, bile salts, bile pigments, and cholesterol.Bile salts act as emulsifying agents in the digestion and absorption of fats. Cholesterol and bile pigments from the breakdown of hemoglobin are excreted from the body in the bile. PANCREAS: The pancreas has both endocrine and exocrine functions. The endocrine portion consists of the scattered islets of Langerhans, which secrete the hormones insulin and glucagon into the blood. The exocrine portion is the major part of the gland. It consists of pancreatic acinar cells that secrete digestive enzymes into tiny ducts interwoven between the cells. Pancreatic enzymes include anylase, trypsin, peptidase, and lipase. Pancreatic secretions are controlled by the hormones secretin and cholecystokinin. #9 Ham sandwich digestion salivary amylase in mouth begins breakdown of starch (in bread) to maltose in the mouth pepsin breaks down protein (ham) into peptides in the stomach pancreatic amylase (from pancreas) continues to break down starch into maltose in the intestines. trypsin from pancreas breaks down more protein into peptides in the intestines maltase from small intestine breaks down maltose into glucose peptidases from small intestine break down peptides into amino acids lipase, from the pancreas, digests fat (in meat and oils/fats) molecules after they have been emulsified by bile and digests them into glycerol and 3 fatty acids (monoglycerides that can be packaged as chylomicrons in the villi cells and then enter the lacteals. Digestion ch34 Mader #10 Good nutrition provides us with energy, essential amino acids, fatty acids and all necessary vitamins and minerals for all body functions. Consuming too many calories from any food source contributes to body fat, increasing a person’s risk of obesity. Obesity is having 30% more than the ideal body weight for your height and body build. People with type 2 diabetes can develop cardiovascular disease since they develop impaired insulin production and insulin resistance. When you have insulin resistance, the body’s cells fail to take up glucose, even when insulin is present. Glucose levels are high and show up in urine