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Chapter 43 Digestion and Nutrition The feeding habits of animals can be generally typed as herbivorous, carnivorous, and omnivorous. To be of use, food must be processed before it can be assimilated into the body. Food processing occurs in the animals digestive tract. Types of Digestive Tracts Incomplete Tact (see fig. 43.1 a.k.a. gastrovascular cavity, a blind sac with only one opening, the mouth. Found in cnidarians (such as hydra and jellyfish) and in flatworms (such as planaria). Complete Digestive Tract (see fig. 43.2 and 43.5) a.k.a. alimentary canal, a tubular system flowing from mouth to anus. The one-way passage allows for regional specialization. For example, the stomach, small intestines, and large intestines are three regions of specialization each performing a different function in food processing. Types of feeding
Substrate Feeders eat what it lives in, ex. earthworms Filter Feeders filters large volumes of fluid for particles of food, ex. Barnacles and baleen whales. Fluid Feeders feed on fluid food, ex. mosquitoes Bulk Feeders bite off chunks of food Elimination
of indigestible waste following digestion Gastrovascular cavities
regurgitate. Alimentary tracts eliminate via anus (rarely regurgitate) Human Digestive Tract Mouth helps form the bolus (ball of food to be swallowed), saliva moistens and begins starch digestion. Pharynx region between mouth and esophagus; here the respiratory and digestive tracts intersect (must get food past the pharynx without choking). Esophagus - moves food via peristalsis - rhythmic waves of contraction (peristalsis pushes food through entire alimentary canal, not just the esophagus).. Stomach J-shaped muscular bag in mammals, secretes pepsin (helps break down proteins into smaller proteins) and HCl (acidifies the stomach contents and helps liquefy the food forming acid chyme). Small Intestines the first segment is called the duodenum and it is the duodenum that receives the secretions from the bile duct and the pancreatic duct. Bile (made in the liver, stored in gall bladder) emulsifies lipids aiding in the digestion of lipids. Enzymes from the pancreas actually digest lipids and all other organic compounds (e.g. proteins, carbohydrates). The small intestines are small in diameter yet long in length (ca. 20 ft.). Their linings are made of villi, fingerlike extensions of intestinal wall, each villus covered by a single epithelial layer and houses blood and lymph capillaries, the latter called a lacteal. The blood capillaries absorb amino acids and sugars, and the lacteal absorbs lipids. Large Intestines a.k.a. the colon, large in diameter but relatively short in length (1 ½ meters). Includes the cecum (blind end of large intestine that supports an appendix). The large intestine functions in:
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