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Chapter 23

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Biology 1225
Michael Butler

Chapter 23 Digestion and Excretion pg.450 23.2 Animal Digestive Systems pg 451 ingestion – taking food into the digestive system digestion – breakdown of food into smaller bits and then into its component molecules nutrient absorption – movement of nutrient molecules from a digestive cavity into cells that line the digestive chamber elimination – expulsion of unabsorbed material from the digestive tract gastrovascular cavity – Saclike gut with one opening complete digestive tract –tubular gut with two openings anus – opening through which wastes leave a complete digestive tract 1 ***Digestion is generally defined as: a. eating food b. absorption of nutrient molecules from the stomach c. moving nutrient molecules into the body across the gut wall d. mechanically and chemically breaking food down into small nutrient molecules ***An essential nutrient cannot be made in the body ***Fat is the most concentrated energy source - Nutrition encompasses all of the processes by which we consume and digest food, then absorb its nutrients - The digestive system transports, processes and stores food - As food moves through the digestive system, it is physically and chemically broken down into nutrients, some of which are absorbed while the unabsorbed residues are excreted - Adequate nutrition also requires that the body be supplied with vitamins, minerals and amino and fatty acids that the body itself does not produce Digestion and absorption of food are vital to homeostasis Most animals have a digestive system that carries out these tasks: a. Ingestion – taking food into the digestive system b. digestion – breakdown of food into smaller bits and then into its component molecules c. nutrient absorption – movement of nutrient molecules from a digestive cavity into cells that line the digestive chamber d. elimination – expulsion of unabsorbed material from the digestive tract Where do animals digest their food? 1. In some invertebrates digestion occurs in a saclike gastrovascular cavity – The gastrovascular cavity of flatworms and cnidarians is saclike, with a single opening. 2. Other invertebrates and all vertebrates have a more efficient complete digestive tract (a tube with 2 openings – mouth and anus – and specialized areas between them) which is a tube that has specialized regions along its length 2 23.3 Human Digestive System pg 452 esophagus – muscular tube that connects the pharynx (throat) to the stomach stomach –muscular organ that mixes food with gastric fluid secreted by its lining to make chime gastric fluid – fluid secreted by the stomach lining; contains enzymes, acid and mucus chime – mix of food and gastric fluid sphincter – ring of muscle that controls passage through a tubular organ or body opening bile – mix of salts, pigments and cholesterol produced by the liver; aids in fat digestion liver – organ that produces bile, stores glycogen and detoxifies many substances gallbladder – organ that receives bile from the liver and expels it into the small intestine pancreas – organ that secretes digestive enzymes into the small intestine and hormones into the blood small intestine – longest portion of the digestive tract and the site of most digestion and absorption villi – multicelled projections from the lining of the small intestine microvilli – thin projections that increase the surface area of brush border cells 3 essential fatty acids – fatty acids that the body cannot make and must obtain from the diet large intestine – organ that concentrates and stores waste, then delivers it to the anus for excretion Colon – longest portion of the large intestine Appendix – tubular projection from the first part of the large intestine Rectum – portion of the large intestine that stores feces until they are expelled Feces – unabsorbed food material and cellular waste that is produced by digestion 4 1. Mouth a. Mechanical and chemical break down of food begins in the mouth. b. Saliva contains an enzyme ***(amylase) that begins ***carbohydrate digestion – Chewing mixes food with saliva. An enzyme (amylase) in saliva starts the process of ***starch/***carbohydrate digestion c. ***Amylase is secreted by the pancreas and the salivary glands d. The swallowing reflex moves food from the throat into the esophagus and then into the stomach 2. Stomach a. Food continues through a sphincter into the stomach b. a muscular sac with a lining that secretes*** gastric enzymes that break down proteins. c. ***Protein digestion begins in the stomach d. Chime (food mixed with gastric fluid) is produced in the stomach and then goes to the small intestine e. ***Erosion of the mucus layer of the stomach can cause ulcers 5 3. The small intestine a. ***the longest segment of the digestive tract in humans b. ***Most digestion and absorption occurs in small intestine c. intestinal and pancreatic enzymes complete digestion of ***proteins and carbohydrates d. Intestinal and pancreatic enzymes together with ***Bile which is made in the liver and
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