Key Concepts Chapter 3 Digestive Tract

KEY CONCEPTS CHAPTER 3 24. What are the organs of the digestive tract and the functions necessary for digestion and absorption? ● Digestive Tract Role in Wellness ○ Growth, maintenance, and energy needs depends on the nutrients available ○ The digestive system, responsible for breaking food down to essential nutrients and making delivery to the cells. ○ Processes of digestion, absorption, and metabolism work together to provide all body cells with energy and nutrients ● Organs of Digestive Tract ○ GI Tract ■ Mouth ● Chemical digestion: action of saliva, that not only moistens, but contains amylase, an enzyme that begins the digestive process of starches. ● Mechanical digestion: depends on the teeth, where it tears and pulverize the food. ● More than 2000 taste buds in our tongue. ■ Esophagus: muscular tube through which the bolus travels from the mouth to the stomach. ● Process begins with Peristalsis, which is involuntary movements of circular and longitudinal muscles. ● You have the mucosa, then submucosa, and digestion depends blood vessels and nerves of the submucosa. ● Muscularis surrounds the submucosa. ● Serosa: outermost layer of the GI wall and is actually the peritoneum lining the abdominal pelvic cavity and covers organs. ● Churning action allows secretions to mix with food mass. Rhythmic contractions of the muscles cause the action of peristalsis. ● Segmentation: combined effect of the circular and longitudinal muscles. ■ Stomach: consist of fundus, body, and pylorus. Formation of chyme. ● Function of stomach: ○ hold food for partial digestion, ○ produce gastric juice, ○ provide muscular action that, ○ combined with gastric juice, mixes and tears food into smaller pieces, ○ secretes intrinsic factor for vitamin B12 absorption, r ○ releases gastrin. ○ Destruction of pathogenic bacteria. ● Gastric secretions occur in 3 phases: Cephalic, Gastric, and Intestinal. ○ Cephalic Phase: also called the “psychic phase” because mental factors can stimulate gastrin, a hormone stimulated by stomach mucosa. ○ Gastric Phase: gastrin increases release of gastric juices when the stomach is distended by food. ○ Intestinal Phase: gastric secretion change as chyme, a semiliquid mixture of food mass, passes through the duodenum. ● Hormones regulate the release of gastric juices and enzyme. ■ Small Intestine ● Chyme moves through the jejunum and ileum of the small intestine. ● In small intestine, nutrients in chyme are prepared for absorption. ● Small intestine is the major organ for digestion and final stages of the digestive process occurs here. ● Bile: secreted in the liver and stored in the gallbladder, is released to emulsify fats, aiding in digestion of lipids. ● Secretin: hormone released by the small intestine, causes the pancreas to send bicarbonate to the small intestine to reduce the acidic content of the chyme. ■ Large Intestine ● Consist of the cecum, colon, and rectum. ● Cecum: is a blind pocket, therefore the mass bypasses it and enters the ascending colon, then leads to the transverse colon running across the abdomen over the small intestine to the descending colon, then the descending colon extends down the left of the abdomen into the sigmoid colon and leads into the descending colon, on to the rectum and into the anal canal. ○ Digestive Tract TABLE 3-1 Digestive Processes MECHANISM DESCRIPTION Ingestion Process of taking food into the mouth, starting it on its journey through the digestive tract Digestion A group of processes that break complex nutrients into simpler ones, thus facilitating their absorption; mechanical digestion physically breaks large chunks into small bits; chemical digestion breaks molecules apart Motility Movement by the muscular components of the digestive tube, including processes of mechanical digestion; examples are peristalsis and segmentation Secretion Release of digestive juices (containing enzymes, acids, bases, mucus, bile, or other products that facilitate digestion); some digestive organs secrete endocrine hormones that regulate digestion or metabolism of nutrients Absorption Movement of digested nutrients through the gastrointestinal mucosa and into the internal environment Elimination Excretion of the residues of the digestive process (feces) from the rectum, through the anus; defecation ○ Digestion Chewing and swallowing Depends on texture and quantity Esophagus 5-7 seconds Stomach 2-6 hours Small intestine Approximately 5 hours Large intestine 9-16 hours Total 16-27 hours ingestion to elimination 25. What are the 3 phases of the gastric secretion process and what happens in each? ● Gastric secretions occur in 3 phases: Cephalic, Gastric, and Intestinal. ○ Cephalic Phase: also called the “psychic phase” because mental factors can stimulate gastrin, a hormone stimulated by stomach mucosa. ○ Gastric Phase: gastrin increases release of gastric juices when the stomach is distended by food. ○ Intestinal Phase: gastric secretion change as chyme, a semiliquid mixture of food mass, passes through the duodenum. 26. How do the following hormones/enzymes affect digestion/absorption/metabolism: amylase, gastrin, chyme, secretin, CCK, bile, hydrochloric acid, bicarbonate? ● Cholecystokinin (CCK): hormone secreted by intestinal mucosa. inhibits gastric secretions. It’s also called “Pancreozymin” ● Bile: secreted in the liver and stored in the gallbladder, is released to emulsify fats, aiding in digestion of lipids. ● Secretin: hormone released by the small intestine, causes the pancreas to send bicarbonate to the small intestine to reduce the acidic content of the chyme. ● Chyme: a semiliquid mixture of food mass that passes through the duodenum. ● Gastrin: hormone secreted by the stomach mucosa, it increases the release of gastric juices when the stomach is distended by food. ● Amylase: enzyme in the mouth that begins the digestive process of starches. ● Hydrochloric acid: the stomach wall contains gastric mucosa with gastric pits. At the base of the pits are the gastric glands whose chief cells create gastric juice, a mucous fluid containing digestive enzymes, and parietal cells, which secrete stomach acid called “hydrochloric acid” ● Bicarbonate: reduces the acidic content of the chyme. 27. What are the differences between digestion, absorption, and metabolism? ● Digestion: a group of processes that break complex nutrients into simpler ones, thus facilitating their absorption; mechanical digestion physically breaks large chunks into small bits; chemical digestion breaks molecules apart. ● Absorption: movement of digested nutrients through the gastrointestinal mucosa and into the internal environment. ● Metabolism: process which absorbed nutrients are used by the body for energy to form and maintain body structures and functions.