1. Anatomy and function of the GI system components; normal intestinal flora a. GI system carries out following digestive processes: i. Ingestion of food ii. Propulsion of food and wastes from mouth to anus iii. Secretion of mucus, water, enzymes iv. Mechanical digestion of food particles v. Chemical digestion of food particles vi. Absorption of digested food vii. Elimination of waste products by defecation viii. Immune and microbial protection against infection b. Mouth and Esophagus: i. Mouth-site for chewing and mixing of food w/ saliva 1. Salivation a. 3 pairs of salivary glands secrete 1L saliva daily b. Saliva is mostly water that contains varying amts of mucus, sodium, bicarbonate, chloride, K, and salivary a-amylase (ptyalin), an enzyme that initiates carbohydrate digestion in mouth and stomach 2. Swallowing a. Esophagus is hollow muscular tube 25cm long that conducts substances from oropharynx to stomach via peristalsis b. 2 phases: i. Oropharyngeal (voluntary) phase-food segmented into bolus by tongue and forced towards pharynx and into esophagus ii. Esophageal (involuntary) phase-bolus transported to stomach c. Stomach-hollow muscular organ that stores food during eating, secretes digestive juices, mixes food w/ these juices, and propels partially digested food (chyme) into small intestine i. Few substances absorbed in stomach-impermeable to water but can absorb alcohol, aspirin and other NSAIDs ii. Gastric motility-increases w/ peristalsis (approx. 3 per min; influenced by neural and hormonal activity) 1. Gastrin, motilin, and vagus nerve increase rate of contraction by lowering threshold potential of muscle fibers 2. Sympathetic activity and secretin are inhibitory and raise threshold potential iii. Gastric secretion 1. Specialized cells throughout gastric mucosa produces mucus, acid, pepsinogen, enzymes, hormones, intrinsic factor, and gastroferrin 2. Gastric glands of mucosa are primary secretory units 3. Rate of secretion varies w/ time of day: lower in AM and higher in afternoon/evening 4. Major fx of gastric hydrochloric acid are to dissolve food fibers, act as bactericide against swallowed microorganisms, and convert pepsinogen to pepsin. Also facilitates absorption of ferric iron 5. 3 Phases: a. Cephalic phase-anticipatory and sensory experiences of smelling, seeing, tasting, chewing, and swallowing food b. Gastric phase begins w/ arrival of food to stomach i. 2 major stimuli have secretory effect: 1. Distention of stomach 2. Presence of digested protein c. Intestinal phase-movement of chyme from stomach to duodenum d. Small intestine i. 3 segments: duodenum, jejunum, and ileum ii. Arterial supply to duodenum arises primarily from gastroduodenal artery (small branch of celiac artery). Jejunum and ileum are supplied by branches of superior mesenteric artery iii. Absorption occurs through villi (functional units of intestine) Box 41.1: Sources of Digestive Enzymes Salivary glands Amylase, lingual lipase Stomach Pepsin, gastric lipase Pancrease Amylase, trypsin, chymotrypsin, carboxypeptidase, elastase, lipase-colipase, phospholipase A2, cholesterol esterase-nonspecific lipase Small intestine Enterokinase, disaccharidases (maltase, sucrase, lactase, aa-1 trehalase), isomaltose, peptidases (amino-oligopeptidase, dipeptidase) iv. Epithelial cells of small intestine are hydrophobic-water and electrolytes are transported in both directions (towards capillary blood or toward intestinal lumen) through tight junctions and intercellular spaces rather than across cell membranes. Water diffuses passively across hydrostatic pressure and osmotic gradients est. by active transport of sodium and other substances v. 85-90% of water that enters GI tract absorbed by small intestine vi. Sodium passes through tight junctions and is actively transported across cell membranes vii. K moves passively across tight junctions w/ changes in electrochemical gradient viii. Chloride actively secreted throughout lg and small intestines ix. Digestion/absorption of fat occur in 4 phases: 1. Emulsification and lipolysis a. Emulsification-process by which emulsifying agents in small intestinal lumen cover small fat particles and prevent them from re-forming into fat droplets b. Lipolysis-lipid hydrolysis of emulsified fats 2. Micelle formation-products of lipid hydrolysis must be made water soluble to be efficiently absorbed; accomplished by formation of water-soluble molecules (micelles) a. Formed of bile salts, products of fat hydrolysis, fat-soluble vitamins, and cholesterol 3. Fat absorption 4. Resynthesis of triglycerides and phospholipids x. Intestinal motility is regulated by enteric nervous system, vagal stimulation, and hormones. 2 movements promote motility: haustral segmentation and peristalsis e. Lg intestine i. Primary type of colonic movement is segmental-facilitates absorption of water f. Intestinal tract is sterile @ birth but becomes colonized w/ E. coli, clostridium welchii, and streptococcus w/in a few hours. By 3-4 weeks after birth, normal flora is established and become stable by age 2 2. Know disorders of GI tract and accessory organs of digestion: pathophysiology, etiology, prevention, clinical manifestations, diagnostics, treatment and complications a. Anorexia: lack of desire to eat despite physiologic stimuli that would normally produce hunger b. Constipation: difficult or infrequent defecation i. Not significant until it causes health risks (severe Abd distention or fecal impaction) or impairs quality of life ii. Primary constipation: 3 categories 1. Normal transit (functional) constipation-normal rate of stool passage, difficulty w/ stool evacuation. Most common