Transcript Digestion4
The Digestive System …cont’d Wednesday, January 20th, 2010 Today’s Targets! • Functions of anaerobic bacteria in the colon • Review the actions of various enzymes • Understand how release of enzymes controlled by hormones • Understand the regulation of hormones The Large Intestine (or Colon) • Size: ~1.5 m long, 6.5 cm in diameter • LI joins SI in lower right corner of abdomen - near top of pelvic bone junction is at right angles but not quite at the end - there is a blind end to the LI called the cecum (projecting from the cecum is the appendix) The Large Intestine Major parts: • cecum • ascending colon rises up right side of abdomen, • transverse colon crosses top of abdomen • descending colon goes down left side becoming… • sigmoid colon, which curves to join rectum The Large Intestine 1. Mechanical Movement - peristalsis moves feces along 2. Absorption - water and some salts absorbed from feces Figure 41.25 3. Bacteria (E. coli ) work on undigested food from the SI and produce gases flatulence- about 1.5 L/day (mainly nitrogen gas, and carbon dioxide, with small amounts of hydrogen, methane and hydrogen suphide), amino acids and some vitamins amino acids and vitamins (K) produced absorbed through intestinal lining (LI does not have villi like SI) 4. Defecation - reflex contraction of muscles lining the filled rectum force the sphincter muscles open and expel the feces 5. Feces contain bile pigments, heavy metals and billions of E. Coli Animation: Reflexes in the Colon • http://highered.mcgrawhill.com/classware/ala.do?isbn=0072956208& alaid=ala_996422&showSelfStudyTree=true Physical Digestion: -teeth, tongue, mouth Chemical Digestion: -Salivary amylase (carbohydrates disaccarides) Liver SI (Physical): -bile (emulsify fats) Pancreas SI: Amylase, trypsin, peptidase, lipase, nuclease, HCO3SI: maltase, lactase, sucrase, peptidase Saliva: water, mucus, HCO3-, salivary amylase Physical Digestion: -peristalsis Physical Digestion: -peristalsis Gastric Juice: mucus HCL (kills pathogens, lowers pH, stimulates pepsin production), pepsinogen pepsin (protein peptides) Control of Digestive Gland Secretions • NERVOUS STIMULATION – sight and smell receptors send messages to brain and cause release of saliva, gastric and pancreatic juices • PRESENCE OF FOOD in digestive system triggers exocrine glands to secrete enzymes and bicarbonate • HOW? HORMONES released from endocrine glands into blood travels to glands to trigger release of enzymes Control of Digestive Gland Secretions • As with all body systems, the nervous system and endocrine system tightly control digestion • The amount of saliva produced, the amount of stomach acid produced, the timing and amount of pancreatic and gall bladder secretions and the rate of peristalsis all controlled Gastrin (Hormonal) Regulation • When food eaten, sensory cells in stomach detect presence of peptides • Other sensory receptors detect stomach distending (i.e. stretching) • This causes specialized stomach cells in the lower stomach to release GASTRIN into the blood. Gastrin travels through the blood to the upper stomach which causes the release of gastric juices, (HCl and pepsinogen) Gastrin (Hormonal) Regulation STRETCHING HCl PEPSINOGEN FOOD BLOOD GASTRIN (hormone) CCK (Hormonal) Regulation • Presence of amino acids or fatty acids in duodenum triggers release of CHOLECYSTOKININ (CCK) • CCK stimulates the release of digestive enzymes by the pancreas and bile by the gallbladder Secretin (Hormonal) Regulation RECALL: - Most digestion occurs in duodenum - Chyme is acidic when it leaves the stomach • SECRETIN produced by small intestine SI blood pancreas (stimulates release of SODIUM BICARBONATE) Also secretin will decrease motor activity in the stomach GIP (Hormonal) Regulation • ENTEROGASTRONE (or Gastric Inhibitory Peptide, or GIP) is released by small intestine when chyme is rich in fats • Slows digestion by INHIBITING stomach peristalsis and acid secretion (allowing more time to digest) • Hormones help coordinate the secretion of digestive juices into the alimentary canal When acid chyme rich in fats enters duodenum, enterogastrone secreted by duodenum to inhibit peristalsis and acid secretion by stomach Liver Enterogastrone Gallbladder Gastrin CCK Stomach Amino acids or fatty acids in duodenum trigger release of cholecystokinin (CCK), which stimulates release of digestive enzymes from pancreas and bile from gallbladder. Pancreas Secretin Duodenum CCK Key Stimulation Figure 41.22 Gastrin from stomach recirculates via blood back to stomach, where it stimulates production of gastric juices Inhibition Secreted by duodenum, secretin stimulates pancreas to release sodium bicarbonate to neutralize acid chyme from stomach Three Phases of Gastric Secretion • http://highered.mcgrawhill.com/classware/ala.do?isbn=0072956208& alaid=ala_996427&showSelfStudyTree=true Digestion Summary Animation: • http://www.linkstudio.info/portfolio/animatio n08.htm Digestion Song • Posted on website