THE DIGESTIVE SYSTEM ITS INTESTINE TIME bn MAIN

THE DIGESTIVE SYSTEM IT’S INTESTINE TIME!!

bn

MAIN IDEA OF INTESTINES § Small intestine where the major events of DIGESTION & almost all ABSORPTION occur § Large intestine where WATER ABSORPTION, vitamin production, and FECES FORMATION occurs

intestine VALVES! § Valve from stomach to small intestine (S. I. ) pyloric sphincter § Valve from the S. I. to L. I. ileocecal valve/sphincter

3 SECTIONS OF S. I. 1) **DUODENUM 2) JEJUNUM 3) ILEUM

MESENTERY § Layer of membrane (peritoneum) that holds the small intestine coiled together as well as to the posterior abdominal wall

3 IMPORTANT FEATURES OF THE Small Intestine (S. I. ): 1) CIRCULAR FOLDS deep folds of both the mucosa and submucosa of small intestine (like rugae of stomach) *increase surface area PEYER’S PATCHES – collections of lymphatic tissue in submucosa; there are more at the end of S. I. because undigested food contains bacteria

3 IMPORTANT FEATURES OF THE S. I. 2) VILLI finger-like projections of mucosa that increase surface area Contain capillary beds and lymphatic capillaries (LACTEALS)

3 IMPORTANT FEATURES OF THE S. I. 3) MICROVILLI very tiny projections of membrane of mucosa cells on the VILLI ** Both villi & microvilli absorb digested foods through mucosa & submucosa

Small Intestine Note: § ** Enzymes produced by the PANCREAS and bile made by the LIVER enter the DUODENUM!!

Chemical Digestion & Absorption in the S. I. § Chemical digestion is completed in the small intestine due to bile as well as enzymes in the pancreatic and intestinal juices. § Approx. 90% of all ABSORPTION takes place in the S. I. ! (other % in stomach & L. I. )

SMALL INTESTINE labeled: First Figure/19. 11 LABEL (p. 472): § Duodenum § Jejunum § Ileum § Stomach § Large Intestine

SMALL INTESTINE labeled: Second Figure/19. 12 LABEL (p 473): § Mucosa § Submucosa § Muscularis externa § Serosa § Villus § Blood capillary § Lacteal § Simple columnar epithelium

THE LARGE INTESTINE (L. I. )

LARGE INTESTINE § *Is much larger in diameter but shorter in length than the small intestine § runs from the ileocecal valve to the anus

LARGE INTESTINE (COLON) MAIN FUNCTIONS: § Dries out undigested food residue *absorbs water & vitamins § Eliminates residues from the body as wastes (feces)

5 SECTIONS OF Large Intestine: 1) 2) 3) Cecum Appendix Colon (ascending colon, transverse colon, descending colon, and sigmoid colon) 4) Rectum 5) Anal Canal ANUS – opening to exterior

LARGE INTESTINE (L. I. ) § The outer layer of the muscularis externa is bundled into 3 bands called TENIA COLI which bunch up the colon into pouches called HAUSTRA Tenia = flat band Haustra = “drawer” puckered appearance

2 valves in Anal Canal: - External voluntary sphincter (skeletal muscle) - Internal involuntary sphincter (smooth muscle)

Appendix § Hangs from the cecum (first section of L. I. ) § Sometimes bacteria can get into appendix and it becomes inflamed = appendicitis § If it broke open it would empty its contents into the abdominopelvic cavity which could be fatal

Important Features of L. I. § There are NO villi nutrient absorption into bloodstream happened in S. I. § LOTS of goblet cells in the simple columnar epithelium produce mucus (functions as lubricant)

BACTERIA § Bacteria live in the L. I. and break down some of the remaining nutrients which produces gas (flatulence) § FECES contain indigestible food materials, mucus, bacteria, and water

Digestion & Absorption in the L. I. § MECHANICAL DIGESTION in the large intestine includes: § HAUSTRAL churning or contraction of the haustra (pouches of colon) when the walls of the colon fill with chyme § PERISTALSIS (muscular contractions that propel food § MASS PERISTALSIS is a large peristaltic contraction that moves fecal material into RECTUM

DEFECATION REFLEX § Mass peristalsis moves indigestible materials from colon into the rectum: § Stretch receptors in the mucosa of the rectum are stimulated are the rectum is emptied § The internal involuntary sphincter opens due to a combination of pressure and parasympathetic nerve impulses

Chemical Digestion & Absorption in L. I. § The last small bit of digestion occurs in the L. I. by bacteria which break down any small carbohydrates, amino acids, etc. § Products of this breakdown include: gas (flatulence) as well as some vitamins

Chemical Digestion & Absorption in L. I. § L. I. absorbs mostly WATER and vitamins § Remember almost all absorption (including most water absorption happens in S. I. ) § In the L. I. water is absorbed by osmosis

LARGE INTESTINE labeled: First Figure/19. 14 LABEL (p 478): § Haustra § Tenia coli § Cecum § Ileocecal sphincter § Ileum § Ascending colon § Transverse colon § Descending colon § Sigmoid colon § Rectum § Anal canal § Anus

LARGE INTESTINE LABELED: Second Figure/19. 15 LABEL (p 479): § Mucosa § Submucosa § Muscularis externa § Serosa § Simple columnar epithelium

Accessory ORGANS Summary PANCREAS pancreatic enzymes that break down all 4 organic molecule groups are secreted into the duodenum

Accessory ORGANS Summary LIVER § 2 main lobes which are broken up into lobules § Produces bile which enters duodenum through the common hepatic duct § Bile breaks up fat molecules so that enzymes can digest them

Accessory ORGANS Summary GALLBLADDER § On inferior surface of liver § Stores bile when food is not being digested

Accessory ORGANS Summary SALIVARY GLANDS § *Salivary amylase And salivary lipase TEETH § Mechanical digestion of food § Deciduous: first teeth/baby teeth