THE DIGESTIVE SYSTEM IT’S INTESTINE TIME!!

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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) Cecum 2) Appendix 3) 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