Small Intestine• Duodenum:

smallest section– Stomach empties

here• Jejunum: middle

section• Ileum: final section– Joins large intestine

at ileocecal sphincter

Small Intestine• 21 feet of small intestine with added

structures to increase surface area– Almost all absorption occurs here

• Circular folds: folds in the mucosa to splash chyme and enhance absorption

• Villi: fingerlike projections that contain capillaries, arteries, veins, all to move absorbed substances quickly

Small Intestine• Microvilli:

smaller projections on the villi to further increase surface area and absorption

Small Intestine• Intestinal glands: in mucosa that

secrete intestinal juice– Clear, yellowish liquid quickly

reabsorbed– pH 7.6 with water and mucous– Enzymes for Chemical Digestion:• Maltase, sucrose, lactase: disac. To monosa.• Peptidases: peptides to amino acids• Ribonuclease, dioxyribonuclease: nucleic

acids

Small Intestine• Mechanical Digestion: – Segmentation: Concentration of chyme

and juice that sloshes between areas of contraction of the muscularis

– Perstalsis: moves the chyme steadily through intestines

Absorption in Small Intestine• Passage of digested substances and

nutrients from the lumen to into the blood or lymph

• 90% of all absorption takes place here

• Substances absorbed by diffusion, osmosis, and active transport

Absorption in Small Intestine• Carbohydrates absorbed as

monosaccharides• Proteins absorbed as amino acids • Lipids absorbed as monoglycerides

and fatty acids• Water —9 liters enter daily and 8

are reabsorbed

Large Intestine• Main functions:– Completion of

absorption– Manufacture certain

vitamins– Formation of feces– Elimination of feces

Large Intestine• Cecum: pouch after ileocecal sphincter• Colon: ascending, transverse, descending,

sigmoid– Surface area increased by pouch-like divisions: haustra

• Rectum: last part, stores waste– Last inch is anal canal

• Anus: opening to exterior– Two sphincters: internal anal sphincter

(involuntary), external anal sphincter (voluntary)

Chemical Digestion of Lrg. Intestine

• No enzymes• Bacteria ferment remaining

carbohydrates– Release hydrogen, carbon dioxide, and

methane • Vitamins K and some B’s are made

and absorbed

Mechanical Digestion of Lrg. Intestine

• Haustral churning: walls contract when haustra fill to a certain level

• Peristalsis: slower than other areas• Mass peristalsis: strong muscular

wave that pushes waste into the rectum

Absorption & Feces Formation• Chyme in the colon for 3-10 hrs.

becomes rather solid: feces– Water, epithelial cells from mucosa,

bacteria, undigested food

• All but 100mL of the 1L of water is absorbed

Defecation• Emptying of the rectum• Diarrhea: not enough water is

absorbed because chyme travels too quickly through intestine– Can cause dehydration

• Constipation: feces remains in colon too long, almost all the water is absorbed

Digestive System Attachments• Peritoneum & serosa: secrete slippery fluid to

glide organs over each other – Outermost layer of GI tract

• Visceral peritoneum: covers some organs in abdominal cavity

• Parietal peritoneum: the walls of the abdominal cavity

Digestive System Attachments• Mesentery: binds small intestine to

posterior abdominal wall• Mesacolon: binds large intestine to

posterior abdominal wall• Falciform ligament: attaches liver to

the anterior abdominal wall and diaphragm

Digestive Disorders• Ulcers: lesions in a membrane– Peptic —from gastric juice– Gastric —in stomach– Esophageal —in esophagus– Duodenal —in small intestine

• Appendicitis: inflammation of appendix

Digestive Disorders• Cirrhosis: scarred liver due to chronic

inflammation• Colitis: inflammation of colon and

rectum• Hernia: protrusion of an organ through a

membrane or cavity wall