Small Intestine

Small Intestine tubular organ that extends from the pyloric sphincter to the cecum (start of lg intestine) many loops and coils greater omentum drapes over sm. intestine to help prevent the spread of infection ileocecal sphincter joins ileum to cecum receives secretions from pancreas, liver and gallbladder completes digestion of nutrients in chyme absorbs nutrients (major function) transports residue to large intestine

Parts of Sm. Intestine 3 parts duodenum jejunum ileum 25 cm long and 5 cm wide, follows a C-shaped path receives secretions from accessory organs jejunum proximal 2/5, greater diameter, thicker wall, more vascularized more active than duodenum ileum remainder of small intestine

Structure of Wall mucosa – appears velvety due to many tiny projection called villi villi increase surface of sm. intestine which aids in the absorption of digestive products villi are a layer of simple columnar epithelium, capillaries and nerves capillaries carry away absorbed nutrients nerves transmit impulses to stimulate or inhibit villus activities

Secretions mucosa – mucus and digestive enzymes peptidase: peptides  amino acids sucrase, maltase, lactase: disaccharides (sucrose, lactose, maltose)  monosacchrides (glucose, fructose, galactose) intestinal lipase: fatty acids  glycerol submucosa – thick, alkaline mucus to help neutralize chyme intestinal glands – large am. of watery fluid (neutral, no digestive enzymes) that bring digestive enzymes to villi

Regulation of Secretion neural and mechanical mechanical chyme stimulates mucous glands to secrete neural distension of wall activates nerves that trigger the release of enzymes

Review Questions Describe the parts of the small intestine. What is the function of the intestinal wall? What is the function of intestinal glands? List the intestinal digestive enzymes.

Absorption most important absorbing organs carbohydrates proteins fats start in mouth (salivary amylase) pancreatic and intestinal enzymes villi absorb simple sugars proteins start in stomach (pepsin) villi absorb amino acids fats start in small intestine (lipase) villi absorb fatty acids and glycerol become LDL/HDL, converted to energy, stored in adipose tissue electrolytes water

Movements mixing: moves chyme back and forth peristalsis: weak contractions push food forward slowly 3 – 10 hours if sm. intestine wall becomes irritated or over distended a strong peristaltic rush sweeps contents into lg intestine w/o normal absorption diarrhea results in more frequent defecation and watery stool prolonged diarrhea can lead to water and electrolyte imbalances

Review Questions Which substances resulting from the digestions of carbohydrates, proteins, and fats does the small intestine absorb? Describe the movements of the small intestine.