1. Small Intestine

2. 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

3. 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

5. 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

7. 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

8. 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

9. 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.

10. 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

12. 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

13. 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.