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Digestive System

Digestive System. Part 2. Small Intestine. Functions to: 1. Complete digestion 2. Absorb nutrients 3. Produce regulating hormones. Duodenum. The first section of the small intestine is called the duodenum

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Digestive System

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  1. Digestive System Part 2

  2. Small Intestine Functions to: 1. Complete digestion 2. Absorb nutrients 3. Produce regulating hormones

  3. Duodenum • The first section of the small intestine is called the duodenum • Ducts from pancreases and liver enter the duodenum, with fluids that contain enzymes to complete digestion

  4. Small Intestine • Slightly basic (pH = 8.5) • Pancreatic fluid contains sodium bicarbonate NaHCO3 to neutralize acidic chyme

  5. Pancreatic Juices • The PANCREAS secretes “pancreaticjuice” which contains sodium bicarbonate (NaHCO3) (making it basic) and digestive enzymes:

  6. Pancreatic Enzymes • Pancreatic Amylase: • (starch + H2O--> maltose) b. Trypsin: • (protein + H2O --> peptides)

  7. c. Lipase • (fat droplets + H2Oglycerol+ fatty acids) BEFORE Lipase this step occurs: Emulsification: fat + bile salts (produced in liver) fat droplets

  8. d. Nuclease • DNA/RNA + H2O--> nucleotides

  9. Some Structures Up Close: Villi Microvilli The Small Intestines: • small in diameterbut not in length! (approximately 6 meters long) • Large surface area due to convoluted villi and microvilli lining the lumen (hole)

  10. Villi Capillaries (aa and glucose enters) • Nutrients absorbed into vessels within villi • blood capillaries absorb water-soluble monomers such as glucose and amino acids, lacteals absorb fatty acids and glycerol into lymphatic system, and are eventually absorbed into the blood stream Villi Lacteal (fat and glycerol enters) Lymph drains lacteal

  11. Duodenal cells • Produce 2 hormones: a) secretin – stimulated by acid in the chyme b) CCK (cholecystokinin) – stimulated by partially digested protein and fat Both target pancreasesand liver, increasing pancreatic juice and bile production

  12. In the intestines: the mucosa of the intestinal villi secrete 3 enzymes: a. Peptidase • (peptides + H2Oamino acids)

  13. b. Maltase • finishes starch breakdown • ( maltose + H2Oglucose) c. Nucleosidase Nucleotides  sugar + phosphate group + nitrogenous base

  14. Large Intestine (colon) Key Functions: • Absorption of water and salts • Contains bacteria that produce vitamins • Prepare feces for elimination

  15. Transverse Colon Ascending Colon Descending Colon Cecum (blind end of intestine) Appendix(no function; may help infection, subject to inflammation; appendicitis) Sigmoid Colon Rectum

  16. Large Intestine • Incubates bacteria (E. coli) which break down indigestible material, produce vitamin K, gas, amino acids and growth factors • Dead bacteria, mucus, water and undigested materials (cellulose/fibre) are moved to the rectum by peristalsis and stored in the rectum • Stretching of the rectal wall stimulates the defecation reflex (peristalsis of rectum and relaxation of internal anal sphincter)

  17. Interesting Fact • contains bacteria(including E.coli.) that live on unabsorbed and undigested nutrients • the bacteria fermentany remaining carbohydrates and release H+, CO2, and methane gas. (flatus (flatulence) • by-products of the bacterial digestion account for the colorand the smellof the feces.

  18. Anal Sphincter • External anal sphincter is under voluntary control

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