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 Ducts from pancreases and liver enter the duodenum, with fluids that contain enzymes to complete digestion

Small Intestine Slightly basic (pH = 8.5) Pancreatic fluid contains sodium bicarbonate NaHCO 3 to neutralize acidic chyme

Pancreatic Juices The PANCREAS secretes “pancreatic juice” which contains sodium bicarbonate (NaHCO 3 ) (making it basic) and digestive enzymes:

Pancreatic Enzymes a. Pancreatic Amylase : (starch + H 2 O --> maltose) b. Trypsin : (protein + H 2 O --> peptides)

c. Lipase (fat droplets + H 2 O  glycerol + fatty acids) BEFORE Lipase this step occurs: Emulsification: fat + bile salts (produced in liver)  fat droplets

d. Nuclease DNA/RNA + H 2 O --> nucleotides

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

Villi 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 Capillaries (aa and glucose enters) Lacteal (fat and glycerol enters) Lymph drains lacteal

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 pancreases and liver, increasing pancreatic juice and bile production

In the intestines: the mucosa of the intestinal villi secrete 3 enzymes: a. Peptidase (peptides + H 2 O  amino acids)

b. Maltase finishes starch breakdown ( maltose + H 2 O  glucose) c. Nucleosidase Nucleotides  sugar + phosphate group + nitrogenous base

Large Intestine (colon) Key Functions: 1.Absorption of water and salts 2.Contains bacteria that produce vitamins 3.Prepare feces for elimination

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

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)

Interesting Fact contains bacteria (including E.coli.) that live on unabsorbed and undigested nutrients the bacteria ferment any remaining carbohydrates and release H +, CO 2, and methane gas. (flatus (flatulence) by-products of the bacterial digestion account for the color and the smell of the feces.

Anal Sphincter External anal sphincter is under voluntary control