Chapter 41 & Chapter 42

Today in class we discussed the breakdown of molecules through the digestive system and how the breakdown of these molecules (Carbohydrates, Proteins, Nucleic Acids, and Lipids) all end in the small intestine.

1) In small intestine pancreatic amylase breaks down starch, glycogen, and small polysaccharides into di saccharides. Breakdown of di saccharides occur at the wall of the intestinal epithelium, and then mono saccharides are quickly absorbed into blood.

2)Proteins- Pepsin, Pepsinogen prior to release in stomach,begins breakdown of proteins in stomach, Typsin breaks polypeptides into smaller into smaller chains. Then other enzymes (aminopetidase) break polypeptides into amino acids.

3)Nucleic Acids- Broken down by nucleases into nucleotides, sugars, nitrogenous bases, sugars, and phosphate groups.

4) Fats- Digestion of fats start in the small intestine (SI). Bile salts coat fat droplets to keep them from coalescing (in emulsification) and lipase hydrolyzes them. Most fat enters the lymphatic system first.

Coalescing-to come together

Stage 3 of digestion- Absorption

1)Absorption occurs in SI in epithelial lining with folds called villi which have micro villi, both increase surface area for absorption.

- Each villi has a set of tiny blood vessels called capillaries and a lymph vessel called lacteal

-- Lacteal absorbs fatty acids

- Mono saccrides such as glucose enters blood stream via passive diffusion (requiring little energy) while amino acids and dipeptides enter via active transport (requiring energy).

2) All caoillaries and veins from villi all join at the hepatic portal vessel, which brings the blood to the liver. The liver metabolizes the organic molecules in various ways.

- Liver has smooth ER ( endoplasmic reticulum) organelles that detox the blood.

Hormones

- An important hormone in digestion is gastrin, which stimulates the secretion of gastric juice.

Stage 4- Elimination

Large intestine, colon, is connected to small intestine by a sphincter. The point of connection is the site of the cecum, a small pouch with an extension called the appendix.

- Main function of the large intestine is to compact waste and recover water from it.

- End of colon is rectum where feces are stored until they are eliminated.

Chapter 42- Circulation and Gas Exchange

- Both open and closed circulatory systems have blood, vessels, and a heart structure.

- Open circulatory system- blood bathes the organs directly.

- Blood+Lymph= hemolymph; the heart pumps hemolymph into cavities called sinuses

(Definitions for lymph and hemolymph can be found in ch. 42 voc.)

Questions

1) What hormone stimulates the secretion of gastric juice?

A) lymph

B) gastrin

C) pepsin

D) aminopetidase

2) What substance in stomach aids in breakdown of proteins

A) pepsin

B) bile

C) amylase

D) lipase

3) What structure in small intestine is vital for absoption?

A) lipids

B) sphincter

C) bile

D) villi

Answers: B,A,D