Summary Mastering Biology notes for Chapter 42 Animal Digestive System

Chapter 42 The Animal Digestive System

The stomach and its secretions




Lumen = space inside stomach
Pits = interior surface of stomach, lined by epithelium
Gastric juice
Chief cell: secretes pepsinogen into lumen
Parietal cell: actively transports Hydrogen ions into lumen, Chlorine ions diffuse to lumen
In lumen, H+ and Cl- atoms combine to form HCl. In lumen not in cells to not denature
proteins
HCl makes gastric juice acidic, pH = 2. Low pH aids digestion
- Distrupts ECM
- Denatires proteins
- Converts pepsinogen to active pepsin in positive feedback (the product pepsin
catalyzes further reactions)
Layer of mucus lining the lumen. Cells are constantly regenerate
Mucous line lumen => prevents gastric juice from digesting epithelium
Gastric juice passes from pits to main stomach chamber
Muscular contractions: mix gastric juices with food
Sphincter keeps food contained in stomach. Upper and lower sphincters

Digestive system function
Large molecules to smaller molecules
- Carbohydrates => monosaccharides
- Proteins => amino acids
- Nucleic acids => nucleotides
- Fats => glycerol and fatty acids

Digestion of carbohydrates
Monosaccharide: directly absorbed. e.g.: fructose