I. Nutrients A. Organic 1. carbohydrates (4.1 calories/gram) 2. proteins (4.1 cals/g) - 8 essential amino acids 3. fats (9.3 cals/g) 4. fiber

B. Vitamins

C. Minerals

II. Digestive System A. Structures

B. Layers 1. epithelial lining 2. muscular wall 3. external covering

C. Chewing/Initial Digestion 1. teeth a. herbivores - flat teeth for grinding - longer intestines b. carnivores - pointed teeth for tearing c. omnivores - both pointed and flat teeth

2. crop a. softening b. storage - for regurgitation - to avoid predators c. milk (males or females)

3. gizzard - grinding and churning - some storage

4. saliva - moisture - mucus - enzymes (amylase, lysozyme)

D. Swallowing - epiglottis

E. Esophagus 1. peristalsis 2. sphincter - true in rodents, cattle, and horses - rats and mice cannot vomit (rare in horses)

F. Stomach 1. expansive 2. churning action 3. gastric juice a. parietal cells (HCl) b. chief cells (pepsinogen  pepsin)

4. protein digestion 5. chyme 6. little absorption

7. ulcers - excessive acid - Helicobacter pylori 80% of gastric ulcers Robin Warren and Barry Marshall (Nobel 2005) Marshall proved by infecting himself

G. Small intestine (about 6 meters in humans)

G. Small intestine (about 6 meters in humans) 1. duodenum a. is the initial segment (about 25 cm) b. focal point of digestion - chyme from stomach - digestive enzymes from pancreas - bile from liver and gallbladder

2. jejunum/ileum a. villi b. microvilli c. huge increase in surface area for absorption - about 300m2 in humans

H. Cecum 1. pouch at beginning of colon

2. prominent in some herbivores - contains cellulose-digesting bacteria or protists - some of the nutrients absorbed by cecum and colon

I. Colon 1. no villi or folds 2. no digestion (except for cecum in herbivores)

3. absorption a. water b. ions c. vitamins - biotin - folic acid - K - K from normal flora in mammalian colon

4. feces - 30% of dry weight is bacteria 5. rectum 6. anus

J. Ruminants (cattle, sheep, deer) - 4 chambered stomach 1. bacteria or protozoa in rumen and reticulum 2. regurgitation (rumination) 3. enzymatic digestion begins in abomasum - some of the microbes are also digested

K. Coprophagy 1. rodents and lagomorphs (rabbits and hares) 2. because cecum is critical for cellulose digestion