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.

I. NutrientsA. Organic

1. carbohydrates (4.1 calories/gram)2. proteins (4.1 cals/g)

- 8 essential amino acids3. fats (9.3 cals/g)4. fiber

B. Vitamins

C. Minerals

II. Digestive SystemA. Structures

B. Layers1. epithelial lining2. muscular wall3. external covering

C. Chewing/Initial Digestion1. teeth

a. herbivores- flat teeth for grinding- longer intestines

b. carnivores- pointed teeth for tearing

c. omnivores- both pointed and flat teeth

2. cropa. softeningb. 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. Esophagus1. peristalsis2. sphincter

- true in rodents, cattle, and horses- rats and mice cannot vomit (rare in horses)

F. Stomach1. expansive2. churning action3. gastric juice

a. parietal cells (HCl)b. chief cells (pepsinogen pepsin)

4. protein digestion5. chyme6. little absorption

7. ulcers- excessive acid- Helicobacter pylori

80% of gastric ulcersRobin 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/ileuma. villib. microvillic. huge increase in surface area for absorption

- about 300m2 in humans

H. Cecum1. 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. Colon1. no villi or folds2. no digestion (except for cecum in herbivores)

3. absorptiona. waterb. ionsc. vitamins

- biotin- folic acid- K- K from normal flora in mammalian colon

4. feces - 30% of dry weight is bacteria

5. rectum6. anus

J. Ruminants (cattle, sheep, deer)- 4 chambered stomach1. bacteria or protozoa in rumen and reticulum2. regurgitation (rumination)3. enzymatic digestion begins in abomasum

- some of the microbes are also digested

K. Coprophagy1. rodents and lagomorphs (rabbits and hares)2. because cecum is critical for cellulose digestion