Chapter 51 fueling the body: digestion and nutrition

I. Types of Digestion

A. single cell organisms digest intracellularly

B. multicellular organisms digest extracellularly

1. two way digestive tract: (flatworm)one opening, no specialization due to exposure to particles at all levels of digestion. (gastrovascular cavity)

2. One way digestion: specialized regions for specialized breakdown.

Nematode(roundworm)èannelida(earthworm)èèhigher vertebrates

3. ingestion, storage, fragmentation, digestion, absorption.

II. ingestion:

A. teeth: tear or grind

carnivors: specialized ripping/tearing

omnivores: tearing and grinding

herbivores: specialized grinding

B. gizzard of birds grind

C. structures of mouth

1. tongue

D. enzymes of mouth:

1. salivary glands

III. Transport to stomach

A. Esophagus

1. Peristalsis: rythmic contractions initiated by swallowing

B. Cardiac sphincter: to the stomach

C. Stomach

Gastric juice

Protease (pepsin) è pepsinogen

HCL (activates pepsin, denatures proteins, kills bacteria

D. Pyloric sphincter: to the SI

IV. Small vs. large intestine

Small intestine

A. divided into duodenum, jejunum, ileum

B. enzymes of the small intestine: brush border

1. peptidaseè short polypeptides into amino acids

2. nucleases è nucleotides into sugars and nucleic acid bases

3. lactase, maltase, sucraseè disaccharides into monosaccharides

4. lipase è triglycerides into fatty acid and glycerol

C. absorption by small intestine

1. into blood: amino acids and monosaccharides.

2. Into lymphatic: fatty acids and monoglycerides

Large intestine

A. absorption of water, sodium and potassium.

B. Vestigeal structure: appendix serves a function in some mammals, but none in humans

C. Bacterial flora present in LI aids digestion in some mammals through fermentation, but due to lack of absorption in humans only produces gas.

V. Accessory organs

A. pancrease: secrete enzymes into and activated by brush border of SI

1. pancreatic fluid secreted through pancreatic duct:

from pancreatic cells

a. trypsin & chymostrypsin è protein breakdown

b. pancreatic amylase è starch breakdown

c. lipase è fat breakdown

from acini

d. bicarbonate è neutralize HCl from stomach

from islets of langerhans (not a digestive function)

e. glucagon from alpha cells (increase sugar in blood)

f. insulin from beta cells (decrease sugar in blood)

B. liver: produces bile

1. bile pigments: come from breakdown of RBC;s è waste only

2. bile salts: emulsifies fats in small intestine

C. gall bladder: stores bile

1. delivers through common bile duct into SI

D. Regulation for homeostasis:

1. hepatic portal vein takes blood from stomach/intestine directly to liverè takes out alcohol, drugs, steroid hormones, poisons and converts to less toxic forms. Converts ammonia (from intestinal bacteria) è urea for kidney removal.

2. Insulin and glucagon regulate blood sugar levels by Ièstoring sugar in liver as glycogen, Gè releasing sugar from liver stores. (fasting can cause gluconeogenesis from amino acids/lactic acid from muscle cells = burning muscle.) (insulin ineffectivenessè diabetes mellitus)

VI. digestive systems variation:

A. ruminants: stomach divisions (cow/deer)

1. 1^st chamber partially digests

2. regurgitated for more chewing

3. 2^nd , 3^rd chambers further digest

4. 4^th chamber has gastric juices like stomach.

B. other herbivores (horses, rodents, rabbits)

1. enlarged cecum that has bacteria that ferment to breakdown cellulose

2. eating of feces to pass nutrients though a second time

C. wax eaters(birds/some fish/crustaceans)

1. rely on bacteria to breakdown wax

D. most animals rely on microorganisms to make vitamin K (for blood clotting)

VII. nutrition

1. satiety factor: ob/ob gene translates into a mutated form of leptin released by adipocytes which do not cause satietation as does the normal form of leptin.

2. essential nutrients: must be obtain through dietè vitamins, minerals, amino acids, some cant produce fatty acids.