Digestion Chapter 43

1. DigestionChapter 43 Types of digestion, ingestion, digestion, energy from food

2. Single celled = intracellular digestion • Herbivores, carnivores, omnivores • Two-way vs. one way digestion • Specialization = storage, fragmentation, digestion, absorption • Fragmentation • Chemical digestion • Absorption • Waste excretion

3. Ingested, swallowed, transported • Adaptations depending on environment • Fish = large pharynx • Birds have gizzards • Vertebrates have teeth • Carnivores = pointed, • herbivores = flat, omnivores • Omnivores = mullet teeth (sharp in front, flat in back) • Mouth adds mucous, saliva • Tongue moves to back

4. Esophagus and Stomach • Peristalsis = muscle contractions to move food to stomach (swallow upside down) • Stomach like balloon, 50 ml empty, 2-4 liters of food • Mixes with gastric juice (2L/day) • Kills most bacteria, H. pylori • Only proteins partially digested in stomach • Chyme = partially digested food and acid • Rest moves on to small intestine • Alcohol, aspirin, water absorbed by stomach • Storage main responsibility

5. Small Intestine • http://health.howstuffworks.com/adam-200088.htm • Capacity limited, process takes time • 4.5 meters; duodenum, jejunum, ileum • Receives chyme, digestive enzymes, bile; digestion • Villi = projections of epithelial wall • Covered with microvilli • 300 square meters surface area • Digestion of macromolecules

7. Accessory to Small Intestine • Pancreas – large gland contributes secretion, exocrine organ • Enzymes that digest protein, starch, and fat • Released as inactive, activated by brush border of small intestine • Bicarbonate neutralizes stomach acid • Also secretes via isle of Langerhans, hormones to regulate blood sugar (insulin and glucagon) • Liver = largest, exocrine secretion of bile • Pigments = breakdown of red blood cells, released into small intestine to be eliminated • Salts = digestion of fats, work as detergents • Gallbladder stores bile until fat sensed (gallstone)

8. After digestion, absorption • Amino acids and monosaccharides transported across brush border into epithelial, across membrane, into blood, carried to liver via hepatic portal • Digested fats absorbed differently • Triglycerides hydrolyzed into fatty acids and monoglycerides, absorbed into epithelial, reassembled, lymphatic capillaries

9. Large intestine (colon) • Shorter, but larger diameter • No digestion, 4% absorption, concentrates waste • Undigested (cellulose) and bacteria (500ml gas/day), beans = undigested substrate • Fiber = roughage, helps compact • Peristalsis = compact before rectum-anus, two sphincters control (involuntary, voluntary)

11. Variations • Cellulose – bacteria and protists • Ruminant = grazing herbivore with large undivided stomach (regurgitate and rechew) • Other animals = enlargement of cecum, must eat feces • Wax digestion • Microorganisms provide vitamin K (clots blood)

12. Neural/hormonal regulation • Nervous stimulates salivary and gastric secretions, gastric acid controlled by negative feedback loop, enterogastrones inhibit gastric motility (fatty meals stay in stomach longer) • Liver metabolizes substances before sent on to body, alcohol, pesticides, ammonia • Brain receives glucose from blood, blood glucose lvls must be controlled (storage as glycogen stimulated by insulin)

13. Food energy and energy expenditure • Provides source of energy & raw materials • Basal metabolic rate • Age, sex, body size, exercise • Glycogen reserves limited = store as fat • Obesity • Genetic and environment • Expressed only in fat cells • Reduced sensitivity to leptin (satiety factor) in brain