Zoology 101: Animal Biology Last Lecture Outline Lecture 21 1. Finish up of last lecture and Fermentation2. Energy and exchange Current Lecture Outline1. Small intestine2. Large Intestine 3. Respiration4. Beginning of Tracheal system Small Intestine • Chemical digestions- in duodenum, aided by accessory organs ◦ Pancreatic amylase: carbs ◦ Pancreatic proteases: proteins ▪ Trypsin, chymotrypsin ▪ Secreted as inactive precursors: trypsinogen, chymotrysinogen ▪ activated in small intestine ◦ Pancreatic nuclease: nucleic acids ◦ pancreatic lipase: fats • Mechanical digestion: ◦ bile emulsifies (breaks into smaller globules) fat; larger surface area for lipase ◦ Bile made in liver, stored in gallbladder • Absorption: exchange into circulation across small intestine (jejunum and ilium) ◦ Big folds have folds → villi▪ single layer lined with epithelial cells (exchange▪ Supplied with blood capillaries ▪ Lacteals (center of villi)- Circulatory ◦ Microvilli: on the actual epithelial cells; have folds on lumen side, brush border • Fats → chylomicrons (lipoprotein complexes) → lacteals → lymph system → blood stream• All other molecules → capillaries Large Intestine • We want to get rid of undigested material while still conserving water → elimination • Reabsorption of water → waste/undigested material becomes more solid → feces eliminated from the body• Microbiome• Tight junctions (protein connections): connect epithelial cells lining digestive system ◦ Hold cells together◦ Inhibit movement of dissolved materials through the space between cells ◦ Problems? Crohn's?, cancer, diarrhea • Intestinal adaptations:◦ Herbivore: cellulose cell walls are hard to digest, longer small intestine to allow more time for chemical digestion to occur, more surface area for absorption ◦ omnivore: shorter small intestine ◦ Cecum pouch: anaerobic chamber, contains cellulose-digesting microbes (big in herbivores)◦ Ruminents (herbivores): rumen contains cellulose-digesting microbes ◦ Bird digestive system is adapted for flight; mechanical digestion: gizzard (muscular action) and small rocks) and crop (expandable, storage → stores food while in flight) Respiration• Exchange of gases • Exchanger surface=respiratory surface, living cells • Gases move by diffusion, move down pressure gradient • Variety of forms; common features:◦ thin, large surface area, moist, contact with circulatory system (usually)• Some animals use body surface • Skin surface as gas exchange in few complex animals • Small body surface relative to volume; surface impermeable to gases → skin cells are dead • Gills provide sufficient gas exchange in water ◦ gas exchange hard in water ▪ much less oxygen than in air ▪ oxygen diffuse much slower than in air ▪ water more dense/viscous ◦ huge surface area directly in contact with water • Ventilation mechanism: respiratory medium over respiratory surface (water flows over gills)• One way flow of respiratory medium • Countercurrent exchange: maximize oxygen from water ◦ direction of water flow opposite direction of blood flow • Oxygen in respiration surface always higher than oxygen in blood • gradient for diffusion all along capillary bed Beginning of Tracheal System• Extensively branched system of internal tubules • Adapted for gas exchange in terrestrial environments • brings outside environment close enough to nearly every cell to diffuse • no direct contact with blood vessels
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