Regulation of Temperature and Body Fluids
|38.1 How Do Animals Regulate Their Temperature?
1. Adaptations permit animals to regulate body temperatures, the amount of water in their bodies, and solute concentrations in body fluids, which enable them to populate diverse habitats.
2. Ectotherms regulate body temperature by seeking an environment with the appropriate temperature. Endotherms use internal metabolism to generate heat.
3. Animals regulate their body temperatures metabolically, behaviorally, and with anatomical and physiological adaptations.
4. Adaptations to cold include shunting blood to interior organs; countercurrent exchange systems of blood vessels; antifreeze-like chemicals in blood; heat-seeking behaviors; blubber, feathers, and oxidation of fatty acids in brown fat; and shivering and nonshivering thermogenesis.
5. Heat-resisting adaptations include evaporative cooling; circulatory specializations such as the carotid rete; and body forms and behaviors.
38.2 How Do Animals Regulate Water and Ion Balance?
6. Osmoregulation is the control of ion concentrations in body fluids. Specific osmoregulatory adaptations depend on habitat.
7. Osmoconformers are aquatic organisms that have permeable body surfaces. Their body fluids have solute concentrations similar to those of the surrounding water.
8. Osmoregulators include aquatic animals in coastal regions that conserve ions under some conditions and lose excess ions in others. Terrestrial animals have many adaptations to conserve water and regulate ion composition.
38.3 How Do Animals Rid Themselves of Nitrogenous Wastes?
9. Animals must remove wastes. Most nitrogenous wastes come from protein breakdown and include ammonia, urea, and uric acid.
10. Ammonia formation requires the least energy but releases the most water. Urea requires more energy but is less toxic and helps conserve water. Uric acid requires the most energy to produce but can be excreted in an almost solid form, saving water.
11. Animals have diverse excretory systems to remove nitrogenous wastes, including nephridia, Malpighian tubules, and kidneys.
38.4 The Human Urinary System
12. The human urinary system excretes nitrogenous wastes (mostly urea) and regulates water and electrolyte levels. The kidneys, each of which drains into a ureter, produce urine. Ureters drain urine into the urinary bladder for storage. Urine leaves the body through the urethra.
13. The functional unit of the kidney is the nephron. Blood is filtered from the glomerulus into the glomerular capsule. As the resulting filtrate moves along the renal tubule, its composition is adjusted. Important materials are reabsorbed from the filtrate back to the blood and other substances are secreted into the urine.
14. Composition adjustment begins in the proximal convoluted tubule. The filtrate moves into the nephron loop that dips into and then out of the center, or medulla, of the kidney. The nephron loop helps to concentrate urine. Water leaves the filtrate because an osmotic gradient forms in the fluid around the nephron loop by a countercurrent exchange system built by Na+ and urea reabsorption.
15. In the distal convoluted tubule, more reabsorption and secretion occur. The reabsorption of Na+ helps control Na+ balance. Secretion of H+ helps regulate blood pH.
16. The filtrate then moves to the collecting duct and finally to the central cavity of the kidney, the renal pelvis, before draining through the ureter.
38.5 Control of Kidney Function
17. Antidiuretic hormone (ADH) regulates the amount of water reabsorbed from the distal convoluted tubule. The posterior pituitary gland secretes ADH in response to signals from the hypothalamus, which senses the osmotic pressure of blood. ADH increases permeability of the distal convoluted tubule and the collecting duct so more water is reabsorbed and urine is concentrated.
18. Aldosterone increases the kidneys’ salt retention. The adrenal glands release aldosterone in response to either low sodium concentration in the plasma or low blood pressure. Some water reabsorption always follows Na+ reabsorption.