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Homeostasis

Homeostasis. Chapter 36 and section 31.3. Homeostasis maintaining internal stability, regardless of external conditions stability maintained for many variables cannot maintain stability for long in bad env . c ond. coordinated response of numerous body systems and parts of systems

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Homeostasis

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  1. Homeostasis Chapter 36 and section 31.3

  2. Homeostasis • maintaining internal stability, regardless of external conditions • stability maintained for many variables • cannot maintain stability for long in bad env. cond. • coordinated response of numerous body systems and parts of systems • keeps body within a range of variables that are conducive to life • Feedback Mechanisms • feedback • result of a process affects the process itself • negative feedback • more common • result inhibits further action at the start • positive feedback • result stimulates further action at the start • often indicates a problem

  3. An example of negative feedback

  4. Fig. 31.10 Regulation of room temperature. An example of negative feedback.

  5. Fig. 31.11 Regulation of body temperature. Another example of negative feedback.

  6. Thermoregulation • regulation of body temperature • endotherms • maintain constant body temperature • heat is generated internally through metabolic reactions • tolerate a wide range of environmental conditions • require a lot of food and energy • major evolutionary adaptation • preventing heat loss • shunting blood away from extremities • countercurrent heat exchange • fat reserves, hair, and feathers • radiation and conduction • shivering • increasing heat loss • shunting blood toward skin and resp. passages • radiation, convection, conduction • evaporative cooling • behavioral, cellular, and hormonal means of thermoregulation

  7. Heat exchange between an organism and its environment

  8. ectotherms • body temp. fluctuates with environment • heat is absorbed from environment through a wide variety of behaviors • maintain fairly constant body temp. • requires less food and energy • cannot tolerate wide range of environmental conditions • heterotherms • intermediate situation • endothermic or ectothermic • hummingbirds, bats, bees, etc. Relationship between body temperature and ambient temperature in an ectotherm and endotherm.

  9. Osmoregulation and Excretion • osmoregulation • regulation of water and ions within body • excretion • removal of metabolic wastes from body • most metabolic wastes involve nitrogen – nitrogenous wastes • deamination • amino group (-NH2) removed from compounds  toxic ammonia • ammonia is excreted or stored in some other form • types • fish = ammonia • insects, birds, reptiles = uric acid (often a “paste”) • other inverts., amphibians, mammals = urea+ H2O urine

  10. Fig. 36.1 Nitrogenous wastes

  11. osmotic environments • marine • ions diffuse into an animal’s body, water diffuses out • water conservation is biggest problem • ways animal can counteract this • must constantly drink seawater • osmoconformers • tissues become isotonic with surrounding water • osmoregulators • salt actively transported out (salt-secreting cells) • freshwater • water diffuses into an animal's body, ions diffuse out • water conservation is not an issue, but retaining ions is • do not drink freshwater • inverts.: flame cells • verts.: kidneys

  12. terrestrial • chief problem is obtaining and conserving water • inverts.: nephridia • insects: Malpighiantubules • verts.: kidneys Fig. 36.4 Body fluid regulation in bony fishes

  13. Human Excretory System • structures involved • kidneys ureters urinary bladder  urethra  out of body • renal artery and vein (renal circuit) Fig. 36.7 The human excretory system

  14. kidneys • functions • filtration • reabsorption of water and other useful ions • water conservation • tubular secretion • excretion • structure • cortex, medulla, renal pelvis • nephrons • mostly in cortex • collecting ducts • mostly in medulla Key function of excretory systems, an overview

  15. Fig. 36.8 Macroscopic and microscopic anatomy of the kidney

  16. nephrons • actual filtering, functional units of kidneys • urine formed here • components • Bowman’s capsule • glomerulus • filtration occurs here • proximal tubules • looping tubule (Loop of Henle) • distal tubules  join with collecting ducts • nephrons empty into collecting ducts • ducts pass through medulla  empty into renal pelvis ureter

  17. Fig. 36.9 Nephron anatomy

  18. reabsorption of water and other useful ions • takes place across the peritubular capillaries • countercurrent exchange, osmosis, active/passive transport • excess water remains in nephrons and will be excreted • tubular secretion • excess ions/waste secreted from capillaries into nephrons

  19. Fig. 36.11 Processes in urine formation

  20. control of nephron function • antidiuretic hormone (ADH) controls water reabsorption • secreted by pituitary gland • under control of hypothalamus • ADH present  H2O reabsorbed • ADH absent  H2O excreted • aldosterone controls salt reabsorption • secreted by adrenal glands • high levels of aldosterone  increase in reabsorption of salt • salt used to keep blood 0.9% saline (isotonic)  homeostasis! • also promotes excretion of K+ ions • atrialnatriuretic hormone (ANH) promotes excretion of salt and Na+

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