chapter 32 pt 2

• Osmoconformers


  Organisms that are in osmotic equilibrium with their environment
• Osmoregulators


  Maintain a relatively constant blood osmolarity despite different concentrations in their environment
• Vertebrate Kidney


  • Made up of thousands of repeating units - nephrons
  • All vertebrates can produce a urine that is isotonic or hypotonic to blood
  • Only birds and mammals can make a hypertonic urine (more concentrated than blood)

  
• Evolution of the Vertebrate Kidney

  1. Kidneys are thought to have evolved among the freshwater teleosts, or bony fishes

  2. Fishes do not drink water and excrete large amounts of dilute urine

  3. Reabsorb ions across nephrons

  4. Actively transport ions across gills into blood

  
• Freshwater Fish


  • Gain water and lose salt when ventilating gills
  • Kidneys produce copious dilute urine
  • Specialized gill epithelial cells transport Na+ and Cl- from water into fish's capillaries
• Saltwater Fish


  • Gain salts and lose water across gills
  • Produce very little urine
  • Drink seawater to replace water lost
  • Expend energy to transport excess salt out of body through gill epithelial cells
• Mammalian Kidney


  • Filtration - Fluid in the blood is filtered out of the glomerulus into the tubule system
  • Reabsorption - Selective movement of solutes out of the filtrate back into the blood via peritubular capillaries
  • Secretion - Movement of substances from the blood into the extracellular fluid, then into the filtrate in the tubular system

  
• Nephron Organization


  1. Glomerulus

  2. Bowman's capsule

  3. Proximal tubule

  4. Loop of Henle

  5. Distal tubule

  6. Collecting duct

  
• Increase in blood osmolarity


  Stimulates release of ADH
• Low levels of Na+ in the blood

  Stimulates secretion of aldosterone
• Increased blood volume


  Stimulates secretion of atrial natriuretic hormone (ANH)
• Homeostasis


  Maintaining a relatively constant internal environment despite changes in the external environment