Kidney and homeostasis

• Homeostasis

  The maintenance of a constant internal environment by negative feedback
• Function of homeostasis

  Prevents wild fluctuations, beyond optimal range, allowing cells and metabolism to function efficiently
• Negative feedback

  When a corrective mechanism is in place to bring the changed value back to a set point
• How does negative feedback work?

  1. receptor detects internal environment
  2. receptor communicates with coordinator
  3. coordinator communicates with effectors
  4. A response occurs to bring the level back to a set point
  5. Corrective response stops
• Excretion

  Removal of metabolic waste from the body, produced by chemical reactions inside the body cells
• Where does urea filtered from the kidney come from?

  Excess amino acids, from protein in the diet, are deaminated in the liver. The amino group forms ammonia and is then converted into a less toxic urea.
• Deamination of excess amino acids

  Amino acids are broken down into organic acids and ammonia. Ammonia is then converted into urea.
• Why does deamination occur?

  Ammonia is highly toxic so it is quickly converted to urea.

  The urea is then transported in the blood plasma to the kidneys
• Ultrafiltration

  Filtration under high pressure in the Bowmans capsule
• Why is there a high hydrostatic pressure in the Bowmans capsule

  The afferent arteriole has a larger diameter than the efferent arteriole
• What enters the Bowmans capsule

  Small molecules and ions are forced from the blood capillaries into the Bowmans capsule
• Name of the fluid in the Bowmans capsule

  Glomerular filtrate
• Where does selective reabsorption take place

  Proximal convoluted tubule
• What mechanisms are used for selective reabsorption

  Facilitated diffusion

  Active transport
• Adaptations of the PCT for selective reabsorption

  • Large surface area, due to the length of the pct
  • Cuboidal epithelia, increase the surface area with microvilli
  • Lots of mitochondria, which release ATP for active transport
  • Tight junctions between cells, preventing molecules diffusing back into the Bowmans capsule
  • Close to the capillaries, as they are pulled to them by podocytes for reabsorption
• Descending limb

  Permeable to water so water leaves by osmosis.

  Na+ and Cl- enter the descending limb by facilitated diffusion
• Ascending limb

  Not permeable to water

  Allows Na+ and Cl- to leave by facilitated diffusion and then by active transport
• Na+ and Cl- are actively pumped out of the filtrate in the ascending limb into the tissue fluid creating a low water potential. the low water potential in the tissue fluid allows water to leave the descending limb by osmosis and is carried away by the plasma of the vasa recta to the rest of the body.
• Contents of the descending limb become more concentrated as water is lost by osmosis
• As the filtrate passes up the ascending limb it becomes more dilute due to the loss of ions
• Osmoregulation

  Occurs by negative feedback.

  Control of water content and solute composition of body fluids
• Osmoregulation

  Osmoreceptors in the hypothalamus detect change, such as low water potential in the blood plasma.

  This causes a signal to be sent to the pituitary gland which will then secrete ADH.

  ADH is carried in the blood to the collecting duct walls and distal convoluted tubule and binds with protiens.
• Osmoregulation

  The proteins ADH binds with are aquaporins. This allows more water to be reabsorbed by osmosis