WATER REABSORPTION /KIDNEYS

• OSMOREGULATION= Process of controlling blood water potential
• what could be in the glomerular filtrate

  • water
  • glucose
  • urea
  • amino acids
  • Na+ ions
• what happens in Bowmans capsule (renal capsule) ?

  • ULTRAFILTRATION
  • Afferent arteriole is wider than efferent arteriole creating high hydrostatic pressure
  • This forces small molecules and water out of capillaries into the renal capsule
  • Large proteins and blood cells remain in blood as too large to pass through
• What happens in PCT

  • useful substances eg glucose are reabsorbed along pct by active transport and diffusion
• What happens in loop of henle?

  • epithelial cell of tubule cells carry out active transport
  • sodium ions actively transported out of ascending limb against conc grad into surrounding tissue creating a Low water potential for water reabsorption
  • water moves out of descending limb and out of DCT and collecting duct via osmosis down this water potential gradient
  • ascending limb is impermeable to water meaning water remains in tubules here
• longer loop of henle= lower water potential
• what components are found in urine

  • water
  • dissolved salts
  • urea
  • hormones
  • excess vitamins
• HYPOTHALAMUS= regulates water potential
• effect of adh

  • makes walls of DCT and collecting duct more permeable by releasing aquaporins to inc water absorption
• EXPLAIN ADH REL according to DEHYDRATION

  • water conc in blood decreases therefore water potential decreases
  • This is detected by osmoreceptors in hypothalamus
  • stimulates posterior pituitary gland to release more ADH
  • ADH binds to complementary receptors in DCT and collecting duct
  • ADH releases aquaporins into blood and makes DCT and collecting duct more permeable to water so more water is reabsorobed
  • small amount of conc urine produced
•  Which hormone causes the decrease in the water content in the distal convoluted tubule?

  adh
•  The glomerular filtration rate is the total volume of filtrate formed per minute. Explain the effect on the glomerular filtration rate of a large loss of blood from the body

  decreased blood pressure
• Explain two ways in which the cells of the proximal convoluted tubule are adapted for reabsorption.

  • microvilli provide large surface area;
  • carrier proteins (in membrane) for active transport;
  • channel proteins for facilitated diffusion;
  • many mitochondria for active transport;
• A person with diabetes may have a plasma glucose concentration greater than the threshold value for glucose reabsorption. Explain what causes this raised plasma glucose concentration.

  • decrease in insulin production

  OR

  receptors not responsive to insulin
• Where does ultrafiltration occur?

  Bowmans capsule/ renal capsule
• Give one component of the blood which is not normally present in the filtrate.

  • blood cells
  • proteins
  • platelets
•   Name the gland which releases ADH

  posterior pituitary gland
•      Explain how the structure of protein molecules allows them to form channels through which only water molecules can pass.


  each protein has a specific tertiary structure

  specific to channel
• Explain how the cells of the collecting duct are able to absorb water from the filtrate through the protein channels in their plasma membranes.

  lower water potential in tubule cells

  water enters via osmosis
•  Describe how urea is removed from the blood.

  • hydrostatic pressure causes ultrafiltration at Bowmans capsule
  • through basement membrane
  • urea is small so passes through
•  Explain how urea is concentrated in the filtrate.

  •  reabsorption of water

  by osmosis;

  at the PCT

  at the DCT

  active transport of ions / glucose creates gradient
• The kangaroo rat takes in some water by feeding and drinking. Describe another method by which the kangaroo rat could obtain water.

  • respiration using oxygen