AQA A level Biology- kidneys and osmoregulation

• Describe Osmoregulation when a person is more hydrated

  Osmo receptors detect change

  Posterior pituitary gland releases ADH

  DCT and CDs permeability decreases

  Less water is reabsorbed

  Large volume of unconcentrated urine is produced
• What do aquaporins do?

  Increase rate of H2O passing (kidney and plant root cells)
• What is an aquaporin?

  water channel protein in a cell
• Describe Osmoreggulation when a person is dehydrated

  Change is detected by osmoreceptor is in the hypothalamus

  This causes impulses to be sent to the posterior pituitary gland and ADH is released and transported to the kidneys via the blood

  ADH binds to receptor is in the epithelial membrane of the cells that line the DCT and CD

  This causes AquaPorins to be inserted into the membrane

  The DCT and CDs permeability increases

  More water moves out of the DCT and CD through aquaPorins into the capillaries via osmosis

  Decreased volume of unconcentrated urine is produced
• Describe reabsorption in the loop of Henle?

  (Spec answer)

  Cells in the thick upper part of the ascending limb actively pump sodium and calcium ions from the filtrate into the surrounding tissue

  Ascending limb is impermeable to water so water can't follow a water potential gradient and move into the surrounding tissue

  This leads to a higher water potential in the filtrate and lower water potential in the surrounding tissue

  The descending limb is relatively impermeable to ions so only some of the sodium and chlorine ions move in by diffusion

  The descending limb is permeable to water so water moves out via osmosis down the water potential gradient

  The loss of water creates a high concentration of ions in the descending limb

  The filtrates moves into the thin ascending limb

  Sodium and chlorine ions diffused out of the ascending limb by facilitated diffusion

  The filtrate passes along the DCT and down the collecting duct

  Water can be reabsorbed from the DCT Ans CD by osmosis

  The volume of water reabsorbed depends on the water potential gradient and permeability of nephron walls

  The water passes into the surrounding blood capillaries which eventually join the renal vein
• Describe reabsorption in the loop of henle? (Detailed)

  Fluid enters loop of Henle at a rate of:

  - 40-45 mL/min.

  
  

  Chemical Composition of Tubular Fluid:

  - Glucose

  - amino acids

  - other nutrients no longer present.

  
  

  Osmolarity of Tubular Fluid:

  - Close to same osmolarity of blood

  - because water reabsorption keeps pace with reabsorption of solutes all along the proximal convoluted tubule.

  
  

  Reabsorption in Loop of Henle:

  
  

  Filtered Water: 15% (Mostly absorbed in descending limb of loop of Henle)

  Filtered Na+, K+: 20-30%

  Filtered Cl-: 35%

  Filtered HCO3-: 10-20%

  Filtered Ca2+ and Mg2+: Variable Amount

  
  

  Independent Regulation of Volume and Osmolarity of Fluids:

  - Loop of Henle is mostly impermeable to water

  - osmosis is not automatically coupled with reabsorption of solutes.

  
  

  1) Na+-K+-2Cl- Symporters

  Located in:

  - thick ascending limb of loop of Henle

  
  

  Simultaneously reclaims:

  - one Na+

  - one K+

  - 2 Cl-

  - from fluid in tubular lumen

  
  

  Main effect is:

  - reabsorption of Na+ and Cl-.

  
  

  Na+ that is actively transported:

  - into interstitial fluid

  - at the base and sides of the cell

  - diffuses into the vasa recta

  
  

  Cl- moves through:

  - leakage channels

  - in the basolateral membrane

  - into interstitial fluid

  - then into the vasa recta.

  
  

  K+ leakage channels:

  - are present in apical membrane

  - K+ brought in through symporters

  - travel back down their concentration gradient

  - into the tubular fluid.

  
  

  2) Reabsorption via Paracellular Route

  
  

  Positively charged K+ moving into tubular fluid:

  - through apical membrane channels

  - leaves interstitial fluid more negative

  - compared to the tubular fluid

  - in the ascending limb of loop of Henle

  
  

  The relative negativity promotes:

  - reabsorption of cations

  - Na+

  - K+

  - Ca2+,

  Mg2+

  
  

  Little or no water is reabsorbed in the:

  - ascending limb of loop of Henle.
• What are features that increase the rate of absorption?

  Large surface area due to the presence of microvilli

  Many carrier proteins in the cell membrane

  Many mitochondria which produce lots of ATP for active transport

  Many capillaries close to PCT so there is a short diffusion pathway

  Blood is always moving so concentration gradient for glucose is maintained
• Describe the selective absorption in the PCT

  All glucose molecules are reabsorbed by facilitated diffusion and active transport

  All amino acid are reabsorbed by facilitated diffusion and active transport

  Most of the ions are reabsorbed by facilitated diffusion and active transport

  Most of the water is reabsorbed by osmosis glucose and amino acid levels lower the water potential in the blood so water moves into the blood down a water potential gradient

  Some urea molecules are reabsorbed as they move down a concentration gradient
• What creates the high blood pressure that pushes the filtrate out of the capillaries?

  Contraction of the left ventricle

  Blood pressure in the glomerulus is kept high because the diameter of the efferent arterial is it smaller than the afferent (bottleneck effect)
• What occurs during ultrafiltration?

  Cappilary endothelium:

  Large pores that allow the plasma to pass through but hold back the cells

  Basement membrane:

  Main fine filter,hold back plasma proteins

  Podocytes:

  Epithelium cell wall of Bowmans capsule has feet like extensions that support the basement membrane

  allow the filtrate to pass through the filtration slits
• Draw and label the nephron?

  
• Describe Osmoregulation when a person is more hydrated

  Osmo receptors detect change

  Posterior pituitary gland releases ADH

  DCT and CDs permeability decreases

  Less water is reabsorbed

  Large volume of unconcentrated urine is produced
• What do aquaporins do?

  Increase rate of H2O passing (kidney and plant root cells)
• What is an aquaporin?

  water channel protein in a cell
• Describe Osmoreggulation when a person is dehydrated

  Change is detected by osmoreceptor is in the hypothalamus

  This causes impulses to be sent to the posterior pituitary gland and ADH is released and transported to the kidneys via the blood

  ADH binds to receptor is in the epithelial membrane of the cells that line the DCT and CD

  This causes AquaPorins to be inserted into the membrane

  The DCT and CDs permeability increases

  More water moves out of the DCT and CD through aquaPorins into the capillaries via osmosis

  Decreased volume of unconcentrated urine is produced
• Describe reabsorption in the loop of Henle?

  (Spec answer)

  Cells in the thick upper part of the ascending limb actively pump sodium and calcium ions from the filtrate into the surrounding tissue

  Ascending limb is impermeable to water so water can't follow a water potential gradient and move into the surrounding tissue

  This leads to a higher water potential in the filtrate and lower water potential in the surrounding tissue

  The descending limb is relatively impermeable to ions so only some of the sodium and chlorine ions move in by diffusion

  The descending limb is permeable to water so water moves out via osmosis down the water potential gradient

  The loss of water creates a high concentration of ions in the descending limb

  The filtrates moves into the thin ascending limb

  Sodium and chlorine ions diffused out of the ascending limb by facilitated diffusion

  The filtrate passes along the DCT and down the collecting duct

  Water can be reabsorbed from the DCT Ans CD by osmosis

  The volume of water reabsorbed depends on the water potential gradient and permeability of nephron walls

  The water passes into the surrounding blood capillaries which eventually join the renal vein
• Describe reabsorption in the loop of henle? (Detailed)

  Fluid enters loop of Henle at a rate of:

  - 40-45 mL/min.

  
  

  Chemical Composition of Tubular Fluid:

  - Glucose

  - amino acids

  - other nutrients no longer present.

  
  

  Osmolarity of Tubular Fluid:

  - Close to same osmolarity of blood

  - because water reabsorption keeps pace with reabsorption of solutes all along the proximal convoluted tubule.

  
  

  Reabsorption in Loop of Henle:

  
  

  Filtered Water: 15% (Mostly absorbed in descending limb of loop of Henle)

  Filtered Na+, K+: 20-30%

  Filtered Cl-: 35%

  Filtered HCO3-: 10-20%

  Filtered Ca2+ and Mg2+: Variable Amount

  
  

  Independent Regulation of Volume and Osmolarity of Fluids:

  - Loop of Henle is mostly impermeable to water

  - osmosis is not automatically coupled with reabsorption of solutes.

  
  

  1) Na+-K+-2Cl- Symporters

  Located in:

  - thick ascending limb of loop of Henle

  
  

  Simultaneously reclaims:

  - one Na+

  - one K+

  - 2 Cl-

  - from fluid in tubular lumen

  
  

  Main effect is:

  - reabsorption of Na+ and Cl-.

  
  

  Na+ that is actively transported:

  - into interstitial fluid

  - at the base and sides of the cell

  - diffuses into the vasa recta

  
  

  Cl- moves through:

  - leakage channels

  - in the basolateral membrane

  - into interstitial fluid

  - then into the vasa recta.

  
  

  K+ leakage channels:

  - are present in apical membrane

  - K+ brought in through symporters

  - travel back down their concentration gradient

  - into the tubular fluid.

  
  

  2) Reabsorption via Paracellular Route

  
  

  Positively charged K+ moving into tubular fluid:

  - through apical membrane channels

  - leaves interstitial fluid more negative

  - compared to the tubular fluid

  - in the ascending limb of loop of Henle

  
  

  The relative negativity promotes:

  - reabsorption of cations

  - Na+

  - K+

  - Ca2+,

  Mg2+

  
  

  Little or no water is reabsorbed in the:

  - ascending limb of loop of Henle.
• What are features that increase the rate of absorption?

  Large surface area due to the presence of microvilli

  Many carrier proteins in the cell membrane

  Many mitochondria which produce lots of ATP for active transport

  Many capillaries close to PCT so there is a short diffusion pathway

  Blood is always moving so concentration gradient for glucose is maintained
• Describe the selective absorption in the PCT

  All glucose molecules are reabsorbed by facilitated diffusion and active transport

  All amino acid are reabsorbed by facilitated diffusion and active transport

  Most of the ions are reabsorbed by facilitated diffusion and active transport

  Most of the water is reabsorbed by osmosis glucose and amino acid levels lower the water potential in the blood so water moves into the blood down a water potential gradient

  Some urea molecules are reabsorbed as they move down a concentration gradient
• What creates the high blood pressure that pushes the filtrate out of the capillaries?

  Contraction of the left ventricle

  Blood pressure in the glomerulus is kept high because the diameter of the efferent arterial is it smaller than the afferent (bottleneck effect)
• What occurs during ultrafiltration?

  Cappilary endothelium:

  Large pores that allow the plasma to pass through but hold back the cells

  Basement membrane:

  Main fine filter,hold back plasma proteins

  Podocytes:

  Epithelium cell wall of Bowmans capsule has feet like extensions that support the basement membrane

  allow the filtrate to pass through the filtration slits
• Draw and label the nephron?