| Control of water requires what processes | A means of detecting the osmolarity of ECF and triggering physiological responses to correct disturbances
A means of altering intake of water
A means of conserving or losing water through the kidneys |
| What process is used to make hypotonic urine | Diuresis
The only way to make the filtrate hypotonic is to remove solute but leave water behind which happens in the distal nephron
The tubular cells pump solute mostly NaCl out of the filtrate but water does not follow since the walls are impermeable to water |
| What value is isotonic | A value of 300 milliosmoles.l-1 is isotonic |
| If the ECF has higher osmolarity then ICF | ECF is hypertonic so water moves out of cells and leads to cell shrinkage |
| If the ECF has lower osmolarity then ICF what happens | ECF is hypotonic so water moves into cells leading to swelling even rupture |
| What is the response if ECF is hypertonic | This leads to the secretion of ADH, which promotes anti-diuretic response and also the stimulation of thirst
As a result this leads to the formation of concentrated urine |
| What is the response if ECF is hypotonic | This leads to the promotion of diuretic response so more dilute urine is formed |
| Where are the osmoreceptors located | Supraoptic nuclei ( SON ) and organum vasculosum of the lamina terminalis ( OVLT )
In the hypothalamus |
| What is the mechanism of action of ADH | When ADH is released, aquaporin 2 (AQP2) channels are inserted into the apical membranes of the cuboidal epithelium in the connecting tubules and the collecting ducts
Water can then enters the cells via the AQP2 channels |
| What is the difference between the 2 limbs of the Loop of Henle | The descending limb is permeable to water via AQP1 but impearmable to solutes
The TAL is impermeable to water but actively transports solutes from the lumen into the interstital fluid via Na+/K+/Cl- transporters |
| What are the processes that increase the hypertonicity of the renal medulla | Counter current multiplier in the LOH
Accumulation of urea in the renal medulla interstitum by recycling urea from the collecting duct |
