case 7 - renal physiology Flashcards
what is the difference between the cortical and juxtamedullary nephrons
the cortical nephrons are located much further up into the cortex than the juxtamedullary nephrons
what do the juxtamedullary nephrons have
particularly long loops of Henle, that dip way down into the medulla close to the renal papilla and it is these long nephrons that are responsible for your ability to produce concentred urine
what is the counter-current multiplier
loop of henle
what is the counter current exchanger
vasa recta
what is the descending limb impermeable to
the descending limb is impermeable to NaCl - cannot exit
what is the ascending limb impermeable to
The ascending limb is impermeable to water - cannot exit
what is the max gradient difference between the tubular fluid concentration and the interstitial fluid concentration
200mOsm/Kg
what happens in the loop of henle
Water moves out of the tubule in the descending limb, and this means the fluid is more concentrated.
Then it goes into the ascending limb, and this is where NaCl leaves which decreased the concentration.
what does this process do
dilutes the urine. and means we have reabsorbed water and sodium and chloride
how is urine concentrated
in the actions of ADH (vasopressin)
what produces ADH and where is it stored
this hormone is produced in the hypothalamus and is stored in the posterior pituitary.
when is ADH released
It is released into the general circulation in response to a number of factors, primarily an increase in plasma osmolality. So therefore if you become dehydrated, osmoreceptors in the hypothalamus detect that, and this causes the release of ADH into the circulation
what does ADH do to the collecting duct
ADH makes the collecting duct permeable to water and therefore water is reabsorbed and you end up with a concentrated urine - maximum conc. urine = 1200mOsm/g
what does ADH bind to when it is released into the circulation
when ADH is released into the circulation, it binds to V2 receptors on the collecting duct cells and activation of V2 receptors by ADH, leads to the insertion of water channels, specifically, AQP2 into the membrane on the apical side
what happens in the absence of AQP2
this membrane is not permeable to wayer
what does water leave through
The water leaves through AQP3/4 on the basolateral side of the membrane - these are permanently inserted
how much potassium is lost in urine
92%
what happens to potassium in the proximal tubule
65% K+ reabsorbed
what happens to K+ in the loop of henle
25% K+ reabsorbed
what happens to K+ in the distal and collecting duct
Variable K+ reabsorption and secretion
what happens in the proximal tubule to urine
The net charge of the urine at the start of the proximal tubule is negatively charged but through selective reabsorption and K+ ions being introduced, it becomes positively charged. As a result of this, potassium ions that are now in the tubule fluid will move through passive diffusion through a parallel cellular pathway back into the blood. So potassium is reabsorbed down the electrochemical gradient in the proximal tubule.
what happens in the collecting duct
Further down in the collecting duct, we also see reabsorption of potassium. The transporter NKCC2 is taking up sodium and chloride as part of the concentration process as tubular fluid is going up the ascending limb. At the same time, to maintain electrical neutrality between sodium and chloride, potassium is also taken into the cell. So potassium can be reabsorbed through this mechanism and leave through potassium channel on the basolateral membrane.
what is on the apical side of the membrane in the collecting duct
On the apical side, there is another potassium channel called ROMK2. This channel allows recycling of potassium, so when ROMK2 opens, potassium floods out and can be picked up again by NKCC2 and recycled.
what are the two different cell types in the collecting duct
There are two types of cells in the collecting duct, the principal cell and the intercalating cell.
what are the two different potassium channels on the apical side of the mmrabne
There are two different potassium channels, ROMK1 and 3 on the apical side of the membrane which allows potassium to enter the tubular fluid.
what happens in situations where we need to retain sodium and reabsorb it
In situations where we need to retain sodium and reabsorb it, there is a channel on the basolateral side which allows potassium to flow out of the intracellular fluid and back into the blood. This will be a situation where we need to conserve potassium.
what is another mechanism of aldosterone via potassium
Another mechanism of aldosterone is it reverses the direction of the potassium channel on the basolateral membrane. So now potassium instead of going from the intra cellular space to the extracellular space is doing the opposite. - it is flowing into the cell because there is a movement of potassium ions out through ROMK1 and 3.
what is this stimulated by
high K+ plasma loss
what happens in a situation when we have acidosis
In a situation where we have acidosis, we have a situation in the intercalated cells. What happens in these cells, is if we need to retain potassium or we need to get rid of hydrogen ions, we can pump hydrogen ions out in exchange for potassium ions being pumped in. This requires energy. In this situation, if we are seeing acidosis, or low plasma potassium, and we need to retain potassium ions, these two pumps are activated.
what happens if we have hypo/hypercalcaemia:
lower/raise depolarisation threshold
what happens if we have hypo/hypermagnesaemia:
raise/lower heart rate
what happens in the proximal and loop of Henle in Ca2+ and Mg2+ reabsorption
91% of Ca2+ reabsorbed - paracellular route
89% Mg2+ reabsorbed - paracellular route
what happens in the distal in Ca2+ and Mg2+ reabsorption
3-7% Ca2+ reabsorption
5-6 Mg2+ reabsorption
what is the calcium channel on the apical side of the membrane
the calcium channel on the apical side of the membrane is the TRPV5 channel
what is calcium transporter through the cell bound to
Calcium is transported through the cell bound to calbindin-D28k
what are the two routes via which calcium leaves the cell
Calcium can exit the cell through one of two routes; there is a calcium ATPase pump which pumps calcium out against a concentration gradient and specifically in the distal tubule, we have PMCA1b and NCX1
what is this process regulated via
Klotho - endocrine regulator on the apical side
PTH, vitamine D and sex hormones on the basolateral side
what is the magnesium channel and what do we know about it
We know there is a magnesium channel called the TRPM6 channel. Electrical gradient. This stimulated epidermal growth factor.
