Pierce session 3 Flashcards
what cell does ADH act on to allow for water permeabillity
Principle cell!
What happens to Urea when the ADH increases
During anti-diuresis, water but not urea is absorbed in the cortical collecting duct, but Urea will continue to flow down the duct in to the inner medulla
- at High concentration of urea in the inner medullary collecting duct the urea will passively reabsorb into the intersitium
- then it will encounter the loop of henle where the concentration of Urea is lower and it will flow back into the LOH to then continue this cycle back up to the CCD
this occurs when ADH is present
what happens to the NKCC2 channels in the THick ascending Limb when ADH is present
ADH increases the permeabillity of NaCl at the apical membrane of the TAL by increasing the presence of NKCC2 channels
- this leads to additional NaCl being reabsorbed increasing the osmolality of the interstitium
- when combined with urea being reabsorbed in the IMCD, the meduallry interstitium bevomes very concentrated
- the greater the medullary hyperosmolarity the greater the urine concentrating abillity (pull water out of the tubule)
what are the 3 big things that ADH do to the nephron
1) increase water permeabillity of principle cells of the late distal tubule and collecting ducts via insertion of aquaporin channels
2) increase urea permeabillity in the IMCD (but not cortical or OMCD)
3) Increase activity of NKCC2 in TAL
Salty medulla explained
The medullary osmolality is due to the presence of NaCl and urea
-the interstitial osmotic graident is enhanced by additional presence of NaCl and Urea in the interstitum, regulated by ADH
- THe gradient first occurs by the salts being actively pumped out by the ascending limb of LoH makes the entire medullary interstitium salty (hypertonic)
- Since the descending limb is only permeable to water, the interstituum will passively pull water out of the descending LoH
- THis is important for reabsorbing water, but also to contribute to forming a concentrated urine
how does the countercurrent process work in the Kidney?
First establish the nephron:
- Filtraate enters PCT at 300 and heads into the descending LoH
- Since the descending LoH is only permeable to water, water leaves the tubule and enters the interstitial space as it gets to the bottom of the LoH, meanwhile the LoH is getting more and more concentrated (1200)
- Then as the the fluid enters the ascending LoH it is only permeable to solutes therefore solutes are pumped out into the interstitum as it travels up and dilutes the remaining fluid till it gets to the DCT where it is 100 hypotonic
Meanwhile, blood exits the efferent arteriole and enters the Peritubular capillary system,
- the descending portion first passes the ascending LoH and while the fluid in the ascending LoH is heading upward the blood vessel is flowing downward (countercurrent)
- blood is passing through an interstital space that is becoming more and more concentrated as the vessel plunges downward
- lower concentrated blood begins to pick up solutes that are passing down concentration gradient from interstitum into the vessel and as it reaches the bottom the blood vessel is very concentrated
- at the hairpin turn the blood is just as concentrated as the interstitum (1200)
- as the solutes enter the blood from the interstitum, there is more incentive for the ascending LoH to pump more solutes to replace them
- THen blood wll begin to go back upward and pass along side the descending LoH (only permeable to water)
- as blood ascends the water that is leaving the descending LoH will passively flow into the highly concentrated blood vessel
- more and more water gets picked up that the blood concentration decreases as it ascends and gets back to 300
the significance of the countercurrent
by grabbing solutes first and water second, you almost return everything back to the body that was filtered by the glomerulus
the 1-1.5 liters urine that is lost per day are primarily regulated at the most finite levels due to small changes in reabsorption rates due to the presence of ADH and aldosterone
what is free water clearance
The difference between water excretion (urine flow rate) and osmolar clearance. its the rate the body excretes solute free water. free water means water without any solutes in it
Ch20 = V - Cosm
=V- (Uosm x V)/Posm
when Ch20 is negative means excess solutes are removed wter conservation
when Ch2o is positive water is being excreted forming dilute urine and water excess
Osmolar Clearance
The total clearance of solutes from the blood can be expressed as the osmolar clearance (Cosm)
this is the volume of plasma cleared of solutes each minute in the same way that of a single substance is calculated
Cosm = (Uosm x V)/Posm
Obligatory Urine volume
The minimal volume of urine required to excrete waste solutes needing to be excreted from the body. this volume is variable depending on daily solute excretory load and the maximum urinary concentration achievable.
The maximal urine concentrating abillity in humans is 1200 mOsm/L which is dependant on the length of the loop of henle
OUV = (minimum solute excretion per day)/ (max urine concentrating abillity)
What is natriuresis
the excretion of excessive sodium in the urine
this may be inducted by a drug (natriuretic), homone (ANP) or by significantly elevated renal perfusion presure (pressure natriuresis)
what is Diuresis
A large urine output. when the urine primarily contains water, it is referred to as a water diuresis, which is contrast to diuresis seen with the administration of diuretic agents,
The latter case, the urine output is large, but the urin contains solute plus water, which may be termed a solute diuresis
What is Antidiuresis
when plasma ADH is high, a small volume of concentrated urine is excreted
