renal part 5 Flashcards
What are the sources of input and output in maintaining water balance?
Which of the following correctly lists sources of water input and output?
A) Input: Ingested liquids, water from metabolism
Output: Sweat, urine, GI tract, respiratory loss
B) Input: Water from metabolism, sweat
Output: Insensible loss, Na+ reabsorption
C) Input: Ingested liquids, urea excretion
Output: Urine, protein catabolism
D) Input: Water reabsorbed in the collecting duct
Output: Sweat, insensible loss, ADH release
Input: Ingested liquids, water from metabolism;
Output: Sweat, urine, GI tract, respiratory loss
How is water processed in different segments of the renal tubule?
water is mainly reabsorbed in the proximal tubule ~67% and the loop of henle ~15%, and the large distal tubule and collecting duct (8-17%)
What is the countercurrent multiplier mechanism?
a mechanism in the kidneys that makes a hyposmotic environment in the renal medulla.
The countercurrent multiplier mechanism is a process in the Loop of Henle that creates a progressively hyperosmotic environment in the renal medulla. This mechanism allows the kidney to concentrate urine and conserve water.
The descending limb of the Loop of Henle is permeable to water but impermeable to solutes, so water moves out into the hyperosmotic interstitium.
The ascending limb is impermeable to water but actively transports NaCl out into the interstitial fluid, making the surrounding medulla more concentrated.
The filtrate moving through the loop flows in opposite directions, creating a countercurrent effect that amplifies the osmotic gradient.
This gradient draws water out of the collecting duct under the influence of ADH, leading to concentrated urine.
What factors are involved in maintaining the countercurrent mechanism?
permeability of the loop of henle
active transport of NACL in the acending lomn
vasa recta as a counter exchanger
urea recycling
What is the outcome of having a countercurrent multiplier mechanism in the kidneys?
the ability to concentrate urine and efficiently reabsorb water
What is the role of the vasa recta in countercurrent exchange?
the vasa recta maintains the osmotic gradient created by renal tubules by exchange if salt and water, causing the increase of Na+ in the medulla interstitual space (the medulla is salty)
How is urea trapped in the medulla? how is urea ultimately excreted? how much is secreted back into the loop of henle?
urea is mainly trapped in the medulla due to the minimal uptake of urea by the vasa recta
15% is excreted
50% is secreted back into the loop of henle
why does water reabsorption depend on Na+ reabsorption?
because Na+ reabsorption sets up an osmotic gradient, causinf this driving force of water
which hormone regulates water reabsorption?
a. aldosterone
b. vasopressin
c. antidiuretic hormone (ADH)
d. angiotensin II
vasopressin and ADH
why does the distal tubule have no mechanism of water reabsorption?
because the distal tubules contrain no aquaporins
how do the mechanisms of w
how does reabsorption differ in the proximal tubule, loop of henle, distal tubule, and the large distal tubule and collecting duct?
proximal tubule=contains passive AQP-1 (ALWAYS OPEND)
LofH=passive APQ-1
Distal tubule= no aqp
large distal + collecting duct = passive (AQP-2,-3,-4)
describe the mechanism of water reabsorption in the PCT
- Na+/K+/Atpase pump pumps out sodium into basolateral side and generates an electrochemical gradient
- Na+ from the lumen goes down its electrical chemical gradient into the epithelial cell
- the movement of Na+ into the cell will decrease the local osmolarity in the LUMEN (more water around, water moves from llow to high osmolarity on the basolateral side)
- water moves through the tight junctions and across the celll via diffusion to the basolateral side
- by bulk flow, water and sodium enter the peritubular capillaries
why does the loop of henele have different transport capabilities on each side of the tubule?
this is because the ascending and descending loop of henle reabsorp different things
water reabsorption occurs due to the descending loop of henle PASSIVELY
salt (NACl)reabsorption throguh the ascending portion of the loop of henle through active transport (bc there are no aqua porins)
what does a longer loop of henle mean in terms of the counter current multiplier
when you ascend down the loop of henle, the osmolarity you start with will multiply by 1,2,3,4,….until it reaches a maximum (peep lecture slides).
you have increased multiplication of the gradient down the loop of henle, leading to a higher salt concentration and more water conservation
As filtrate moves through the Loop of Henle and beyond, what happens to its osmolarity?
A) It becomes progressively more concentrated in the ascending limb and remains concentrated in the distal tubule.
B) It becomes more concentrated in the descending limb and more dilute in the ascending limb before reaching the distal tubule.
C) It remains at a constant osmolarity throughout the nephron due to continuous Na+ and water reabsorption.
D) It is most dilute in the descending limb and becomes progressively more concentrated in the ascending limb.
It becomes more concentrated in the descending limb and more dilute in the ascending limb before reaching the distal tubule.
how does the vasa recta help us?
- the blood flow in the vasa recta serves as counter current exchanges and helps maintain the gradient in the interstitual gradient
note the flow of blood in the vasa recta is opposite to the direction of filtrate flow in the loop of henle
- blood flow in the medulla is slow
- maintains medulla hyperosmolarity (the capillaries move freely to permeable ions, urea and water )
how is the role of ADHimportant in water reabsorption in the collecting ducts and fluid inside the tubule?
ADH regulates water absorption and allows more water to be reabsorbed in the CORTICAL collecting duct by inserting aquaporins
how is counter current exchange different in the vasa recta
in the vesa recta( the capillaries, not the nephron)
- water moves from descending limb to ascending limb
- NaCl moves from ascending limb to the descending limb
(remember its the opposite than the loop of henle)
How does the vasa recta prevent the washout of the medullary osmotic gradient?
A) By actively pumping NaCl into the interstitial space to maintain osmolarity.
B) By keeping blood flow slow and allowing passive exchange of water and solutes.
C) By increasing its permeability to water only when ADH is secreted.
D) By absorbing all the urea and preventing its recycling.
By keeping blood flow slow and allowing passive exchange of water and solutes.
Why is urea recycling important for medullary osmolarity?
A) It increases the concentration of NaCl in the ascending limb.
B) It creates a hyperosmotic environment, enhancing water reabsorption from the collecting duct.
C) It prevents excessive water loss in the descending limb of the Loop of Henle.
D) It decreases the effectiveness of the countercurrent multiplier.
It creates a hyperosmotic environment, enhancing water reabsorption from the collecting duct.
Urea is trapped and recycled in the medulla, increasing osmolarity, which pulls water out of the collecting duct when ADH is present.
How does the collecting duct respond to changes in ADH levels?
A) When ADH is high, the collecting duct becomes impermeable to water, leading to dilute urine.
B) When ADH is low, the collecting duct actively pumps water into the interstitial fluid.
C) When ADH is high, aquaporins allow water to leave, making the urine more concentrated.
D) When ADH is low, NaCl is actively transported out of the collecting duct to conserve wat
C) When ADH is high, aquaporins allow water to leave, making the urine more concentrated.
*ADH loves holding onto water
how does the minimal uptake of urea in the vasa rectaspace help maintain high osmolarity in the medulla?
minimal uptake by the vasa recta maintains high osmolarity by trappincg and recycling urea in the interstitual space, contributing to the hyperosmotic environment, allowing for water reabsorption
