Exam 3 Lecture: Formation of Urine Flashcards
What does osmotically active mean?
the solute contributes to generating an osomotic pressure = it will cause osmosis
What do osmolarity differences drive?
water movement in the loop, distal tubule, and collecting duct
At any point in the descending limb, how is the osmolarity in the tubular fluid related to the interstitia surrounding it?
The osmolarity of the tubular fluid is always lower than the osmolarity of the interstitia surrounding it
What direction does water move in the descending limb?
water passively moves out of the descending limb
At any point in the ascending limb, how is the Na concentration in the tubular fluid related to the interstitia surrounding it?
the sodium concentration in the tubular fluid is always higher than the sodium concentration of the interstitia
What direction does sodium move in the ascending limb?
Na moves out of the ascending limb
What creates the osmotic gradient in the descending limb?
active reabsorption of Na in the early distal tubule
What is the active reabsorption of Na in the early distal tubule done by?
NKCC1
What occurs at the hairpin loop?
the osmolarity of the tubular fluid equals the osmolarity of the interstitium; the solutes creating the osmolarity is not the same
What is the high tubular fluid osmolarity in the hair pain due to?
Na
What is the high intersitial osmolarity in the hair pin due to?
Na and urea
What is the sodium concentration like at the distal straight tubule?
Na inside equals Na on the outside which is where NKCC1 comes into play
What is the tubular fluid like in the distal straight tubule?
hypotonic
What happens when there is no/low levels of ADH?
diuresis and water is expelled from animal urine
What happens when there are high levels of ADH?
antidiuresis and water is conserved by animal; water is reabsorbed back to blood and not wasted in urine
What are the stimuli for ADH release?
ECF osmolarity and ECF volume
What is a high ECF osmolarity sensed by?
osmoreceptors
What does high ECF osmolarity trigger?
the release of ADH
What is a low ECF volume sensed by?
baroreceptors
What does low ECF volume trigger?
ADH release
What are the functions of ADH?
changes collecting duct permeability to water, changes medullary collecting duct permeability to urea
How does ADH make collecting ducts more permeable to water?
it increases the expression of water channels in the luminal membrane of the epithelium
In the loop, why and where is water reabsorbed?
in the descending loop due to high interstitial osmolarity caused by Na and urea
In the loop, why and where is Na reabsorbed?
in the ascending limb due to the concentration gradient established by water reabsorption
Without ADH what happens?
no water is reabsorbed in either the distal tubules or collecting ducts
How does low ADH relate to ECF volume and ECF osmolarity?
reduces ECF volume, increase ECF osmolarity
How does high ADH relate to ECF volume and ECF osmolarity?
increases ECF volume, decreases ECF osmolarity
How much urine is created when ADH is present and is it diluted or concentrated?
a small amount of concentrated urine and high osmolarity
What is the role of urea?
to act as an effective osmole at the loop
In the distal tubule, what is the urea concentration like in the tubule vs the interstitia surrounding it?
the urea concentration in the tubule is higher than in the interstitia surrounding it creating a urea concentration gradient
What effect does ADH have on the diffusion of urea?
it allows passive diffusion to occur
Where is urea an ineffective osmole?
in the collecting duct
Where is urea an effective osmole?
in the loop
What does the increased interstitial urea concentration in the loop do?
increases the interstitial osmolarity around the loop, draws even more water out than normal, and leads to an even lower volume of concentrated urine being produced
What mechanisms make sure urea does not keep accumulating in the interstitum?
- ADH levels are reduced so urea does not accumulate
- ascending limb is kind of permeable to urea so it can move into the ascending limb and be recycled
- vasa recta is permeable to urea and can cycle it away
What is the vasa recta?
straight arterioles adjacent to the loop of Henle
What would happen if water that was reabsorbed into the interstitium at the loop and collecting duct were to stay?
it would dilute osmotic gradient and impair renal function
What is the goal of the vasa recta?
to remove water from the interstitium and keep Na in the interstitium
What is the difference between the loop of henle and the vasa recta?
The descending and ascending limb are both permeable to Na and H20 of the vasa recta
Since water is permeable in the ascending limb of the vasa recta, what does that mean?
water moves down the osmotic gradient into the ascending limb and is carried away from the medulla into the bloodstream
Since Na is permeable in the descending limb of the vasa recta, what does that mean?
Na can move into the descending limb if it wants to, so it does which allows Na to constantly circulate around the medulla
