Exam 3 - Lecture 38 (Formation of Urine) Flashcards
What is osmolarity?
[ ] of osmotically active atoms per L/kg solvent.
What is the normal osmolarity for canine ECF?
300 mOsm/kg
What is an effective osmole?
A molecule that cannot cross a membrane and so generates osmotic pressure.
In what osmolarity direction does water move?
Low –> high osmolarity
What causes water to move across a membrane?
Presence of an osmolarity gradient
What is an ineffective osmole?
Molecule that crosses a membrane and doesn’t contribute to tonicity.
What happens during countercurrent multiplication at the Loop of Henle?
Fluid moves in opposite directions in each limb and thing happening in one limb amplifies what is happening in the other.
What is the descending limb of the LoH permeable/impermeable to?
Permeable = H2O Impermeable = Na+
What is the ascending limb of the LoH permeable/impermeable to?
Permeable = Na+ Impermeable = H2O
What is the osmolarity of the fluid leaving the PT?
isoosmotic
What happens to interstitial osmolarity as you progress down the descending limb of the LoH?
Increases
What is the osmolarity of the descending limb of the LoH vs. the interstitial fluid?
Lower
What creates an osmotic gradient in the early DT?
ACTIVE reabs. of Na+
How does water leave the descending limb of the LoH?
passively
What happens at the hairpin?
Water has concentrated Na+ above interstitial [ ] so now there is an Na+ gradient; H2O reabs. stops
How does Na+ leave the ascending limb of the LoH?
passively down its [ ] gradient
How does Na+ leave the early DT?
actively
What is the end result of the countercurrent multiplication in the LoH (2 things)?
- Water and Na+ are reabs.
2. Hypotonic fluid delivered to DTs
Which statement about the physiology at the LoH is true?
A) Na+ is reabsorbed passively at the descending limb
B) Water is reabsorbed down an osmolarity gradient (low to high osmolarity)
C) Interstitial osmolarity decreases towards papilla
D) Distal tubule fluid is hypertonic to interstitium
B) Water is reabsorbed down an osmolarity gradient (low to high osmolarity)
Where is antidiuretic hormone produced?
Hypothalamus
From where is ADH released?
Posterior pituitary gland
What is the general role of ADH?
Determines whether kidney retains or expels water
What are the 2 triggers for ADH release?
- Changes in body fluid osmolarity
2. Changes is plasma volume or arterial pressure
What are osmoreceptors and how do they react?
Bundles of cells that are very sensitive to changes in ECF osmolarity; will shrink when ECF osmolarity is too low = release of ADH
What are baroreceptors and how to they react?
Specialized nerve cells sensitive to stretch; will trigger release of ADH when BP or volume is too low
Where are baroreceptors found?
aortic arch and carotid sinus
Where are osmoreceptors found?
hypothalamus
What 2 things does ADH change?
- Increases late DT and CT permeability to water thru aquaporins
- Changes medullary (inner medulla only) CT permeability to urea (increases exp. of urea transporters in the luminal membrane)
What is diuresis?
High production of urine/dilute urine; ADH is low/zero
What happens to water in the DT and CT if ADH is low?
Cannot be reabs. so only way for it to go is down the CT and into the urine
What is antidiuresis?
Low volume of concentrated urine produced; ADH is high
What happens to water in the DT and CT if ADH is high?
Most water is reabs. thru aquaporins, so very little amount goes down CT into the urine.
During diuresis, which of the following is true?
A) Medullary urea [ ] is relatively low
B) CT permeability to water is high
C) Water reabsorption in the descending limb of the loop is increased
D) Fluid in the CT is hypertonic to interstitium
A) Medullary urea [ ] is relatively low
Urea is an _____ osmole at the CT. Why?
ineffective bc it does not affect water reabsorption.
Urea is an _____ osmole at the descending limb of the LoH. Why?
effective bc H2O is reabsorbed more readily than normal when [urea] is high.
The vasa recta preserves medulla _____.
hypertonicity
What removes water that has been reabsorbed from the medullary CD and how?
vasa recta as a countercurrent multiplier
During diuresis, which of the following is true?
A) A small volume of concentrated urine is produced
B) Urea permeability in medullary CD is low
C) Na+ is reabsorbed in descending limb of LoH
D) ADH levels are high
E) Water reabsorption in the CD is high
B) Urea permeability in medullary CD is low
Mannitol can be used to change fluid retention in the kidney. It is freely filtered and acts as an effective osmole at the CD, increasing tubular fluid osmolarity. What happens to urine volume (ADH is present)?
A) It will increase
B) It will decrease
A) It will increase
