Exam 3- Urine Concentration and Dilution in the Kidneys - Knaak Flashcards
What is responsible for the yellow color of urine?
Urochrome (a product of hemoglobin) billirubin or urobillin)
What does darker urine an indication of?
Your body trying to conserve water.
What is most/least concentrated your urine can be?
30 mOsm/L to 1200 mOsm/L (Osmolarity)
How much intake do we take in on average per day?
What is the least amount that we must excrete per day?
2500 mOsm/L.
600 mOsm/L.- if not toxicities will occur
What makes up the least/ most source of OUTPUT?
Feces (least at 4 percent)
Urine (most at 60 percent)
What makes up the least/most INPUT?
Metabolism (least at 10 percent)
Beverages (most at 60 percent)
Dehydration Equation- Obligatory Urine Volume
600 mOsm/day divided by 1200 mOsm/L = 0.5 L/day
Over Hydration Equation - Obligatory Urine Volume
600 mOsm/day divided by 30 mOsm/L = 20 L/day
Why can’t we drink salt water?
It has 2000 mOsm.
2000 mOsm + 600 mOsm divided by 1200 mOsm= 2.2 L/day
What is happening to the following components as water is being ingested?
- Osmolarity
- Urine Flow Rate
- Urine Solute Excretion
- plasma
- Osmolarity: decreasing (urine beind diluted)
- Urine Flow Rate: increasing and getting rid of solutes
- Urine Solute Excretion: isn’t changing much???
- plasma: stays the same
What is the osmolarity trend in the kidney?
Osmolarity increases from the cortex to the medulla.
downward through the renal pyramid towards the calyces.
What is the mOsm of the CORTEX?
300 mOsm
What creates the osmolarity gradient in the kidneys?
The nephron loops and the vasculature
Where is ADH located in the nephron and what is it’s function?
It is located in the collecting duct where it allows for the reabsorption of water via aquaporins in times of dehydration. Final osmolarity= 30 mOsm (dilute urine)
As we go through the nephron, what happens to mOsm?
- descending tubule
- ascending tubule
- collecting duct
- descending tubule: losing water ONLY = increase in osmolarity (mOsm)
- ascending tubule: losing solutes ONLY= decreasing osmolarity (mOsm)
- collecting duct: losing more solutes -ADH is present = decreasing osmolarity (mOsm) even more.
What would happen if ADH was not present?
Water would not be reabsorbed and urine would go straight out?
What is the normal mOsm for blood?
300 mOsm
What activates ADH?
-INCREASED levels of Osmolarity (dehydration)
How is ADH activated?
- INCREASED osmolarity = osmoreceptor release of ADH (pituitary gland)
- ADH= increases permeability in the collecting ducts/tubules and water is absorbed.
- result= back to homeostasis
What mediates ADH (vasopressin) activation? How?
V2 (Gq) receptors on principal cells.
- ADH binds to the V2 receptors
- this increases exocytosis and decreases endocytosis
- increase in aquaporin release + decrease in break down. New + old ones are staying present.
Where does the counter multiplier and the countercurrent exchanger occur?
counter multiplier (tubules) countercurrent exchanger (vasa recta) - juxtamedullary nephrons only
What is required to make concentrated urine during dehydration?
Vasopressin ADH
What forms and maintains the interstitial osmolarity gradient?
countercurrent mechanism
What is responsible for 40 % of the medullary osmotic gradient?
Urea
