Concentration And Dilution Of Urine Flashcards
What is plasma osmolarity?
290 mOsm/L(we use 300 for calculations)
What happens when plasma osmolarity changes?
If this changes then.
-kidneys can either retain or excrete water. This process is called osmoregulation
Water regulation is independent of solute excretion
- To osmoregulate the urine can be very dilute or concentrated
- Thus depends on if Antidiuretic (ADH) is high or low
How are hypo-hyper and isoosmot8c ruined defined?
Hyperosmotic- above 300 mOsm/L
Isosmot8c urine- 300 mOsmoles/L
Hyposmoles- below 300 mOsmoles/L
How does the kidney dilute or concentrate the urine?
Solute wastes- 600 mOsm /day must be excreted in urine
-If maximum urine concentration ability is 120p mOsm/L, then the minimum ursine volume that needs to be excreted is 600/1200mOSM/day= 0.5L/day
This is called the obligatory volume. Normal urine volume is about 1.5-2.5L/day
What are the 3 processes that contribute to corticopapillary osmotic gradient?
- Countercurrent multiplication
- Urea recycling
- Slow rates flow
How does the medullary interstitium get so concentrated?
-Descending LH is water permeable not solutes
—Thin and thick ascending LH are impermeable to water
-Thick ascending LH pumps NaCl actively into the interstitium
- Thin ascending is permeable to NaCl
- Movement is passive
Collecting duct: depends on ADH
What generates & maintenance in the medullary interstitium is due to…
- ATP dependent solute transport
- Increase in medullary osmolarity
- Slow tubular fluid flow through vasa recta
This occurs throughout the length of the loop
There is a 200 mOsm gradient difference between the tubule & the interstitium
What is the function of urea in the counter current multiplier?
-Na+, K+, CL- can establish,y up to 600 mOsm
How do we get to 1200-1400 mOsm?
Through urea. Urea is the end-product of muscle metabolism
What are the sites of of tubular urea transport?
In the presence of ADH
-As the H2O is reabsorbed from CD, urea concentration rises
- ADH unregulates UTA1 & UTA3 transporters
- Urea diffuses passively via transporters into the interstitium
- Some of its secreted into both thin Loops of Henle
This is urea cycling.
50% is absorbed in proximal tubule. Of the 50% in the lumen after recycling 20% is excreted
How does the counter current multiplier work?
Urea is necessary for increasing osmolarity of inner medulla
Contributes to-half the hyperosmotic gradient
Urea is passively reabsorbed from the tubule(MCD)
-Requires ADH
Low protein states- urea is a by product of protein metabolism infants below age 1
Both have limited ability to concentrate urine
How do we stop the gradient in hyperosmotic interstitial fluid from simply disappearing?
Blood flow rates. Prevent medullary hypertonicity
Vasa recta: counter current exchangers
Describe counter current exchange in vasa recta
-Passive- no energy required
Downstream-gains NaCl & loses water, so plasma osmolarity increases to 1200 mOsm at the tip of the medulla
Upstream- it gains water & salt so plasma restores to 300 mOsm it drains into systemic circulation
How is osmoreceptors coupled to ADH secretion?
ADH is synthesized in the hypothalamus & stored in posterior pituitary & released if plasma osmolarity is high or fluid loss> 10%
Why does the loop of henle deposits more salt than water in the interstitium so;
Medullary interstitium becomes hypertonic- potential for urine concentration
What 8s the effect of low ADH?
Collecting duct is impermeable to water
No urea Reabsorption
Medullary slightly hyperosmotic
