Regulation of Plasma Osmolarity Flashcards
For body balance of water, what is normal gain and loss number-wise? What contributes to gain, and what contributes to loss? When does kidney excrete more water or less water, osmolarity-wise? What happens to CNS with any deviations in plasma osmolarity?
2500 mL for both; for gain, think of ingested food, fluids, and metabolism, and for loss, think of urine (regulated) and feces, skin/sweat, exhaled air; Excrete more when hypoosmotic, excrete less when hyperosmotic; Compromised function because of transmembrane Na and K gradients changed
What is urine when (U/P)osm is =, 1? What would be the ECF osmolarities in those cases? For a case of hypotonic urine, what does that indicate the kidney is trying to do? What will a decrease in osmolarity do with respect to ADH?
Isotonic, hypotonic, and hypertonic urine; for each case, ECF osmolarity is the same as the urine; kidney trying to minimize and correct plasma hypoosmolarity by eliminating water in excess of solutes; induce decrease in ADH, and vice versa if you had increased osmolarity
What is osmolar excretion equal to? What is OE typically equal to numerically? With high water intake vs. restricted water intake, what happens to Uosm? What does that mean in terms of how the kidney can dilute or concentrate urine?
OE = Uosm x V; 600 mOsm; Uosm can go down to 30 mOsm (20 L/day of urine) or up to 1200 mOsm (.5 L/day of urine); Dilute it to 10-fold less than plasma and concentrate it to 4-fold more than plasma!!!
In the case of a deficit of water consumption, what happens to plasma osmolarity and what is a way to minimize this change in plasma osmolarity? What if you had too much water intake?
Increases; minimize excretion of water without a change in solute excretion; Decreases; excrete the water consumed without change in excretion in solute!!!
What is free water defined as? What does it mean when the kidney excretes a concentrated urine with respect to (U/P)osm ratio and water relative to solute?
Water not osmotically obligated to remain in the tubular fluid due to solute being there; It means that the ratio is >1 and water is being reabsorbed in excess of solute to decrease plasma osmolarity
What does increase in osmolarity lead to with respect to ADH? What about a decrease in osmolarity?
Increase, decrease
What happens if the kidney excretes a dilute urine regarding the (U/P)osm ratio and what happens with water relative to solute?
It means that (U/P)osm ratio is <1 and more water can be taken in excess of solute and be added to the tubular fluid, decreasing hypoosmolarity and concentrating plasma
What is “free water” clearance of water equal to? What can be substituted for one of the terms? When would kidney neither add or remove free water from plasma? What if (U/P)>1, Cosm>V, and CH20 is consequently 0? What about a (U/P)
CH20 = V - Cosm; Cosm = UosmV/Posm; (U/P)osm = 1, Cosm = V, CH20 = 0; Means that water will be retained to add to the ECF since a hypertonic urine is being made; Water will be added to tubular fluid from ECF, meaning a positive free water clearance
In the case of hypertonic urine, how can negative free water clearance be conceptualized?
Volume of distilled water that needs to be added to make hypertonic urine isotonic to plasma
In solute balance, what does consuming a diet low in solute mean for water clearance? What about high in solute?
Increase neg free water clearance, decrease pos free water clearance, alllow for more “free water” that can be reabsorbed; Opposite of when consuming low solute, meaning more free water is “osmotically obligated” to stay in the tubular fluid and less is available for reabsorption
With solute balance and 600 mOsm/day consumed, what is osmolarity of largest and smallest volumes of urine? How much can be excreted per day? With solute balance and 1200 mOsm/day consumed? How much can you excrete per day? Which values are indicative of pos free water clearance and neg?
30 and 1200, respectively; 20 and .5 L; 30 and 1200 respectively; 40 and 1.0L; 20 and 40 are positive water clearance since more water is in urine, .5 and 1 are negative since you’re really concentrating the urine
Bottom line, what does consuming a diet low in solute mean for free water clearance, pos and neg? And for high solute?
Increase neg, decrease pos; vice versa
Where in the nephron can urine be diluted? What can help with concentrating urine? What do these segments permit in terms of water clearance?
Thin and thick ascending limbs, along with distal convoluted tubule; Solute reabsorption in thick ascending limb and consequent osmotic equilibration of tubular fluid in collecting duct with hypertonic interstitium; former permits positive free water clearance, latter with negative
Why does the kidny not correct increase or decrease in plasma osmolarity by secreting or reabsorbing solute, respectively?
Corrects changes in plasma osmolarity, but would change plasma volume and cause isotonic fluid loss or retention, substituting hypo/hypervolemia for hypo/hyperosmolarity
What is relative osmolarity of tubule fluid to plasma in prox tubule? Trhough loop of Henle? At end of loop of Henle? What about at the end of the collecting duct? What four parts does ADH/AVP act on? With no ADH, which type of free water clearance is favored?
1; above one; below one; above or below one based on if ADH/AVP is present; initial and cortical collecting tubules, outer and inner medullary collecting ducts; positive
