Regulation of Na, osmolarity and ECFV Flashcards Preview

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Flashcards in Regulation of Na, osmolarity and ECFV Deck (65)
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Unregulated fluid loss occurs due to

- sweat
- stool
- respiratory


Regulated fluid loss occurs due to

- urine can vary from 50-1200 mOsm
- measured as specific gravity (1.002-1.050)
- obligate urine volume to eliminate waste products


Fluid intake

- stimulus generates desire for and allow the intake of water


Electrolyte loss

Occurs with accompanying water loss
- unregulated: sweat, stool
- regulated: renal


Electrolyte intake

Cravings or hunger
- depends on availability


Why is the electrolyte balance across cell membranes essential?

- partitioning water between intra and extracellular fluid spaces
- keeping cells from shrinking/swelling
- allows for electrical charge related actions


In a person after drinking 1 liter of water:

Little change in
- plasma mOsm
- urine electrolyte conc.
Big change in
- urine mOsm
- urine production
*primarily regulated by ADH in the distal segments of the nephron*


What happens when there is excess water in the body?

Body fluid osmolarity is reduced, kidney excretes urine with a low osmolarity


What happens when there is a deficit of water in the body?

Extracellular fluid osmolarity is high, kidney excretes urine with a high concentration


Kidney can excrete a large volume of dilute urine or a small volume of concentrated urine without major changes in ______

Rates of excretion of solutes (Na and K)


____ of sodium and water excretion is regulated reabsorption

- one can be regulated independently of the other


Formation of dilute urine

Decrease reabsorption of water


How do you decrease reabsorption of water?

Decrease ADH release, which decreases water permeability of the distal tubule, cortical and medullary duct


In the proximal tubule, water and solutes are reabsorbed ______

At the same pace (iso-osmotic)


Water reabsorption in the thin descending loop

Passive due to interstitial concentration gradient
- unregulated
- could get renal medullary washout due to overconsumption of water


When the renal medulla is no longer hypertonic, the kidney can no longer ______

Concentrate urine


Remaining urine after the thick ascending loop becomes more ____ without _____

Dilute; any increase in volume


The ability to form concentrated urine is dependent on what 2 things?

- ADH: production in the CNS and appropriate tubular response
- renal medullary hypertonicity


Continuous reabsorption of electrolytes adds to _____

Increasing renal medullary hypertonicity


What are the 2 basic requirements for forming concentrated urine?

- high level of ADH
- hihg osmolarity of renal medullary interstitial fluid


How does increased reabsorption of water occur?

Increase ADH release
- increases water permeability of distal tubule, cortical and medullary collecting ducts
- increases urea permeability of medullary collecting duct, which increases medullary tonicity


Countercurrent multiplier mechanism

Process by which renal medullary interstitial fluid becomes hyperosmotic
- depends on arrangement of loops of Henle and vasa recta


Factors contributing to renal medullary hypertonicity

- active transport of solutes from thick ascending limb into medullary interstitium without reabsorption of water
- active transport of Na from medullary collecting ducts into interstitium (increased with aldosterone)
- facilitated diffusion of urea from medullary collecting ducts into interstitium (ADH)
- diffusion of small amounts of water into medullary interstitium, which is rapidly removed
- counter-current multiplier mechanism


Loop of Henle is only able to establish a ______ gradient

200 mOsm, before back diffusion of electrolytes results in equilibration


Why are juxtamedullary nephrons most susceptible to NSAID toxicity?

O2 tension decreases the deeper you go into the renal medulla, but the tubular epithelial cells are the most metabolically active as we progress to dehydration


What is a major reason for high medullary osmolarity?

Active transport of sodium and co transport of potassium, chloride, etc from thick ascending loop into the interstitum


Parallel current flow transfer is dependent on

- diffusion constant
- time/flow ratio
--> less transfer than counter current flow
--> once equilibrium is achieved there is no further exchange


Counter current flow is dependent on

- diffusion constant (same)
- time/flow ratio
--> overall greater transfer than parallel flow (utilizes whole contact area)
--> never reaches equilibrium, will always have a gradient directing flow


What helps preserve a high medullary interstitial fluid osmolarity?

The fact that the large amounts of water reabsorbed from the cortical collecting tubule is being reabsorbed into the cortex, instead of the medulla


What causes urea to diffuse out of the tubule into the renal interstital fluid?

High concentration of urea in the tubular fluid of the inner medullary collecting duct
- diffusion facilitated by urea transporters that are activated by ADH