6. Control Of Volume Flashcards
What does a change in Na+ ion concentration in the extracellular fluid result in?
Affects the effective circulating volume, effecting BP.
How is Na consumed in the diet?
Salt.
Why do you need to add isosmotic solution to increase ECF?
So that plasma osmolarity doesn’t change.
Where in the nephron is the most Na+ absorbed?
Proximal convoluted tubule and thick ascending limb of the loop of Henle.
Where is the most water reabsorbed in the nephron (and so the most aquaporins are found here)?
Proximal convoluted tubule and collecting duct.
What 3 factors alter proximal convoluted tubule Na+ reabsorption?
Changes in osmotic pressure.
Changes in hydrostatic pressure.
RAAS.
What is pressure natriuresis?
Increased renal artery BP leading to increased sodium excretion.
What is pressure diuresis?
Increased renal artery BP leading to increased water excretion.
How is Na+ reabsorption altered when renal artery BP increases?
Reduction in the number of Na-H antiporters and reduction in Na-K ATPase activity in the proximal tubule.
What aquaporins are found in the proximal convoluted tubule?
AQP1.
AQP7.
What aquaporins are found in the collecting duct?
AQP2.
AQP3.
AQP4.
How is chloride reabsorbed from the nephron?
Transcellular (active) and some paracellular (passive) reabsorption. Couples to 3Na-2K-ATPase pumps. So when talk about Na+ reabsorption, Cl- is implied.
In which area of the proximal convoluted tubule are Na+ and Cl- mainly reabsorbed?
S2 and S3.
What 3 forces drive water reabsorption in the PCT?
Osmotic gradient established by solute absorption (increased osmolarity in interstitial spaces).
Increased hydrostatic force in interstitium.
Increased oncotic force in the peritubular capillary.
What part of the nephron is impermeable to water?
Thick ascending limb of the loop of Henle.
What is the purpose of water reabosprtion in the descending limb of the loop of Henle?
Concentration of Na+ and Cl- in the lumen of the descending limb, ready for active transport in the ascending limb.
Is Na+ reabsorption active or passive in the thin ascending limb of the loop of Henle?
Passive.
Which region of the nephron is particularly sensitive to hypoxia and why?
Thick ascending limb of the loop of Henle, as it uses lots of active transport channels to move Na+, K+ and Cl-, so is very metabolically active.
What part of the nephron is known as the diluting segment and why?
Ascending limb of the loop of Henle, as absorbs NaCl but not water.
In the late distal convoluted tubule and collecting duct, water permeability is variable depending on what hormone?
ADH.
What are the two regions of the DCT called?
DCT 1 (early). DCT 2 (late).
What area of the nephron is a major site for calcium reabsorption?
Distal convoluted tubule.
Describe the reabsorption of calcium once it has entered a DCT cell.
Cytosolic calcium immediately binds to cal Indian, shuttles calcium to the basolateral aspect of the DCT cell. Transported out of the cell into the blood across the basolateral membrane by sodium calcium exchanger (NCX).
What 2 hormones tightly regulate calcium reabsorption in the nephron?
Parathyroid hormone.
1,25-dihydroxyvitamin D (calcitriol).
What are the two cell types found in the cortical portion of the collecting duct? What ions do they reabsorb?
Principle cells - Na+. Intercalated cells (acid and bicarbonate secreting types) - Cl-.
