Lecture 8 - salt balance Flashcards
Na, Cl and H2O are all ….. and so most (99%) of what’s filtered is …… . They are not normally ……
freely filtered
reabsorbed
secreted
How does Na+ reabsorption take place?
It is active and happens via a trasncellilar rpite that is powered by the basolateral Na-K-ATPase
How does Cl- reabsorption take place?
it is passive (paracellular) and active (transcellular). Both of these routes are coupled with Na+ reabsorption.
How does H2O reabsorption take place?
It takes place by osmoiss and secondary to reabsorption of solute especially Na+.
What will changes in Na+ concentrations do to the ECF volume.
Increase in Na+ concentrations will increase the ECF volume whereas decrease in Na+ concentrations will decrease the ECF volume.
how is the requirment for salt reabsoprtion or excretion measured in the body?
It is measured in terms of volume or pressure changes.
What are the different pathways for sodium output?
- ) Urine
- ) feces
- ) Sweat
How how Na is inhested a day and how much ends up in the diffrent output pathways?
Ingested - 120mM
Feces - 10 mM
urine - 100 mM
Sweat - 10 mM
How much Na is filtered and reabsorbed every day?
Filtered - 25,500
Reabsorbed - 25,400
What proportion of filtred Na is reabsorbed?
99 %
How much Na does the proximal tubule absorb?
65 %
How much Na does the thick ascending limb of the loop of henle reabsorb?
25 %
How much Na does the distal convuluted tubule and collecting duct reabsorb?
The rest - so about 9 percent
How much Na does the final urine contain?
Less than 1 %
What controls the reabsorption of Na?
Physiollogically controlled nuronally and hormonally.
Since such a huge amount of Na is …… , a small change in …… can result in a …. change in Na excretion.
Filtered, reabsorption rate, large
What do the primary active transport mechanism (Na-K-ATPase pumps) in the basolateral membrane do in nephron segments? Why is it significant?
THey keep intracellular levels of Na+ low and this is significant becaues low intracellular levels of Na+ means that the Na+ in the tubular lumen (which is at a higher concentration) can ,ove into the cell down its electrochemical gradient.
Why is plasma Na concentrations normally constant?
Because of ADH and thirst mechanism which maintains ECF volume by regulating the total body Na+. essentially, the input = output.
How much NaCl is ingested in a normal diet?
8-15 g a day or 150-200 mEQ/day
If we retain one day intake of sodium what would happen?
We would retain 1 L of water to maitain tonicity which will increase thebody water weight by 1 kg.
What happens in regards to regional handling of Na, Cl, and H2O in the proximal tubule?
iso osmotic reabsorption
What happens in regards to regional handling of Na, Cl, and H2O in the loop of henle?
seperation of salt and H2O
What happens in regards to regional handling of Na, Cl, and H2O in the distal tubule and collecting duct?
reabsorption is regulated
What are the mechanisms to regulate Na+?
- ) change in GFR - change in Na+ reabsorption
- ) renin-angiotensin-aldosterone - decreases Na+ excretion, ARDN (aldosterone responsive distal nephron)
- ) Atrial natriuretic peptide and other naturetics - increase Na excretion.