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.
What happens when ECF volume changes in regards to RBF ?
it can decrease by sympathetic nerves, catecholamine and AG-II
What happens when GFR changes?
The PCT reabsorbs a constant fraction of the filtered load. So when GFR increases, the PCT reabsorption also increases. This is called glomerulotubular balance.
What is the Renin Angiotensin system?
essentially it is a multistep pathway that maintains ECF volume and BP.
Steps of the Renin angiotensin system?
- ) renin is released which is stimulated hy sympathetics due to low MAP or low NaCl delivery to the macula densa
- ) this converts angiotensinogen to angiotensin I
- ) then angio tensin converting enzyme (ACE) which is found in endothelial cells of all blood vessels converts angiotensin I to Angiotensin II
- ) Angiotensin II stimulates the release of aldosterone
Angiotensin II is a …… vasoconstrictor which …… RPF, but because its dominant effects is on the ……. arteriole, it mainains glomerular …… and reduces … at the peritubular capillaries. These effects ….. GFR, …. filtration fraction and peritubular capillary osmotic pressure and ….. proximal tubule reabsorption of Na and water.
- potent
- decreases
- efferent
- Pc (Capillary hydrostatic pressure)
- Pc
- maintain
- increase
- increase
What does Angiotensin II stimulate in the proximal tubule?
Na-H exchange and Na-bicarbonate reabsorption
What does angiotensin II stimulate in the adrenal cortex?
release of aldosterone
What is aldosterone ?
potent mineralocorticoid that promotes active sodium reabsorption along the DT and CD.
Aldosterone is released in response to what?
- Ang II
- high plasma K
- large decreases in plasma Na
what is the stimulus for the release of renin?
- JG (juxtaglomerular) cells pressure sensitive, decrease in pressure causes and increase in renin secretion.
- sympathetic neurons can also stimulate the release of renin
- macula densa - JG cells here and it monitors GFr and pressure
What are the function of AG II?
- )
- aldosterone secretion
- na reabsorption
- ecf volume
- blood pressure - ) increase output of CVCC, increase HR, increase CO, increase BP
- )Thirst
What does aldosterone do?
high aldosterone results in increase na erabsorptionand it effects the final 2-8% of Na remaining in the nephron.
What is aldosterone released from?
High pottasium or low osmolarity in the adrenal corrtex.
Also indirectly by angiotensin II
Where is ANP stored?
granules in the myocytes of the atria
What is the effect of ANP on the kidney?
increase in GFR and so receptors in the brain inhibit the release of renin. TH enet effect is to promote Na+ excretion.
What does ANP do?
- it is a potent vasodilator that increases RPF, GFR and peritubular Pc which increases filtration and reduces prximal tubule reabsorptioin of Na and water.
- inhibits Na reabsorption at the CD
What senses changes in ECFV?
stretch receptors at the low pressure side of circulation such as the atrial stretch receptors. When they are stretched they send fewer neural inhibitory impulses to the central sympathetic nervous system.
