Lecture 5. The Role Of The Kidney In Regulating Total Body Na+ Flashcards
Na+ and H2O outputs are primarily under the influence…
Of the kidney. Which is filtering your plasma and determining according to what hormones are present. How much sodium or water you are going to pee out
What CANT the kidney do in regards to Na+ and H2O?
The kidney
CANNOT
Correct for inadequate dietary sodium and water
What is the “pressure natriuresis” mechanism?
Kidney/body fluid “pressure natriuresis” mechanism.
Pressure natriuresis mechanism,
Relationship between sodium, ECF (plasma) volume and blood pressure (MAP)
If sudden drop in MAP or decreased arterial pressure leads to less urinary excretion of sodium and water this helps conserve plasma volume and bring MAP back up to normal.
If sudden increase in MAP or increased arterial pressure, will have greater urinary excretion of both sodium and water, this reduces plasma volume and contributed to reduction in mean arterial pressure.
High total Na+ leads to …
High plasma (ECF) volume and high CVS pressure
How does the body sense changes in Na+ levels?
There are no sodium receptors in the body.
(1) cardiovascular stretch-sensitive & baroreceptors (atria, veins, arteries)
(2) renal sensors (intrarenal baroreceptors, macula densa)
Stretch-sensitive baroreceptors in the kidney.
Whats happening during diahorrea?
What control mechanisms come in?
Diahorrea–> your losing salts and fluids. You will want to decrease the amount of sodium and water your losing through urine. How to do this?
Can decrease the glomerula filtration rate (GFR)
- losing sodium and water
- decreased plasma volume
- decreased venous pressure, venous return, atrial pressure, EDV, SV and CO
- decreased arterial pressure (MAP)
This will decrease the net glomerula filtration pressure (NFGR) which means a decrease in the hydrostatic pressure driving filtration. Thus you will have decreased GFR and thus decreased levels of sodium and water excreted in urine.
Decreased arterial pressure will then increase activity of sympathetic renal nerves (baroreflex?). This will constrict the afferent arteriole, which decreases NFGR and thus GFR. And thus decreased sodium and water in urine excreted.
Decreased MAP or arterial pressure will
A decrease in the MAP or arterial pressure will also bring into play baroreceptor reflex (the ones with discussed in CVS.
- SA node, contractility (ventricles), veins, arterioles.
What does aldosterone do?
Controls sodium reabsorption in distal tubule and collecting ducts. Sodium reabsorption here controls only about 2% of the filtered load.
Where is aldosterone secreted from?
Adrenal glands
By the zona glomerula cells.
It is a steroid hormone. Mineralcorticoid
Variations in plasma aldosterone offers fine control of sodium reabsorption.
What are the actions of aldosterone on the late distal tubule and collecting duct?
Aldosterone- steroid hormone.
Diffuses through cell membrane and binds onto a mineralcorticoid receptor on the nucleus of the cell.
The ultimate effect is protein synthesis of proteins involved in reabsorption of sodium. Increased production of sodium channels on the luminal membrane and increased synthesis of Na+/K+ ATPase pumps on the basolateral membrane.
Because we are talking about protein synthesis. This process is much slower than reabsorption of water. Takes DAYSSS to get rid of excess sodium.
Na+ and H2O intake are controlled by…
Thirst and salt appetite.
Affect of ingesting 0.3 mol sodium chloride?
Initial effect: increase ECF osmolarity.
Final effect: increase osmolarity of ECF and ICF compartments
Increase ECF volume. Decrease ICF volume
Cells shrink
How does the body sense changes in the Na+ levels?
No Na+ receptors in the body
Cardiovascular stretch-sensitive & baroreceptors (atria, veins, arteries)
Renal sensors (intrarenal baroreceptors, macula densa)
How does ANP lower BP?
ANP Increases urinary sodium excretion.
1) acts on collecting ducts to decrease sodium reabsorption
2) inhibits the secretion of renin, thereby inhibiting secretion of aldosterone, thereby inhibiting reabsorption of sodium
3) increases GFR
By dilating afferent arteriole and constricting efferent arteriole.
Increased GFR, less time for reabsorption of the filtered load, so increased excretion.
So less sodium is reabsorbed and thus lowered BP
