Regulation of ECF II Flashcards
What is the effect of atrial natriuretic peptides of Na+?
Promotes Na+ excretion
What is the effect of aldosterone given to a Pt on an adequate Na diet?
There will be Na+ retention and K+ loss in the blood. There will be a weight gain of 2-3kg due to the Na+ and H2O retention. After a couple of days, a spontaneous diuresis occurs secondary to volume expansion, although K+ loss persists.
What is the effect of aldosterone on Na and K?
Distal tubule:
↑ Na+ reabsorption
↑ K+ secretion
What is the effect of aldosterone due to changes in Na and K?
- ↑ weight because of retention of H2O with ↑ Na+
- Volume expansion
- Stimulation of release of ANP from atrial cells
- Loss of Na+ and H2O ie Natriuresis
But aldosterone ->. continued K loss because still ↑ K secretion
What is the effect of ANP on aldosterone?
ANP overrides aldosterone effects on Na reabsorption because of volume expansion = ‘aldosterone escape’ - ensures the body doesn’t overload with too much salt
What is Conn’s Syndrome?
Hyperaldosteronism, due to a tumour of the adrenal cortex, they are K+ depleted but not hypernatraemic (due to ANP counter-effect)
What secretes ANP?
Atrial cells in response to expansion of ECF volume and causes natriuresis, loss of Na and H2O in urine
What is the action of ANP?
Inhibit secretion of renin, generally oppose the actions of angiotensin II
What are the effects of atrial natriuretic peptides?
- Hypothalamus -> less ADH
- Kidney -> Increased GFR, decreased renin
- Adrenal cortex -> less aldosterone
- Medulla -> decreased blood pressure
What occurs in uncontrolled DM in terms of reabsorption?
[BG] is not kept within strict control, the high plasma glucose level exceeds the maximum reabsorptive capacity in the proximal tubule (out with Tm)
What is the effect of XS Glc in the proximal tubule in uncontrolled diabetes?
- Exerts osmotic effect to retain H2O
- Therefore [Na] in the tubule is decreased
- > Na reabsorption will be decreased as concentration gradient decreased
- > Therefore decreased ability to reabsorb Glc as it shares a symport with Na
What is the effect of XS Glc in the Loop of Henle in uncontrolled diabetes?
- In the descending limb, reduced reabsorption of H2O as Glc and ↑ Na exerts osmotic effect to retain H2O in tubule
Therefore, fluid is LoH not as concentrated, so conc. gradient is decreased, so less Na transported into interstitium
- So fluid entering ascending limb is less concentrated and as NaCl pumps are gradient limited, medullary interstitial gradient is much less (as [Na] decreased in tubule)
So large volume of NaCl and H2O delivered to distal tubule AND interstitial gradient is gradually abolished. Decreased ability of ADH to conserve H2O.
What is the effect of XS Glc in the distal tubule in uncontrolled diabetes?
- Under normal conditions, a large volume of NaCl and H2O delivered to the distal tubule means there is excess ECF volume and therefore need to get rid of NaCl and H2O.
The macula densa will detect the high rate of delivery of NaCl so that renin secretion will be suppressed and therefore Na+ reabsorption at the distal tubule will be decreased.
Describe the urine that is produced in uncontrolled DM
A large volume of nearly isotonic urine will be excreted -> decreased plasma volume
Pts produce urine volumes of up to 6-8 l/day, causing severe salt and water depletion.
What is the effect of decreased plasma volume caused by large volume of urine produced in uncontrolled diabetes?
Stimulates ADH release via baroreceptors (decreased volume) but is ineffective as interstitial gradient run down
