Regulation of ECF Volume - Pt 2 Flashcards
What does aldosterone promote?
Na+ reabsorption
What does atrial natriuretic peptide (ANP) promote?
Na+ excretion
What happens if aldosterone is given to normal subject on adequate Na diet?
There will be Na retention and K loss
Weight gain of 2-3kg due to Na and H2O retention
After a couple days - spontaneous diuresis occurs secondary to volume expansion although K loss persists
Where does aldosterone cause Na reabsorption and K secretion?
Both at distal tubule
What does retention of water and Na cause?
Volume expansion and stimulation of ANP from atrial cells
What does stimulation of ANP from atrial cells cause?
Loss of Na and H2O - natriuresis
Can inhibit secretion of renin, and generally opposes the actions of angiotensin II
Why does ANP override aldosterone on Na reabsorption?
Volume expansion - aldosterone escape
What is ANP secreted by atrial cells in response to?
Expansion of ECF volume
Where do natriuretic peptides act on and effects?
Hypothalamus - less vasopressin
Kidneys - increased GFR and decreased renin
Adrenal cortex - less aldosterone
Medulla oblongata - decreased BP
What happens in uncontrolled DM where BG conc. levels not in control?
High plasma glucose level exceeds max. absorptive capacity in proximal tubule - glucose remains in tubule and exerts osmotic effects to retain H2O
What happens when H2O is retained in the proximal tubule?
Na conc. in lumen is decreased as Na is present in larger volume
Na reabsorption is decreased
How does Na gain access to proximal tubule cells?
Passive diffusion down a conc. gradient created by active transport out of basolateral surfaces
What is decreased Na reabsorption effect on glucose reabsorption?
Decreased as shares the same symport as Na
What happens in descending limb of Henle if excess glucose and Na?
Reduced movement of H2O into interstitium as osmotic effect to retain H2O
Fluid is then not as concentrated
What does less concentrated fluid in the ascending limb lead to?
NaCl pumps are gradient limited so medullary interstitium is much less - reduction in H2O and NaCl reabsorbed in loop of Henle
What happens to the interstitial gradient in loop of Henle during uncontrolled DM?
Gradually abolished
Then large volume of NaCl and H2O delivered to distal tubule
Under normal conditions, what does a large volume of NaCl and H2O delivered to distal tubule mean?
Excess ECF volumes and therefore need to get rid of NaCl and H2O
What happens when macula densa detects high rate of delivery of NaCl?
Renin secretion will be suppressed and Na reabsorption at distal tubule will be decreased
So normal response accelerates the uncontrolled DM problem
What is normal reabsorption of NaCl and H2O in renal tubule?
65-75% NaCl and H2O reabsorbed in proximal tubule
15-20% in loop of Henle
5-20% from distal tubule to collecting duct
What is the osmotic diuresis of uncontrolled DM?
Decreased reabsorption of NaCl and H2O in proximal tubule, loop of Henle, and distal tubule
Wrecks interstitial gradient so decreased ability of ADH to conserve H2O
So excrete 6-8l of urine a day
What can osmotic diuresis lead to?
Hypovolaemia
What happens when a large isotonic urine amount is excreted?
Decreased plasma volume
Which stimulates ADH release via baroreceptors but not effective
Why is ADH not effective in uncontrolled DM?
Interstitial gradient has run down
What are the results of uncontrolled DM?
Severe salt and water depletion
Raging thirst
Then hypotension can lead to hyperglycaemic coma
What cause a hyperglycaemic coma?
Inadequate BF to brain
What can any solute in tubule lead to?
Osmotic diuresis - NaCl or urea
What does the active transport mechanism that operates on luminal surface of think ascending loop of Henle?
K+ ions as well as NaCl
Na+-K+-2Cl- co transporter
What can loop diuretics also cause?
K+ ion wasting
