ECF Regulation 2 Flashcards
What promotes Na excretion?
ANP
What is the function of ANP?
Regulate Na excretion
Aldosterone promotes what?
Na+ reabsorption
K+ secretion
How does aldosterone increase weight?
Retention of water following ↑Na+
How does increased volume cause Na+ excretion?
↑Na+ = ↑water
↑water = ↑volume
↑volume triggers ANP from atrial cells
↑ANP = Natriuresis
Aldosterone acts where?
Distal tubule
What is Conn’s syndrome?
Primary hyperaldosteronism due to tumour of adrenal cortex
Too much ANP
How does Conn’s syndrome present?
Hypokalemia
NO hypernatraemia
ANP is secreted in response to what?
Expansion of ECF volume
What is the action of ANP?
Inhibit renin
Oppose actions of angiotensin II
What is the effect of ANP on the hypothalamus?
Reduced ADH release
What is the effect of ANP on the kidney?
Decreased renin
Increased GFR
(more salt and water excretion)
What is the effect of ANP on the adrenal cortex?
Less aldosterone
What is the effect of ANP on the medulla oblongata?
Decreased blood pressure
Why does excess glucose in the collecting duct cause diuresis?
Glucose in the tubule has an osmotic effect and H2O is retained
The osmotic effect in the proximal tubule has what effect on sodium?
Dilution - reducing the driving force of Na into the cell (the gradient)
Why does excess glucose in the proximal tubule cause reduced Na reabsorption?
Main driver of reabsorption is the gradient, excess glucose means excess water which means ↓ [Na]
How does reduced Na reabsorption effect glucose?
Na+ and Glucose share a symport
If Na+ isnt taken up, glucose isnt either
How does uncontrolled diabetes effect the descending limb?
Excess glucose and Na+ in the descending loop exerts an osmotic effect - retaining H2D
Fluid in descending limb is not as concentrated
How does uncontrolled diabetes effect the ascending limb?
Fluid arriving is less concentrated
NaCl pumps are gradient limited, so it stays in the tubule
What is the effect of uncontrolled diabetes on the interstitium?
Similar to loop diuretic - loss of interstitial gradient
In uncontrolled diabetes, what happens at the distal tubule?
Large volumes of NaCl and H2O are delivered
Large volumes of NaCl and H2O in the distal tubule have what pathological effect?
Macula Densa detects high levels of NaCl, so it will inhibit secretion of renin
What is the net effect of uncontrolled diabetes on the loop of henle?
Loss of interstitial gradient
Very little NaCl or H2O is reabsorbed
What should the osmolarity of the distal tubule be?
100mOsM
What does the Macula densa do when detecting a high rate of NaCl delivery?
Supress renin secretion
Leading to reduced Na+ reabsorption at distal tubules
How much NaCl and H2O is reabsorbed at the proximal tubule?
65-75%
How much NaCl and H2O is reabsorbed at the distal tubule/collecting duct?
15-20%
How much NaCl and H2O is reabsorbed at the loop of Henle?
5-20%
What is the most important factor controlling reabsorption of NaCl and H2O in the proximal tubule?
Oncotic pressure
How does diabetes affect the collecting duct?
Abolishing the interstitial gradient means water no longer flows down that gradient into the vasa recta from the lumen of the collecting duct
What sort of urine will be excreted in uncontrolled diabetes?
Large volume of nearly isotonic urine
What will the net effect of large volumes of nearly isotonic urine being excreted be?
Decreased plasma volume
Severe salt and water depletion
Uncontrolled DM can produce urine up to what volumes?
6-8L/day
What is the cause of hyperglycaemic coma?
Inadequate brain perfusion due to hypotension
What is the cause of hypoglycaemic coma?
Inadequate glucose for the brain
Why does baroreceptor activation in uncontrolled diabetes not cause a reduction in diuresis?
↓baroreceptor = ↑ADH, but there is no interstitium gradient for water to follow
Why is over-excretion of glucose not self-limiting in uncontrolled diabetes?
Liver - glycogenolysis/gluconeogenesis
How do Loop diuretics cause K+ wasting?
Active transport mechanism on luminal surface is Na-K-2Cl-cotransporter
Blocking Na absorption also blocks K+ ion absorption
