Renal System Flashcards
What are the five classes of diuretics?
1) Carbonic anhydrase inhibitors
2) Loop Diuretics
3) Thiazide Diuretics
4) Potassium-sparing diuretics
5) Osmotic diuretics
How do carbonic anhydrase inhibitors mainly produce their diuretic effect?
Reducing reabsorption of bicarbonate in the proximal convoluted tubule.
Describe the mechanism of action for carbonic anhydrase inhibitors
1) They inhibit the function of carbonic anhydrase
2) This prevents H2CO3 from being converted into H2O and CO2 (in the lumen)
CO2 and H2O from being converted into H2CO3 in the cell.
3) H2CO3 (bicarbonate) is lost in urine
H+ isn’t available to be pumped out of sodium hydrogen ion exchanger and Na+ is not reabsorbed (Water always follows sodium) so is lost in urine
Why do carbonic anhydrase inhibitors have a mild diuretic effect?
Because they act at the proximal convoluted tubule and reabsorption of Na+ and H2O can occur later in the nephron
What are some of the side effects of carbonic anhydrase inhibitors?
Hypokalemia - Caused by increased sodium delivery to the distal nephron and its reabsorption there in exchange for potassium
Metabolic acidosis (increased plasma acidity) - H2CO3 is wasted which usually acts as a buffer in the blood
How do loop diuretics produce their diuretic effects?
Inhibit sodium-potassium-2-chloride cotransporter in thick ascending limb
Where are 100% of amino acids and glucose reabsorbed in the nephron?
The proximal convoluted tubule
Where is 90% of NaHCO3 (Sodium Bicarbonate) reabsorbed?
The proximal convoluted tubule
Where are 65% of Na+, K+ and H2O reabsorbed?
The proximal convoluted tubule
What is secreted in the descending loop of of henle?
H2O
The walls are impermeable to sodium
What is reabsorbed in the thick ascending limb of the loop of henle?
Na+ passively (as water is impermeable here so cannot be reabsorbed meaning sodium leaves)
Na+ actively (via sodium-potassium 2 chloride co-transporter)
Describe the mechanism of action of loop diuretics
1) The Na+-K+-2Cl- co-transporter is inhibited, reducing the level of these ions in the cell.
2) The concentration of K+ (owing to the co-transporter and ATPase on interstitial side) in the cell decreases.
3) This means K+ does not leak out of the cell, therefore no driving force is created for paracellular reabsorption of Mg2+ and Ca2+.
4) Loss of water owing to Na+ (and other ions) lost
Normally the Na+-K+-2Cl- co-transporter causes reabsorption of these ions in the ascending limb. The Na+ K+ ATPase exchanger allows K+ into the cell and Na+ into the blood, which causes a high level of K+ in the cell. K+ usually leaks out of the cell into the lumen, creating a +++ outside the cell. This electrical driving force = paracellular reabsorption of Mg2+ and Ca2+.
What are the side effects of loop diuretics?
Electrolyte imbalance
Acute blood volume loss = acute hypovolemia
Ototoxicity - damage to hearing (the Na+-K+-Cl- co-transporter is also in ear)
Some of them compete with transport of uric acid (blocking secreation) = hyperuricemia and worsening of gout
What hormones act on the principle cell in the collecting duct?
What are their actions?
Aldosterone - increased Na+ reabsorption + increased K+ secretion
Antidiuretic hormone - increases water permeability and therefore water reabsorption
What hormones act on intercalated cells in the collecting duct?
What does this hormone cause this cell to do?
The primary function of the cell is to recreate H+ and reabsorb K+ - this is regulated by aldosterone
