🚨Reabsorption of K+
✅ involves an H+
, K+-ATPase in the luminal membrane of the α-intercalated cells.
✅ occurs only on a low-K+
diet (K+ depletion). Under these conditions, K+ excretion can be as low as 1% of the filtered load because the kidney conserves as much K+ as possible.
b. Secretion of K+
⭕ occurs in the principal cells.
⭕ is variable and accounts for the wide range of urinary K+
excretion.
⭕ depends on factors such as dietary K+
, aldosterone levels, acid–base status, and
urine flow rate.

✅Mechanism of distal K+ secretion :⬇️⬇️⬇️
(a) At the basolateral membrane, K+ is actively transported into the cell by the Na+–K+ pump.
As in all cells, this mechanism maintains a high intracellular K+concentration.
(b) At the luminal membrane, K+
is passively secreted into the lumen through K+channels.
The magnitude of this passive secretion is determined by the chemical and electrical driving forces on K+ across the luminal membrane.
✔️ Maneuvers that increase the intracellular K+concentration or decrease the luminal K+ concentration will increase K+ secretion by increasing the driving force.
✔️Maneuvers that decrease the intracellular K+ concentration will decrease K+secretion by decreasing the driving force.

📱Factors that change distal K+ secretion :
(a) Dietary K+
✔■ A diet high in K+
increases K+ secretion, and a diet low in K+ decreases K+secretion.
■ On a high-K+ diet, intracellular K+ increases so that the driving force for K+secretion also increases.
■ On a low-K+ diet, intracellular K+ decreases so that the driving force for K+secretion decreases. Also, the α-intercalated cells are stimulated to reabsorb K+ by the H+, K+-ATPase.
✔(b) Aldosterone
■ increases K+ secretion.
■ The mechanism involves increased Na+ entry into the cells across the luminal membrane and increased pumping of Na+ out of the cells by the Na+–K+pump.
Stimulation of the Na+–K+ pump simultaneously increases K+ uptake into the principal cells, increasing the intracellular K+ concentration and the driving force for K+secretion.
Aldosterone also increases the number of luminal membrane K+
channels.
■ Hyperaldosteronism increases K+ secretion and causes hypokalemia.
■ Hypoaldosteronism decreases K+ secretion and causes hyperkalemia
✔Acid–base
■ Effectively, H+ and K+ exchange for each other across the basolateral cell
membrane.
■ Acidosis decreases K+ secretion. The blood contains excess H+; therefore, H+enters the cell across the basolateral membrane and K+ leaves the cell.
As a result, the intracellular K+ concentration and the driving force for K+secretion decrease.
■ Alkalosis increases K+ secretion. The blood contains too little H+, therefore, H+leaves the cell across the basolateral membrane and K+ enters the cell. As a result, the intracellular K+
concentration and the driving force for K+secretion increase.

✔Thiazide and loop diuretics
■ increase K+ secretion.
■ Diuretics that increase flow rate through the distal tubule and collecting ducts (e.g., thiazide diuretics, loop diuretics) cause dilution of the luminal K+concentration, increasing the driving force for K+ secretion.
Also, as a result of increased K+ secretion, these diuretics cause hypokalemia.
K+
✔K-sparing diuretics
■ decrease K+ secretion
If used alone, they cause hyperkalemia.
■ Spironolactone is an antagonist of aldosterone; triamterene and amiloride act directly on the principal cells.
■ The most important use of the K+-sparing diuretics is in combination with thiazide or loop diuretics to offset (reduce) urinary K+losses.
✔Luminal anions
■ Excess anions (e.g., HCO3
-) in the lumen cause an increase in K+ secretion by increasing the negativity of the lumen and increasing the driving force for K+secretion.🖋
⚡️⚡️⚡️⚡️⚡️⚡️⚡️⚡️⚡️⚡️
👍⭐❤

Question
Acetazolamide causes the following ❓
a. metabolic acidosis
b. hyperkalaemia
c. hypernatraemia
d. renal calculi
e. hypercalcaemia

❓Which books is better to read in physiology?

النسخه الاحدث 🔼🔼🔼
والشكر لمن أرسله د رؤى عصام

How Non-steroidal anti-inflammatory drugs (NSAID) like aspirin cause peptic ulcer ?.
Core physiology book 📚 answer:
- These inhibit synthesis of prostaglandins from arachidonic acid.
- Since prostaglandins inhibit HCL synthesis and increase mucus
secretion, then chronic use of aspirin, which inhibits its formation from arachidonic acid, results in increased HCL secretion and decreasedmucus production causing peptic ulcer.