Potassium Balance Flashcards
Where is ROMK (renal outer medullary potassium channel) found? and what’s its function?
K channel that allows the K+ that is reabsorbed to be recycled back across the luminal membrane into the tubule
- K that comes out increases the lumen positivity that causes passive paracellular transport of +ve charges such as K, Ca, Na, and Mg.
Where is K+ secreted?
Occurs in the principle cells of the Cortical DCT and Medullary DCT
- The K secretion is associated with Na reabsorption in the segment
What are the Mechanistic effects of aldosterone on Potassium secretion?
Aldosterone => stimulates the Na/K ATPase pump to move Na out of the cells and K into cells
=> synthesis of new Na and K channel for apical membrane.
- Na passively flows in through new apical channel (due to inc pump activity)
- K then flows out (secretion) to maintain the electroneutrality
Factors that effect K secretion in the principle cells?
- concentration gradient of K across the basolateral membrane – it depends upon serum K concentration
- electrical gradient across the luminal membrane – it depends upon the reabsorption of Na through the Na channels in the luminal membrane. Which in turn depends upon the Na concentration in the tubular lumen (distal delivery of Na)
- K permeability of the luminal membrane - that depends upon the number of open K channel on the luminal membrane. Which is affected by the aldosterone
What is the effect of aldosterone on K+ secretion?
Aldosterone => Potassium secretion
What happens to K+ secretion on a low potassium diet?
Constant low level secretion
- even with inc Na delivery to distal tubule
- happens because low K will remove stimulation of aldosterone secretion.
What happens to K+ secretion on a high potassium diet?
Enhanced secretion
- increases the serum K level which will increase the:
1. K concentration gradient between intracellular and extracellular K level
- Serum aldosterone level (“most potent stimulator” - wiki)
In what conditions would you see decreased potassium secretion?
- Renal failure
- Distal tubule dysfunction
- Decreased distal tubule flow
- Hypoaldosteronism (or if it’s action is blocked
What occurs if potassium secretion id decreased below normal?
K+ remains in plasma
=> hyperkalemia
In what conditions would you see increased potassium secretion?
A. Increased distal Na delivery
- Diuretics - loop and thiazides
- Bartter’s syndrome
- Gitelman’s syndrome
B. Hyperaldosteronism
i. ) Primary
ii. ) Secondary:
1. Vomiting and NasoGastric suction
How is the internal K+ balance maintained?
by regulating the K transport across the cell membrane via:
- Na/K ATPase pump
- passive K+ outflow channels
Factors that affect the internal balance of potassium (I.e. movement across the cell membrane)
- Plasma K concentration
- Insulin
- Epinephrine
- Acid-base disturbance
- Plasma tonicity (osmolarity)
- Cell lysis and proliferation
How does insulin effect the movement of K across the cell membrane?
Insulin moves K+ INSIDE the cells, but it does not directly work on Na/K pump
- Instead, insulin stimulates a NaH exchanger on the cell membrane that moves Na+ in and H+ out
- this intracellular Na than activate the NaKATPase pump and moves K INSIDE the cells.
How does epinephrine effect the movement of K across the cell membrane?
Activate the NaKATPase pump by stimulating beta receptor.
- Any other hormones or drugs that can stimulate beta receptor will stimulate NaKATPase pump.
- Examples:
1. Albuterol (beta receptor agonists and used in bronchial asthma)
2. Deficiency of insulin (as in diabetic patients)
3. Beta Blockers (Na/K-ATPase pump activity will be impaired w/ decrease movement of K from ECF to ICF. But the K channel which is not affected by the hormones will remain open and will continue to move K ICF to ECF which will result in elevated K in ECF)
How does the plasma K+ level affect movement across the cell membrane
Directly affects the K diffusion out of the cells
- If the serum K level is low then gradient will be high and so there will be more K coming out of the cells.
