💧 Renal🟢 BasicElectrolyte Balance

Serum Electrolytes: Sodium and Potassium

The two main charged salts of body fluids, whose blood levels are tightly controlled and whose disturbance affects nerves, muscle and the heart.

Key points

Sodium is the main positive ion outside cells and sets the volume and osmolality of the extracellular fluid, so its balance is tied to water balance.
Potassium is the main positive ion inside cells and sets the resting membrane potential, so abnormal levels disturb nerve and heart function.
A low or high sodium (hyponatraemia or hypernatraemia) usually reflects a problem with water rather than with salt itself.
A high potassium (hyperkalaemia) is dangerous because it can cause life-threatening changes in heart rhythm, seen as peaked T waves on the electrocardiogram.
Aldosterone from the adrenal cortex raises sodium reabsorption and potassium loss in the kidney, linking the handling of the two ions.

Memory trick

Sodium sits outside and follows water (osmolality); potassium sits inside and sets the membrane potential (heart danger when high); aldosterone keeps sodium and dumps potassium.

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💧 Renal🟢 BasicElectrolyte Balance

Serum Electrolytes: Sodium and Potassium

The two main charged salts of body fluids, whose blood levels are tightly controlled and whose disturbance affects nerves, muscle and the heart.

Key points

Sodium is the main positive ion outside cells and sets the volume and osmolality of the extracellular fluid, so its balance is tied to water balance.
Potassium is the main positive ion inside cells and sets the resting membrane potential, so abnormal levels disturb nerve and heart function.
A low or high sodium (hyponatraemia or hypernatraemia) usually reflects a problem with water rather than with salt itself.
A high potassium (hyperkalaemia) is dangerous because it can cause life-threatening changes in heart rhythm, seen as peaked T waves on the electrocardiogram.
Aldosterone from the adrenal cortex raises sodium reabsorption and potassium loss in the kidney, linking the handling of the two ions.

Memory trick

Sodium sits outside and follows water (osmolality); potassium sits inside and sets the membrane potential (heart danger when high); aldosterone keeps sodium and dumps potassium.

All of Biochemistry More Renal