How is body sodium sensed? What are the major control systems that regulate body sodium?
What will be an ideal response?
Answer: Body sodium content is partly sensed by its correlation with blood pressure, since NaCl is the major salt in all body fluids. Baro-receptor reflexes influence body sodium concentration partly by influencing glomerular filtration rate; higher blood pressures stimulate GFR and sodium loss in the urine, while low blood pressures do the opposite., High body sodium and blood pressures also trigger atrial natriuretic hormone release, which increases glomerular filtration and reduces tubular reabsorption of Na+, causing more Na+ to be lost in the urine. If body sodium and blood pressures are low, this can also trigger the renin-angiotensin system which increases blood pressure and reduces urine output, partly by reducing GFR. Long-term, low blood sodium is sensed by the macula densa cells, which trigger a rise in angiotensin II (via renin release), which then triggers aldosterone secretion from the adrenal cortex. Aldosterone increases Na+ reabsorption by the distal tubule and collecting duct. High blood sodium (and high blood pressure) does the reverse, reducing renin, angiotensin II, and aldosterone, and increasing sodium loss in the urine.
2. Why is high body sodium content generally associated with high blood pressures?
Sample Answer
Sodium chloride accounts for about 90% of the osmotic pressure in the extracellular fluid. If sodium content of the body is higher, this will tend to pull water by osmosis into the extracellular compartment, including the plasma, raising blood volume and blood pressure.
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