Which organ is primarily responsible for regulating the composition of circulating blood?

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Multiple Choice

Which organ is primarily responsible for regulating the composition of circulating blood?

Maintaining the precise composition of circulating blood—in terms of electrolyte levels, acid-base balance, and fluid volume—is done mainly by the kidneys. They filter plasma through the glomeruli and then finely tune what is reabsorbed or secreted along the tubules. This system allows the kidneys to keep sodium, potassium, calcium, chloride, and bicarbonate within tight ranges, regulate pH by reclaiming bicarbonate and excreting hydrogen ions, and adjust total body water through water reabsorption under hormonal control. They also influence blood pressure and volume via mechanisms like renin release. The liver contributes in other important ways, such as synthesizing most plasma proteins that affect the blood’s osmotic pressure and processing metabolic waste, but it does not regulate the immediate ionic composition or pH of circulating blood the way the kidneys do. The lungs participate in acid-base balance by adjusting CO2, and the heart simply pumps blood; neither is the primary regulator of blood composition.

Maintaining the precise composition of circulating blood—in terms of electrolyte levels, acid-base balance, and fluid volume—is done mainly by the kidneys. They filter plasma through the glomeruli and then finely tune what is reabsorbed or secreted along the tubules. This system allows the kidneys to keep sodium, potassium, calcium, chloride, and bicarbonate within tight ranges, regulate pH by reclaiming bicarbonate and excreting hydrogen ions, and adjust total body water through water reabsorption under hormonal control. They also influence blood pressure and volume via mechanisms like renin release.

The liver contributes in other important ways, such as synthesizing most plasma proteins that affect the blood’s osmotic pressure and processing metabolic waste, but it does not regulate the immediate ionic composition or pH of circulating blood the way the kidneys do. The lungs participate in acid-base balance by adjusting CO2, and the heart simply pumps blood; neither is the primary regulator of blood composition.

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