Question
Which of the following represents the most stable and long-term mechanism of homeostasis in the human body?
| A. |
Respiratory rate |
| B. |
Urine output |
| C. |
Heart rate |
| D. |
SpO2 |
|
Correct Answer � B Explanation |
 |
– Homeostasis maintains internal stability (pH, fluid volume, electrolytes, osmolarity) despite external changes.
– Some mechanisms regulate short-term balance; others provide long-term control.
Urine output (B):
– Reflects renal function, a major long-term regulator of:
• Fluid balance
• Electrolyte levels
• Blood pressure
• Acid-base balance
– Kidneys adjust water & solute excretion via:
• Antidiuretic hormone (ADH)
• Renin-angiotensin-aldosterone system (RAAS)
• Atrial natriuretic peptide (ANP)
– Renal compensations are sustained, supporting long-term blood pressure & fluid volume regulation.
Why Other Options Are Incorrect:
A. Respiratory rate:
– Changes quickly to correct CO₂/pH (e.g., metabolic acidosis)
– Serves as short-term acid-base compensator
– Not sufficient for long-term homeostasis
C. Heart rate:
– Modifies rapidly via autonomic input (sympathetic/parasympathetic)
– Aids short-term perfusion & blood pressure support (e.g., hemorrhage)
– Does not maintain long-term internal balance
D. Peripheral oxygen saturation (SpO₂):
– Indicates hemoglobin oxygenation status
– Fluctuates with lung function or perfusion
– A monitoring parameter, not a homeostatic regulator
