Approximately how many minutes does it take to circulate the total blood volume of a 150-pound person at rest?

Question

BlackTom AI · Accepted Answer

Blood volume divided by cardiac output gives the circulation time.

Relevant knowledge points:
- Typical blood volume ≈ 70 mL per kg of body weight (or about 7% of body weight).
- Resting cardiac output (amount of blood the heart pumps) ≈ 5 liters per minute in an average adult.
- Circulation time = total blood volume / cardiac output.

Step-by-step calculation:
1. Convert 150 pounds to kilograms: 150 lb × 0.453592 kg/lb = 68.04 kg.
2. Estimate total blood volume: 68.04 kg × 70 mL/kg = 4,762.8 mL ≈ 4.76 L.
3. Use resting cardiac output: ≈ 5.0 L/min.
4. Circulation time = blood volume / cardiac output = 4.76 L ÷ 5.0 L/min = 0.952 min.

Intermediate values shown: 
- 150 lb → 68.04 kg
- Blood volume ≈ 68.04 × 70 mL/kg = 4,762.8 mL (4.76 L)
- Time = 4.76 L / 5 L/min = 0.952 min ≈ 1 minute

Why the correct answer is correct:
A resting adult pumps roughly 5 liters per minute; since a 150-lb person has about 4.76 L of blood, the entire blood volume passes through the heart in about one minute (≈0.95 min). This is consistent with the commonly cited figure that whole-body circulation takes about one minute at rest.

Why the other options are incorrect:
- 5 minutes would require an unrealistically low cardiac output (~0.95 L/min).
- 15 minutes or 30 minutes would require impossibly low cardiac outputs (~0.32 or ~0.16 L/min), inconsistent with normal physiology.

Conclusion: The circulation time is approximately 1 minute, matching the provided correct answer (1).

Approximately how many minutes does it take to circulate the total blood volume of a 150-pound person at rest?单项选择题

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