Normal CSF production rate is approximately 0.35 mL/min (500 mL/day), yet total CSF volume is only 150 mL. This implies CSF turns over approximately _____ times per day.
- A 3–4 times per day ✓
- B 1 time per day
- C 8–10 times per day
- D Once every 3 days
Correct answer: A. 3–4 times per day
Explanation
With production of ~500 mL/day and total CSF volume of ~150 mL: turnover rate = 500/150 ≈ 3.3 times per day. This high turnover rate maintains CSF homeostasis and clears metabolic waste (including amyloid-beta via the glymphatic system). Production occurs at choroid plexus in all four ventricles (predominantly lateral ventricles); absorption occurs mainly at arachnoid granulations into dural venous sinuses. Obstruction of flow or absorption results in hydrocephalus.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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