A 32-year-old man sustains a head injury and later shows increased thirst and confusion. What condition is most likely affecting the nephron?

• A. Central diabetes insipidus
• B. Aplastic anemia
• C. Chronic myelogenous leukemia
• D. Vitamin B12 deficiency

Answer: (C)

The presentation of increased thirst and confusion following a head injury suggests the possibility of a disorder affecting the regulation of water balance in the body, particularly regarding the actions of antidiuretic hormone (ADH).

Central diabetes insipidus occurs when there is insufficient ADH production due to a dysfunction in the hypothalamus or pituitary gland, which can be triggered by trauma to the head. In this condition, the kidneys fail to concentrate urine, leading to excessive urination and consequential increased thirst. The symptoms of confusion could arise from hypernatremia, which is a potential consequence of the unreabsorbed water.

Aplastic anemia, chronic myelogenous leukemia, and vitamin B12 deficiency do not directly relate to the nephron's function in the context of the symptoms presented after a head injury. Aplastic anemia involves the bone marrow and does not cause the symptoms related to thirst and confusion stemming from nephron function. Chronic myelogenous leukemia is a hematological malignancy that primarily affects blood cell production and does not specifically lead to a renal concentrating issue. Vitamin B12 deficiency primarily affects red blood cell production and neurological function rather than directly influencing the actions of ADH and renal handling of water.

Thus, the condition most likely affecting the neph