Which ARS subsystem has a threshold of 20 Gy?

• A. Central Nervous System
• B. Skin
• C. Gastrointestinal
• D. Bone Marrow

Answer: (A)

The main idea here is that different parts of Acute Radiation Syndrome (ARS) have distinct dose thresholds, with the Central Nervous System requiring the highest dose to produce a syndrome. The nervous system shows damage and life-threatening effects only at very high doses, around 20 Gy. At this level, rapid neurological deterioration occurs—things like confusion, ataxia, seizures, and brain edema—leading to death within days despite supportive care.

In contrast, the bone marrow subsystem (hematopoietic) becomes evident at much lower doses, typically around a couple of grays, with marrow failure leading to infection and bleeding. The gastrointestinal subsystem requires higher doses than hematopoietic but still less than CNS, often several grays (roughly in the 6–10 Gy range) and presents with vomiting, diarrhea, and electrolyte losses. The skin can show local radiation injury at lower doses if exposure is superficial, but that’s a localized effect rather than the high-dose, systemic ARS syndrome.

So, a threshold of about 20 Gy points to the central nervous system as the subsystems’ highest-dose ARS threshold.