A neonate exposed to room temperature shortly after birth mounts a heat response that does not involve shivering. The molecular event directly responsible for heat generation in this response is:

• A Activation of sarcolemmal calcium ATPase in skeletal muscle generating futile cycling
• B Uncoupling of mitochondrial oxidative phosphorylation by UCP1 in brown adipose tissue ✓
• C Hydrolysis of creatine phosphate in white adipose tissue releasing heat
• D Uncoupling of ATP synthase by thyroxine acting directly on hepatocyte membranes

Explanation

Non-shivering thermogenesis depends on brown fat, which is rich in mitochondria containing uncoupling protein 1 (thermogenin). Norepinephrine released by sympathetic nerves activates beta-adrenergic lipolysis, and the liberated fatty acids open UCP1, dissipating the proton gradient as heat instead of ATP. Shivering is poorly developed in neonates, and white fat, creatine phosphate cycling and direct thyroid membrane uncoupling are not recognized mechanisms of neonatal heat production.

Reference: Ganong's Review of Medical Physiology, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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