Which statement best describes brown adipose tissue in newborns?

• A. It has a larger content of mitochondrial cytochromes and greater heat production.
• B. It has fewer mitochondria and less heat production.
• C. It is primarily involved in oxygen transport.
• D. It is identical to white adipose tissue in function.

Answer: (A)

Brown adipose tissue in newborns is built for heat production. It is rich in mitochondria and cytochromes, which give it a brown color and the capability to generate heat rather than store energy. When a newborn is exposed to cold, the sympathetic system activates these brown fat cells, and the mitochondria use fatty acids to produce heat through a process that uncouples oxidative phosphorylation from ATP production. This non-shivering thermogenesis helps maintain body temperature in early life. White fat, in contrast, has fewer mitochondria and mainly stores energy, not heat. Oxygen transport is a function of blood, not brown fat, and brown fat is not identical in function to white fat. So the description of greater mitochondrial cytochrome content and increased heat production best captures brown adipose tissue in newborns.