- The mechanisms of thermogenesis in brown adipose tissue (BAT) in cold are described in the following proposed statements:
A. A thermogenic uncoupling protein, UCP1 helps in the heat production in BAT
B. Norepinephrine secretion from sympathetic nerve endings in BAT is decreased
C. Lipolysis is increased by low level of norepinephrine in BAT
D. A high content of mitochondria in BAT helps in the oxidation of fatty acids
E. Oxidation produces much heat as ATP synthase activity is low
Which one of the following Options represents the combination of correct statements?
(1) A, B and C (2) A, D and E
(3) B, C and D (4) B, D and EUnderstanding Thermogenesis in Brown Adipose Tissue (BAT) During Cold Exposure
Brown adipose tissue (BAT) plays a crucial role in non-shivering thermogenesis, enabling humans and other mammals to generate heat in response to cold environments. Multiple biochemical and physiological mechanisms work together to make BAT a highly efficient thermogenic organ.
Review of the Proposed Statements
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A. A thermogenic uncoupling protein, UCP1 helps in the heat production in BAT
True. UCP1, located in the inner mitochondrial membrane, facilitates heat generation by uncoupling oxidative phosphorylation, allowing the proton gradient to dissipate as heat instead of ATP. -
B. Norepinephrine secretion from sympathetic nerve endings in BAT is decreased
False. Norepinephrine release actually increases in response to cold, activating β3-adrenergic receptors on brown adipocytes to boost thermogenesis. -
C. Lipolysis is increased by low level of norepinephrine in BAT
False. Lipolysis in BAT is stimulated by high levels of norepinephrine, which enhances the release of free fatty acids used as fuel for thermogenesis. -
D. A high content of mitochondria in BAT helps in the oxidation of fatty acids
True. BAT is rich in mitochondria, which oxidize fatty acids actively during cold exposure to provide substrates for heat generation. -
E. Oxidation produces much heat as ATP synthase activity is low
True. The activity of ATP synthase is reduced due to UCP1’s uncoupling effect, causing energy from oxidation to be released primarily as heat.
Correct Combination of Statements
Based on current scientific understanding, the correct set of accurate statements is:
A, D, and ESummary Table: Thermogenesis Statements in BAT
Statement Content Correctness A UCP1 aids heat production in BAT True B Norepinephrine secretion decreased in cold False C Lipolysis increased by low norepinephrine levels False D Mitochondria-rich BAT oxidizes fatty acids True E Heat production due to low ATP synthase activity True Conclusion
Thermogenesis in brown adipose tissue during cold stress relies on UCP1, enhanced mitochondrial fatty acid oxidation, and reduced ATP synthase activity converting energy into heat rather than stored ATP. Norepinephrine secretion increases to stimulate these processes, and lipolysis occurs at high norepinephrine levels.
Therefore, the correct answer to the question is:
(2) A, D, and E -
