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Physiology

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Central Nervous System

Question
15 out of 18
 

True about non shivering thermogenesis



A Glucose converted to lactate

B Fatty acids show uncoupled oxidative phosphorylation

C ADP is burnt into heat

D Adipose tissue is entirely absent

Ans. B Fatty acids show uncoupled oxidative phosphorylation

I. Sympathetic stimulation- “Non-shivering thermogenesis” (= Chemical thermogenesis):

Steps are -

a. Stimulation of the sympathetic nervous system liberate — nor epinephrine and epinephrine→↑metabolic rate

b. Glycogenolysis and a more important effect on brown fat in causing marked liberation of heat

c. Brown fat contains large numbers of mitochondria and many small globules of fat when these cells are stimulated by sympathetic nerves heir mitochondria produce a large amount of heat but almost no ATP (i.e. the process of oxidative phosphorylation in mitochondria is mainly uncoupled)

d. The neonate has a considerable no. of such fat cells (brown fat) and maximal sympathetic stimulation can increase the child’s metabolism more than 100% (this is called non-shivering thermogenesis) QNon-shivering thermogenesis may also serve as a buffer against obesity.

II. Non-shivering thermogenesis

Cold stress

Sympathetic stimulation Q to Brown fat

Release of Norepinephrine Q

acts via β3-adrenergic receptors Q

Increases lipolysis and increases fatty acid oxidation in mitochondria, increases heat production (uncoupled oxidative phosphorylation — i.e. production of heat without ATP generation Q

  1. Mechanism of uncoupling

i. Short-circuit conductance by uncoupling proteins

1) UCP-1 — in Brown fat

2) UCP-2 — in both white and Brown fat

ii. A thermogenic uncoupling protein:

1) Thermogeninacts as a proton conductance pathway dissipating the electro-chemical potential across the mitochondrial membrane.

  1. “Therefore Non-shivering thermogenesis is mediated via Norepinephrine,β3 , receptor, UGP-1, UGP-2 and thermogeninQ

i. It increase melanocortin secretion but its action are not affected by melanocortin.

ii. High levels of glucocorticosteriods causes an increase of NPY by directly activating type II glucocorticosteriodsreceptors and, indirectly, by abolishing the negative feedback of CRF on NPY synthesis and release.

iii. Neuropeptide Y (NPY)-ergic neurons of the hypothalamic arcuate nucleus (ARC) that project to the paraventricular nuclei (PVN) and dorsomedial nuclei (DMH) control energy balance by stimulating feeding and inhibiting thermogenesis, especially under conditions of energy deficit.

iv. Its levels are increased in starvation, anorexia nervosa etc.

Central Nervous System Flashcard List

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