Answer to Question #68112 in Human Anatomy and Physiology for francesca
The adrenocorticotrophic hormone travels to the adrenal cortex where it triggers the secretion of the glucocorticoids. How it triggers?
The adrenocorticotrophic hormone (ACTH) binds to the adrenocorticotrophic hormone receptors on the surface of adrenocortical cells, primarily located in the adrenal cortex. Then it triggers the secretion by rapid short-term and slower long-term actions. ACTH rapidly stimulates cholesterol delivery to the mitochondria where the P450scc enzyme is located. This enzyme acts as a catalyst in the first step of steroidogenesis that is cleavage of the side-chain of cholesterol. The slower action is that ACTH stimulates the transcription of the genes for steroidogenic enzymes, especially the P450scc enzyme mentioned above, the steroid 11β-hydroxylase, and their associated electron transfer proteins. Another action is that ACTH also stimulates lipoprotein uptake into cortical cells; thus increasing the bioavailability of cholesterol in the cells of the adrenal cortex which is needed for the synthesis of glucocorticoids.
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