Tiff
Forum Guru
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A 25 year old woman sees her physician because of exhaustion and diarrhea. Physical exam shows that she has low blood pressure, and blood studies show that she is anemic. Other studies show that she has a tumor of the pituitary gland. An IV drip of ACTH fails to increase the concentration of urine 17-hydroxycorticoids. The rate limiting step stimulated byu ACTH involves the formation of:
A. Cortisol from cholic acid
B. 7-Dehydrocholesterol from cholesterol
C. Mevalonate from HMG CoA
D. Pregnenolone from cholesterol
E. Progesterone from pregnenolone
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| sigh
Forum Senior
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D
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| new_n_lost
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D. Pregnenolone from cholesterol
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| Tiff
Forum Guru
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 D is correct.
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| hottie99
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could u please explain it, thanks!
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| Tiff
Forum Guru
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ACTH stimulates the conversion of cholesterol to pregnenolone in the adrenal cortex. It's the intitiating portion in steroid hormone synthesis.
Here is the explanation provided: The patient has signs of pituitary hypofunction (exhaustion, diarrhea, low blood pressure, and anemia) and is diagnosed with a tumor of the pituitary gland, in the sella turcica. Formation of pregnenolone from cholesterol is the rate limiting step in the senthesis of steroid compounds. It is regulated by the action of ACTH on the cytochrome P450 side chain cleavage enzyme.
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| hottie99
Forum Elite
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kool thx so much!!
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