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An experiment is conducted in which researchers are investigating the effect of various substances during the menstrual cycle. Substance X was found to directly stimulate expression of growth factors involved in blood vessel formation. Which of the following is most likely to be substance X?
A. Luteinizing hormone
B. Androstenedione
C. Follicle stimulating hormone
D. Estrogen
E. Progesterone
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D - Estrogen promotes angiogenesis while progesterone promotes tortuosity of blood vessels
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E is the correct answer
Progesterone is a steroid hormone secreted by the gonads, the placenta, as well as the brain. It prepares the reproductive tract for a pregnancy (think progesterone = pro-gestation), stimulates development of the spiral arteries in the endometrium by promoting the expression of angiogenic factors (angiopoietin-1, vascular endothelial growth factor (VEGF), fibronectin). As the main hormone of the secretory phase of ovulation, it causes endometrial glands to enlarge and secrete glycogen, a essential nutrient for the thickened uterus. If no fertilization occurs, the spiral arteries undergo spasms and necrosis, and then disintegrate in the stratum functionalis.
Answer A is incorrect; although luteinizing hormone stimulates the release of progesterone, it does not directly stimulate the endometrial events (vessel formation, gland enlargement)
Answer B is incorrect; androstenedione is an intermediate in the pathway of testosterone synthesis
Answer C is incorrect; follicle stimulating hormone is released by the anterior pituitary, and stimulates the formation of estrogen by increasing the expression of aromatase in the gonads and other tissues in the body (brain, skin, bone, adipose, etc)
Answer D is incorrect; estrogen is the main hormone in the proliferate phase. The influence of estrogen peaks right before ovulation. After ovulation, levels of estrogen reduce and the corpus lustrum starts to make progesterone, which marks the secretory phase.
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Fair enough. But, the research shows that estrogen also directly stimulates VEGF so IMO this question is out-dated. But, thanks for sharing though.
