During early pregnancy, the trophoblastic cells secrete which of the following hormones in order to maintain the corpus luteum?
Correct Answer: Human chorionic gonadotropin (hCG)
Description: At approximately the midpoint of the menstrual cycle, the ovum is expelled. Once this occurs, the surrounding granulosa and theca cells undergo luteinization and begin to secrete a large amount of estrogen and progesterone. This mass of hormone secreting cells is known as the corpus luteum (because of its yellow color). If pregnancy does not occur, the corpus luteum will persist for 14 days, after which point it degenerates. With the degeneration of the corpus luteum, hormone levels drop, the endometrium sloughs, and menstruation occurs. If a pregnancy does occur, the trophoblastic cells of the pregnancy will secrete human chorionic gonadotropin (hCG). This hormone goes to the corpus luteum and prevents its degradation, signaling it to continue its excretion of estrogen and progesterone to maintain an environment that is orable for pregnancy. The presence of human chorionic gonadotropin forms the basis for the urine and serum pregnancy test. hCG steadily increases over the first several weeks of the pregnancy, reaching a peak at approximately 10 weeks. After that, hCG levels decrease gradually during the remainder of the pregnancy. During early pregnancy, most women experience some nausea. One of the leading theories for the cause of this nausea is the hormone hCG, because the nausea of early pregnancy appears to mirror the rise and fall of the hCG levels--peaking at roughly 10 weeks and improving after that. Note: Estrogen and progesterone are produced by the corpus luteum during early pregnancy. The corpus luteum does not degenerate in a pregnant woman, as it does in the nonpregnant woman, because the trophoblastic cells secrete human chorionic gonadotropin (hCG). After the first months of pregnancy, the placenta takes over the role of secreting the large amounts of estrogen and progesterone that are needed to continue a healthy pregnancy. Once the placenta has taken over this role, the corpus luteum degenerates. Luteinizing hormone (LH) is produced by the anterior pituitary gland. Its rate of secretion is controlled mainly by the hypothalamus, through hypothalamic luteinizing hormone-releasing hormone (LHRH, also called GnRH) secretion. The LH surge, which occurs roughly at the midpoint of the menstrual cycle, appears to cause ovulation, which occurs approximately 24 hours after the surge. LH also appears to induce the theca and granulosa cells to become the corpus luteum. Also Know: Chorionic gonadotropin is a glycoprotein with a molecular weight of 36,000 to 40,000 Da. It has the highest carbohydrate content of any human hormone--30 percent. Although hCG is produced almost exclusively in the placenta, it also is synthesized in fetal kidney. The intact hCG molecule is detectable in plasma of pregnant women 7 to 9 days after the midcycle surge of LH that precedes ovulation. Thus, it is likely that hCG enters maternal blood at the time of blastocyst implantation. Plasma levels increase rapidly, doubling every 2 days, with maximal levels being attained at 8 to 10 weeks. Ref:Cunningham F.G., Leveno K.J., Bloom S.L., Hauth J.C., Rouse D.J., Spong C.Y. (2010). Chapter 3. Implantation, Embryogenesis, and Placental Development. In F.G. Cunningham, K.J. Leveno, S.L. Bloom, J.C. Hauth, D.J. Rouse, C.Y. Spong (Eds), Williams Obstetrics, 23e.
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Gynaecology & Obstetrics
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