Final answer:
During pregnancy, the secretion of LH and FSH is primarily regulated by hormones such as estrogens, progesterone, and hCG secreted from the placenta, maintaining the corpus luteum and suppressing the ovarian cycle.
Step-by-step explanation:
The secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) during pregnancy is regulated primarily by hormones secreted from the corpus luteum and later, by the placenta, such as estrogens, progesterone, and human chorionic gonadotropin (hCG). During pregnancy, the presence of these hormones, specifically hCG, maintains the corpus luteum which in turn secretes sufficient levels of estrogen and progesterone to reduce the release of FSH and LH. This results in the suppression of the ovarian cycle during pregnancy.
FSH and LH are critical for reproductive functions. They are produced by the pituitary gland in response to the release of gonadotropin-releasing hormone (GnRH) from the hypothalamus. In females not pregnant, these hormones regulate the menstrual cycle and prepare the body for possible pregnancy. However, during pregnancy, high levels of estrogen and progesterone inhibit the release of GnRH, which consequently reduces the secretion of FSH and LH from the pituitary gland, thereby maintaining the pregnancy.
Therefore, throughout the pregnancy, the placenta takes over the endocrine role of controlling the levels of FSH and LH, which in a non-pregnant state would be regulated primarily by the hypothalamus and the pituitary gland.