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Understanding Female Cycle, Ovulation, and Pregnancy Hormones

This article explores the intricate processes of the female menstrual cycle, highlighting the hormonal regulation involved in ovulation and pregnancy. It explains how estrogen and progesterone work in concert to prepare the body for potential fertilization and supports early pregnancy. The role of the placenta, human chorionic gonadotropic hormone (HCG), and lactation hormones is also discussed. By understanding these biological systems, readers can gain insight into female reproductive health and the physiological changes that occur during pregnancy and childbirth.

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Understanding Female Cycle, Ovulation, and Pregnancy Hormones

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  1. Female cycle and pregnancy

  2. Ovulation • When estrogen level is at its highest, it exerts positive feedback on the hypothalamus • Which secretes GnRH • Which causes a sharp increase in production of LH • The surge in LH causes ovulation • After this, negative feedback by estrogen and progesterone cause all 4 hormones to decline until menstruation finally occurs

  3. Pregnancy • If fertilization occurs, cycle is stopped and the developing zygote embeds itself in endometrium (implantation) • Layer of cells surrounding zygote releases HCG (human chorionic gonadotropic hormone) • HCG prevents disintegration of corpus luteum and causes it to secrete even more progesterone • Corpus luteum remains for up to 6 months

  4. Placenta • Originates from fetal and maternal tissue • Exchange of molecules between fetus and mother (blood doesn’t mix, instead things diffuse between mother and placental capillaries) • First 3 months of pregnancy: placenta forms • Produces HCG and estrogen and progesterone. These shut down anterior pituitary so no new follicles mature • They also maintain uterine lining • Pregnancy tests check for HCG

  5. Female sex hormones: estrogen • Stimulates growth of uterus and vagina at puberty • Secondary sex characteristics (breasts, hips, body hair, enlarged pelvic girdle) • Onset of menstrual cycle • Egg maturation • (both estrogen and progesterone required for breast development)

  6. Female sex hormones: Lactogenic Hormone (prolactin) • Needed for lactation to begin • Lactation begins several days after delivery (until then, colostrum is produces which increases protein and antibodies and decreases fat)

  7. Female sex hormones: Oxytocin • Released by posterior pituitary • Acts on uterus to cause contractions (along with prostoglandins) • Positive feedback: uterine contraction causes the release of more oxytocin, which in turn causes more contractions • Also: breastfeeding – when breast is suckled, nerve endings in areola are stimulated and the nerve impulses travel to hypothalamus, causing the posterior pituitary to release oxytocin (which causes milk letdown)

  8. Breasts • Mammary glands unique to mammals • 15 – 25 lobules with its own milk duct that begin at the nipples and divide into other ducts called alveoli

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