Female cycle and pregnancy

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

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

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

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)

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)

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)

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