OVARIAN AND UTERINE CYCLES

Ovarian cycle: cycle where an oocyte will mature, erupt from an ovary, and travel down the oviduct to the uterus

Uterine cycle: cycle where the lining of the uterus grows and prepares for an embryo to implant, but if an oocyte is not fertilized then menstruation occurs

GnRH: gonadotropin releasing hormone stored in the hypothalamus triggers the release of FSH and LH
LH: luteinizing hormone produced by an implanted embryo; when released it causes the follicle to release the egg (ovulation); triggers remaining follicle cells to differentiate into the corpus luteum (which secretes estrogen and progesterone)
FSH: follicle-stimulating hormone produced in the pituitary gland; stimulates ovarian follicles to grow which begins the secretion of estrogen

Estrogen: increased levels of estrogen serve as a source of positive and negative feedback to regulate the levels of FSH and LH

Progesterone: secretion from a follicle that released an egg; responsible for the thickening of the endometrium and preparing to support embryonic development

hCG: human chorionic hormone is secreted once the egg has been fertilized and is detected in pregnancy tests

Positive Feedback Loops: An increase in the hormone levels after the release of an egg into the ovary because more hormones are needed to aid in the proper development of the zygote to a fetus (when fertilized)
Negative Feedback Loops: a decrease in the hormone levels within the body which decreases GnRH levels

Menstruation vs. Pregnancy: hormone levels are much lower during menstruation than during pregnancy which is an easy source for differentiating between the two processes

Fetal development

First trimester: zygote is turning into a fetus; embryo is made of three layers; organs in the fetus are in their first stages

            Second trimester: fetus continues to grow and develop; brain and lungs form

            Third trimester: fetus is growing the most rapidly