Accelerated Biology

 Some important vocabulary  Follicle – a cluster of cells that surrounds an immature egg and provides it with nutrients (where the egg develops)  Ovulation – Release of an ovum from an ovary  Corpus Luteum – ruptured follicle  Endometrium – bloody uterine lining

 Ovarian Cycle – The ovaries prepare and release an ovum  2 phases 1. Follicular phase – the egg matures (ovulation occurs) 2. Luteal phase – Corpus luteum is formed  Menstrual Cycle – The uterus prepares for pregnancy  The lining of the uterus thickens preparing for implantation of a fertilized ovum  If pregnancy does not occur, the uterine lining is shed  Menstruation – begins the cycle, days 1 –4  Both cycles generally last 28 days, varies from female to female

The Menstrual Cycle - Narrated 3D Animation

 The hypothalumus and anterior pituitary initiate the reproductive cycle.  Hypothalamus monitors the levels of estrogen and progesterone in blood  Low levels of estrogen and progesterone stimulate the hypothalamus to secrete gonadotropin releasing hormone (GnRH)  negative feedback  GnRH stimulates the anterior pituitary to secrete Follicle Stimulating Hormone (FSH) and Leutinizing Hormone (LH)  positive feedback

 FSH stimulates the development of follicle  The follicle produces estrogen  Estrogen aids in the growth of the follicle

 Positive feedback from rising levels of estrogen stimulate the anterior pituitary to produce a sudden surge in Luteinizing Hormone (LH).  This high level of LH triggers ovulation (release of the ovum from an ovary)  Ovulation occurs on day 14 of the menstrual cycle  The ruptured follicle then turns into the Corpus Luteum

 After ovulation, the ruptured follicle, now called the corpus luteum, continues to develop. The Corpus Luteum secretes estrogen and progesterone  Estrogen and progesterone stimulate the development of endometrium (bloody uterine lining)  Negative feedback from high levels of estrogen and progesterone (monitored by hypothalamus) cause anterior pituitary to stop production of LH and FSH, thus terminating the reproductive cycle

 Without LH and FSH the corpus luteum deteriorates  Causes progesterone and estrogen to stop being produced  Without these the endometrium is unable to be maintained  Result  Menstruation

 Positve and Negative Feedback –McGraw Hill Animation Positve and Negative Feedback –McGraw Hill Animation

But wait! What if fertilization occurs?

 Implanted embryo sustains the endometrium  The embryo secretes human chorionic gonadotropin (HCG) to sustain the corpus luteum  Corpus luteum will continue to produce estrogen and progesterone to maintain the endometrium  Without HCG menstruation begins and embryo is aborted.  Pregnancy tests check for presence of HCG in urine

 Hypothalamus secretes GnRH which triggers the anterior pituitary to secrete FSH and LH  In males LH is also called ICSH (interstitional cell stimulating hormones)  LH stimulates the interstitial cells in testes to produce testosterone and other male sex hormones (androgens)  Testosterone and estrogen stimulate the development of secondary sex characteristics in both males and females