Human Reproduction The Menstrual Cycle

What is the Menstrual Cycle? Cycle of events involving changes in the ovaries and uterus in preparation for reproduction Starts at puberty, and ends at menopause (around age 45-55).

Endocrine & Reproductive Systems work together Hormone = chemical signal released into blood-- communicates messages throughout body Endocrine & Reproductive Systems work together

Menstrual Cycle Four major hormones involved: FSH & LH (released by pituitary); progesterone & estrogen (released by ovarian cells)

The Menstrual Cycle is broken down into four phases

Menstrual Cycle A. Menstruation phase- lasts 4-7 days 1. The uterine lining is discharged 2. FSH and LH released by pituitary

B.  Follicle Phase - lasts 10-16 days (overlaps menstruation) 1.  Estrogen levels low 2.  Follicles develop due to increase in Follicle Stimulating Hormone (FSH).

a. FSH causes a follicle and the egg to mature.

Follicle Phase

3.  As the follicle develops, it begins to secrete estrogen, which: a. causes the lining of the uterus to thicken b. Causes an increase in LH

C.  Ovulation - lasts ~1 day 1.  The pituitary gland releases a sudden rush of FSH and LH. a. LH spike causes the follicle to break open, releasing the mature ovum

Ovulation

Ovulation

D. Luteal Phase - lasts ~14 days 1.  Ruptured follicle develops into the corpus luteum.

a. The corpus luteum continues to release estrogen and also releases progesterone. i. Progesterone helps the maturing of the uterine lining; keeps it thick. ii. Progesterone inhibits FSH.

If no fertilization… the corpus luteum disintegrates (it has a “life” of only about two weeks)

If no fertilization… A cascade of events results: estrogen and progesterone levels go very low These low levels causes the uterine lining to detach from the uterine wall beginning of cycle starts again with menstruation and increase in FSH and LH

Menstrual Cycle

If there is fertilization… A. Fertilization occurs within 1 day of ovulation. B. Sperm must be present in the oviduct (can survive there about 4-5 days). C.  Sperm merges with egg; egg finishes last division of meiosis. Resulting cell = zygote.

If there is fertilization… 1.  Rapid mitosis of zygote begins-- forms a solid ball of cells. 2.  Embryo embeds itself into uterine wall.

If there is fertilization… 3. A layer of cells in embryo produces human chorionic gonadotropin (hCG) This keeps Corpus Luteum functional Corpus Luteum keeps uterine wall thick to nourish embryo.

If there is fertilization… 4. Tissues in embryo produce estrogen and progesterone Prevents pituitary from releasing FSH and LH WHY?

Human Development

What about male hormones? FSH: Stimulates testes to produce sperm LH: Stimulates production of testosterone Also know: Testosterone: major male hormone; triggers puberty (development of secondary sex characteristics) and sperm production

How can one prevent pregnancy?

How can one prevent pregnancy?

FSH E & P E