Biology 30 Alberta: The Menstrual Cycle

What is menstruation?

The periodic discharge of blood and fluid from the uterus. Caused by low levels of estrogen and progesterone at end of monthly cycle

What is the menstrual cycle?

Repetitive sequence of shedding uterine lining (endometrium), development and release of egg (ovulation), and replacement of endometrium

When does the menstrual cycle begin and end?

Begins at puberty and continues to menopause

What causes most of the pain felt during menstrual cramps?

Uterine contraction triggered by prostaglandins. Contractions inhibit blood flow to the lining of the uterus (endometrium)

When is the flow phase?

Days 1-5

What happens during days 1-5 of the mesntrual cycle?

Flow phase. Marked by the shedding of endometrial lining. Triggered by a decrease in ovarian hormones (particularly progesterone), which stimulates FSH and LH. Corpus luteum degenerates, forming corpus albicans

What is thought to be responsible for headaches, cramps, nausea, and mood changes during menstration?

Low hormone levels

When is the follicular phase?

Days 6-13

What happens during days 6-13 of the menstrual cycle?

Follicular phase. Lasts until ovulation. Governed by estrigen released by developing follicle (stimulated by FSH). Endometrial lining thickens. FSH decreases (neg. feed. from estrogen). LH production increases (pos. feed. from estrogen). Follicle matures

When is ovulation?

Day 14

What happens on day 14 of the menstrual cycle?

Ovulation. Estrogen and LH levels peak. Follicle erupts, ovum is released into fallopian tube. Females temperature peaks

When is the luteal phase?

Days 15-28

What happens on days 15-28 of the menstrual cycle?

Luteal phase. Corpus luteum develops. Lasts until menstruation. Governed by progesterone released by the corpus luteum (stimulated by LH). Further ovulation and uterine contractions are inhibited (progesterone). Endometrial lining continues to thicken, preparing for pregnancy (progesterone and estrogen from corpus luteum). Progesterone and estrogen inhibit LH release (neg. feed.), corpus luteum starts to degenerate, endometrium breaksdown, back to flow phase

What does a drop in progesterone result in?

Menstruation or miscarriage

What does an increase in LH result in?

Positive ovulation test (for trying to get pregnant)

What does an increase in HCG result in?

Positive pregnancy test

What is endometriosis?

A sometimes debilitation disease caused by endometrial lining forming inside the abdominal cavity (and is still shed monthly)

How do birth control pills work?

Prevent ovulation (progesterone prevents ovulation)

What is an ectopic pregnancy?

Occur when implantation is in the fallopian tube instead of the uterus. The pregnancy will rupture the fallopian tube if allowed to continue