The Menstrual Cycle
= a monthly cycle that occurs in women, involving morphological changes in the _______________ and the ____________________________________ of the uterus, caused by ___________________________________________________ of the hypothalamus, pituitary gland and ovaries
Click here for diagram of the hormonal feedback loop between the brain and ovaries.
Length of the cycle is extremely variable:
Menstrual cycle actually consists of two interrelated and interdependent cycles:
Ovarian cycle can be divided into 3 phases:
Endometrial cycle can also be divided into 3 phases:
*The menstrual and proliferative
phases occur during the follicular phase of the ovarian cycle.
**The secretory phase is synchronized with the luteal phase of the ovarian cycle.
Click here for a diagrammatic overview of the two cycles.
The Ovarian Cycle in Detail
1. Follicular Phase: duration is highly variable, but typically lasts 11-16 days. Click for diagram.
2. Ovulation: the shortest phase; an instantaneous event; typically occurs on day 14 (of 28 day cycle). Click for diagram.
The Endometrial Cycle in Detail
1. Menstrual Phase: period of
bleeding; duration usually 4 - 6 days. Click for
2. Proliferative Phase: proliferation of new cells in uterine lining; duration usually 8 – 10
Click here for a diagram illustrating the fluctuating hormone levels and sequential events of the menstrual cycle. (You may need to also click on the image to enlarge the diagram.)
Click on the following two links for a two-part summary of all the events that occur during the menstrual cycle:
Click here for an overview of the hormones involved and their functions. (But note that this table fails to acknowledge the role of LH in stimulating ovarian follicles to synthesize and secrete estrogen.)
1. Dysmenorrhea = _______________________
2. Amenorrhea = ________________________
3. Endometriosis = abnormal growth of endometrial tissues ________________________________________________
o Endometrial tissue may dislodge from uterus and grow in the ovaries, oviducts, bladder, urethra, intestines, rectum, cervix, vagina or lymph glands
depending on location, but usually involve severe pain and excessive bleeding
during each menstruation period
4. Toxic Shock Syndrome
o Symptoms: high fever, sun-burn like rash, vomiting, diarrhea, muscle aches, drop in blood pressure, kidney failure, liver abnormalities, death (10% of cases)
o Caused by buildup of specific type of _______________________, which produce ______________________ that enter bloodstream
use of high absorbency tampons, particularly if left in for long periods of
time (but can also occur in children and men)
5. Premenstrual Syndrome (_____________) = a combination of ________________________ ailments and __________________________ difficulties exhibited (most often) during the week before menstruation
o Cause is still _____________________________. Given such a wide variety of symptoms, there is not likely to be a single cause. Probably multifactorial. There are two prevailing theories, each with supporting evidence:
1. changes in hormone levels – drop in progesterone (P)?, simultaneous drop in P and E?
1. psychological effects of cultural influences
Same as for dysmenorrhea, in addition to dizziness, breast tenderness, acne, migraine headaches, muscle aches and edema (swelling) in the hands and feet (due to water retention)
Fatigue, tension, anger, irritability, depression, anxiety, nervousness, insomnia, food cravings, difficulty concentrating, memory loss