The amount of menstrual fluid is determined by the size of the uterus and the hormonally induced endometrial thickness. During the follicular phase (about the first 2 weeks) of the menstrual cycle, estrogen gradually builds up the uterine lining (endometrium). Estrogen causes the proliferation (growth) of endometrial stroma cells (connective tissue), epithelial cells (tissue), glands, vascular cells and the number of gap junctions. Estrogen increases myometrial excitability and stimulates uterine contractility.
Progesterone is the hormone that promotes uterine relaxation. During the secretory phase (last 2 weeks) of the menstrual cycle, progesterone stops growth of the endometrial tissue. Progesterone holds down the excessive tissue growth effects of estrogen. Heavy or irregular bleeding often occurs because estrogen dominance causes the temporary layer of the endometrium to overgrow. To much endometrial tissue builds up and then breaks down in a disorderly way. Low levels of progesterone cannot counteract the excess estrogen.
Cortisol is a hormone released due to stress. Cortisol impairs or diminishes progesterone activity; for many women low levels of progesterone contributes to excess menstrual bleeding and heavy cramping.
To a certain degree, stress can contribute to endometrial tissue buildup because stress drains the body of hormone balancing and healing nutrients. Stress increases cortisol levels. Cortisol impairs progesterone activity, by blocking or competing for progesterone receptors. Low progesterone contributes to estrogen dominance. This unbalance of excess estrogen contributes to the growth of the uterine lining (endometrium); this tissue over growth often contributes to heavy or irregular bleeding. Stress is not the primary factor, but it can be a contributing factor.
A bit more about progesterone
Progesterone decreases the biological activity of estradiol (estrogen) on the endometrium by decreasing the concentration of estradiol receptors, increasing the activity of 17 B-hydroxysteriod dehydrogenase type II, the enzyme responsible for the conversion of estradiol to estrone, and by increasing the activity of estrone sulfotransferase.
The primary role of progesterone is to support egg implantation and sustain pregnancy. Progesterone supports pregnancy by inhibiting uterine contractions and by suppressing the immune systems response to the developing embryo as a foreign body.
Just before ovulation progesterone secretion is 2 – 3 mg per day. After ovulation progesterone secretion is 20 – 25 mg per day, one week post ovulation 30 mg per day and during the third trimester of pregnancy 300 – 400 mg per day.