[Biology Class Notes] on Hormonal Control of Menstrual Cycle Pdf for EXAM

The menstrual cycle is a sequence of natural changes that take place in hormone production and in the structures of the uterus and ovaries of the female reproductive system that makes the woman’s body ready for pregnancy. 

Hormonal Control of Menstrual Cycle

There are 4 hormones that control the menstrual cycle controlled by the interaction of hormones: luteinizing hormone, follicle-restoring hormone, and the female sex hormones estrogen and progesterone. The ovarian hormones are circulated in the blood and are then excreted in the forms of urine. The cyclic events in the ovary depend on gonadotropic hormones secreted by the anterior lobe of the pituitary gland; There are three gonadotropic hormones: luteinizing hormone (LH), follicle-stimulating hormone (FSH), and, possibly, luteotropic hormone (LTH).

The Menstrual Cycle has Three Phases:

• Before the release of the eggs – Follicular phase

• The egg release – Ovulatory phase

• After the egg release – Luteal 

The follicular phase commences with the menstrual cycle, which begins with menstrual bleeding (menstruation). The levels of estrogen and progesterone are low in this phase. Due to this, it leads to the breakage of the top layers of the thickened lining of the uterus (endometrium) and shed in the form of blood. At this time, the development of several follicles in the ovaries is stimulated by the increased level of FSH follicle-stimulating hormone. Each follicle has an egg. After this, only one follicle continues to develop with the decrease in the follicle-stimulating hormone level. This follicle further leads to the production of estrogen.

The ovulatory phase commences with an increase in luteinizing hormone and FSH (follicle-stimulating hormone) levels. Luteinizing hormone vitalizes the release of the egg (ovulation), which occurs 16 to 32 hours after the surge starts. The estrogen level decreases, and progesterone increases during the surge. 

During the luteal phase, there is a decrease in luteinizing hormone and follicle-stimulating hormone levels. The follicle, which is ruptured, closes after the release of the egg and leads to a formation of a corpus luteum, which results in the production of progesterone. The estrogen level is high during most of this phase: estrogen and progesterone cause the lining of the uterus to thicken as a preparation for possible fertilization.

The corpus luteum degenerates if the egg is not fertilized, and hence the production of progesterone stops, and also the estrogen level decreases, which leads to the breakage of the top layers of the lining and are shed in the form of menstrual bleeding. 

However, if the egg is fertilized, the corpus luteum works during early pregnancy. It helps maintain the pregnancy.

Hormonal Pills for Periods

There is a huge role of hormones in maintaining the menstruation cycle. The hormonal regulation of the menstrual cycle will determine the fertility of the women. There are types of hormonal contraception (for example, the oral contraceptive pill, IUD coil, injection) that may have an effect on your menstrual cycle. This could cause a change in your periods’ frequency or flow. 

Generally, oral contraceptive pills will help you to make your periods lighter. You may notice that the flow of your period’s changes and your periods have become while your cycle adapts to the changing hormones. After months of taking the pill, your periods should have now taken a regular routine. Some women have also said that their periods stop after taking the contraceptive pill.

Hormonal injections can also cause irregularity in your periods for a while before your body adapts to the hormones. However, some women experience heavier periods when they start getting hormonal injections, although periods usually become much lighter over time. A contraceptive implant can also give you irregular periods. 

The IUD (Mirena) coil can also affect your periods. You may experience some irregular spotting (light bleeding at an irregular time of your cycle) or bleeding if it has been fitted in the last six months. After that, many women find that their periods stop. Some also shared that their periods become much irregular or lighter. This is quite common among women. 

Hormonal Pills for Irregular Periods

Some women use medication and lifestyle modification to regularize the periods. You can use hormonal contraception for this purpose which includes:

• a combined oral contraceptive pill (‘the pill’)

• progesterone, which helps in stimulation of the uterus and induces bleeding

• the hormonal implants

• vaginal contraceptive rings

• intrauterine devices have progesterone.

The progesterone and oestrogen in hormonal contraception interact with the body’s control of the menstrual cycle and ovulation. The oral contraceptive pill function by ‘switching off the ovaries’ means that if a woman consumes the contraceptive pill, her production of hormones such as testosterone is significantly decreased.

The oral contraceptive pill (‘the pill’) decreases the ovarian production of testosterone and other androgens. It also helps in the body’s production of sex hormone-binding globulin (SHBG). This leads to a reduction in the role of testosterone and hence reduces the symptoms of male hormone or androgen excess.

Oral contraceptives can badly affect insulin resistance and increase the risk of type 2 diabetes, especially in very obese women with PCOS. 

There are medications used for irregular periods. The most famous is Medroxyprogesterone is used to treat irregular vaginal bleeding or abnormal menstruation (periods). Medroxyprogesterone is also used to normalize the menstrual cycle in women who menstruate naturally in the past but who have not been menstruated for at least six months and are not pregnant or undergoing menopause (change of life). Medroxyprogesterone is also aids in the prevention of overgrowth of the lining of the uterus (womb) and can also reduce the risk of cancer of the uterus in patients who are consuming estrogen. It functions by restricting the growth of the lining of the uterus and hence causes the uterus to produce some hormones.