Menstrual Cycle - Phases Of Menstrual Cycle And Role of Hormones: Overview, Phases

Definition Of The Menstrual Cycle

The menstrual cycle is a natural biological process by which the female body gets prepared every month for pregnancy. It is changes that occur in the ovaries and lining of the uterus and are regulated by hormonal fluctuations. The menstrual cycle forms an integral part of reproductive health, and its regularity often signifies good general health.

Commonly, the length of the menstrual cycle is about 28 days, although, in adults, it can also be anywhere between 21-35 days. This variability can be attributed, at least in part, to factors such as stress, diet, or general health. It undergoes four major phases: menstrual, follicular, ovulation, and luteal phases, each with peculiar hormonal changes and physiological events.

Anatomy And Physiology Of The Female Reproductive System

The female reproductive system includes some very fundamental organs that relate to each other to provide for the menstrual cycle and reproduction.

Anatomy of the Female Reproductive System

• Ovaries: Small, almond-shaped glands that produce eggs (ova) and secrete hormones, including estrogen and progesterone.

• Fallopian Tubes: Tubes that convey the egg from the ovary to the uterus; the site where fertilization generally occurs.

• Uterus: A hollow, muscular organ where a fertilized egg implants and develops into a fetus.

• Cervix: The lower portion of the uterus that opens into the vagina; it produces mucus which changes in consistency during the menstrual cycle.

• Vagina: A muscular canal connecting the cervix to the outside of the body; functions as a birth canal and the exit for menstrual blood.

Basic Physiology

• Ovarian function refers to the production of eggs and hormones, namely estrogen and progesterone, that control the menstrual cycle.

• Uterine function refers to the preparation of the lining of the uterus, endometrium, and its shedding during menstruation if implantation does not occur.

Phases Of The Menstrual Cycle

The different phases of the menstrual cycle include four distinct phases. All these phases are hormonally mediated and oriented toward preparing the body for pregnancy.

Menstrual Phase

• Duration: Day 1 to Day 5

• Endometrial shedding: The lining of the uterus is lost and leads to menstrual bleeding.

• Symptoms and biological changes: Cramps, bloating, and mood swings are some of the common complaints during this phase.

• Hormonal levels: Estrogen and progesterone levels are low.

Follicular Phase

• Duration: Day 1 to Day 13

• Follicle development in the ovaries: Many follicles start maturing, but usually only one is going to develop fully.

• Role of FSH: Follicle Stimulating Hormone stimulates the growth of ovarian follicles.

• Increased estrogen secretion: As follicles mature, they begin to secrete a greater amount of estrogen.

• Thickening of the endometrial lining: The thickness of the uterine lining begins to increase in anticipation of an impending pregnancy.

Ovulation Phase

• Duration: Day 14

• Release of the egg from the ovary: The ovary releases the mature egg into the fallopian tube.

• Surge in LH: Luteinizing Hormone surges to its peak, followed by ovulation.

• Role of estrogen and progesterone: Estrogen peaks a little before ovulation, whereas progesterone starts increasing after ovulation.

• Signs of ovulation: Basal body temperature increases, the cervical mucus changes and there may be mild pelvic pain.

Luteal Phase

• Duration: Day 15 to Day 28

• Formation of corpus luteum: The ruptured follicle is now known as the corpus luteum. It secretes progesterone.

• Secretion of progesterone and estrogen: These hormones prepare the endometrium for implantation.

• Endometrial preparation for possible implantation: The lining of the uterus becomes thick and rich in nutrients.

• Hormone levels drop in the absence of fertilization: In the absence of fertilization, estrogen and progesterone levels fall.

• Premenstrual symptoms: These can include mood changes, breast tenderness, and bloating.

Role Of Hormones In The Menstrual Cycle

Hormones are what essentially control the menstrual cycle and each hormone participates at different times during the cycle or in different phases of buildup and breakdown.

Estrogen

• Production sites: Principally produced in the ovaries.

• Functions during the menstrual cycle: Causes growth of the endometrium and acts as a negative feedback on the release of FSH and LH.

• Effects on secondary sexual characteristics: Breast development, body fat distribution, and the menstrual cycle.

Progesterone

• Production sites: Progesterone is produced in the corpus luteum of the ovary.

• Functions during the menstrual cycle: Prepare the endometrium for implantation and later maintain early pregnancy.

• Role in pregnancy: Maintains the uterine lining and prevents contractions.

Follicle Stimulating Hormone (FSH)

• Production site: Pituitary gland

• Role in follicular development: Stimulates the growth and maturation of ovarian follicles.

• Luteinizing Hormone (LH)

• Production site: Pituitary gland

• Role in ovulation: Triggers the release of a mature egg from the ovary.

Gonadotropin-releasing Hormone (GnRH)

• Role in the regulation of FSH and LH: GnRH from the hypothalamus regulates the release of FSH and LH from the pituitary gland.

• Feedback mechanisms: Estrogen and progesterone levels control GnRH release through negative feedback loops.

Common Menstrual Disorders

• Dysmenorrhea: Pain at the beginning of menstruation, often consisting of abdominal cramps.

• Amenorrhea: Absence of menstruation, either primary (never started) or secondary (stopped).

• Menorrhagia: Excessive bleeding at menstruation.

• Premenstrual Syndrome (PMS): A collection of symptoms, including mood swings, bloating, irritability, and more, that occurs a week or more before menstruation.

• Polycystic Ovary Syndrome (PCOS): A hormonal disorder that causes irregular periods, ovarian cysts, and a variety of other symptoms.

Diagnosis and Treatment

Diagnostic Tests: Ultrasonography, hormone level tests, and physical examinations for the diagnosis of menstrual disorders.

Treatment Options: Medications for pain relief and hormonal treatments, lifestyle modifications involving diet and exercise, and surgical interventions in some cases.

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