Female Reproductive Cycle
The female reproductive cycle begins at puberty between the age of 13-15 and ends between the ages of 45-50 years (menopause). The formation of gamete only takes place during the reproductive period. The cycle consist of regular, repeated changes in the uterine lining, which result to menstrual bleeding commonly known as period, or menses. At the same time, there are also changes in the ovary, which constitute the ovarian cycle.
The onset of the female reproductive cycle is called monarch, it occurs after the ovaries and other organs of the reproductive control system have matured and begun responding to certain hormones.
The menstrual cycle is a cyclic event that occurs in a rhythmic fashion during reproductive period of a woman's life. Certain hormones produced by the pituitary gland influence the changes that takes place during ovarian cycle. and such hormone called luteinizing hormone (LH) which triggers ovulation, and after ovulation follicular cells gives rise to corpus luteum which in turn influence other parts of the female reproductive system (uterus) resulting in cycle of changes called uterine menstrual cycle or menstruation. A menstrual cycle begins with the onset of menstrual bleeding and ends just before the next menstruation.
Note: menstruation is the monthly shading of blood or blood flow from the lining of the uterus.
The normal period of menstruation comes once every 28 days and lasts 4-5 days, but under physiological condition, it may vary between 20-40 days, termed irregular menstruation but does not mean anything is wrong.
The changes associated with menstrual cycle involves various structure that makes up the uterine endometrium. The structures includes:
(1) The epithelium lining: this is the surface of the endometrium
(2) The stroma: this contains numerous simple tubular gland
(3) The arteries that supply the endometrium.
THE PHASES OF THE FEMALE REPRODUCTIVE CYCLE
During each menstrual cycle, along with ovarian changes uterian changes also occurs simultaneously. These changes in the uterus takes place in three phases.
(1) Menstrual phase
(2) Proliferative phase
(3) Secretary phase
- MENSTRUAL PHASE
The menstrual phase is the period whereby blood and tissue fluid is shade from the uterine lining and expelled through the vagina. It last about 4-5 days. This occurs after ovulation whereby the sperm cell does not fertilize the egg cell released at ovulation. The corpus luteum begins to degenerate on about the 24th day of the cycle. Eventually, connective tissue replaces it. When the corpus luteum ceases to function, concentration of estrogens and progesterone decline rapidly and blood vessels in the endometrium, constrict. This reduces the supply of oxygen and nutrients to the thickened uterine lining, and the lining tissues soon disintegrate and slough off. At the same time, blood leaves damaged capillaries creating a flow of blood and cellular debris that passes through the vargina as the menstrual flow. This flow usually begins about 28th day of the cycle and continues for 4-5 days while the concentration of estrogens are low. The menstrual flow marks the end of a reproductive cycle and the beginning of a new cycle.
- POLIFERATIVE PHASE
This phase extends usually between the 5th-14th day of menstruation i.e. between the day when menstruation stops and the day of ovulation. During this phase, endometrium cells proliferate rapidly and epithelium reappears on the surface of endometrium within the first four to seven days. Near the 14th day, the anterior pituitary cells releases the LH, which it has stored in response to the GnRH, pulses. The resulting surge in LH concentration, which last about 36hours weakens and ruptures the bulging follicular wall, which sends secondary oocyte and follicular fluid from the ovary (ovulation). The thickness of-4 millimeter at the end of this phase.
- SECRETORY PHASE
This phase extends between 15th and 28th day of menstrual cycle i.e. between the day of ovulation and the day when the menstruation of the next cycle begins. After ovulation, corpus luteum is developed in the ovary and at this stage; the endometrium becomes thicker under the influence of estrogen and progesterone. The secretory phase is the preparation period during which the uterus is prepared for pregnancy or for implantation of the fertilized ovum. If a fertilized ovum is implanted during this phase, and developed into fetus further changes takes place in the uterus for the survival of the developing fetus. However, if the ovum is not fertilized and implanted then mentration occurs starting the new reproductive cycle.
Abnormal menstruation or irregularity in the length of time between periods may be normal for some women, but for others it may be a sign of chronic illness, anemia, malnutrition, or an infection in the womb. Some abnormal menstruation are listed below
(7) Anovulatory cycle