Ovulation and fate of the ovum – Menstrual cycle

The shedding of the ovum from the ovary is called ovulation. The ovarian
follicle enlarges and reaches the surface of the ovary. The stroma and the theca
of the Graffian follicle ruptures and the ovum is shed from the ovary. As it reaches
the fallopian tube it may get fertilized. The fertilized egg reaches the uterus and
gets implanted on its wall. If the ovum is not fertilized in the fallopian tube it dies
in 12- 24 hours.

Corpus luteum

The corpus luteum is an important structure needed at the time of
pregnancy. It is derived from the empty graafian follicle after ovulation. The
corpus luteum secretes a hormone called progesterone. It is a steroid hormone,
secreted in significant amounts by the corpus luteum and placenta.

Menstrual cycle

The functioning of the reproductive system in human adult female is
characterized by the menstrual cycle. While the changes concerned within ovulation and the formation of the corpus luteum, are going on in the ovary, the uterine endometrium shows striking cyclical changes.

The rhythmical series of changes in the sex organs occur for about 28 days through out the reproductive life of women from puberty to menopause (except during times of pregnancy). It is called the menstrual cycle.

The most prominent feature of this cycle is a monthly flow of blood from
the genital canal. This is called menstruation or menses. A menstrual cycle begins with the onset of menstrual bleeding and ends just before the next menstruation.

The menstrual cycle is usually divided into the following phases on
the basis of changes taking place in the uterine endometrium.
The follicular phase or Proliferative phase ( 5th day – 14th day)

The follicular phase is initiated by the release of follicle stimulating
hormone (FSH) from the anterior pituitary gland. During this phase, a
primary follicle begins to enlarge. While it is growing, the follicles secrete
oestrogen and smaller quantities of progesterone into the blood. Under the
effects of oestrogen from the developing follicle, the endometrium starts
regenerating from the basal portion. Deeper parts of the glands start proliferating.

By day 14, graffian follicle has matured and pushed up against
the ovary surface. The secretion of FSH ceases at the end of follicular phase.
The Luteal phase or Premenstrual phase (15th day – 28th day)

The luteal phase begins at day 14. Under the influence of Leutenizing
hormone (LH) released by the anterior pituitary, rupture of graffian follicle
and release of ovum (ovulation) occurs. After ovulation, the empty follicle is
transformed into a transitory endocrine gland called corpus luteum. The
corpus luteum slowly increases in size and releases a large quantity of
progestrone and smaller amount of oestrogen into the blood.

The progesterone acts on endometrium of the uterus, preparing it to receive the
fertilized ovum. To maintain pregnancy and to prevent the contraction of
uterus, the progesterone hormone is highly essential. If there is no fertilisation,
the corpus luteum degenerates and is reabsorbed by the ovary at the end of
luteal phase.

The menstrual phase (1st – 5th day)

The decline in progesterone and oestrogen initiates shedding of the
endometrium and severe bleeding in a process called mensus or
menstruation. During this phase, all the extra layers are sloughed off along
with unfertilized egg. At the termination of menstruation, the corpus luteum is
converted into a scar tissue called corpus albicans.

Ovulation and fate of the ovum – Menstrual cycle

Menstrual cycle

The menstrual phase (1st – 5th day)

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