Most useful notes on the concept of ‘Ovulation’
In the course of becoming a Graafian follicle an egg produced from a primary oocyte first becomes partially detached from its surrounding epithelial cells beneath the tunica albuginea.
As the primary follicle matures it starts moving further into the stroma and assumes deeper position there.
Side by side it begins to enlarge and its surrounding cells continue to grow in number, forming many layers.
A homogeneous covering of mucoprotein, zona pellucida, appears between the developing oocyte or ovum and the follicular celts.
The follicle cells start differentiating and form a layer of granular cells (granulosa) around the zona pellucida and developing ovum or egg.
Zona pellu;ida actually is the layer in which polar bodies produced during the meiotic division of the primary oocyte, are entrapped and this layer remains with the ovum until its implantation or death.
Under the influence of pituitary gonadotropins a follicular fluid is secreted by the surrounding follicular cells and the cells immediately surrounding the egg become separated from the more remote cells (zona pellucida) and thus a large cavity, the antrum is formed.
The fully developed follicle with an antrum, well established granulosa and theca is called a Graafian follicle. Graafian follicle measures about 10 mm in diameter and contains an ovum some 100 to 150p in diameter.
The Graafian follicle during final stages of its development, moves to the surface of the ovary and produces a thin blister-like elevation, which eventually bursts releasing the ovum into the abdominal cavity.
Now the ovum is swept into one of the oviducts as a result of the movement of the cilia located at the finger-like projections of the opening of the oviducts. From the oviduct the ovum is transported into uterus.
In case the ovum is fertilized, it is implanted in the endometrium of the uterus but if it is not fertilized, it liquefies and discarded through the vagina.
The follicles, which enlarge but do not undergo ovulation, finally degenerate and form atretic follicles.
The follicle which ovulates is converted into a blood filled cavity called corpus haemorrhagicum just after the discharge of the ovum Blood comes from the blood vessels injured during the ovulation of ovum.
Soon after this clotted blood is replaced by yellow body of lipids or luteal cells proliferated from the granulosa and theca cells and thus corpus luteum is formed.
The formation and maintenance of corpus luteum are under the influence of luteinizing hormone of anterior pituitary.
If the ovum is fertilized, the corpus luteum enlarges and remains during the first seven months of gestation; if the ovum is not fertilized, the corpus luteum degenerates and becomes corpus albicans which appears as disorganized scarred globules.