Short notes on the structure of the mature Graffian follicle
A mature human egg is called Graffian follicle. The young ovum develops and undergoes maturity in the follicles of the ovary called Graffian follicles. The mature egg has a typical cell structure and consists of the following parts –
The outermost layer is a double layered connective tissue sheet and it is differentiated into two layers namely theca externa and theca interna. The theca externa is the outer fibrous layer. It is made up of spindle shaped cells and fibres. The theca interna is composed of the inner vascular layer and it is supplied by a number of blood capillaries. In a mature follicle there is a fluid filled cavity which is eccentric and it is called antrum. The fluid itself is called liquor follicle. The antrum is lined by a membrane called granulosa there is a homogenous basement membrane called glassy membrane.
Internal to the theca interna is a membrane called zona pellucida. This is comparable to the vitelline membrane. Surrounding the zona pellucida is a region called corona radiata. This is formed from the other follicle cells. The cytoplasm of the egg is known as the ooplasm. The ooplasm consists of a large amount of reserve food materials.
There is very little yolk however in the cytoplasm. The peripheral part of the ooplasm is known as the cortex. It consists of many microvilli. The microvilli are formed as protruberances of the plasmalemma (plasma membrane). The microvilli help in the transportation of the substances from follicle cells to the egg during its development. The cytoplasm consists of the anu of mitochondria, lipoproteins, pigment granules, ribosomes, golgi complex and a number of other cell inclusions. The egg consists of a single nucleus which is usually vesicular in shape.