Question

The antrum is a cavity of-
a. Ovary
b. Graafian follicle
c. Blastula
d. Gastrula

Answer 1

Hint: The antrum is a term used for a cavity or chamber. It may have a specific meaning about certain organs or sites in the body. A cavity is a fluid-filled space that holds and protects the organs of the body. The ventral and dorsal cavity are the two largest cavities of the human body. The ovaries produce egg cells that are transported and fused with sperm to form a zygote.

Complete answer:
During the development of the fetus in an embryo, many oogonia are produced. These oogonia undergo mitosis and form primary oocytes which remain at prophase of meiosis I throughout childhood. Primary oocytes are enclosed by a single layer of cells, the granulosa cells, and form structures known as primordial follicles.

The primordial follicle first becomes a primary follicle as the granulosa cells multiply and form many layers of cells around the primary oocyte. Also, the cells from the stroma of the ovary form further layers of granulosa cells and the theca and collectively known as secondary follicles. As the secondary follicle develops, fluid is secreted by granulosa cells which contain the hormone estrogen.

A fluid-filled space or cavity, which is called the antrum, develops in the follicle which is now called the tertiary follicle. Oestrogen stimulates the growth of this follicle, which eventually becomes a mature follicle, the Graafian follicle.

Hence, the correct answer is option (B).

Additional information:
- Within the ovary, there exists a system of communicating cavities, the ovarian cavity, which caudally continues with the oviduct. The ovarian cavity is bordered by an epithelium which is secretory active and covered with microvilli.
- In blastula, the cells form an epithelial (covering) layer, called the blastoderm, enclosing a fluid-filled cavity, the blastocoel.
- The cavity of the gastrula is called the archenteron cavity which is formed by the invagination of cells.

Note: The Graafian follicle is marked by the formation of a fluid-filled cavity adjacent to the oocyte, called the antrum. It is hampered only by the availability of follicle-stimulating hormone (FSH), Antral follicles can attain a tremendous size, which is dependent on in this stage of folliculogenesis.