Antrum is filled with fluid and is found in:
The correct answer is option 'C' - Graafian follicle of ovary.

Explanation:
The antrum is a fluid-filled cavity that is found in the Graafian follicle of the ovary. The Graafian follicle is a mature ovarian follicle that contains a single ovum or egg. The antrum is formed as the follicle grows and develops.

Functions of Antrum:
The antrum plays a crucial role in the process of ovulation and the release of the egg. It performs several important functions, including:

1. Secretion of Hormones: The cells lining the antrum produce hormones such as estrogen and progesterone, which are essential for the regulation of the menstrual cycle and preparation of the uterus for pregnancy.

2. Maturation of Ovum: Within the antrum, the ovum undergoes final maturation and development. The follicular fluid present in the antrum provides nourishment to the ovum and helps in its growth.

3. Formation of Cumulus Oophorus: The antrum also participates in the formation of the cumulus oophorus, which is a cluster of cells that surrounds the ovum. The cumulus cells provide support and protection to the developing ovum.

4. Ovulation: When the Graafian follicle reaches its maximum size and maturity, it ruptures, leading to the release of the ovum. This process is known as ovulation, and the antrum plays a critical role in facilitating the rupture and release of the egg.

5. Corpus Luteum Formation: After ovulation, the remaining cells of the ruptured follicle form a structure called the corpus luteum. The corpus luteum secretes hormones that support early pregnancy if fertilization occurs.

In conclusion, the antrum is a fluid-filled cavity found in the Graafian follicle of the ovary. It performs various functions related to ovulation and the maturation of the ovum.