D. Graffian follicle
Since Graffian follicle after ovulation further changes to corpus luteum, Which secrete progesterone.

Answer:

After ovulation, the Graafian follicle in the ovary of mammals acts as an endocrine gland. Let's understand this in detail:

1. Ovulation:
Ovulation is the process in which a mature egg is released from the ovary in preparation for fertilization. It occurs in the middle of the menstrual cycle and is regulated by hormones such as luteinizing hormone (LH) and follicle-stimulating hormone (FSH).

2. Graafian Follicle:
The Graafian follicle is a mature follicle in the ovary that contains a fully developed egg. It is the largest and most dominant follicle in the ovary during the menstrual cycle. The Graafian follicle develops under the influence of FSH and secretes estrogen.

3. Endocrine Gland:
An endocrine gland is a gland that releases hormones directly into the bloodstream. These hormones then travel throughout the body, regulating various physiological processes. The Graafian follicle, after ovulation, acts as an endocrine gland by releasing hormones.

4. Hormones Secreted:
After ovulation, the Graafian follicle undergoes changes and transforms into the corpus luteum. The corpus luteum is a temporary endocrine structure that secretes hormones, primarily progesterone.

5. Progesterone:
Progesterone is a hormone that plays a crucial role in preparing the uterus for pregnancy. It helps in thickening the uterine lining, maintaining pregnancy, and preventing further ovulation.

6. Role of the Corpus Luteum:
The corpus luteum, derived from the Graafian follicle, secretes progesterone. This hormone prepares the uterus for implantation and supports early pregnancy. If fertilization and implantation occur, the corpus luteum continues to produce progesterone to maintain pregnancy until the placenta takes over hormone production. If fertilization does not occur, the corpus luteum degenerates, hormone production decreases, and the menstrual cycle starts again.

In conclusion, after ovulation, the Graafian follicle in the ovary acts as an endocrine gland by transforming into the corpus luteum and secreting progesterone. This hormone is essential for preparing the uterus for pregnancy and supporting early pregnancy.