Explanation:

Ovulation is the release of an ovum from the mature Graafian follicle. The hormone responsible for ovulation is estrogen. Estrogen is produced by the developing follicle and stimulates the release of luteinizing hormone (LH) from the anterior pituitary gland.

The surge in LH causes ovulation to occur, leading to the release of the ovum from the Graafian follicle. The released ovum then moves into the fallopian tube, where it can be fertilized by a sperm.

Therefore, the correct answer is option D, high concentration of estrogen.

Hormone Levels and Ovulation

Ovulation is the process by which a mature egg is released from the ovary. This process is controlled by a complex interplay of hormones.

Estrogen and the Follicular Phase

- During the follicular phase of the menstrual cycle, the follicles in the ovary are stimulated to grow and mature by follicle-stimulating hormone (FSH).
- As the follicles grow, they produce increasing amounts of estrogen.
- Estrogen has a number of effects on the reproductive system, including thickening the uterine lining and making cervical mucus more hospitable to sperm.
- However, the most important effect of estrogen in the context of ovulation is that it triggers a surge of luteinizing hormone (LH).

LH Surge and Ovulation

- The LH surge is a sudden increase in the amount of luteinizing hormone that is released by the pituitary gland in response to high levels of estrogen.
- This surge triggers the release of the mature egg from its follicle, a process known as ovulation.
- Once the egg is released, it travels down the fallopian tube towards the uterus, where it may be fertilized by sperm.

Progesterone and the Luteal Phase

- After ovulation, the empty follicle that contained the egg turns into a structure called the corpus luteum.
- The corpus luteum produces progesterone, which helps to prepare the uterine lining for implantation of a fertilized egg.
- If fertilization does not occur, the corpus luteum eventually breaks down, causing progesterone levels to drop.
- This drop in progesterone triggers the start of a new menstrual cycle.

Conclusion

In summary, the hormone levels that cause release of ovum (ovulation) from the graafian follicle are high levels of estrogen, which trigger a surge of luteinizing hormone (LH). This surge causes the mature egg to be released from its follicle and begin its journey down the fallopian tube. While progesterone plays an important role in preparing the uterus for pregnancy, it is not directly involved in the process of ovulation.