In human females, the ovarian cycle begains when the:

Options

A. levels of oestrogen reach their maximum
B. hypothalamus stimulates the anterior pituitary to increase its output of FSH and LH
C. level of progesterone drops precipitously
D. hypothalamus increases its release of FSH and LH

Answer

**Step-by-Step Solution:**

1. **Understanding the Ovarian Cycle**: The ovarian cycle in human females is a series of events that occur in the ovaries, leading to the maturation and release of an egg (oocyte).

2. **Initiation of the Cycle**: The ovarian cycle begins at puberty, which typically occurs around the age of 10.5 years in girls. However, menstruation, which is a part of the cycle, usually starts around 12.5 years.

3. **Role of the Hypothalamus**: At the onset of puberty, the hypothalamus releases a hormone called Gonadotropin-Releasing Hormone (GnRH). This hormone is crucial as it signals the anterior pituitary gland to start its activity.

4. **Action of GnRH**: The GnRH travels to the anterior pituitary gland, stimulating it to release two important hormones: Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH).

5. **Effect of FSH and LH**: FSH and LH act on the ovaries. FSH promotes the growth and maturation of ovarian follicles, while LH triggers ovulation and the subsequent formation of the corpus luteum.

6. **Development of Oocytes**: The primary oocyte within the ovarian follicles begins to develop under the influence of FSH, leading to the formation of a mature Graafian follicle.

7. **Hormonal Feedback Mechanism**: As the follicles mature, they produce estrogen and inhibin. Estrogen helps in the proliferation of the endometrium in the uterus, while inhibin provides negative feedback to reduce FSH levels.

8. **Ovulation**: Around the 14th day of the cycle, a surge in LH occurs, leading to ovulation, where the mature Graafian follicle bursts and releases the secondary oocyte.

9. **Formation of Corpus Luteum**: After ovulation, the remnants of the Graafian follicle transform into the corpus luteum, which secretes progesterone to maintain the endometrium.

10. **Menstrual Cycle**: If fertilization does not occur, the corpus luteum regresses, leading to a decrease in progesterone. This results in the shedding of the endometrium, known as menstruation, marking the end of one cycle and the beginning of another.

**Final Answer**: The ovarian cycle in human females begins when the hypothalamus releases Gonadotropin-Releasing Hormone (GnRH) at the onset of puberty.

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