Preovulatory

Preovulatory Phase

The preovulatory phase, also known as the follicular phase, is a critical part of the menstrual cycle in females. This phase occurs after menstruation and before ovulation, playing a vital role in preparing the body for potential fertilization and pregnancy.

Overview

The preovulatory phase begins on the first day of menstruation and ends with the onset of ovulation. It typically lasts about 10 to 14 days, but this can vary among individuals. During this phase, the body undergoes several hormonal changes that prepare the ovaries to release an egg.

Hormonal Changes

The preovulatory phase is characterized by a rise in follicle-stimulating hormone (FSH), which stimulates the growth of ovarian follicles. These follicles contain immature eggs. As the follicles mature, they produce increasing amounts of estrogen.

Follicle-Stimulating Hormone (FSH)

FSH is secreted by the anterior pituitary gland and is crucial for the growth and maturation of ovarian follicles. The rise in FSH levels marks the beginning of the preovulatory phase.

Estrogen

As the follicles develop, they secrete estrogen, which has several effects:

• Thickening of the endometrium (the lining of the uterus), preparing it for potential implantation of a fertilized egg.
• Regulation of the hypothalamic-pituitary-gonadal axis, leading to a decrease in FSH and an increase in luteinizing hormone (LH) as the phase progresses.

Follicular Development

During the preovulatory phase, several follicles begin to develop, but usually only one becomes the dominant follicle. This dominant follicle will eventually release an egg during ovulation.

Dominant Follicle

The dominant follicle is the one that grows larger and faster than the others. It produces more estrogen, which further suppresses the growth of other follicles. The selection of the dominant follicle is a complex process influenced by hormonal signals and local ovarian factors.

Endometrial Changes

The increase in estrogen levels during the preovulatory phase leads to the proliferation of the endometrial lining. This thickening is essential for creating a suitable environment for a fertilized egg to implant and develop.

Transition to Ovulation

As estrogen levels peak, they trigger a surge in LH, known as the luteinizing hormone surge. This surge is the signal for the dominant follicle to release its egg, marking the end of the preovulatory phase and the beginning of ovulation.

Clinical Significance

Understanding the preovulatory phase is important for various clinical applications, including:

• Fertility treatments, where timing of ovulation is crucial.
• Contraception, where knowledge of the menstrual cycle can aid in preventing pregnancy.
• Diagnosing and managing menstrual disorders.

Also see

• Menstrual cycle
• Ovulation
• Luteal phase
• Hormonal regulation
• Reproductive endocrinology