Menstrual Cycles

Definition

Menstrual cycles refer to the periodic physiological changes that occur in the female reproductive system, particularly the uterus and ovaries, which prepare the body for potential pregnancy. This cyclical process is a key aspect of the development and function of the female reproductive system.

5 Must Know Facts For Your Next Test

1. The average menstrual cycle lasts between 21 and 35 days, with the average being 28 days.
2. The menstrual cycle is divided into two main phases: the follicular phase and the luteal phase.
3. The follicular phase begins on the first day of menstruation and ends with ovulation, during which the ovarian follicles develop and the uterine lining thickens.
4. Hormonal changes, such as the rise and fall of estrogen and progesterone, regulate the various stages of the menstrual cycle.
5. Menstrual cycles are influenced by factors such as age, stress, and underlying medical conditions, which can lead to irregularities or abnormalities.

Review Questions

• Describe the key events that occur during the follicular phase of the menstrual cycle.
  • During the follicular phase, which begins on the first day of menstruation, the ovarian follicles develop and mature under the influence of follicle-stimulating hormone (FSH). As the follicles grow, they produce increasing amounts of estrogen, which causes the uterine lining to thicken in preparation for potential implantation. This phase culminates in ovulation, the release of a mature egg from the ovary, which is triggered by a surge in luteinizing hormone (LH).
• Explain the role of hormonal changes in regulating the different stages of the menstrual cycle.
  • The menstrual cycle is primarily regulated by the fluctuations in the levels of reproductive hormones, such as estrogen, progesterone, FSH, and LH. During the follicular phase, rising estrogen levels stimulate the growth and development of the ovarian follicles and the thickening of the uterine lining. The LH surge then triggers ovulation, marking the transition to the luteal phase. In the luteal phase, progesterone levels increase, maintaining the uterine lining and preparing it for potential implantation. If implantation does not occur, progesterone levels drop, leading to the shedding of the uterine lining and the onset of menstruation, starting the cycle anew.
• Analyze how factors such as age, stress, and medical conditions can influence the regularity and characteristics of the menstrual cycle.
  • Menstrual cycles can be affected by various factors, both physiological and environmental. As women age, particularly approaching menopause, the menstrual cycle may become more irregular due to hormonal changes and the gradual depletion of ovarian follicles. Stress, whether physical or psychological, can disrupt the delicate hormonal balance and lead to missed or irregular periods. Underlying medical conditions, such as polycystic ovary syndrome (PCOS), endometriosis, or thyroid disorders, can also interfere with the normal functioning of the reproductive system, resulting in menstrual irregularities, abnormal bleeding, or even the absence of menstruation. Understanding how these factors can influence the menstrual cycle is crucial for maintaining reproductive health and identifying potential issues that may require medical attention.

Related terms

Ovulation:

The release of a mature egg from the ovary during the menstrual cycle, which occurs approximately halfway through the cycle.

Menstruation:

The monthly shedding of the uterine lining, which is the visible sign of the menstrual cycle and indicates that pregnancy has not occurred.

Luteal Phase:

The second half of the menstrual cycle, which begins after ovulation and is characterized by the production of the hormone progesterone.