What Causes Menopause?

What causes menopause? In short, getting older. This natural biological aging process marks the end of a woman’s reproductive years. As we age, complex interactions between our reproductive cycle and hormones trigger significant changes in our bodies. These changes ultimately lead to menopause.

In this blog post, we’ll explore the intricacies of the reproductive cycle, the role of various hormones, and the physiological shifts that occur during this important life transition.

By understanding what causes menopause, we can gain valuable insights and better prepare for the changes it brings.

Causes of Menopause: Reproductive Phase

Before we can fully appreciate the significance of menopause, it is essential to understand the fundamentals of the female reproductive cycle.

This intricate biological process forms the foundation of a woman’s fertility and marks the transition to menopause, a natural phase that celebrates the end of a remarkable ability and the beginning of a new chapter in a woman’s life.

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The Hypothalamus and GnRH

The hypothalamus is a small region in the brain that is essential for initiating the reproductive cycle. It produces gonadotropin-releasing hormone (GnRH). The primary function of GnRH is to regulate the release of two key hormones from the anterior pituitary gland: Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH). These hormones are necessary for the normal  functioning of the ovaries.

The release of GnRH is not continuous but occurs in intermittent bursts (pulses). This rhythmic secretion is essential because the frequency and strength of GnRH pulses determine the levels of these hormones, which in turn affect reproductive processes such as follicle development and ovulation.

The Anterior Pituitary: FSH and LH 

The anterior pituitary gland responds to GnRH by releasing FSH and LH into the bloodstream. These hormones travel to the ovaries, where they play pivotal roles in maturing ovarian follicles. Each follicle contains an egg, and female babies are born with a finite number of these eggs, estimated to be between 500,000 and 1,000,000. During each menstrual cycle, FSH stimulates a batch of these follicles to begin the maturation process.


FSH: Each ovary contains hundreds of thousands of immature primordial follicles that, as they develop into primary follicles, acquire FSH receptors. FSH then stimulates these follicles to grow and mature. During this process, the granulosa cells within the follicles produce Antimüllerian hormone (AMH). AMH helps control follicle development by reducing the number of immature follicles that start growing and by influencing how sensitive the follicles are to FSH. This regulation affects how many follicles continue to develop in each cycle.

Inhibin-B: Produced by the granulosa cells of the follicles in response to FSH. This hormone’s role is providing feedback to the anterior pituitary. It regulates FSH levels, ensuring that not too many follicles mature at once.

LH: Working in tandem with FSH, LH further stimulates the growth of follicles. A surge in LH levels, triggered by the rising estrogen produced by the maturing follicles, prompts the dominant follicle to release its mature egg.

Follicle Maturing and Estrogen Production 

As follicles mature, they start producing estrogen, which is important for several reasons:

 

Ovulation and the Corpus Luteum 

Ovulation is the process where the dominant follicle releases its mature egg into the fallopian tube. After ovulation, the ruptured follicle transforms into the corpus luteum, a temporary gland that produces hormones to support a potential pregnancy.

Corpus Luteum: The corpus luteum produces the hormones progesterone and some estrogen, which are essential for preparing and maintaining the inner lining of the uterus for a fertilized egg to attach. If pregnancy occurs, the developing embryo releases human chorionic gonadotropin (hCG), signaling the corpus luteum to continue producing progesterone and estrogen, which support the early stages of pregnancy.

However, if pregnancy does not occur, the corpus luteum breaks down after about 10-14 days, leading to a drop in hormone levels and triggering menstruation. The corpus luteum then degenerates into a small mass of scar tissue known as the corpus albicans, which is eventually absorbed by the ovary.

Causes of Menopause: Transition Phase 

Menopause marks the beginning of a new and vibrant phase of life, characterised by freedom from the menstrual cycle and the possibility for renewed focus on personal growth and well-being.

As a natural part of aging, menopause is brought about by complex changes in the body’s hormonal balance, particularly involving a decline in estrogen and progesterone levels.

While these changes lead to the end of a woman’s reproductive years, they also open the door to embracing this stage as a time of wisdom, self-discovery, and new opportunities.

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This phase is marked by significant hormonal changes and variations in menstrual patterns, preparing the body for the eventual end of menstruation and the beginning of a new, liberating stage of life.

 

 

Biological Changes That Cause Menopause

As women approach their late 40s or early 50s, they enter a phase known as perimenopause, or the Early Menopause Transition. This period, classified as Stage -2 in the STRAW+10 system, marks the beginning of significant changes in the reproductive system.

The hallmark of this transition is the natural decline in ovarian function, primarily driven by a diminishing pool of ovarian follicles. This reduction in follicle count is a pivotal factor in the journey towards menopause, setting the stage for the hormonal and physiological changes that follow. 

During this time, women may begin to notice subtle shifts in their menstrual patterns and experience occasional symptoms that hint at the approaching end of their reproductive years.

This transitional phase offers a perspective into the gradual process that ultimately causes menopause, bridging the gap between regular reproductive function and the end of menstruation.

Increased FSH and LH Levels

As estrogen levels decline, the body compensates by raising FSH and LH levels in an attempt to stimulate the remaining follicles to ovulate. However, this prolonged exposure to high levels of FSH and LH gradually desensitises the follicles. As a result, they become less responsive to these hormones, diminishing their ability to trigger ovulation and form the corpus luteum.

This change is an important part of the transition toward menopause, as it signifies a shift in the body’s reproductive function.

 

Decline in Follicle Responsiveness

As the number of follicles responding to the high levels of FSH and LH decreases, ovulation becomes less frequent. This decline in follicle responsiveness leads to a reduction in corpus luteum formation. Consequently, progesterone production decreases, which can further disrupt the regularity of the menstrual cycle.

 

Onset of Menopause

Eventually, the ovaries stop releasing eggs as the number of remaining follicles diminishes. With no ovulation, the corpus luteum does not form, which leads to a significant drop in both estrogen and progesterone levels. This hormonal change culminates in menopause, defined as 12 consecutive months without a menstrual period. This marks the beginning of Stage +1 of the STRAW+10 system, known as the Early Postmenopausal phase.

 

How Hormonal Changes Cause Menopause

Menopause is characterised by low levels of estrogen and progesterone, alongside elevated levels of FSH and LH. The decline in estrogen can lead to a range of symptoms, including hot flashes, night sweats, mood swings, and vaginal dryness.

Summarising What Causes Menopause

Menopause represents the culmination of a complex interplay between hormones and the reproductive system.

As women age, their ovaries gradually become less responsive to hormonal signals, resulting in a decline in estrogen and progesterone production. This hormonal shift progressively disrupts the menstrual cycle, eventually leading to no menstruation at all and marking the transition from perimenopause to postmenopause.

Understanding menopause offers valuable insights into this natural transition. Embracing this stage can be empowering, marking not just an end but the start of a new and vibrant chapter in life.