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Ginecologia: Ciclo Menstrual
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Ginecologia: Ciclo Menstrual

Introduction to the Menstrual Cycle

In this section, we will discuss the menstrual cycle, which involves the synchronization and coordination of morphological and physiological changes primarily in the ovaries and endometrium.

The Ovarian Cycle

  • The ovarian cycle is responsible for follicular development and ovulation.
  • The first two weeks of the menstrual cycle are known as the preovulatory phase or follicular phase.
  • The hypothalamus plays a crucial role in coordinating the functions of the ovaries through the release of gonadotropin-releasing hormone (GnRH).
  • GnRH stimulates the pituitary gland to produce follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which directly affect the ovarian follicles.

The Menstrual Cycle

  • The menstrual cycle begins on the first day of menstruation.
  • The ovary and endometrium undergo a 28-day journey, with different tasks assigned to each half of this period.
  • During the first two weeks, multiple primary follicles develop within the ovary. Two specialized cell types, granulosa cells and theca cells, surround each primary oocyte.
  • These cells produce hormones such as estradiol under the influence of FSH and LH.
  • Estradiol thickens and matures the endometrium inside the uterus.

Hormonal Influence

  • Estradiol has a direct effect on both ovarian follicles and endometrial growth.
  • As estradiol levels rise, it triggers negative feedback on FSH production by reducing its secretion from the pituitary gland.
  • This reduction in FSH leads to competition among developing follicles, resulting in only one dominant follicle surviving while others regress.

Second Phase of the Menstrual Cycle

In this section, we will explore the second phase of the menstrual cycle and the role of hormones in follicle development.

Hormonal Interactions

  • Granulosa cells develop receptors for both FSH and LH as they approach day 14.
  • The dominant follicle continues to produce estradiol, which influences the pituitary gland through negative feedback.
  • This feedback mechanism reduces FSH production, causing most developing follicles to regress and only the dominant one to survive.

Follicle Maturation

  • The dominant follicle within the ovary completes its maturation by day 14.
  • Estradiol levels reach their peak during this time.
  • The rise in estradiol triggers changes in the endometrium, leading to a proliferative phase characterized by growth and thickening.

Conclusion of First Half of Menstrual Cycle

In this section, we will discuss the conclusion of the first half of the menstrual cycle and summarize key points.

Final Stages

  • By day 14, estradiol levels peak, marking the end of the first stage of the menstrual cycle.
  • The dominant follicle survives while others regress due to reduced FSH production.
  • The next phase involves ovulation and preparation for potential fertilization.

This summary covers only a portion of the video transcript.

The Influence of Pituitary Hormones on Ovulation

This section discusses the influence of pituitary hormones on the dominant follicle and the process of ovulation.

The Role of Pituitary Hormones in Follicle Development

  • The generous sun-like effect of both pituitary hormones (follicle-stimulating hormone and luteinizing hormone) influences the dominant follicle.
  • By day 14, the dominant follicle reaches its maximum development due to the influence of these hormones.
  • These hormones allow for the opening of the follicle's envelope and the expulsion of the ovum.

Ovulation Process

  • Ovulation is when the matured ovum is released from the dominant follicle and travels through the fallopian tube in search of sperm for fertilization.
  • This marks the end of the first part of the menstrual cycle.

The Second Part: Post-Ovulatory Phase

This section focuses on the second part of the menstrual cycle, known as the post-ovulatory phase or luteal phase.

Attention Shift to Empty Follicle

  • In this phase, attention shifts to focus on the empty follicle left inside the ovary after ovulation.
  • If fertilization does not occur within three days, this empty follicle regresses and disappears.

Transformation into Corpus Luteum

  • The empty follicle is now called corpus luteum, which plays a crucial role in this second phase known as luteal phase.
  • The corpus luteum still contains cells from its envelope, including granulosa cells that are now called luteinized granulosa cells.

Progesterone Production by Luteinized Granulosa Cells

  • Luteinized granulosa cells, with both follicle-stimulating hormone and luteinizing hormone receptors, start producing progesterone.
  • Progesterone is a reproductively active hormone that gradually increases in quantity.

The Role of Progesterone and Feedback Mechanism

This section explains the role of progesterone in the second part of the menstrual cycle and its feedback mechanism.

Negative Feedback on Pituitary Gland

  • The increasing levels of progesterone have a negative feedback effect on the pituitary gland.
  • This leads to a decrease in the production of follicle-stimulating hormone and luteinizing hormone.

Dominance of Progesterone

  • Progesterone becomes the dominant hormone in this phase due to the dramatic decrease in estradiol levels.
  • Progesterone directly affects the endometrium, causing it to enter a secretory phase.

Focus on Empty Follicle and Corpus Luteum

This section discusses the continued focus on the empty follicle (corpus luteum) during the post-ovulatory phase.

Continued Production by Corpus Luteum

  • The corpus luteum continues to produce progesterone while undergoing involution.
  • It decreases in size and function, eventually becoming an atrophic structure called corpus albicans.

Endometrial Changes and Menstruation

This section explains how endometrial changes occur during the menstrual cycle's second part and lead to menstruation.

Effect of Progesterone on Endometrium

  • By day 14, when ovulation occurs, the endometrium has reached its maximum growth.
  • Under the influence of progesterone, the endometrium matures and fills with nutrients, oxygen, water, carbohydrates, proteins, and lipids.

Preparation for Pregnancy

  • The purpose of these changes is to prepare the endometrium for possible pregnancy and support it for 40 weeks.

Menstruation

  • If pregnancy does not occur, the corpus luteum's progesterone production decreases dramatically by day 28.
  • This leads to a metabolic inability to sustain the endometrium, resulting in its detachment from the uterine cavity and menstruation.

Conclusion and Next Steps

This section concludes the discussion on the menstrual cycle and suggests further study topics.

Recap and Repetition

  • It is recommended to review and repeat the information until a thorough understanding is achieved.
  • This knowledge will be valuable for future gynecology classes and when studying hormonal contraceptives.

Closing Remarks

  • The speaker expresses gratitude for attention and invites questions or comments.