Female reproduction: Ovary-2, oviduct, uterus, cervix, vagina

Overview of the Reproductive System

Introduction

  • Presentation Focus:

    • Final discussion on ovaries, corpus luteum, luteal phase

    • Overview of the reproductive tract (oviduct, uterus, cervix, vagina)

    • Upcoming topics: mammary gland and pregnancy.

Ovarian Function

  • Hormones from corpus luteum:

    • High levels of progesterone.

    • Estradiol as the predominant estrogen produced.

  • Production Mechanism:

    • Initial trace production of progesterone by granulosa cells during late follicular phase.

    • Major production by granulosa lutein cells in luteal phase:

    • New function: uptake of cholesterol and conversion to progesterone.

    • Thecal cells continue to provide androgens throughout the 28-day cycle.

  • Feedback Mechanisms:

    • Negative Feedback:

    • Progesterone exerts negative feedback on hypothalamus and pituitary, reducing GnRH and gonadotropin response.

    • Inhibin A takes over from Inhibin B, selectively reducing FSH levels.

    • Fall in estrogen levels allows estradiol to affect positive feedback at hypothalamus/pituitary when conditions favor follicle development.

  • Luteal Phase Explanation:

    • Purpose: ensure no new follicle development until previous ovulation is resolved.

  • Corpus Luteum Dynamics:

    • Survives on LH; regresses to corpus albicans without sufficient LH.

    • Histological changes documented; acellular sheet representing previous cycles.

Corpus Luteum of Pregnancy

  • Blastocyst Implantation:

    • Implantation leads to secretion of //human chorionic gonadotropin (hCG)//, similar to LH, rescuing and maintaining corpus luteum.

  • Role of hCG:

    • Maintains estrogen and progesterone production from corpus luteum, essential for sustaining endometrial environment for fetal development.

  • Consequences of hCG Absence:

    • Fall in LH levels leads to corpus luteum regression; loss of necessary hormones results in endometrial shedding and potential loss of pregnancy.

Hormonal Levels and Menstrual Cycle Overview

  • Hormonal Level Variability:

    • Graph representation of FSH, LH, estradiol, progesterone, and inhibins throughout a 28-day cycle.

    • Knowledge of units and scales is crucial for interpretation of hormone levels.

    • Ensure correct comparison (e.g., milli units, picomoles, etc.).

  • Ovarian Cycle Phases:

    • Sequence: follicular phase, LH surge, ovulation, and luteal phase.

Menopause

  • Definition: Cessation of menstruation around age 50, marked by the loss of ovarian follicles (approximately 1,000 remaining).

  • Hormonal Changes:

    • Lack of estrogen and progesterone leads to dysregulation of hypothalamic-pituitary feedback mechanism.

    • Elevated levels of LH and FSH observed post-menopause due to absence of feedback inhibition.

  • Consequences of Menopause:

    • Symptoms: osteoporosis, hot flashes, cognitive decline, and increased coronary artery disease risk.

  • Hormone Replacement Therapy (HRT):

    • Historical use of Premarin (derived from horse urine), current focus on more refined hormone preparations like estradiol.

The Reproductive Tract Overview

Oviduct (Fallopian Tubes)

  • Functions:

    • Discharges ovum, provides fertilization environment, and conducts preimplantation embryo to uterus.

  • Structure:

    • Three layers: mucosa, muscularis, serosa.

    • Mucosal epithelium: simple columnar with ciliated and secretory peg cells.

  • Fertilization and Hormonal Regulation:

    • Estradiol increases ciliary action and secretions, while progesterone regulates smooth muscle contraction.

Uterus

  • Structure:

    • Comprised of endometrium, myometrium, and parametrium.

  • Functions:

    • Supports implantation, fetal development, and expulsion at term.

  • Hormonal Regulation:

    • Estrogen proliferates the endometrium; progesterone differentiates the glands for secretion.

    • Spiral arteries supply the endometrium, increasing with hormonal support.

Cervix

  • Functions:

    • Protects uterus and fetus; produces mucus to facilitate sperm penetration and prevents infection.

  • Structure:

    • Transformation zone transitioning from columnar to stratified squamous epithelium; glands present for mucus secretion.

  • Regulation:

    • Estrogen promotes watery mucus; progesterone induces thick and viscous mucus post-ovulation.

Vagina

  • Functions:

    • Excretory duct, organ of copulation, birth canal.

  • Structure:

    • Stratified squamous epithelium for protection against friction, highly vascularized.

  • Hormonal Regulation:

    • Estrogen increases epithelial thickness and glycogen production; progesterone decreases proliferation and promotes differentiation.

Conclusion

  • Summary of ovarian cycle and uterine responses, hormone regulation across reproductive tract structures, and implications for menopause and reproductive health.

  • Upcoming topic: mammary glands and pregnancy in next lecture.