endo final 11

Male and Female Reproductive Physiology

Male Reproductive Organs

• Testes:

  • Function: Development of sperm and secretion of testosterone.

• Epididymis:

  • Function: Maturation and storage of sperm.

• Vas (ductus) deferens:

  • Function: Transport of sperm from the epididymis to the ejaculatory duct.

• Ejaculatory duct:

  • Function: Transport of sperm from the vas deferens through the prostate to the urethra.

Male Reproductive Glands

• Seminal vesicles:

  • Function: Secretes 60% of seminal fluid, which is rich in fructose and prostaglandins.

• Prostate gland:

  • Function: Secretes 30% of semen, providing nourishment for sperm.

• Bulbourethral gland:

  • Function: Secretes mucus.

The Testes

• Description: The male gonads responsible for producing sperm and hormones.

• Spermatogenesis:

  • Definition: The process of sperm cell development occurring in the seminiferous tubules of the testes.

  • Duration: Approximately 74 days.

• Hormone Production:

  • Primary Hormone: Testosterone, critical for male development and sexual function.

• Endocrine Cells of the Testes:

  • Sertoli Cells:

  • Location: Inside seminiferous tubules.

  • Function: Provide nutrients to support sperm development, secrete inhibin and estrogen.

  • Leydig Cells:

  • Location: Outside seminiferous tubules.

  • Function: Secrete testosterone.

Male Reproductive Endocrinology

• Hypothalamus:

  • Secretes Gonadotropin-Releasing Hormone (GnRH).

• GnRH:

  • Stimulates gonadotroph cells in the anterior pituitary to produce Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH).

• LH:

  • Function: Stimulates Leydig cells to produce testosterone.

• Testosterone:

  • Function: Promotes the growth of sexual glands (seminal vesicles and prostate gland) and stimulates spermatogenesis.

  • Feedback Mechanism: Inhibits production and release of GnRH and LH.

• FSH:

  • Function: Stimulates Sertoli cells to release factors that promote spermiogenesis.

  • Inhibin secretion by Sertoli cells inhibits FSH secretion.

• Note: Both testosterone and FSH are essential to initiate spermatogenesis.

Testosterone

• Definition: Testosterone is an androgen; a steroid hormone.

• Binding: Circulates bound to plasma proteins (albumin and sex-steroid binding globulin); about 2% is unbound.

• Conversion: Converted to Dihydrotestosterone (DHT) in tissues by the enzyme 5 alpha-reductase; DHT is more potent than testosterone.

• Mechanism: Both testosterone and DHT bind to intracellular androgen receptors to regulate gene/protein expression.

Functions of Testosterone

• Fetal Development: Triggers the development of male internal and external reproductive organs.

• Puberty: Increases testosterone levels promote the development of primary (sexual) and secondary sexual characteristics:

  • Changes include growth of body and facial hair, deepening of voice, increases in height and muscle mass.

• Adulthood: Stimulates sperm production, maintains muscle mass, and bone density—exhibiting anabolic effects.

Female Reproductive Anatomy

• Ovaries:

  • Function: Oocyte development and hormone production.

• Fallopian Tubes (Uterine Tubes):

  • Function: Transport of oocyte; primary site of fertilization and early embryo development.

• Uterus:

  • Function: Ovarian hormone-responsive; primary site of implantation and embryo development.

• Vagina:

  • Function: Pathway for menstrual fluid, sexual functions, and birth canal.

The Ovaries

• Description: Female gonads housing female germ cells (oocytes) inside follicles, producing reproductive hormones (estrogen and progesterone).

• Function: Coordinate a monthly cycle where a mature egg is released (ovulation).

• Endocrine Cells of the Ovaries:

  • Granulosa Cells: Layer surrounding the oocyte; secretes estrogen.

  • Theca Cells: Surround the follicles; secrete androgens.

Folliculogenesis

• Definition: The process of development and maturation of ovarian follicles from their earliest stages to ovulation.

• Components: Functional unit composed of an oocyte surrounded by somatic cells that house and nurture germ cells and produce hormones essential for female fertility.

• Gonadotropin Role: Hormones from the anterior pituitary are critical for folliculogenesis.

• Stages of Folliculogenesis:

  • Primordial Follicle: Primary oocyte surrounded by a single layer of granulosa cells.

  • Primary Follicle: Granulosa cells begin to proliferate and gain FSH receptors.

  • Secondary Follicle: Theca cells differentiate and form layers around granulosa cells.

  • Tertiary (Antral) Follicle: Formation of a fluid-filled space called the antrum.

  • Graafian Follicle (Preovulatory): The most mature follicle, ready for ovulation.

Ovulation

• Definition: The release of a mature oocyte, usually occurring around day 14 of a typical reproductive cycle.

• Trigger: Surge in LH.

• Dominant Follicle: Most mature follicle; sensitive to LH and expresses a large number of LH receptors.

• Process: The follicle ruptures, releasing the ovum and some granulosa cells (corona radiata).

• Post-Ovulation: The follicle transforms into the corpus luteum via luteinization.

• LH's Role Post-Ovulation: Transforms granulosa and theca cells into progesterone-secreting luteal cells.

Female Reproductive Endocrinology

• Hypothalamus:

  • Secretes GnRH.

• GnRH: Stimulates anterior pituitary to produce FSH and LH.

• FSH: Stimulates ovarian follicles to grow and secrete estrogen.

• Estrogen:

  • Positive feedback mechanism triggers LH surge during ovulation.

• LH: Induces ovulation and luteinization, which secrete estrogen and progesterone.

• Estrogen and Progesterone Function: Stimulate the uterus to proliferate and differentiate, facilitating embryo implantation.

• Negative Feedback: Estrogen and progesterone inhibit the release of GnRH, FSH, and LH.

The Female Hormones

• Estrogen and Progesterone: Steroid hormones transported in blood bound to albumin or specific binding proteins.

• Mechanism: Bind to intracellular receptors and function as transcription factors to regulate gene expression.

• Estrogen Target Tissues and Effects:

  • Uterus: Increases size of reproductive organs post-puberty, proliferation of endometrium.

  • Breast: Development and growth of breast tissue.

  • Bone: Stimulates growth and closure of the epiphyseal plate.

  • Metabolism: Increases fat deposition in breast and subcutaneous tissue.

• Progesterone Target Tissues and Effects:

  • Uterus: Promotes endometrium differentiation for pregnancy establishment and maintenance, increases uterine gland secretions.

  • Breast: Promotes mammary gland development.

The Female Reproductive Cycle

• Duration: Average of 28 days, where typically only one ovum is released per month from an ovary.

• Uterine Endometrium Preparation: Must prepare for potential implantation.

• Ovarian Cycle Phases:

  • Follicular Phase: Focus on folliculogenesis; primary hormone is estrogen.

  • Ovulation: Release of mature ovum.

  • Luteal Phase: Formation of corpus luteum; primary hormone is progesterone.

• Uterine Cycle Phases:

  • Proliferative Phase: Uterine lining thickens in response to estrogen.

  • Secretory Phase: Uterus prepares for implantation.

  • Menstrual Phase: Shedding of the uterine lining if no fertilized egg occurs.

The Menstrual Cycle

• Proliferative Phase:

  • Begins during early menstruation.

  • Estrogen promotes regeneration of the endometrium, increasing thickness (3-5 mm by day 14).

• Secretory Phase:

  • Begins after ovulation.

  • Progesterone transforms endometrial glands into secretory cells, crucial for embryo implantation.

• Menstruation:

  • Shedding of uterine lining triggered by decreased estrogen and progesterone (corpus luteum degeneration).

  • Typically lasts for 7 days; menstrual fluid consists of blood, endometrial cells, enzymes, and cytokines.

  • Cycle repeats with growing follicles aiding in endometrial regeneration for the next cycle.