Reproductive System Overview

The Reproductive System

• The reproductive system is vital for the continuation of the human species.
• It is focused on perpetuating the genetic lineage, not on basic survival.
• The system includes internal organs (gonads), sex hormones, gametes, and supportive structures (glands, ducts, external genitalia, brain parts) to facilitate reproduction.
  • Internal Sex Organs (Gonads): Testes (males) and ovaries (females) produce gametes (sperm and eggs) and sex hormones.
  • Sex Hormones: Important for sexual development and reproductive functions.
  • Gametes: Sperm and eggs contain half the genetic material needed for a new organism.
  • Support Structures: Facilitate mating, fertilization, and offspring creation.

The Female Reproductive Anatomy

• External Genitalia (Vulva): Includes the mons pubis, labia majora, labia minora, and vestibule (with urethral and vaginal openings).
• Internal Organs:
  • Vagina: Connects external genitalia to the uterus.
  • Ovaries: Primary female reproductive organs:
    • Structure: Enclosed in a fibrous sac (tunica albuginea) with germinal epithelium. The interior has a cortex (egg development) and a medulla (blood vessels, nerves).
    • Function: Produce and release female gametes (eggs) and sex hormones (estrogen, progesterone).
    • Ovarian Follicles: Tiny sac-like structures containing the primary oocyte (incomplete egg) surrounded by follicle cells.
    • Primordial Follicles: Females are born with millions, most undergo atresia before puberty.

The Ovarian Cycle

• Oogenesis (Egg Creation): Delayed until puberty, when the body is ready for reproduction.
• Process:
  • Puberty: Starts the ovarian cycle through hypothalamus and pituitary gland interaction.
  • GnRH (Gonadotropin-releasing Hormone): Released by the hypothalamus, prompting FSH and LH release from the pituitary.
  • FSH (Follicle-Stimulating Hormone): Stimulates a follicle's growth into maturity via estrogen production.
  • LH (Luteinizing Hormone): Triggers the oocyte's final meiotic divisions (completion of meiosis I and entry into metaphase II).
  • Ovulation: Follicle ruptures, releasing the mature oocyte.
  • Corpus Luteum: The remaining follicle transforms into a corpus luteum, secreting progesterone, estrogen, and inhibin.
  • Inhibition of FSH & LH: Progesterone and estrogen inhibit further FSH and LH release, preventing further follicle development.

The Menstrual Cycle

• Overview: Repeating 28-day changes in the uterus, driven by ovarian cycle hormones.
• Phases:
  • Menstrual Phase (Days 1-5): Shedding of the uterine lining (endometrium) due to declining progesterone and estrogen from the degenerating corpus luteum.
  • Proliferative Phase (Days 6-14): Regeneration of the uterine lining by rising estrogen from developing follicles; preparing for a fertilized egg.
  • Secretory Phase (Days 15-28): Progesterone from the corpus luteum thickens the lining, preparing for implantation. If no fertilization, the corpus luteum deteriorates, leading to the menstrual phase.
  • Fertilization: If fertilization occurs, the corpus luteum continues progesterone production, maintaining the lining for implantation and pregnancy.

The Journey of the Egg and Fertilization

• Fallopian Tubes: Approximately 10 cm long, not directly connected to the ovaries.
• Ovulation: The egg is released from the ovary, travels through the peritoneal cavity, and is captured by the fallopian tube.
• Fertilization: If fertilized, the egg completes meiosis II, becoming an ovum.
• Uterus: A muscular organ that receives an egg (fertilized or not).
  • Structure: Three layers, perimetrium (outer), myometrium (muscle), and endometrium (inner lining).
  • Implantation: Fertilized egg implants in the endometrium for gestation.