The Reproductive Systems

Overview of Reproductive Systems

• Sexual Dimorphism: Differences in trait expressions between male and female.

Important Disclaimer

• Discusses sex in evolutionary and biological terms (XX and XY chromosomes).
• Distinguishes between sex (biological) and gender (identity).

Lecture Objectives

• Explain sexual dimorphism with examples.
• General features of the chromosomally female and male reproductive systems.
• Mechanisms of oogenesis and phases of the ovarian cycle.
• Phases of the menstrual cycle.
• Hormonal control of the reproductive cycle.
• Description of menopause.
• Mechanisms of spermatogenesis and fertilization.

Male vs. Female Reproductive Systems

• Functionally different but structurally homologous systems.
• Sexually Indifferent Stage: Gonads and primordial germ cells; Wolffian and Mullerian ducts are involved.

Sexual Dimorphic Traits

• Primary Sex Characteristics: Present at birth (chromosomes, gonads, reproductive organs).
• Secondary Sex Characteristics: Develop at puberty (breasts, facial hair, voice pitch).

Intersex Variations

• Caused by rare chromosomal combinations (e.g. XXY, XYY).
• Occurs in approximately 1.6% of the population.
• Note on identities: Intersex relates to biological traits; transgender refers to identity.

Examples of Intersex Variations

Female Reproductive System

• Anatomy includes ovaries, fallopian tubes, uterus, cervix, vagina, and external genitalia (vulva).

Oogenesis

• Formation of ova (eggs) occurs within the ovaries.
• Phases: Primary oocytes formed before birth; a significant reduction remains by puberty.
• Meiosis: 4 distinct daughter cells, haploid (23 chromosomes each).

Ovarian Cycle Overview

• A 28-day cycle consisting of:
  1. Follicular Phase (Days 1-13): Development of follicles; one dominant follicle emerges.
  2. Ovulation (Day 14): Release of secondary oocyte.
  3. Luteal Phase (Days 15-28): Formation of corpus luteum, degeneration if no fertilisation occurs.

The Menstrual Cycle

• Phases: 1) Menstrual phase (shedding endometrium), 2) Proliferative phase (repair), 3) Secretory phase (preparation for potential implantation).

Hormonal Control of the Female Cycle

• Key Hormones: FSH, LH, Oestrogen, Progesterone.
• Glands involved: hypothalamus, anterior pituitary, ovaries.
• Hormones regulate both ovarian and menstrual cycles.

Menopause

• Typically occurs aged 45-55.
• Signaled by decline in ovarian oestrogen production; cycles cease.

Male Reproductive System

• Anatomy: Includes testes, ductus deferens, prostate, and accessory glands (seminal vesicles, bulbourethral glands).
• Spermatogenesis: Formation of sperm; takes about 65-75 days; begins with spermatogonia -> primary spermatocyte -> meiosis.

Male Hormonal Control

• Key role of testosterone, regulated by LH & FSH from the pituitary.

Fertilization

-Occurs when sperm binds to the zona pellucida of an oocyte and penetrates, forming a zygote, ready for implantation in the uterus.