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
| Syndrome | Chromosomes | Characteristics |
|---|---|---|
| Klinefelter Syndrome | XXY | Poorly functioning testes, normal male genitalia. |
| Turner Syndrome | X | Varying symptoms; no secondary characteristics without therapy. |
| XXYY Syndrome | XXYY | Sterility, low testosterone, learning difficulties. |
| XX Male Syndrome | XX | Male reproductive organs; external/internal ambiguity. |
| XY Gonadal Dysgenesis | XY | Female organs but non-functional gonads. |
| Androgen Insensitivity | XY | Ambiguous genitalia; absent secondary characteristics. |
| Congenital Adrenal Hyperplasia | XX/XY | Hormonal defects affecting traits. |
| Vaginal Agenesis | XX | Absence of vaginal opening. |
| Mullerian Agenesis | XX | Absence of uterus, cervix, vagina due to duct failure. |
| Hypospadias | XY | Abnormal urethra placement. |
| Ovotestes | XX/XY | Both ovarian and testicular tissue, ambiguous genitalia. |
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:
- Follicular Phase (Days 1-13): Development of follicles; one dominant follicle emerges.
- Ovulation (Day 14): Release of secondary oocyte.
- 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.