28.1 Overview of the Reproductive Systems

Common Elements in Male and Female Systems

The human reproductive systems share several structural and functional elements, though they differ in specific organs and processes.

• Gonads: Ovaries in females, testes in males. These organs produce gametes and sex hormones.

• Gametes: Oocytes (eggs) in females, sperm in males. Gametes are haploid cells involved in sexual reproduction.

• Sex Hormones: Estrogen and progesterone (females); testosterone (males). These hormones regulate reproductive function and secondary sex characteristics.

• Accessory Reproductive Organs: Ducts, glands, and external genitalia that support gamete transport and fertilization.

Sexual Maturation

• Puberty: The period during adolescence when individuals become capable of sexual reproduction.

• Hormonal Control: The hypothalamus releases GnRH (Gonadotropin-Releasing Hormone), stimulating the anterior pituitary to secrete:

  • FSH (Follicle-Stimulating Hormone): Stimulates gamete production.

  • LH (Luteinizing Hormone): Stimulates gonadal hormone secretion.

Perineum

• Diamond-shaped region between the thighs.

• Divided into the urogenital triangle (external genitalia) and anal triangle.

28.2 Gametogenesis

Chromosomes & Heredity

Human cells contain chromosomes that carry genetic information. Gametes are produced through meiosis, ensuring genetic diversity.

• Diploid (2n) cells: 46 chromosomes (somatic cells).

• Haploid (n) cells: 23 chromosomes (gametes).

Meiosis

• Produces haploid gametes through two divisions.

• Meiosis I: Homologous chromosome pairs separate.

• Meiosis II: Sister chromatids separate.

• Crossing Over: Occurs in Prophase I, increasing genetic diversity.

Nondisjunction Disorders

• Trisomy 21 (Down Syndrome): Extra chromosome 21.

• Monosomy (Turner Syndrome): Missing X chromosome in females.

28.3 Female Reproductive System

Ovaries

• Produce oocytes and hormones (estrogen, progesterone)

  • At birth, ovaries contain 2 million primary oocytes

    • most degenerate in a process called atresia

    • puberty: FSH stimulates ovaries

      • stuck in prophase 1 (meiosis) until puberty

      • those stimulated to finish meiosis 1 produce haploid (secondary oocytes)

Follicular Development

1. Primordial Follicle: Present at birth.

2. Primary Follicle: Secretes estrogen.

   1. stuck in prophase meiosis 1 until puberty

3. Secondary Follicle: Develops multiple layers.

   1. primary oocytes inside

   2. release of FSH from pituitary (GnRH from hypothalamus)

   3. theca cells produce estrogen

4. Tertiary Follicle: Fluid-filled cavity forms.

5. Mature (Graafian) Follicle: Ready for ovulation.

6. Corpus Luteum: Secretes progesterone and estrogen.

7. Corpus Albicans: Degenerated corpus luteum.

Oogenesis & Ovarian Cycle

• Oogenesis: Maturation of oocyte.

  • Starts with oogonium which produces 2 primary oocytes

    • primary oocytes are diploids (46 chromosomes)

• Phases of the Ovarian Cycle:

  1. Follicular Phase (Days 1-13): Follicle growth.

     1. primordial, secondary, tertiary

     2. tertiary ovarian follicle creates a bulge in the ovary

        1. surrounded by zona pellucida and granulosa cells

        2. rising LH levels prompt completion of meiosis 1

  2. Ovulation (Day 14): LH surge releases oocyte.

  3. Luteal Phase (Days 15-28): Corpus luteum secretes hormones.

Uterine Tubes & Uterus

• Fallopian Tubes: Fertilization occurs in the ampulla.

• Uterus: Site of implantation and fetal development.

Uterine Cycle Phases

1. Menstrual Phase (Days 1-5): Shedding of functional layer.

2. Proliferative Phase (Days 6-14): Endometrial regrowth.

3. Secretory Phase (Days 15-28): Uterine glands secrete nutrients.

External Genitalia (Vulva)

• Labia Majora & Minora, Clitoris, Vestibular Glands: Structures of the female external genitalia.

Mammary Glands

• Prolactin: Stimulates milk production.

• Oxytocin: Stimulates milk ejection.

28.4 Male Reproductive System

Scrotum & Testes

• Testes: Site of sperm production.

Spermatogenesis

1. Spermatogonia: Stem cells.

2. Primary Spermatocyte: Undergoes meiosis I.

3. Secondary Spermatocyte: Undergoes meiosis II.

4. Spermatids: Mature into sperm.

Hormonal Regulation

• GnRH → FSH & LH → Testosterone

• Testosterone: Stimulates sperm production and secondary sex characteristics.

Male Duct System

• Epididymis → Ductus Deferens → Ejaculatory Duct → Urethra: Pathway for sperm transport.

Accessory Glands

• Seminal Vesicles: Fructose for sperm energy.

• Prostate Gland: Secretes fluid for sperm motility.

• Bulbourethral Glands: Lubrication.

• Semen: Sperm + seminal fluid.

Penis & Male Sexual Response

• Erection: Parasympathetic control (nitric oxide release).

• Ejaculation: Sympathetic control.

28.5 Development and Aging of the Reproductive System

Sex Differentiation

• Genetic Sex: Determined at fertilization (XX or XY).

• SRY Gene: Present on Y chromosome, directs male development.

Puberty

• Increased GnRH, FSH, LH secretion.

• Females: Breast development, menarche (first menstruation).

• Males: Testicular and penile growth, voice deepens.

Menopause & Male Climacteric

• Menopause: Cessation of menstruation (ages 45-55).

• Male Climacteric: Gradual testosterone decline, prostate issues.