Reproductive System

Reproductive System

Introduction

·       The reproductive system is essential for the survival of the species rather than the individual.

·       Unlike other systems, its primary role is not homeostasis but the production of gametes, fertilization, development of offspring, and ensuring continuity of genetic material.

·       It consists of organs and structures specialized for:

·        Production of male gametes (sperm) and female gametes (ova).

·        Provision of an environment for fertilization and fetal development.

·        Hormonal regulation of reproductive processes.

Male Reproductive System

1. Structure

The male reproductive system includes external and internal organs:

• External organs:
• Penis: Copulatory organ; delivers sperm into the female tract. Contains erectile tissues (corpora cavernosa, corpus spongiosum) and urethra.
• Scrotum: Sac of skin that houses testes; regulates temperature (2–3°C below body temperature) for optimal spermatogenesis.
• Internal organs:
• Testes:
• Paired, oval organs in the scrotum.
• Surrounded by tunica albuginea.
• Contain seminiferous tubules (site of spermatogenesis).
• Interstitial (Leydig) cells produce testosterone.
• Epididymis: Long coiled tube on posterior testis; stores and matures sperm.
• Vas deferens: Muscular tube carrying sperm from epididymis to ejaculatory duct.
• Seminal vesicles: Glands producing alkaline fluid rich in fructose (energy for sperm).
• Prostate gland: Produces milky, slightly acidic secretion enhancing sperm motility.
• Bulbourethral (Cowper’s) glands: Secrete mucus to lubricate urethra and neutralize traces of acidic urine.
• Urethra: Common passage for urine and semen.

2. Functions

• Testes: Produce sperm and testosterone.
• Duct system: Transports, stores, and matures sperm.
• Accessory glands: Provide fluids for semen that nourish and protect sperm.
• Penis: Ejaculation and delivery of sperm into the female reproductive tract.

Female Reproductive System

1. Structure

The female reproductive system consists of external and internal organs:

• External organs (Vulva):
• Mons pubis, labia majora, labia minora, clitoris, vestibular glands. Provide protection and sexual arousal.
• Internal organs:
• Ovaries:
• Paired, almond-shaped.
• Covered by tunica albuginea.
• Contain ovarian follicles at different stages.
• Functions: produce ova and hormones (estrogen, progesterone).
• Fallopian tubes (Oviducts):
• Narrow tubes connecting ovaries to uterus.
• Parts: infundibulum (with fimbriae), ampulla (site of fertilization), isthmus.
• Function: capture ovum, transport it, site of fertilization.
• Uterus (womb):
• Pear-shaped muscular organ.
• Layers: endometrium (inner, cyclical changes), myometrium (muscular), perimetrium (outer).
• Function: implantation, nourishment, fetal development, labor.
• Cervix: Narrow neck opening into vagina; produces mucus aiding or blocking sperm entry.
• Vagina: Muscular canal for intercourse, menstrual flow, and childbirth.
• Mammary glands (breasts): Modified sweat glands producing milk for infant nourishment.

2. Functions

• Ovaries: Production of ova and female hormones.
• Fallopian tubes: Site of fertilization and ovum transport.
• Uterus: Implantation, support of pregnancy, labor contractions.
• Vagina: Copulation, birth canal, menstrual outflow.
• Mammary glands: Lactation.

Puberty

• Definition: Transition phase when reproductive organs mature and become functional.
• In Males:
• Age: 12–14 years.
• Changes: Growth of testes, penis enlargement, spermatogenesis begins, voice deepens, body hair, muscular growth.
• Hormonal control: Hypothalamus → GnRH → Pituitary → FSH & LH → Testes (testosterone).
• In Females:
• Age: 10–12 years.
• Changes: Breast development, pubic hair, menarche (first menstruation), ovulation onset.
• Hormonal control: Hypothalamus → GnRH → Pituitary → FSH & LH → Ovaries (estrogen, progesterone).

Menstrual Cycle

• Definition: Cyclic changes in the endometrium of uterus under hormonal control, preparing it for implantation (average cycle 28 days).
• Phases:
1. Menstrual phase (Day 1–5): Shedding of endometrium, bleeding.
2. Proliferative/follicular phase (Day 6–14): Estrogen secreted by growing follicles rebuilds endometrium. Ovulation occurs around Day 14.
3. Secretory/luteal phase (Day 15–28): Corpus luteum secretes progesterone; endometrium thickens, glands secrete nutrients.

• If fertilization does not occur → corpus luteum degenerates → progesterone drops → menstruation starts.

Ovarian Cycle

• Definition: Changes in the ovary corresponding with menstrual cycle.
• Phases:
1. Follicular phase (Day 1–14):
• FSH stimulates growth of ovarian follicles.
• Follicles secrete estrogen.
2. Ovulation (Day 14):
• LH surge triggers rupture of Graafian follicle and release of ovum.
3. Luteal phase (Day 15–28):
• Corpus luteum forms, secretes progesterone and estrogen.
• If no pregnancy → degenerates into corpus albicans.

Spermatogenesis

• Definition: Process of sperm production in seminiferous tubules of testes.
• Steps:
1. Spermatogonia (diploid stem cells) divide by mitosis.
2. Primary spermatocytes (diploid) undergo meiosis I → form two secondary spermatocytes (haploid).
3. Secondary spermatocytes undergo meiosis II → form spermatids (haploid).
4. Spermiogenesis: Spermatids mature into spermatozoa (sperm).
• Sperm structure:

• Head: Nucleus with DNA + acrosome (enzymes to penetrate ovum).
• Midpiece: Mitochondria for energy.
• Tail (flagellum): Provides motility.

• Duration: About 64–72 days.
• Hormonal control: FSH (stimulates spermatogenesis), LH (stimulates testosterone from Leydig cells), testosterone (maintains spermatogenesis).

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