Male reproductive system

Male reproductive system

The organ system responsible for producing male gametes, sex hormones, and delivering sperm for internal fertilisation.

Sex chromosomes

Chromosomes that determine biological sex; females are XX and males are XY.

Y chromosome

The chromosome that directs development of male sex characteristics.

Primary male sex organ

Testis.

Secondary male sex organs

Penis, scrotum, epididymis, vas deferens, seminal vesicles, and prostate gland.

Testes

Male gonads that produce sperm and secrete testosterone.

Seminiferous tubules

Coiled tubules within the testes where spermatogenesis occurs.

Spermatogenesis

The production of male gametes from primordial germ cells within the seminiferous tubules.

Leydig cells

Interstitial cells of the testes that secrete testosterone.

Sertoli cells

Epithelial cells in seminiferous tubules that support and regulate sperm development.

Blood–testis barrier

Tight junctions between Sertoli cells that protect developing sperm from immune attack.

Luminal compartment

Area of seminiferous tubules containing developing sperm cells.

Basal compartment

Area of seminiferous tubules containing spermatogonia.

Functions of Sertoli cells

Support sperm development, secrete luminal fluid, androgen-binding protein, inhibin, and stimulate spermatogenesis.

Androgen-binding protein

Protein secreted by Sertoli cells that maintains high testosterone levels in the seminiferous tubules.

Inhibin

Hormone secreted by Sertoli cells that provides negative feedback on FSH secretion.

Mitosis in spermatogenesis

Cell division that amplifies spermatogonia.

Meiosis in spermatogenesis

Cell division that produces genetically varied haploid sperm cells.

Penis

Male copulatory organ that delivers sperm into the female reproductive tract.

Erection

Engorgement of erectile tissue due to increased blood flow during sexual arousal.

Ejaculation

Expulsion of semen through the urethra.

Scrotum

Thin-walled sac that houses the testes and regulates temperature.

Temperature regulation of testes

Maintains testes 2–3°C below body temperature for normal sperm development.

Dartos and cremaster muscles

Muscles that contract or relax to regulate testicular temperature.

Epididymis

Site where sperm mature and are stored.

Vas deferens

Duct that transports sperm from the epididymis to the ejaculatory duct.

Seminal vesicles

Accessory glands that secrete alkaline fluid containing fructose, enzymes, prostaglandins, and seminogelin.

Prostate gland

Accessory gland that secretes citrate, enzymes, and prostate-specific antigen (PSA).

Bulbourethral glands

Accessory glands that secrete viscous mucus for lubrication.

Semen

A mixture of sperm and secretions from accessory glands.

Fructose in semen

Energy source for sperm.

Prostaglandins in semen

Compounds that aid sperm motility and female reproductive tract function.

Testosterone

Primary male androgen responsible for spermatogenesis and male characteristics.

Androgens

Male sex hormones, primarily testosterone and dihydrotestosterone.

Gonadotrophins

Hormones (FSH and LH) secreted by the anterior pituitary.

GnRH

Gonadotrophin-releasing hormone secreted by the hypothalamus that stimulates FSH and LH release.

FSH

Hormone that acts on Sertoli cells to initiate and maintain spermatogenesis.

LH

Hormone that acts on Leydig cells to stimulate testosterone secretion.

Male puberty

Period when GnRH secretion increases, activating testosterone production and spermatogenesis.

Dihydrotestosterone (DHT)

Potent androgen responsible for development of secondary male sex characteristics.

Secondary male sex characteristics

Features such as facial hair, deep voice, increased muscle mass, and body hair.

Prenatal effects of testosterone

Masculinisation of the reproductive tract and descent of testes.

Postnatal effects of testosterone

Growth and maintenance of reproductive system and spermatogenesis.

Negative feedback in males

Testosterone and inhibin suppress GnRH, LH, and FSH secretion.

Blood testosterone levels

Low before puberty and high during puberty and adulthood.

Specialisation of males for reproduction

Continuous production of large numbers of small, motile gametes and internal fertilisation mechanisms.