The Male Reproductive System

The urinary system | Main Anatomy Index

Last updated 30 March 2006

This page was contributed by David Boshell.

• This consists of the testis, epididymis, genital ducts, accessory glands and the penis.

• These are small, paired, oval structures in the scrotum, weighing about 15 g.

• Like the ovary, the functions of the testes are:

1. Gametogenesis. This equates to the production of sperm in the male, and is called spermatogenesis. The optimum temperature for spermatogenesis is about 2 degrees below body temperature. Factors contributing to temperature control include:

• The dartos muscle of the scrotum that pulls the testis closer to the body when it is cold;
• The pampiniform plexus of veins surrounding the testicular artery, providing a countercurrent heat exchange system whereby cooler venous blood returning from the scrotum and testis cools the incoming arterial blood.

2. The production of androgens, namely the steroid hormone testosterone. These steroid hormones are essential for development of the male foetus, development of secondary sex characteristics in puberty, and the maintenance of sperm production in the adult male.

• The structure of the testes consists of:

1. A thick connective tissue capsule: the tunica albuginea, with inwardly projecting septa, creating about 250 lobules.

• Posteriorly, it thickens and projects inwards to form the mediastinum testes, through which structures enter and leave the testes.
• Beneath this layer, a looser tunica vasculosa contains blood vessels.
• The tunica albuginea is a visceral peritoneal layer that is surrounded anteriorly by a parietal layer called the tunica vaginalis, with a peritoneal sac between them.

2. Inner lobules containing long, highly convoluted seminiferous tubules, surrounded by interstitial (Leydig) cells in the stroma.

• The tubules straighten out into tubuli recti (straight tubules) before joining an anastomosing channel system in the mediastinum called the rete testis.

• These are large, polygonal, acidophilic cells in the stroma of the lobules.

• They may contain lipid droplets and cytoplasmic crystals (of Reinke).

• Leydig cells secrete the androgen testosterone that will act inside the seminiferous tubule.

• These tubules are about 50 cm long.

• They have a complex, stratified, seminiferous epithelium with 2 cell types:

1. Spermatogenic cells organised as patches of cells in different stages of evolution throughout the tubule. As they mature, they move inwards from the basal lamina (spermatogonia) to the lumen (spermatids).
2. Sertoli cells. These are columnar, non-dividing, sustentacular cells on the basal lamina, with an ovoid or triangular nucleus.

• Sertoli cells maintain the overall structure of the tubules and each support a small colony of developing sperm, surrounding them with cytoplasmic processes.
• They are bound to each other by Sertoli-Sertoli junctional complexes that form tight junctions.
• This divides the seminiferous epithelium into 2 compartments:

1. A basal compartment containing immature spermatogonia and primary spermatocytes;
2. A luminal compartment containing mature spermatocytes and spermatids.

• It is also the site of the blood-testis barrier, protecting the antigenically foreign haploid sperm from an autoimmune response by circulating antibodies.

• The Sertoli cells have an exocrine function, secreting fluid for the passage of sperm, and an endocrine function, including the secretion of:

1. Androgen Binding Protein (ABP), that concentrates testosterone in the tubular lumen for the developing sperm;
2. Inhibin is involved with feedback inhibition of FSH from the anterior pituitary.

• Sertoli cells themselves are stimulated by FSH and testosterone.

• The seminiferous epithelium is surrounded by lamina propria called tunica propria.
• This contains peritubular contractile cells (myoid cells).
• These cells create peristaltic waves that propel spermatozoa and testicular fluid toward the excurrent ducts and epididymis.

• There are 6 different stages or phases of differentiation of human spermatogonia, called the cycle of the seminiferous epithelium.
• The total time required for spermatogonia to reach the stage where they are released as sperm is 74 days.
• The patch-like distribution of the stages of differentiation along the tubule is called the wave of the seminiferous epithelium.

Back to top

• This is the process by which 1 spermatogonia develops into 4 spermatozoa (sperm).
• It has 3 distinct phases, the spermatogonial phase, the spermatocyte phase, and the spermatid phase.

• Spermatogonia lie in the basal region of the seminiferous tubule with the Sertoli cells, and have large, rounded nuclei.
• Dark type A (Ad) spermatogonia give rise to pale type A (Ap) spermatogonia that are connected by cytoplasmic bridges.
• This ensures synchronous development of each clone.

• After several divisions, type A cells differentiate into type B spermatogonia.

• Type B spermatogonia divide into primary spermatocytes by mitosis.
• Spermatocytes are characterised by prominent nucleoli, due to cell division.

• The primary spermatocytes undergo meiosis, forming diploid, secondary spermatocytes upon the first meiotic division.
• Haploid spermatids are formed upon the second meiotic division.

• Spermatids lie in the luminal region of the tubule, and may have elongated nuclei.
• They develop into mature spermatozoa by the process of spermiogenesis, as follows:

1. The acrosomal vesicle forms next to the nucleus at the anterior pole.
2. The acronemal complex (9+2 microtubule arrangement in the tail) begins to be synthesised at the posterior pole.
3. The acrosomal vesicle spreads over the anterior pole, forming the acrosomal cap.
4. Now the nucleus elongates, moving to the front of the cell whilst the cytoplasm extends backwards into the tail.
5. Finally, the cytoplasm is lost into the tubule, becoming a residual body that is phagocytosed by Sertoli cells.
6. The sperm, now free of the Sertoli cell, has a head (5 micrometres), neck (5 micrometres) and tail (50 micrometres).
7. Final maturation of the sperm occurs in the tail of the epididymis.

• Sperm are stored in the distal portion of the ductus epididymis before ejaculation.
• They can live in the male excurrent system for several weeks, but will only survive for 2-3 days in the female reproductive tract.
• During this time, they will acquire the ability to fertilise the ovum via capacitation.
• This involves the removal and replacement of the glycocalyx components on the sperm membrane.

Back to top

• Terminal sections of the seminiferous tubules straighten into tubuli recti (straight tubules), lined only by Sertoli cells.
• The tubuli recti then narrow, and become lined with simple cuboidal epithelium that is continuous with the rete testis of the mediastinum.
• Cells in the rete testis have a single apical cilium and few apical microvilli.

• This consists of :

1. Efferent ductules (ductuli efferentes);
2. The ductus epididymis;
3. The ductus deferens.

• About 20 efferent ductules join the rete testis to the proximal portion of the ductus epididymis.
• Outside the rete testis, these ducts are highly coiled, forming coni vasculosi that drain into the ductus epididymis.

• Efferent ductules are lined by a pseudostratified columnar epithelium, with tall columnar ciliated cells and short, non-ciliated cells with numerous microvilli.
• This gives the lumen a "cog-wheel" appearance.

• This is the duct of the epididymis, lying posterior to the testis.
• It has a head, body and tail. Sperm acquire motility and undergo capacitation here.
• It is lined by pseudostratified columnar epithelium, containing 3 types of cells:

1. Tall principal cells with numerous, long stereocilia;
2. Small, round stem cells on the basal lamina, called basal cells;
3. Intraepithelial lymphocytes called halo cells.

• The epididymal cells in the proximal portion reabsorb fluids and residual bodies that were not collected by the efferent ductules.
• They also secrete substances aiding the maturation of sperm.

• A thin circular smooth muscle layer in the head of the epididymis thickens towards the tail, adding inner and outer longitudinal layers.
• Mature sperm are stored in the tail.
• In ejaculation, the 3 smooth muscle layers force the sperm into the ductus deferens.

• This is the terminal portion of the excurrent duct system.
• It is continuous with the tail of the epididymis.

• It ascends in the spermatic cord through the scrotum and inguinal canal and enters the abdomen.
• It then descends to the pelvis and ends in the prostatic urethra.
• Here it enlarges, forming the ampulla, and is joined by the duct of the seminal vesicle, continuing as the ejaculatory duct through the prostate gland.

• This opens into the urethra.
• Like the ductus epididymis, it is lined by pseudostratified columnar epithelium with tall columnar cells and rounded basal cells.
• Its lumen is dwarfed by a very thick muscular coat that contracts during ejaculation.

Back to top

• These include:

1. The seminal vesicles;
2. The prostate gland;
3. And the bulbourethral glands.

• These are paired, highly folded tubular glands with a muscular and fibrous coat.
• Mucosal folds create many sac chambers in the lumen.

• They have pseudostratified columnar epithelium that is similar to that of the excurrent ducts.
• Its secretory products, under the control of testosterone, include fructose, which is the principal metabolite for sperm.
• During ejaculation, contraction of the smooth muscle coat discharges the secretions into the ejaculatory ducts and helps flush sperm into the urethra.

• This is the largest accessory gland, consisting of 30-50 tubuloalveolar glands arranged in 3 concentric layers:

1. A mucosal layer, secreting directly into the urethra;
2. A submucosal;
3. And peripheral layer.

• The last two layers, with the main prostatic glands, open into prostatic sinuses on either side of the urethral crest in the prostatic urethra.

• The epithelium of the prostate is generally columnar, although it contains cuboidal, squamous and pseudostratified compartments.
• It is under the control of testosterone.

• It secretes acid phosphatase, fibrinolysin and citric acid.
• During ejaculation, these secretions are pumped into the urethra by contraction of the fibromuscular wall.
• In older men, prostatic alveoli may contain prostatic concretions (corpora amylacea).
• These are precipitated secretory materials appearing as concentric lamellated bodies.

• The bulbourethral glands (Cowper's glands) are pea-sized, paired structures.
• They are compound tubuloalveolar glands in the urogenital diaphragm, resembling mucous secretory glands.

• Their ducts pass through the inferior fascia of the urogenital diaphragm (superficial fascia) to join the initial portion of the penile urethra.
• Its simple columnar epithelium, also under the control of testosterone, secretes a mucoid fluid that lubricates the penile urethra.

Back to top

• Semen is the combined product of all the glandular elements of the male reproductive system. It:

1. Contains fluid and sperm from the testis;
2. Contains secretions from the epididymis, ductus deferens, prostate, seminal vesicles and bulbourethral glands;
3. Is alkaline, contrasted with the acidic environment of the female vagina.

• The average volume of ejaculate is about 3 mL.

1. Erectile tissue, including 2 dorsal corpora cavernosa (singular = corpus cavernosum), and a ventral corpus spongiosum in which the penile urethra is embedded;
2. A fibroelastic layer called the tunic albuginea, encapsulating the erectile tissues;
3. An outer layer of loose connective tissue, to which thin skin is loosely attached, except at the glans penis where it attaches tightly;
4. Smooth muscle and many sensory and autonomic nerves are also present.

• The corpora cavernosa (and, to a lesser extent, the corpus spongiosum) contain many vascular sinuses.
• In the flaccid penis, helicine (spiral) arteries coil outwards from the centrally located deep arteries of each corpus cavernosum.
• Blood drains into peripherally located veins.

• Erection requires 2 conditions:

1. Increased arterial inflow;
2. Decreased venous outflow.

• The process of erection occurs as follows:

1. Parasympathetic stimulus causes relaxation of the smooth muscle surrounding the vascular endothelium, causing vasodilation of the helicine arteries;
2. The vascular sinuses of the erectile tissue become engorged with blood from increased arterial inflow, and the penis becomes rigid;
3. The transmural pressure rises, compressing the peripheral veins, thus decreasing venous outflow and amplifying the erectile response.

• Ejaculation occurs via sympathetic stimulus.
• It involves:

1. Intense contraction of the smooth muscle of the epididymis, ductus deferens, seminal vesicles and prostate;
2. Contraction of the striated muscle in the pelvic and urogenital diaphragms (sphincter utherae) to prevent the passage of urine, and the bulbospongiosus;
3. Emission of the seminal fluid.

Back to top