Testicle

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The gubernaculum is an embryonic cord like ligament that attaches the testes within the inguinal region of a male fetus up through the 7th month of pregnancy.

Between the 28th and 35th week of pregnancy the gubernaculum migrates into the scrotum and creates space for the testes to descend.

The testes follows the gubernaculum downward into the scrotum at the time of birth.

The descent of the testicle can be impaired by inadequate androgen hormone secretion, structural abnormalities of the genitals and defective nerves in the genital region.

Sperm are produced in the testes and stored in the attached epididymis.

During ejaculation, sperm are propelled up the vas deferens, two ducts that pass over and behind the bladder.

Fluids are added by the seminal vesicles and the vas deferens turns into the ejaculatory ducts, which join the urethra inside the prostate gland.

The prostate as well as the bulbourethral glands add further secretions, and the semen is expelled through the penis.

A positive correlation exists between the number of sperm ejaculated and testis size.

Larger testes have also been shown to predict higher sperm quality, including a larger number of motile sperm and higher sperm motility.

The testicle or testis is the male reproductive gland.

It is homologous to the female ovary.

The functions of the testes are to produce both sperm and androgens, primarily testosterone.

Testosterone release is controlled by the anterior pituitary luteinizing hormone.

Sperm production is controlled both by the anterior pituitary follicle-stimulating hormone and gonadal testosterone.

Males have two testicles of similar size contained within the scrotum.

Scrotal asymmetry is not unusual, with one testicle extending further down into the scrotum than the other due to differences in the anatomy of the vasculature.

The average adult testicle is up to 2 inches long, 0.8 inches in breadth, and 1.2 inches in height or 5 × 2 × 3 cm

The testicle is covered by a tough membranous shell, the tunica albuginea.

The coiled tubes, called seminiferous tubules, in the testicle are lined with a layer of germ cells that develop from puberty through old age into sperm cells.

Sperm travels through the seminiferous tubules to the rete testis located in the mediastinum testis, to the efferent ducts, and then to the epididymis where newly created sperm cells mature.

Sperm move to the vas deferens, and are then expelled via the urethra and out of the urethral orifice as a result of muscular contractions.

Within the seminiferous germ cells develop through the process of spermatogenesis.

The spermatozoa gametes contain DNA for fertilization of an ovum.

Sertoli cells, the true epithelium of the seminiferous epithelium, are critical for the support of germ cell development into spermatozoa, and also secrete inhibin.

The seminiferous tubules are surrounded by peritubular myoid cells.

Leydig cells are located between seminiferous tubules and produce and secrete testosterone and other androgens important for sexual development and puberty, secondary sexual characteristics, sexual behavior and libido, support spermatogenesis and erectile function.

Testosterone also controls testicular volume.

The testicle arteries, are paired, and arise directly from the abdominal aorta and descend through the inguinal canal.

The scrotum and the rest of the external genitalia is supplied by the internal pudendal artery, a branch of the internal iliac artery.

The testis has collateral blood supply:

The cremasteric artery, which is a branch of the inferior epigastric artery, which is a branch of the external iliac artery.

The artery to the ductus deferens, which is a branch of the inferior vesical artery, which is a branch of the internal iliac artery.

Lymphatic drainage of the testes follows the testicular arteries back to the paraaortic lymph nodes.

Lymph drainage from the scrotum drains to the inguinal lymph nodes.

The testicle is enclosed by layers of the anterior abdominal wall.

Part of the spermatic cord, the cremasteric muscle, arises from the internal oblique muscle.

As the cremasteric muscle contracts, the spermatic cord is shortened and the testicle is moved up toward the body.

The testicle moving toward the body provide more warmth to maintain optimal testicular temperature.

When cooling is required, the cremasteric muscle relaxes and the testicle is cooled as it is lowered away from the warm body.

The cremasteric muscle contracts in response to stress, and orgasm, and relaxation indicates approach of orgasm.

The cremaster muscle can reflexively raise each testicle individually, as is known as the cremasteric reflex.

The testicles can also be lifted voluntarily using the pubococcygeus muscle.

There are tight junctions between Sertoli cells inhibiting large molecules from passing from the blood into the lumen of a seminiferous tubules.

The spermatogonia are in the basal compartment.

The more mature forms such as primary and secondary spermatocytes and spermatids are in the adluminal compartment.

The function of the blood–testis barrier may be to prevent an auto-immune reaction, as immune tolerance is established in infancy.

Spermatogenesis is enhanced at temperatures slightly less than core body temperature, and is impaired at lower and higher temperatures than 33 °C.

The smooth tissue of the scrotum can move them closer or further away from the body to maintain the temperature at 35 degrees Celsius, 95 degrees Fahrenheit, i.e. two degrees below the body temperature of 37 degrees Celsius, 98.6 degrees Fahrenheit.

Higher temperatures affect spermatogenesis.[6] There are a number of mechanisms to maintain the testes at the optimum temperature.[5]

The human genome includes approximately 20,000 protein coding genes: 80% of these genes are expressed in adult testes.

The testes have the highest fraction of tissue type-specific genes compared to other organs and tissues.

There are about 1000 tissue type specific genes for the testes.

A majority of these genes encode for proteins that are expressed in the seminiferous tubules with functions related to spermatogenesis.

Sperm cells express proteins that result in the development of flagella.

There are two phases in which the testes grow substantially; namely in embryonic and pubertal age.

In 97% full-term, 70% preterm infants, both testes have descended by birth.

In most other cases, when only one testis fails to descend, it will probably occur within a year.

The testes grow in response to the start of spermatogenesis.

Testicle size depends on sperm, interstitial fluid, and Sertoli cell fluid production.

The volume of the testes can be increased by over 500% after puberty as compared to the pre-pubertal size.

Clinical significance

After injury to the testicle, pain travels up from each testicle into the abdominal cavity, via the spermatic plexus, which is the primary nerve of each testicle.

Testicle trauma will cause pain in the hip and the back, and it usually goes away in a few minutes.

Testicular torsion is a medical emergency, as a result of vascular compromise.

Rupture of the testicle by blunt force impact, sharp edge, or piercing impact to one or both testicles can lead to necrosis of the testis in as little as 30 minutes, as is a medical emergency.

Penetrating injuries to the scrotum may cause physical separation or destruction of the testes, and can result in total sterility if the testicles are not reattached quickly.

Regular testicular self-examination is recommended.

Varicocele refers to the presence of swollen veins of the testes, usually affecting the left side.

A hydrocele testis is one with swelling around it caused by accumulation of clear liquid within a membranous sac

The testis is usually normal with hydrocele.

A spermatocele, is a retention cyst of a tubule of the rete testis or the head of the epididymis.

The size and function of the testis may be affected by endocrine disorders.

Testicular descent can be impaired by mutations in developmental genes, resulting in abdominal or inguinal testes which remain nonfunctional and may become cancerous.

In Bell-clapper deformity the testicle is not attached to the scrotal walls, and can rotate freely on the spermatic cord within the tunica vaginalis.

The Bell-clapper deformity is the most common underlying cause of testicular torsion.

Orchitis refers to the inflammation of the testicles.