Testis

Testis (orchis)

Also known as: testicle, testes, male gonad

The paired male gonad, suspended in the scrotum by the spermatic cord, which produces spermatozoa in its seminiferous tubules and secretes testosterone from its interstitial Leydig cells.

Show on body map Male Reproductive Organs Hypothalamic–Pituitary Axis

Overview

Dimensions≈4–5 × 3 × 2.5 cm

Volume≈15–25 mL (≥4 mL marks onset of puberty)

Lobules≈250

Optimal temperature≈2–3 °C below core

Each testis is an ovoid organ about 4–5 cm long, with a volume of ≈15–25 mL in adults. It is wrapped in three layers. The tunica vaginalis is a closed serous sac derived from the processus vaginalis of peritoneum, with a parietal and a visceral layer separated by a film of fluid that lets the testis move freely. The tunica albuginea is a tough fibrous capsule; posteriorly it thickens into the mediastinum testis, from which septa divide the organ into ≈250 lobules. The innermost tunica vasculosa carries vessels.

Each lobule contains 1–4 highly coiled seminiferous tubules (where spermatogenesis occurs) embedded in loose interstitial tissue containing Leydig cells, capillaries, lymphatics and macrophages. Tubules join as short straight tubules (tubuli recti) into the rete testis in the mediastinum, which drains through 12–20 efferent ductules into the head of the epididymis.

Spermatogenesis requires a temperature ≈2–3 °C below core body temperature, maintained by the thin hairless scrotal skin and its sweat glands, the dartos and cremaster muscles (which adjust the testis's distance from the body), and the pampiniform venous plexus, which acts as a countercurrent heat exchanger cooling the incoming testicular arterial blood.

Location: Within the scrotum, suspended by the spermatic cord; the left usually hangs slightly lower than the right. The epididymis lies along its posterolateral border.

Parts & subdivisions

Tunica vaginalis
Parietal and visceral layers of a peritoneum-derived serous sac covering the front and sides of the testis; fluid accumulation forms a hydrocele.
Tunica albuginea
Dense white fibrous capsule; thickened posteriorly as the mediastinum testis; septa create ≈250 lobules.
Seminiferous tubules
Site of spermatogenesis; lined by Sertoli and spermatogenic cells.
Interstitial (Leydig) cells
Testosterone-secreting cells between the tubules.
Rete testis and efferent ductules
Anastomosing channels in the mediastinum and 12–20 ductules (ciliated, absorptive epithelium) leading to the epididymis; they reabsorb most testicular fluid.
Appendix testis
Small vestigial Müllerian remnant at the upper pole; its torsion mimics testicular torsion.

Anatomy

Innervation: Testicular plexus of autonomic fibres around the testicular artery (sympathetic from ≈T10–T11, with visceral afferents) — testicular pain is referred to the periumbilical region. The tunica vaginalis is supplied by the genital branch of the genitofemoral nerve.
Arterial supply: Testicular artery (from the abdominal aorta at ≈L2, travelling in the spermatic cord); anastomoses with the artery to the ductus deferens (from the superior or inferior vesical artery) and the cremasteric artery (from the inferior epigastric artery).
Venous drainage: Pampiniform plexus (8–12 anastomosing veins in the cord) → testicular vein at the deep inguinal ring: right → inferior vena cava; left → left renal vein.
Lymphatic drainage: Along the testicular vessels to para-aortic (lumbar) nodes at ≈L1–L2 — not to the inguinal nodes (which drain the scrotal skin).
Relations: Posterolateral: epididymis (head at upper pole, tail at lower pole) and ductus deferens medial to it. Coverings from outside in: scrotal skin, dartos fascia, external spermatic fascia, cremasteric muscle and fascia, internal spermatic fascia, parietal then visceral tunica vaginalis, tunica albuginea.
Histology: Seminiferous tubules (stratified seminiferous epithelium of Sertoli and germ cells on a basement membrane surrounded by peritubular myoid cells) separated by interstitial connective tissue with clusters of large eosinophilic Leydig cells.
Development: Develops on the posterior abdominal wall from the gonadal ridge (intermediate mesoderm and coelomic epithelium) colonised by primordial germ cells; SRY drives testis differentiation (≈week 7). Descends via the inguinal canal guided by the gubernaculum, normally reaching the scrotum by birth — which explains its aortic blood supply and para-aortic lymph drainage.

Function

Produces spermatozoa (≈50–200 million per day) from puberty onwards.
Secretes testosterone (Leydig cells) and inhibin B, AMH and androgen-binding protein (Sertoli cells).
Small amounts of estradiol and insulin-like peptide 3 (INSL3, needed for testicular descent).

Clinical significance

Testicular torsion

Twisting of the spermatic cord with ischaemia; sudden severe pain, high horizontal testis, absent cremasteric reflex; surgical exploration within 6 h.

Testicular cancer

Commonest solid cancer in men aged 15–35. ≈95 % are germ-cell tumours: seminoma (radiosensitive; may raise hCG modestly) and non-seminomatous tumours (embryonal, yolk sac — AFP; choriocarcinoma — very high hCG; teratoma). Presents as a painless firm lump. Markers: AFP, β-hCG, LDH. Treated by radical inguinal orchidectomy (an inguinal approach avoids opening scrotal lymphatic routes); excellent cure rates even with metastases. Risk factors: cryptorchidism, previous tumour, Klinefelter syndrome, family history.

Hydrocele and epididymo-orchitis

A hydrocele is fluid within the tunica vaginalis — a painless, transilluminating swelling above which one can get. Epididymo-orchitis: in young men usually Chlamydia or gonorrhoea, in older men coliforms from urinary infection; mumps orchitis after puberty may cause atrophy and subfertility.

Test yourself

Which cells form the blood–testis barrier?

Leydig cells
Peritubular myoid cells
Sertoli cells, via tight junctions between adjacent cells
Endothelial cells of testicular capillaries

Answer: Sertoli cells, via tight junctions between adjacent cells

Tight junctions between neighbouring Sertoli cells divide the seminiferous epithelium into basal and adluminal compartments, protecting meiotic and post-meiotic germ cells (which express novel antigens) from the immune system.

A 14-year-old boy has sudden severe left testicular pain for 2 hours. The testis lies high and horizontal and the cremasteric reflex is absent. What is the correct next step?

Antibiotics for epididymo-orchitis
Urgent surgical exploration
Elective ultrasound next week
Analgesia and observation

Answer: Urgent surgical exploration

This is testicular torsion until proven otherwise. Testicular salvage falls sharply after ≈6 hours, so exploration (detorsion and bilateral fixation) should not be delayed by imaging.