This tab covers the testis (gross and microscopic structure, its triple arterial supply, retroperitoneal lymphatic drainage, and innervation), the epididymis, and the vas deferens — with the surgical implications for vasectomy and reconstruction.
Testis: Structure and Microanatomy
The normal testis is 4–5 × 3 × 2.5 cm with a volume of 15–25 mL (averaging ~20 mL); the right hangs lower in ~85% of men. The appendix testis is a Müllerian (paramesonephric) remnant (the appendix epididymis is a Wolffian/mesonephric remnant). The testis has two compartments:
- Seminiferous tubules — contain spermatogenic cells (the bulk of testicular volume) and Sertoli cells, which support spermatogenesis, secrete inhibin (inhibiting FSH), and form the blood-testis barrier by tight junctions. This barrier creates an immune-privileged site and develops at puberty — so a pre-pubertal insult (biopsy, torsion, trauma) does not induce anti-sperm antibodies. Sperm travel: seminiferous tubules → straight tubules (tubuli recti) → rete testis → efferent ductules → epididymis (head→body→tail) → vas deferens → ejaculatory duct → prostatic urethra.
- Interstitial tissue (20–30% of volume) — contains the Leydig cells, which produce testosterone and activin (activin stimulates FSH), plus mast cells, macrophages, nerves, and vessels.
Testis: Vasculature, Lymphatics, and Innervation
Three arteries supply the testis: the testicular (internal spermatic) artery from the aorta (the main supply), the artery of the vas (deferential) from the superior vesical, and the cremasteric (external spermatic) artery from the inferior epigastric ("Cream in the Belly"). The testicular artery's caliber exceeds the other two combined; the deferential and cremasteric can sustain the testis if it is ligated, though atrophy/azoospermia may follow — preserve the testicular artery in a man with a prior vasectomy (whose deferential supply may be compromised). Clinical: biopsy the midsection of the testis, where vessels are fewest.
- Venous — uniquely, the veins do not travel with the arteries; they form the pampiniform plexus, which provides counter-current heat exchange keeping the testis 2–4 °C below rectal temperature. The plexus coalesces into the gonadal vein, which drains into the IVC on the right and the left renal vein on the left (dilated in a varicocele). The deferential veins drain into the internal iliac veins and are spared during varicocele ligation.
- Lymphatics — ascend in the cord to the para-aortic, interaortocaval, and paracaval nodes (flow is right → left): the right testis drains predominantly to interaortocaval nodes, the left predominantly to para-aortic nodes — never to the inguinal nodes.
- Innervation — there is no somatic innervation of the testis; autonomic fibres arrive from the renal and aortic plexuses along the gonadal vessels. The nerves implicated in chronic orchialgia are the perivasal, intracremasteric, and posterior periarterial (lipomatous) complexes (targeted in microdenervation).
Epididymis
The epididymis is a duct on the posterolateral testis divided into caput (head), corpus (body), and cauda (tail), lined by principal cells (absorptive/secretory) and basal cells (precursors). Its functions are sperm transport, storage, and maturation. Blood supply: the superior and medial epididymal arteries (from the testicular artery) supply the caput and corpus, and the inferior epididymal artery (from the artery of the vas) supplies the cauda — with extensive interconnections, so either source alone can sustain the epididymis. During vasoepididymostomy/vasovasostomy the epididymis can be mobilised and the inferior/medial arteries ligated as long as the superior epididymal artery is preserved.
Vas Deferens
The vas is 30–35 cm long (tortuous for its first 2–3 cm), running posterior to the cord vessels, through the inguinal canal, and into the pelvis lateral to the inferior epigastric vessels, reaching the posterior base of the prostate. It has a dual blood supply — the artery of the vas (abdominal end) and the inferior epididymal interconnections (testicular end) — which freely anastomose. Critically, the vas receives no supply from the surrounding cremaster or cord, so if it is divided or obstructed in two locations the intervening segment fibroses — meaning two simultaneous vasovasostomies cannot be safely performed on the same vas once the vasal vessels are interrupted at both sites.
Self-Test
1. What is the normal volume of the testicle? 15–25 mL.
2. Which cells form the blood-testis barrier, and when does it develop? Sertoli cells; it develops at puberty.
3. What is the arterial supply to the testicle and the origin of each artery? Testicular artery (from the aorta), deferential artery (from the superior vesical artery), and cremasteric artery (from the inferior epigastric artery).
4. Where should a testicular biopsy be performed to minimise bleeding? The middle of the testis.
5. Where do the testicular lymphatics drain? To the para-aortic, interaortocaval, and paracaval nodes (right → left flow; the right testis predominantly to interaortocaval nodes, the left predominantly to para-aortic nodes).
6. Which nerves contribute to chronic orchialgia? The perivasal, intracremasteric, and posterior periarterial (lipomatous) complexes.
7. What are the functions and blood supply of the epididymis? Functions: sperm transport, storage, and maturation. The head is supplied by the superior epididymal artery (from the testicular artery) and the body/tail by the inferior epididymal artery (from the deferential artery).
8. What is the normal length of the vas deferens, and its position relative to the cord vessels and the inferior epigastric vessels? 30–35 cm; it lies posterior to the cord vessels and enters the pelvis lateral to the inferior epigastric vessels.