VGO 511: Veterinary Andrology and Reproductive Techniques (1+1)

TESTIS

Synonyms: Orchium, male gonad

• Testis originated from Greek word- Orchis
• Testis is the primary andrological organ which produces spermatozoa and male sex hormone (testosterone).
• Morphologically oval shaped, paired glands. Right and left testicles are separated by muscular septum which is formed by dartos muscle.
• Located outside the abdominal cavity. In most of the species, located between the thighs within the scrotum.
• Testes are intra-abdominal in elephant, whales, seal, dolphin, birds, rhinoceros (testchondas)
• The testis is supported in one of the two scrotal pouches where it is held by its tunics and by the spermatic cord.

The Spermatic cord is composed of

• Spermatic artery
• Spermatic vein
• Spermatic nerve
• Internal cremaster muscle
• Lymphatic vessels
• Vas deferens
• Tunica vaginalis propria

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Embryonic Development

• Origin of testes is initiated from gonadal / genital ridge. It occurs in 4 phases.
  • First Phase
    • Migration of the germ cells at the gonadal ridge.
  • Second Phase
    • Formation and proliferation of the blastema for genesis of indifferent gonad.
  • Third Phase
    • Migration of mesonephric cells into gonad.
  • Fourth Phase
    • Sexual differentiation and its development into testis

The testis consists of the

• Testicular capsule
• Parenchyma
• Mediastinum
• Rete tubules

The testicular parenchyma consists of

• Seminiferous tubules
• Interstitial cells of leydig
• Capillaries
• Lymphatic vessels
• Connective tissue

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Testis proper is covered by 2 capsules

• Tunica vaginalis propria
• Tunica albuginea
• Tunica vaginalis propria is composed of
  • Parietal layer – faces scrotum

Visceral layer – faces testis

Internal features

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• The distal end of the testis is attached to the scrotum by the scrotal ligament
• The testis proper is closely covered by a thin serous membrane - tunica vaginalis propria. Beneath this structure is a dense, thick connective capsule – tunica albuginea, from which septa radiate to the mediastinum testes except in stallion to form the lobules of the testis.
• Within this lobules are the seminiferous tubules, which are lined by germinal epithelium that produces spermatozoa and sertoli cells which are located in between the developing germ cells.
• The sertoli cells are otherwise called as Nurse cells or Pillar like cells or Sustantacular cells.
• The interstitial cells (Leydig), which lie between the seminiferous tubules, secrete male hormones.
• The seminiferous tubules converge at the apex of the lobule at the receptacle to join the straight tubules.
• The straight tubules are also called as tubuli recti that enter the rete testis, a structure of anastomosing spaces located in the mediastinum testis.
• There is no mediastinum testis in the stallion as is present in other animals.
• The collecting tubules join the efferent tubules.
• From the rete testis, 6-24 efferent ducts arise; these ducts form a single duct called as caput epididymis.
• On examination of the testes the torturous configuration of blood vessels is most readily noted in the tunica albuginea in the bull.
• This is a further provision assisting the heat regulatory mechanism of the testis.
• The consistency of the testis is usually turgid.
• The parenchyma is yellow to reddish brown in colour and bulges on section.

Approximate length of seminiferous tubule

Swine	6000 meters
Bull	5000 meters
Ram	4000 meters
Dog	150 meters
Cat	25 meters

Cross section of seminiferous tubules contains three layers

• Outer capsule
• Basement membrane
• Testicular cells

Testicular cells is composed of

• Germinal cells
• Parenchymal cells or testicular somatic cells
• Sertoli cells

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Physiological functions of testis

• It produces male sex hormone(androgen).
• It secretes testicular fluid.
• It nourishes the newly born male gamete.
• It helps in the transportation of spermatozoa.
• It provides blood-testis barrier.
• It secretes estrogen in limited amount.

Associated structures

• Testicular ligament
• Testicular mesentry
• Testicular appendix

Testicular ligament

• Fetal ligament which is a derivative of gubernaculum and present during the descent of the testis in to the scrotum. Later on, it gets atrophied.

Testicular mesentry

• It is a part of primitive mesentry which encloses fetal testis and is present during the descent of testis in the scrotum.
• It continues in the form of peritoneal fold between testes and epididymis during post-natal life of livestock.

Testicular appendix

• It is non-functional residual part of embryonal hood during post-natal life of livestock.

Blood supply

• The testis is richly supplied with blood by the spermatic artery/ testicular artery, a branch of the abdominal aorta.
• The veins on leaving the testicles form a network, the pampiniform plexus around the artery in spermatic cord.
• The spermatic vein which issues from this plexus, usually joins with the posterior venacava on the right side, the left renal vein on left side.

Nerve Supply

• The nerves derived from the renal and posterior mesenteric plexus form the spermatic plexus around the vessels to which they are chiefly distributed.

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