MICROSCOPIC STRUCTURE OF TESTIS

 

Testes are male gonads responsible to produce male gametes spermatozoa and the hormone testosterone.

Testis has 3 intrinsic coverings. From outside to inside, they are..

  1. Tunica vaginalis (serous sac )
  2. Tunica albuginea (fibrous layer )
  3. Tunica vasculosa (connective tissue with blood vessels)

 

Thick connective tissue layer known as TUNICA ALBUGINEA surrounds each testis.

At the posterior border of testis, it thickens to form MEDIASTINUM TESTIS.

Connective tissue septa from the mediastinum testis divides the interior of the testis into 200 to 300 TESTICULAR LOBULES.

Testicular lobules contain SEMINIFEROUS TUBULES that are lined by GERMINAL EPITHELIUM.

Each lobule contains 1 to 4 seminiferous tubules.

Germinal epithelium contains 2 types of cells

  1. SPERMATOGENIC CELLS (divide to form sperm)
  2. SERTOLI CELLS (supporting cells)

SPERMATOGONIA are the immature spermatogenic cells, lie adjacent to the basement membrane of the seminiferous tubules. They divide mitotically.

There are 3 types of spermatogonia…

  1. PALE TYPE A SPERMATOGONIA
  2. DARK TYPE A SPERMATOGONIA
  3. TYPE B SPERMATOGONIA

TYPE A spermatogonia act as stem cells and give rise to other type A and type B spermatogonia.

TYPE B spermatogonia ( 2n diploid ) undergo mitosis to produce primary spermatocytes ( 2n diploid ).

Primary spermatocytes are the largest germ cells in the seminiferous tubules. They undergo the 1st meiotic division to produce smaller secondary spermatocytes ( n haploid ).

Secondary spermatocytes , shortly after its formation , undergo the second meiotic division and are not frequently seen in the seminiferous tubules.

Spermatids ( n haploid ) are produced after the second meiotic division . They lie embedded in the cytoplasm of Sertoli cells.

Spermatids do not undergo any further division but morphologically transform by a process known as SPERMIOGENESIS  to form SPERMATOZOA ( n haploid ).

Sperms are released from the Sertoli cells into the lumen of seminiferous tubules by a process called as SPERMIATION.

Connective tissue extends inwards from tunica vasculosa to form INTERSTITIAL CONNECTIVE TISSUE, which apart from consisting of blood vessels, also contains INTERSTITIAL CELLS OF LEYDIG. These cells are endocrine in nature and produces male sex hormone TESTOSTERONE.

Spermatogenesis is dependent on LH and FSH hormones produced by the anterior pituitary.

LH stimulates interstitial cells of Leydig to produce testosterone.

FSH stimulates Sertoli cells to produce ANDROGEN BINDING PROTEIN ( ABP ). ABP binds to testosterone. Testosterone levels are very essential for normal spermatogenesis.