histological diagram of testis (testes)
The human testis is a compound tubulo-alveolar gland having both exocrine (cytogenous gland) and endocrine portions. The gland is composed of stroma and parenchyma.
The stroma is divisible as capsule, trabeculae and supporting reticular C.T. The testis
is invested by three coverings (tunics), which collectively form the capsule of testis. These tunics are as follows:
Tunica Vaginalis (visceral layer): It is an outermost peritoneal covering lined with simple squamous epithelium.
Tunica Albuglnea: it is a tough, shiny, white connective capsule Tunica Vasculosa: It is present internal to albuginea and consists of loose areolar connective tissue with rich capillary plexus. Posteriorly the tunica albuginea is thickened to form mediastinum testis from which connective tissue trabeculae pass inwards to divide the parenchyma into about 250 lobules. Each lobule contains seminiferous tubules. The spaces between seminiferous tubules are filled by areolar C.T. containing fenestrated blood capillaries nerves, lymph vessels and Leydlg cells.
INTERSTITIAL CELLS OF LEYDIG: These form the endocrine portion of the testis. The Leydig cells are rounded or polygonal with eccentric nuclei (containing 1-3 nucleoli) and acidophilic cytoplasm. Binucleated cells are common. The cells are rich in mitochondria, smooth endoplasmic reticulum, prominent Colgi body and lipid droplets. These cells secrete testosterone.
PARENCHYMA: It is in the form of lobules, which are pyramidal in shape with their bases towards the surface. Each lobule of testis contains between 1-4 highly convoluted seminiferous tubules. Each seminiferous tubule is 30-70 cm in length and 150-250 urn in diameter. Its wall consists of following layers (from without inward):
Tunica propria: It is the outermost flbroelastlc capsule containing single layer of flattened contractile cells (myold cells). Their contraction aids in the transport of sperms.
Basement Membrane: Upon it. the epithelium cells rest.
Epithelium: It is a complex type of stratified epithelium, which is comprised of both cuboidal and columnar cells. It consists of many layers of two type of cells: (a) Sex cells (spermatogenlc cells); and (b) supporting or Sertoli cells.
The sex cells or lineage are seen in various stages of development, e.g.. spermatogonia, primary and secondary spermatocytes, spermatids and spermatozoa. The earlier stages are near the basement membrane while the most advanced cells are found near the lumen of seminiferous tubule. The cells are arranged in 4-8 layers, which extend between basement membrane and the lumen.
• Spermatogonia are small spherical cells (12 nm) with rounded nuclei and are of two types; A and B. Type A spermatogonia are small in size as compared to type B cells, Type A cells are of further two types; pale type A and dark type A cells,
1. Dark type A spermatogonia act as reserve or stem cells and contain dark chromatin material.
2. Pale type A spermatogonia contain pale chromatin material.
3. Type B spermatogonia (progenitor) are large in size with large rounded nuclei.
• Primary spermatocytes are arranged in 2-3 layers
. Secondary spermatocytes
• The spermatids.
• Spermatozoon: During spetmlogenesls, the nucleus of spermatid assume / peripheral position. The cytoplasm is extruded out while the spermatid elongates to form a spermatozoon. The newly formed spermatozoon remains attached to the Sertoli cells for a few days when a spermatozoon is detached from the Sertoli cells and moves freely in the lumen of seminiferous tubule's lumen. A mature spermatozoon has a head, neck and tail (comprised of middle piece, principle piece and end piece). The spermatozoa are present in-groups with their tails projecting towards the lumen only in limited quadrants of few tubules visible in a microscopic field. This can be understood by the cycle of seminiferous epithelium
Sertoli cells are supportive cells. These cells are tall columnar with indistinct outlines and ovoid nuclei. These are present between the spermatogenic cells and rest on the basement membrane but their apical portions reach the lumen of tubules, their cytoplasm and basal nuclei are pale stained. Each cell has a definite nucleolus (nuclei of all the spermatogenic cells lack in nucleoli). Each cell has many mitochondria, smooth endoplasmic reticulum, Colgi body, lipid droplets, lipochrome pigments and lysosomes. The lateral walls of each Sertoli cell are infolded to form many pockets, which lodge all the cells of spermatogenic series. The Sertoli cells do not divide during reproductive period.
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