ULTRASTRUCTURE OF TESTIS IN MAMMALS
The testis is a crucial organ in the male reproductive system
responsible for the production of sperm and the secretion of hormones,
primarily testosterone. The ultrastructure of the testis reveals the detailed
organization of its various components, including the seminiferous tubules
where spermatogenesis occurs and the interstitial tissue where Leydig cells
produce testosterone. Here is an overview of the ultrastructure of the testis
in mammals:
1. Seminiferous Tubules:
- Sertoli
Cells:
- Form the
structural framework of the seminiferous tubules.
- Extend from
the basal lamina to the lumen, providing physical and nutritional support
to developing germ cells.
- Nourish
spermatocytes and spermatids during spermatogenesis.
- Germ Cells:
- Spermatogonia:
Undifferentiated germ cells located along the basal lamina.
- Spermatocytes:
Cells undergoing meiosis to form spermatids.
- Spermatids:
Differentiating into spermatozoa during spermiogenesis.
- Spermatogenic
Cells:
- Located
along the periphery of the seminiferous tubules.
- Progress
through various stages of spermatogenesis.
- Seminiferous
Epithelium:
- Stratified
epithelium lining the seminiferous tubules.
- Comprises
Sertoli cells and spermatogenic cells.
- Undergoes a
cyclic process of spermatogenesis.
2. Interstitial Tissue:
- Leydig
Cells:
- Found in
the interstitial tissue between seminiferous tubules.
- Produce and
secrete testosterone in response to luteinizing hormone (LH) stimulation.
- Contain
prominent smooth endoplasmic reticulum and lipid droplets.
- Blood
Vessels:
- Provide the
testis with oxygen and nutrients.
- Blood
vessels traverse the interstitial tissue.
3. Spermatozoa:
- Head:
- Contains
the nucleus with condensed chromatin.
- The
acrosome at the tip contains enzymes for fertilization.
- Midpiece:
- Contains
mitochondria arranged in a helical pattern.
- Provides
energy for sperm motility.
- Tail:
- Propels the
sperm for locomotion.
- Composed of
a flagellum with a microtubule structure.
4. Basement Membrane:
- Location:
- Surrounds
the seminiferous tubules.
- Provides
structural support and a barrier for the movement of substances.
5. Connective Tissue:
- Location:
- Found
between the seminiferous tubules.
- Provides
additional structural support.
6. Myoid Cells:
- Location:
- Surround
the seminiferous tubules.
- Contractile
cells that help move sperm and fluids through the tubules.
7. Rete Testis:
- Location:
- A network
of tubules that collect sperm from the seminiferous tubules.
- Connects to
the epididymis.
The ultrastructure of the testis reflects its complex organization,
allowing for the highly regulated process of spermatogenesis. This process
involves the production of spermatozoa from germ cells, with critical support
from Sertoli cells and Leydig cells. The intricate cellular and structural
components contribute to the overall functionality of the testis in sperm
production and hormone secretion.
Let's understand this in pointwise and in simple:
- Location
of Male Reproductive System:
- Situated
in the pelvis region.
- Comprises
testes, accessory ducts, glands, and external genitalia.
- Testes
and Scrotum:
- Testes
are located outside the abdominal cavity in the scrotum.
- Scrotum
maintains a lower temperature (2–2.5o C below normal body temperature)
crucial for spermatogenesis.
- Each
testis is oval, measuring approximately 4 to 5 cm in length and 2 to 3 cm
in width.
- Testis
covered by a dense layer.
- Divided
into around 250 testicular lobules, each containing seminiferous tubules
for sperm production.
- Seminiferous
Tubules:
- Compartments
within testicular lobules where sperms are produced.
- Lined
by two types of cells: male germ cells (spermatogonia) and Sertoli cells.
- Male
germ cells undergo meiotic divisions, leading to sperm formation.
- Sertoli
cells provide nutrition to germ cells.
- Interstitial
spaces outside the tubules contain blood vessels and Leydig cells that
synthesize and secrete androgens.
- Male
Sex Accessory Ducts:
- These
ducts, including rete testis, vasa efferentia, epididymis, and vas
deferens, play a crucial role in sperm transportation.
- Seminiferous
tubules connect to vasa efferentia via rete testis.
- The
epididymis, located behind each testis, guides sperm to the vas deferens.
- Vas
deferens travels upward to the abdomen, curves over the bladder, connects
with the seminal vesicle duct, and eventually opens into the urethra as
the ejaculatory duct.
- These
ducts collectively store and move sperm from the testis to the outside
through the urethra.
- Urethra
and Penis:
- Urethra
originates from the urinary bladder and extends through the penis to the
urethral meatus (external opening).
- Penis,
the male external genitalia, is composed of special tissue facilitating
erection.
- Glans
penis, the enlarged end, is covered by foreskin.
- Male
Accessory Glands:
- Include
paired seminal vesicles, prostate, and paired bulbourethral glands.
- Secretions
form seminal plasma rich in fructose, calcium, and enzymes.
- Bulbourethral
gland secretions aid in penis lubrication