ULTRASTRUCTURE OF SPERM
The ultrastructure of a spermatozoon, or sperm cell, is specialized
for its function in fertilization. Here are the main components and structures
of the ultrastructure of a sperm:
1. Head:
- Nucleus:
- Contains
densely packed chromatin.
- Carries
genetic material (DNA) for fertilization.
- Acrosome:
- A
membrane-bound vesicle derived from the Golgi apparatus.
- Contains
enzymes (acrosin) essential for penetrating the egg during fertilization.
- Flagellum
Attachment:
- The base of
the head connects to the midpiece of the sperm.
2. Midpiece:
- Mitochondria:
- Numerous
mitochondria arranged in a helical pattern around the axial filament
(central pair of microtubules).
- Provide the
energy (ATP) needed for sperm motility.
- Axial
Filament:
- Central
pair of microtubules extending from the basal body to the end of the
tail.
- Forms the
core of the flagellum.
3. Tail (Flagellum):
- Principal
Piece:
- Contains
the axial filament and is responsible for most of the tail's length.
- Provides
the main propulsive force for sperm motility.
- End Piece:
- The
terminal part of the tail.
- Functions
to propel the sperm forward.
4. Basal Body:
- Centriole:
- The
microtubule-organizing centre that organizes the microtubules in the
sperm tail.
- Derived
from one of the centrioles of the spermatid during spermiogenesis.
5. Plasma Membrane:
- Surrounds
the entire sperm cell.
6. Glycocalyx:
- A layer of
carbohydrates on the surface of the sperm.
- Involved in
sperm egg recognition during fertilization.
7. Sperm Membrane Proteins:
- Include
receptors for signalling molecules involved in sperm function.
8. Cytoplasmic Droplet:
- Present in
some sperm cells, especially during their passage through the epididymis.
- A remnant of
excess cytoplasm that was not shed during spermiogenesis.
9. Elongated and Streamlined Shape:
- Adapted for
efficient movement through the female reproductive tract to reach the egg.
10. Tail Sheath:
- Surrounds
the flagellum.
- Part of the sperm's
structural organization.
The ultrastructure of sperm reflects its specialized adaptations for
motility, penetration of the egg during fertilization, and the delivery of
genetic material. The unique features, such as the acrosome and mitochondrial
helix, play essential roles in the sperm's ability to reach and fertilize the
egg. The streamlined shape and propulsion provided by the flagellum contribute
to the sperm's successful journey through the female reproductive tract.