Spermatogenesis
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Definition: It is the sequence of events
by which spermatogonia are transformed into mature sperms or spermatozoa.
This maturation
process begins at puberty and continues into old age
In male the
primordial germ cells remain dormant until puberty.
At puberty, after several mitotic divisions
of the spermatogonia, primary spermatocytes (diploid) are formed. They are the largest cells of seminiferous tubules and enters a prolonged
prophase (22 days)
Each primary
spermatocyte is completed meiosis Ito
form two haploid secondary spermatocytes
Subsequently, two
secondary spermatocytes complete the
meiosis II to form four spermatids
Spermiogenesis
The spermatids are gradually
transforms into mature sperm or spermatozoa by a process known as
spermiogenesis.
These changes include:
- Loss of cytoplasm.
- Formation of acrosomes which covers half the nuclear
surface, derived from the golgi region of spermatid contain enzymes that
assist penetration of corona radiata and zona pellucida during
fertilization
- Condensation of nucleus
- Formation of neck, middle piece, and tail
- The mitochondria arranged in the middle piece as
mitochordial sheath
The time required for a
spermatogonium to become a mature spermatozoon is approximately74 days
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