Spermatozoa are the only cell produced in our body
destined to do their work in another body. No other cell has to undergo extreme
environmental conditions as sperm does during its journey in the female
reproductive tract to meet its counterpart oocyte (egg cell).
Scientists are trying their best to understand the sperm; however, we
have not attained complacence in it as because sperm are highly specialized
cells, who possess lots of gordian knots yet to be unraveled. The following
list explores some of the intriguing discovered facts about sperm.
10. Sperm Production
The human testis is a mega factory, which can produce a
whooping amount of 1500 sperm per second. Sperm are usually produced inside the
seminiferous tubules of testis. A human testis consists of 800-1600 numbers of
seminiferous tubules, with a combined length of 600 m, which is double the
height of an Eiffel tower.
9. Sex of
Sperm
Spermatozoa carries the X (female) or Y (male)
chromosome, based on which the sex of future child is determined. It is
possible to differentiate and separate X and Y spermatozoa based on the
differences in their DNA contents. Human X sperm encompasses 2.8% more DNA than
the Y sperm, due to which Y sperm can swim faster than X sperm.
8. Swollen
Sperm
We may think that swollen sperm as abnormal but it is
the characteristic of normal sperm when it is exposed to the hypo osmotic
solution. This characteristic of semen has been tested usually in infertility
clinics.
The principle lies behind is that
normal sperm are covered by intact plasma membrane which allows the influx of
fluid and results in a ballooning of plasma membrane and curling or bending of
sperm tail.
7. Translation
Translation is a process occur in the ribosome to make
a protein which is major structural component of every cell in the body.
However, mature spermatozoa are specialized cells, where translation process is
absent. Then how they modify their function without protein? They do it by the
process namely protein tyrosine phosphorylation. However, translation in sperm
is still mysterious.
6. Is Sperm a
foreign body for female?
Sperm is a foreign body for both male who produced it
and female who received it. In men, sperm do not contact with blood due to
blood testis barrier. Likewise, in women, sperm do not normally come in contact
with blood due to blood tissue barrier.
However, some persons do develop anti-sperm antibodies, due to injuries
and exposure of sperm to blood. Without injuries also some women produce immune
attack against sperm. The causes are unknown because each women’s immune response
variation between person to person. However, fertilization is possible even in
these women due to the newly discovered molecular handshake between sperm and
uterine cells, which helps the sperm to escape the immune attack and direct the
immune system to target the weaker sperm.
5. How does sperm
navigate egg?
The sperm ejaculated from the man’s penis gets
deposited in the front portion of the vagina near cervix. From there sperm
starts voyage to meet its counterpart egg. After reaching the tunnel of love
(fallopian tube), the sperm undergoes some maturation changes by which sperm
acquires the capacity to recognize the chemical signals (chemotaxis) from the
egg and guide their way forward to fertilize.
4. Species
specific sperm receptors
What if sperm of one species entered into the female
reproductive tract of another species? Egg cell has species-specific receptors
for the sperm on its outer layer called zona pellucida. It allows only sperm of
the same species to bind on them.
The exception is the egg cell of hamster, wherein sperm receptors are
present on the vitelline membrane and it is not species specific. Therefore,
egg cell of hamster is used to evaluate the binding and penetration ability of
human spermatozoa.
3. Restricted
Entry
When one sperm enters inside egg cell, it initiates
the release of cortical granules from the cortex. These cortical granules come
outside and hardens the outer layer of an egg (Zona hardening) which in turns
does not allow other sperm to fuse with egg. These cortical granules also
release some proteases, which destroys sperm receptors on the outer membrane of
egg, thereby prevents polyspermy (fusion of multiple sperm to egg cell).
2. Dying
sperm seeks company
Dying sperm (also known as moribund sperm) is the
transition stage between live and dead sperm. These dying sperm are dangerous
than the dead sperm in the ejaculate. Dying sperm releases harmful substances
such as reactive oxygen species which in turns compromise the life of other
normal sperm. This leads to increase in the number dead sperm in the ejaculate
and derange the quality of ejaculate.
1. Do or Die
Getting matured is all fun and happy for everyone but
it is not the case with sperm. Sperm need to undergo lot of detrimental changes
in the lower part of fallopian tube during its penultimate step of maturation
known as capacitation. Even though, sperm attains the capacity to fertilize the
egg during this process, sperm lose its protective outer covering, therefore
life of sperm also compromised. After this process, sperm will be left with
only two options, one is to fertilize and another is to die.
- Dr. Elango K
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