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A sperm cell attempts to penetrate an Ovum coat to Fertilize it
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Human spermatozoön Diagrammatic A Surface view B Profile view In C the head, neck, and connecting piece are more highly magnified
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Spermatozoa
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A or '''spermatozoan''' (''pl.'' '''spermatozoa'''), from the
Ancient Greek ''σπερμα'' (seed) and ''ζων'' (alive) and more commonly known as a '''sperm cell''', is the
Haploid Cell that is the male
Gamete . It
Joins an
Ovum to form a
Zygote . A zygote can grow into a new
Organism , such as a human being.
Sperm cells contribute half of the will lead to a
Male (XY) offspring, while one bearing an X chromosome will lead to a
Female (XX) offspring ( the
Ovum always provides an X chromosome). Sperm cells were first observed by a student of
Antoni Van Leeuwenhoek in
1677 .
1
In humans, sperm cells consists of a head 5
µm by 3 µm and a tail 50 µm long. The
Reynolds Number associated with spermatazoa is in the order of 1E-2, so it is known that the spermatazoa exhibits
Laminar Flow . Spermatazoan stream lines are straight and parallel. The tail
Flagellate s, which we now know propels the sperm cell (at about 1-3 mm/minute in humans) by rotating like a propeller, not side to side like a whip. The cell is characterized by a minimum of cytoplasm. During fertilization, the sperm's
Mitochondria gets destroyed by the egg cell, and this means only the mother is able to provide the baby's mitochondria and
Mitochondrial DNA , which has an important application in tracing maternal
Ancestry . However it has been recently discovered that mitochondrial DNA can be recombinant.
The largest spermatozoa belongs to the
Fruit Fly .
''Main article:''
Spermatogenesis
Spermatozoa are produced in the
Seminiferous Tubule s of the
Testes in a process called spermatogenesis. Round cells called
Spermatogonia divide and differentiate eventually to become spermatozoa. During
Copulation the
Cloaca or
Vagina gets
Inseminat ed, and then the spermatozoa move through
Chemotaxis to the ovum inside a
Fallopian Tube or the
Uterus .
Sperm cells become even more excited when they approach an egg cell. They swim faster and their tail movements become more forceful and erratic. This behaviour is called "hyperactivity."
A recent discovery links hyperactivity to a sudden influx of calcium ion into the tails. The whip-like tail (flagellum) of the sperm is studded with
Ion Channel s formed by a protein called CatSper1. These channels are selective, allowing only calcium ion to pass. The opening of CatSper1
channels is responsible for the influx of calcium. The sudden rise in calcium levels causes the flagellum to spin faster, propelling the sperm more forcefully through the viscous environment. Sperm hyperactivity is necessary for breaking through two physical barriers that protect the egg
from fertilization.
The first barrier to sperm is made up of so-called cumulus cells that encase the egg like
Chain Mail . The cumulus cells develop with the egg and support it as it grows, and then provide a physical barrier to fertilization.
The second barrier is a membrane called the
Zona Pellucida . One of the proteins that make up the zona pellucida binds to a partner molecule on the sperm. This lock-and-key type mechanism is species-specific and prevents the sperm and egg of different species from fusing. There is some evidence that this binding is what triggers the acrosome to release the enzymes that allow the sperm to fuse with the egg.
The female
Ovum is coated in a thick protective
Membrane . When a sperm cell reaches the egg the acrosome releases its enzymes. These enzymes break down the cell membrane, allowing the sperm cell passage into the egg where the sperm
Fuses with the egg cells membrane, and empties its genetic content into the egg.
Upon penetration the membrane of the egg cell undergoes a change and becomes impenetrable, preventing further
Fertilization of the ovum.
