Spermatozoon Spermatozoon Structural geology Category="Andrology"Category="Germ cells"Category="Reproductive system"A sperm cell, spermatozoon (pl. spermatozoa) (in Greek: sperma = semen and zoon = alive), or spermatozoan, is the haploid cell that is the male Gamete. It is carried in fluid called Semen, and is capable of fertilising an egg cell to form a Zygote. A zygote can grow into a new Organism, such as a human being. Sperm cells contain half of the genetic information available to the diploid offspring. Generally, the sex of the offspring is determined by the sperm cells, through the chromosomal pair "XX" (for a Female) or "XY" (for a Male). Sperm cells were first observed by Antoni van Leeuwenhoek in 1679.

Spermatozoan structure and size

Individual spermatozoa are highly differentiated cells, composed normally of a head, basal body (or midpiece), and tail. The head contains some Cytoplasm and the nuclear material for fertilization. The Basal body contains a large concentration of mitochondria that provide the energy for sperm motility through the production of ATP. The spermatozoan tail is typically a Flagellum used for propulsion.

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 flagellates, which we now know propels the sperm cell (at about 1-3 mm/minute in humans) by rotating like a rutter 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.

Sperm cell production

Main article: Spermatogenesis

Spermatozoa are produced in the seminiferous tubules 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 inseminated, and then the spermatozoa move through Chemotaxis to the ovum inside a Fallopian tube or the Uterus.

The acrosome reaction

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 inpenetratable, preventing further fertilization of the ovum.

See also

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