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( Spermatozoon)
A spermatozoon or spermatozoan (pl. spermatozoa), from the ancient Greek sp??µa (seed) and ???? (living being) 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 is a single cell, with a complete set of chromosomes, that normally develops into an embryo. Sperm cells contribute half of the genetic information to the diploid offspring. In mammals, the sex of the offspring is determined by the sperm cell a spermatozoon bearing a Y chromosome 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 Anton van Leeuwenhoek in 1677.[1] The human sperm cell is the reproductive cell in males. Sperm cells come in two types; "male" and "female". Sperm cells that give rise to female (XX) offspring after fertilization differ in that they carry an X chromosome, while sperm cells that give rise to male (XY) offspring carry a Y chromosome. The "female" sperm cell also differs phenotypically in that it has a larger head in comparison to the "male" sperm cell[citation needed]. In male humans, sperm cells consists of a head 5&_160;µm by 3&_160;µm and a tail 50&_160;µm long. The Reynolds number associated with spermatozoa is in the order of 1×10-2, so it is known that the spermatozoa exhibit non-turbulent flow. The tail flagellates, which propels the sperm cell (at about 1–3 mm/minute in humans) by whipping in an elliptical cone.[2]. Semen has an alkaline nature, and they do not reach full motility (hypermotility) until they reach the vagina where the alkaline pH is neutralized by acidic vaginal fluids. This gradual process takes 20–30 minutes. In this time, fibrinogen from the seminal vesicles forms a clot, securing and protecting the sperm. Just as they become hypermotile, fibrinolysin from the prostate dissolves the clot, allowing the sperm to progress optimally.
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