A spermatozoon (alternate spellings spermatozoan, spermatozoön; plural spermatozoa) is a motile sperm cell, or moving form of the haploid cell that is the male gamete. (A non-motile sperm cell is called a spermatium.) A spermatozoon 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.) The term spermatozoon comes from the ancient Greek word σπέρμα (seed) and ζῷον (living being).
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.
Mammalian spermatozoan structure, function, and size
The human sperm cell is the reproductive cell in males and will only survive in warm environments, once leaving the body the sperm's survival is reduced and may cause the cell to die, decreasing the sperm quality. Sperm cells come in two types, "female" and "male". 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.
In male humans, sperm cells consists of a head 5 µm by 3 µm and a tail 41 µm long. The tail flagellates, which propels the sperm cell (at about 1–3 mm/minute in humans) by whipping in an elliptical cone. 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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