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Sperm

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Schematic diagram of a sperm cell, showing the (1) , (2) , (3) , (4) , and (5)  (tail)
Schematic diagram of a sperm cell, showing the (1) acrosome, (2) cell membrane, (3) nucleus, (4) mitochondria, and (5) flagellum (tail)

A sperm cell, or spermatozoon (pl. spermatozoa) (in Greek: sperm = semen and zoon = alive), 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. Sperm cells contain half of the genetic information needed to create life. Generally, the sex of the offspring is determined by the sperm, through the chromosomal pair "XX" (for a female) or "XY" (for a male). Sperm cells were first observed by Antoni van Leeuwenhoek in 1679.

Contents

Sperm 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 m by 3 m and a tail 50 m long. The tail flagellates, which we now know propels the sperm cell 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.

Sperm production

Main article: Spermatogenesis

Sperm are produced in the seminiferous tubules of the testes in a process called spermatogenesis. Round cells called spermatogonia divide and differentiate eventually to become sperm. During sexual intercourse the sperm is deposited in the vagina - and then it moves to the ovum inside the ovary.

The Acrosome Reaction

The female egg is coated in a thick protective membrane. When a sperm reaches the egg the acrosome releases its enzymes. These enzymes break down the cell membrane, allowing the sperm passage into the egg. Upon penetration the membrane undergoes a change and becomes inpenetratable, preventing further fertilization of the egg.

See also

External link

de:Spermium es:Espermatozoide fr:Spermatozode it:Spermatozoo he:זרע (אנטומיה) lt:Spermatozoidas nl:Zaadcel ja:精子 pl:Plemnik pt:Espermatozide ru:Сперматозоид su:Sprma zh:精子

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