Difference between revisions of "Sperm" - New World Encyclopedia
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| − | A '''spermatozoon''' or '''spermatozoan''' (''pl.'' '''spermatozoa'''), from the | + | A '''spermatozoon''' or '''spermatozoan''' (''pl.'' '''spermatozoa'''), from the ancient Greek ''σπερμα'' (seed) and ''ζων'' (alive), is more commonly known as a '''sperm cell'''. It is the [[ploidy|haploid]] [[cell (biology)|cell]] that is the male [[gamete]]. It [[fertilizes]] an [[ovum]], which is the female [[gamete]], to form a [[zygote]]. A [[zygote]] can then grow into a new [[organism]], such as a human being. <br /> |
Sperm cells contribute half of the [[gene|genetic information]] to the [[diploid]] offspring. In mammals, the [[sex]] of the offspring is determined by the sperm cells: 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 a student of [[Anton van Leeuwenhoek|Antoni van Leeuwenhoek]] in [[1677]].<ref>{{cite web|url=http://www.cbc.ca/news/background/genetics_reproduction/timeline.html|title=Timeline: Assisted reproduction and birth control|accessdate=2006-04-06}}</ref> | Sperm cells contribute half of the [[gene|genetic information]] to the [[diploid]] offspring. In mammals, the [[sex]] of the offspring is determined by the sperm cells: 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 a student of [[Anton van Leeuwenhoek|Antoni van Leeuwenhoek]] in [[1677]].<ref>{{cite web|url=http://www.cbc.ca/news/background/genetics_reproduction/timeline.html|title=Timeline: Assisted reproduction and birth control|accessdate=2006-04-06}}</ref> | ||
==Spermatozoan structure and size== | ==Spermatozoan structure and size== | ||
[[Image:Complete diagram of a human spermatozoa.svg|thumb|350px|left|Diagram of a human spermatozoon]] | [[Image:Complete diagram of a human spermatozoa.svg|thumb|350px|left|Diagram of a human spermatozoon]] | ||
| − | In humans, sperm | + | In humans, a sperm cell consists of a head 5 [[micrometre|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 and 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]] contains a minimum of [[cytoplasm]]. During [[fertilization]], the sperm's [[mitochondria]] are destroyed by the egg cell, meaning only the mother is able to provide the offspring's mitochondria [[DNA]]. This plays an important fact in tracing maternal ancestry. However, it has been recently discovered that [[mitochondrial]] [[DNA]] may be recombinant, or a combination of [[genes]] not found together in either parents. |
The largest spermatozoa belongs to the [[fruit fly]]. | The largest spermatozoa belongs to the [[fruit fly]]. | ||
Revision as of 22:23, 31 May 2006
| Sperm | |
|---|---|
| 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. | |
| Gray's | subject #258 1243 |
| MeSH | Spermatozoa |
A spermatozoon or spermatozoan (pl. spermatozoa), from the ancient Greek σπερμα (seed) and ζων (alive), is more commonly known as a sperm cell. It is the haploid cell that is the male gamete. It fertilizes an ovum, which is the female gamete, to form a zygote. A zygote can then grow into a new organism, such as a human 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 cells: 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 a student of Antoni van Leeuwenhoek in 1677.[1]
Spermatozoan structure and size
In humans, a sperm cell 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 and 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 contains a minimum of cytoplasm. During fertilization, the sperm's mitochondria are destroyed by the egg cell, meaning only the mother is able to provide the offspring's mitochondria DNA. This plays an important fact in tracing maternal ancestry. However, it has been recently discovered that mitochondrial DNA may be recombinant, or a combination of genes not found together in either parents.
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
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 channels 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.
See also
- sperm competition
- sperm heteromorphism
ReferencesISBN links support NWE through referral fees
- ↑ Timeline: Assisted reproduction and birth control. Retrieved 2006-04-06.
External links
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