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see spermsperm
or spermatozoon
, in biology, the male gamete (sex cell), corresponding to the female ovum in organisms that reproduce sexually. In higher animals the sperm is produced in the testis of the male; it is much smaller than the ovum and consists primarily of a head,
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the male sexual cell in animals.

In all vertebrates and most invertebrates a flagellum, or tail, enables the spermatozoa to move forward. The spermatozoa of some worms, myriopods, crustaceans, mites, and ticks are tailless and are characterized by a wide variation in structure and by amoeboid movement. Spermatozoa range in length, according to species, from tens to hundreds of micrometers; the spermatozoa of insects may reach several millimeters in length.

Spermatozoa with tails have a comparatively short head that may be spherical, conical, or hooked in shape. A nucleus containing condensed chromatin is found in the head. At the head’s anterior end there is an acrosome containing lysins. Below the head there is a thinner middle piece that ends in a threadlike tail. In most animal species the middle piece is short and encloses a basal granule (centriole) consisting of nine triplets of short microtubules arranged in a ring and surrounded by a halo of four to ten large mitochondria.

Extending from the basal granule is an axial filament, or axo-neme, which by contracting enables the flagellum to beat and the spermatozoon to move. The ultrastructure of the axial filament is virtually the same in all spermatozoa and is similar to that of cilia. A filament consists of fibrils (microtubules 200–250 angstroms in diameter), two of which lie in the center surrounded by a ring of nine peripheral fibril doublets (9 + 2). Sometimes nine additional fibrils are found outside the doublets (9 + 9 + 2). Flagellate peripheral fibrils are transformed directly into microtubules of the basal granule, and the central fibrils remain free. Proteins similar to actin and myosin (found in skeletal muscles) and capable of splitting ATP are found in flagellate axial filaments in fibrils and in structures directly associated with fibrils.

In insects the head of a spermatozoon is very elongated and sometimes spirally coiled, extending almost imperceptibly into a long tail. Much of the tail contains a distinctive structure of mitochondrial origin called a mitochondrial helix.

In many animals several types of spermatozoa are formed in the testes. Most are atypical, resulting from spermatogenic disturbances primarily occurring during meiosis. These spermatozoa apparently cannot fertilize ova.


Wilson, E. Kletka i ee rol’ v razvitii i nasledstvennosti, vol. 1. Moscow-Leningrad, 1936. (Translated from English.)
Rukovodstvo po tsitologii, vol. 2. Moscow-Leningrad, 1966.
Hancock, J. L. “The Ultrastructure of Mammalian Spermatozoa.” In Advances in Reproductive Physiology. London, 1966.



A mature male germ cell. Also known as sperm.


any of the male reproductive cells released in the semen during ejaculation, consisting of a flattened egg-shaped head, a long neck, and a whiplike tail by which it moves to fertilize the female ovum
References in periodicals archive ?
Cryopreservation-induced human sperm DNA damage is predominantly mediated by oxidative stress rather than apoptosis.
Ackerman, "Freeze Preservation of Human Sperm," American Journal of Obstetrics and Gynecology 103 (1969): 660-61.
Chromosome studies in human sperm nuclei using fluorescence in-situ hybridization (FISH).
Human sperm motility and lipid peroxidation in different ascorbic acid concentrations: An in vitro analysis.
Relationships between biochemical markers for residual sperm cytoplasm, reactive oxygen species generation, and the presence of leukocytes and precursor germ cells in human sperm suspensions.
A suspension of human sperm is the only valid quality control for sperm count.
Gray explained that when human sperm and anegg unite, a whole, living, human being comes into existence, one that has the genetic material needed to inform and organize its growth.
However, much more work needs to be done before human sperm and eggs can be successfully grown in the laboratory.
During our efforts to crystallize human sperm protein Sp17, we have obtained cubic crystals belonging to the space group F432 with a=219.
Sofikitis managed to produce normal human sperm in the testicles of mice and rats in 1999, when he was a lecturer at Tottori University.
Dr Steve Publicover, who will help to lead the research, said: 'This project examines how a human sperm interacts with an egg.
Sikka, director of urology research at Tulane University Medical Center in New Orleans, and his associates tested the effects of incubating normal human sperm in sidenafil (125,250, and 750 ng/mL) and in a control solution.

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