 |
|
| A sperm cell attempts to penetrate an ovum coat to fertilize it. | |
 |
|
| Diagram of a human spermatozoon | |
| Latin | spermatozoon |
|---|---|
| Gray's | subject #258 1243 |
| MeSH | Spermatozoa |
| Dorlands/Elsevier | Spermatozoa |
A spermatozoon (alternate spelling spermatozoön; plural spermatozoa; from Ancient Greek: σπέρμα "seed" and Ancient Greek: ζῷον "living being") is a motile sperm cell, or moving form of the haploid cell that is the male gamete. 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.)
Sperm cells contribute approximately half of the nuclear genetic information to the diploid offspring (excluding, in most cases, mitochondrial DNA). 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 X chromosome. Sperm cells were first observed by Anton van Leeuwenhoek in 1677.
The human sperm cell is the reproductive cell in males and will only survive in warm environments; once it leaves the male body the sperm's survival likelihood is reduced and it may die, thereby decreasing the total 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 flat, disc shaped head 5 µm by 3 µm and a tail 50 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. In other words, The Spermatozoon's flagellum and the rest of its morphology is formed within the vaginal walls of a female, however, males with Benign prostatic hyperplasia due to swelling of the prostate, may have premature formation of a Spermatozoon in the urine of a male.
The spermatozoon is characterized by a minimum of cytoplasm and the most densely packed DNA known in eukaryotes. Compared to mitotic chromosomes in somatic cells, sperm DNA is at least sixfold more highly condensed.
The specimen contributes with DNA/chromatin, a centriole and perhaps also an oocyte-activating factor (OAF). It may also contribute with paternal messenger RNA (mRNA), also contributing to embryonic development.
Electron micrograph of human spermatozoa magnified 3140 times.
Sperm cells in the urine sample of a 45 year old male patient who is being followed with the diagnosis of benign prostate hyperplasia.
Another image from the same urine sample as with the image on the left.
Glycoprotein molecules on the surface of ejaculated sperm cells are recognized by all human female immune systems, and interpreted as a signal that the cell should not be rejected. The female immune system might otherwise attack sperm in the reproductive tract. The specific glycoproteins coating sperm cells are also utilized by some cancerous and bacterial cells, some parasitic worms, and HIV-infected white blood cells, thereby avoiding an immune response from the host organism.
The blood-testis barrier, maintained by the tight junctions between the Sertoli cells of the seminiferous tubules, prevents communication between the forming spermatozoa in the testis and the blood vessels (and immune cells circulating within them) within the interstitial space. This prevents them from eliciting an immune response. The blood-testis barrier is also important in preventing toxic substances from disrupting spermatogenesis.
Fertilization relies on spermatozoa for most sexually reproductive animals.
Some species of fruit fly produce the largest known spermatozoon found in nature. Drosophila melanogaster produces sperm that can be up to 1.8 mm, while its relative Drosophila bifurca produce the largest known spermatozoon, measuring over 58 mm in size. In D. melanogaster the entire sperm, tail included, gets incorporated into the oocyte cytoplasm, however, for D. bifurca only a small portion of the tail enters the oocyte.
The wood mouse Apodemus slvaticus possesses spermatozoa with falciform morphology. What makes these gametocytes even more unique is the presence of an apical hook on the sperm head. This hook is used to attach to the hooks or to the flagella of other spermatozoa. Aggregation is caused by these attachments and mobile trains result. These trains provide improved motility in the female reproductive tract and are a means by which fertilization is promoted.
Sea urchins such as Arbacia punctulata-are ideal organisms to use in sperm research, they spawn large numbers of sperm into the sea, making them well-suited as model organisms for experiments.
The gametophytes of bryophytes, ferns and some gymnosperms produce motile sperm cells, contrary to pollen grains employed in most gymnosperms and all angiosperms. This renders sexual reproduction in the absence of water impossible, since water is a necessary medium for sperm and egg to meet. Algae and lower plant sperm cells are often multi-flagellated (see image) and thus morphologically different from animal spermatozoa.
Some algae and fungi produce non-motile sperm cells, called spermatia. In higher plants and some algae and fungi, fertilization involves the migration of the sperm nucleus through a fertilization tube (e.g. pollen tube in higher plants) to reach the egg cell.
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.
Approaching the egg cell is a rather complex, multistep process of chemotaxis guided by different chemical substances/stimuli on individual levels of phylogeny. One of the most significant, common signaling character of the event is that a prototype of professional chemotaxis receptors, formyl peptide receptor (60.000 receptor/cell) as well as the activator ability of its ligand formyl Met-Leu-Phe have been demonstrated in the surface membrane even in the case of human sperms. Mammalian sperm cells become even more active when they approach an egg cell in a process called sperm activation. Sperm activation has been shown to be caused by calcium ionophores in vitro, progesterone released by nearby cumulus cells and binding to ZP3 of the zona pellucida. The cumulus cells are embedded in a gel-like substance made primarily of hyaluronic acid, and developed in the ovary with the egg and support it as it grows.
The initial change is called "hyperactivation", which causes a change in spermatozoa motility. They swim faster and their tail movements become more forceful and erratic.
A recent discovery links hyperactivation 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 proteins called CatSper. These channels are selective, allowing only calcium ion to pass. The opening of CatSper channels is responsible for the influx of calcium. The sudden rise in calcium levels causes the flagellum to form deeper bends, 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 second process in sperm activation is the acrosome reaction. This involves releasing the contents of the acrosome, which disperse, and the exposure of enzymes attached to the inner acrosomal membrane of the sperm. This occurs after the sperm first meets the egg. 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.
ZP3, one of the proteins that make up the zona pellucida, then binds to a partner molecule on the sperm. Enzymes on the inner acrosomal membrane digests the zona pellucida. After the sperm penetrates the zona pellucida, part of the sperm's cell membrane then fuses with the egg cell's membrane, and the contents of the head diffuse into the egg.
Upon penetration, the oocyte is said to have become activated. It undergoes its secondary meiotic division, and the two haploid nuclei (paternal and maternal) fuse to form a zygote. In order to prevent polyspermy and minimise the possibility of producing a triploid zygote, several changes to the egg's zona pellucida renders them impenetrable shortly after the first sperm enters the egg.
Spermatozoa can be stored in diluents such has the Illini Variable Temperature (IVT) diluent, which have been reported to be able to preserve high fertility of spermatozoa for over seven days. The IVT diluent is composed of several salts, sugars and antibacterial agents and gassed with CO2.
Semen cryopreservation can be used for far longer storage durations. For human spermatozoa, the longest reported successful storage with this method is 21 years.
In 1841, wrote Swiss anatomist Albert von Kölliker over spermatozoon his work Untersuchungen uber die Bedeutung der Samenfäden..
|
||||||||||||||||||||||||||||||||||
HOT DESIGNS ▪ Premium designs ▪ Designs by country ▪ Designs by U.S. state ▪ Most popular designs ▪ Newest, last added designs ▪ Unique designs ▪ Cheap, budget designs ▪ Design super sale DESIGNS BY THEME ▪ Accounting, audit designs ▪ Adult, sex designs ▪ African designs ▪ American, U.S. designs ▪ Animals, birds, pets designs ▪ Agricultural, farming designs ▪ Architecture, building designs ▪ Army, navy, military designs ▪ Audio & video designs ▪ Automobiles, car designs ▪ Books, e-book designs ▪ Beauty salon, SPA designs ▪ Black, dark designs ▪ Business, corporate designs ▪ Charity, donation designs ▪ Cinema, movie, film designs ▪ Computer, hardware designs ▪ Celebrity, star fan designs ▪ Children, family designs ▪ Christmas, New Year's designs ▪ Green, St. Patrick designs ▪ Dating, matchmaking designs ▪ Design studio, creative designs ▪ Educational, student designs ▪ Electronics designs ▪ Entertainment, fun designs ▪ Fashion, wear designs ▪ Finance, financial designs ▪ Fishing & hunting designs ▪ Flowers, floral shop designs ▪ Food, nutrition designs ▪ Football, soccer designs ▪ Gambling, casino designs ▪ Games, gaming designs ▪ Gifts, gift designs ▪ Halloween, carnival designs ▪ Hotel, resort designs ▪ Industry, industrial designs ▪ Insurance, insurer designs ▪ Interior, furniture designs ▪ International designs ▪ Internet technology designs ▪ Jewelry, jewellery designs ▪ Job & employment designs ▪ Landscaping, garden designs ▪ Law, juridical, legal designs ▪ Love, romantic designs ▪ Marketing designs ▪ Media, radio, TV designs ▪ Medicine, health care designs ▪ Mortgage, loan designs ▪ Music, musical designs ▪ Night club, dancing designs ▪ Photography, photo designs ▪ Personal, individual designs ▪ Politics, political designs ▪ Real estate, realty designs ▪ Religious, church designs ▪ Restaurant, cafe designs ▪ Retirement, pension designs ▪ Science, scientific designs ▪ Sea, ocean, river designs ▪ Security, protection designs ▪ Social, cultural designs ▪ Spirit, meditational designs ▪ Software designs ▪ Sports, sporting designs ▪ Telecommunication designs ▪ Travel, vacation designs ▪ Transport, logistic designs ▪ Web hosting designs ▪ Wedding, marriage designs ▪ White, light designs E-COMMERCE DESIGNS ▪ Magento store designs ▪ OpenCart store designs ▪ PrestaShop store designs ▪ CRE Loaded store designs ▪ Jigoshop store designs ▪ VirtueMart store designs ▪ osCommerce store designs ▪ Zen Cart store designs CMS DESIGNS ▪ Flash CMS designs ▪ Joomla CMS designs ▪ Mambo CMS designs ▪ Drupal CMS designs ▪ WordPress blog designs ▪ Forum designs ▪ phpBB forum designs ▪ PHP-Nuke portal designs ANIMATED WEBSITE DESIGNS ▪ Flash CMS designs ▪ Silverlight animated designs ▪ Silverlight intro designs ▪ Flash animated designs ▪ Flash intro designs ▪ XML Flash designs ▪ Flash 8 animated designs ▪ Dynamic Flash designs ▪ Flash animated photo albums ▪ Dynamic Swish designs ▪ Swish animated designs ▪ jQuery animated designs WEBSITE DESIGNS ▪ WebMatrix Razor designs ▪ HTML 5 designs ▪ Web 2.0 designs ▪ 3-color variation designs ▪ 3D, three-dimensional designs ▪ Artwork, illustrated designs ▪ Clean, simple designs ▪ CSS based website designs ▪ Full design packages ▪ Full ready websites ▪ Portal designs ▪ Stretched, full screen designs ▪ Universal, neutral designs CORPORATE ID DESIGNS ▪ Corporate identity sets ▪ Logo layouts, logo designs ▪ Logotype sets, logo packs ▪ PowerPoint, PTT designs ▪ Facebook themes VIDEO, SOUND & MUSIC ▪ Video e-cards ▪ After Effects video intros ▪ Special video effects ▪ Music tracks, music loops ▪ Stock music bank GRAPHICS & CLIPART ▪ Pro clipart & illustrations, $19/year ▪ 5,000+ icons by subscription ▪ Icons, pictograms |
| Super Offers |
| Super Offers |
| Custom Logo Design $149 ▪ Web Programming ▪ ID Card Printing ▪ Best Web Hosting ▪ eCommerce Software ▪ Add Your Link |
| © 1996-2013 MAGIA Internet Studio ▪ About ▪ Portfolio ▪ Photo on Demand ▪ Hosting ▪ Advertise ▪ Sitemap ▪ Privacy ▪ Maria Online
|
