Sierra Acai Company
Sierra Acai Company
Open 7 Days a Week
MonaVie Independent Distributor
Distributor Training
Shop Online
Enroll Now
Buy Wholesale and maintain an Active status for 2 months and we will refund your $39 Distributor Fee
Friends
Buy Wholesale and maintain an Active status for 2 months and we will refund your $39 Distributor Fee
20-September-2008 09:29:07 - Spermatozoon Spermatozoon A sperm cell attempts to penetrate an ovum coat to fertilize it. Diagram of a human spermatozoon MeSH Spermatozoa A spermatozoon or spermatozoan pl. spermatozoa, from the ancient Greek σπÎÏ?μα seed and ζῷον living being and more commonly known as a sperm cell, is the haploid cell that is the male gamete. It 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 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 Anton van Leeuwenhoek in 1677.1 Contents 1 Mammalian spermatozoan structure, function, and size 1.1 Humans 1.2 Avoidance of immune system response 2 Spermatozoa in other organisms 2.1 Animals 2.2 Plants, algae and fungi 3 Spermatozoa production in mammals 4 Spermatozoa Activation 5 References 6 External links Mammalian spermatozoan structure, function, and size Humans The human sperm cell is the reproductive cell in males. Sperm cells come in two types; male and female. 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. The female sperm cell also differs phenotypically in that it has a larger head in comparison to the male sperm cellcitation needed. In male humans, sperm cells consists of a head 5 µm by 3 µm and a tail 50 µm long. The Reynolds number associated with spermatozoa is in the order of 1×10-2, so it is known that the spermatozoa exhibit non-turbulent flow. The tail flagellates, which propels the sperm cell at about 1-3 mm/minute in humans by whipping in an elliptical cone. 2. 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. 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.3 During fertilization, the sperm's mitochondria are destroyed by the egg cell, and this means only the mother is able to provide the baby's mitochondria and mitochondrial DNA, which have an important application in tracing maternal ancestry. However it has been recently discovered that mitochondrial DNA can be recombinant 4. Avoidance of immune system response Glycoprotein molecules on the surface of sperm cells are recognised by all human immune systems, and interpreted as a signal that the cell should not be rejected. The male immune system might otherwise attack sperm whilst in the testes, and the female immune system would 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, in order to avoid an immune response from the host organism.5 The blood-testis barrier, maintained by the tight junctions between the sertolli cells of the seminiferous tubules, prevents communication between the forming spermatozoa and the blood vessels within the interstitial space. This gives the forming spermatozoa an immunological advantage and thus prevents them from eliciting an immune response. The blood-testis barrier is also imporant in preventing toxic substances from disrupting spermatogenesis. Spermatozoa in other organisms Motile sperm cells of algae and seedless plants. Motile sperm cells of algae and seedless plants. See also: Sperm Animals Fertilization relies on spermatozoa for most sexually reproductive animals. The fruit fly3 has the largest known spermatozoon relative to its size. Drosophila melanogaster produces sperm that can be up to 1.8 mm in size, which is longer than the adult fly. The incredibly long tail is thought to block other sperm from entering the egg. The entire sperm, tail included, gets incorporated into the oocyte cytoplasm.6 Sea urchins such as Arbacia punctulata-are the workhorses of sperm research, because they spawn large numbers of sperm into the sea, making them well-suited as model organisms for research experiments. Plants, algae and fungi 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 production in mammals 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. Spermatozoa Activation Merge arrow It has been suggested that this article or section be merged into Acrosome reaction. Discuss Acrosome reaction on a Sea Urchin cell Acrosome reaction on a Sea Urchin cell 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 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 hyaluronidase to digest cumulus cells surrounding the oocyte and exposing acorsin attached to the inner membrane of the sperm. 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. Acrosin digests the zona pellucida and membrane of the oocyte. Part of the sperm's cell membrane then fuses with the egg cell's membrane, and the contents of the head sink into the egg. ZP3, 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. 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 cell membranes renders them impenetrable shortly after the first sperm enters the egg. References ^ Timeline: Assisted reproduction and birth control. Retrieved on 2006-04-06. ^ Sumio Ishijima, Shigeru Oshio, Hideo Mohri, Flagellar movement of human spermatozoa, Gamete research, 1986, vol. 13, no3, pp. 185-197 27 ref. 1 ^ Ward WS, Coffey DS 1991. DNA packaging and organization in mammalian spermatozoa: comparison with somatic cells. Biol. Reprod. 44 4: 569-74. doi:10.1095/biolreprod44.4.569. PMID 2043729. ^ Marilena D'Aurelio et al., 'Heterologous mitochondrial DNA recombination in human cells', Human Molecular Genetics 2004 1324:3171-3179; doi:10.1093/hmg/ddh326 2 ^ Sperm clue to 'disease immunity', BBC News 2007-12-17. ^ Gilbert, Scott F., Developmental Biology, Eighth ion. 2006. Sinauer Associates, pp. 254 External links The Handbook of Andrology Sperm hyperactivity Slower conception 'leads to boys' Photos of sperm under a microscope Wikimedia Commons has media related to: Category:Spermatozoon diagrams v d e Male reproductive system Seminal tract Scrotum layers skin, Dartos, External spermatic fascia, Cremaster/Cremasteric fascia, Internal spermatic fascia Perineal raphe Spermatic cord Testes layers Tunica vaginalis, Tunica albuginea, Tunica vasculosa testis Appendix Mediastinum Lobules Septa Leydig cell Sertoli cell Blood-testis barrier Spermatogenesis Spermatogonium Spermatocytogenesis Spermatocyte Spermatidogenesis Spermatid Spermiogenesis Spermatozoon Other Seminiferous tubules Tubuli seminiferi recti, Rete testis, Efferent ducts Epididymis Appendix, Stereocilia Vas deferens Ampulla Ejaculatory duct Urinary tract Internal urethral orifice Urethra Prostatic, Intermediate, Spongy, Navicular fossa External urethral orifice Accessory glands Seminal vesicles Excretory duct of seminal gland Prostate Urethral crest/Seminal colliculus/Prostatic utricle/Ejaculatory duct, Prostatic sinus/Prostatic ducts Bulbourethral glands Penis root Crus, Bulb, Fundiform ligament, Suspensory ligament body Corpus cavernosum, Corpus spongiosum glans Foreskin, Frenulum, Corona fascia superficial/subcutaneous, deep/Buck's Tunica albuginea - Septum of the penis Retrieved from http://en..org/wiki/Spermatozoon Categories: Germ cells | Semen | Human cellsHidden categories: All articles with statements | Articles with statements since April 2008 | Articles to be merged since December 2007 Views Article Discussion this page History Personal tools Log in / create account Navigation Main page Contents Featured content Current events Random article Search Go Search Interaction Community portal Recent changes Contact Donate to Help Toolbox What links here Related changes Upload file Special pages Printable version Permanent link Cite this page Languages Afrikaans العربية Bosanski БългарÑ?ки Català Česky Dansk Deutsch Español Esperanto Français Hrvatski Ido Bahasa Indonesia Italiano עברית Lietuvių МакедонÑ?ки Nederlands 日本語 ‪Norsk bokmÃ¥l‬ Polski Português РуÑ?Ñ?кий Simple English Basa Sunda Suomi Svenska Tiếng Việt Türkçe ייִדיש ä¸æ–‡ This page was last modified on 9 August 2008, at 01:36
39 Reasons to Drink Acai Juice Every Day
What is MonaVie - Watch the 8-minute video
Discovering MonaVie video
The Power of You video
Log into your Wholesale MonaVie Account
So many of us do not eat a balanced diet, get enough sleep, have too much stress, or are impacted with toxins and pollutants. Drinking 2 ounces of MonaVie twice a day will help your body detoxify as well as build your immune system. Its the smartest thing you can do for yourself, so start today. Buying MonaVie through our company guarantees you support 7 days a week and, if you would like to share MonaVie with your family and friends we will guide you from start to finish.
1. Click on Enroll Now (30 - 55% off retail price)
2. Pay $39 for your Wholesale ID number.
3. NO minimum order required.
4. MonaVie is delivered to your door in 3 to 5 days.