File Name: structure of sperm and ovum .zip
During fertilization , a sperm must first fuse with the plasma membrane and then penetrate the female egg cell to fertilize it. Fusing to the egg cell usually causes little problem, whereas penetrating through the egg's hard shell or extracellular matrix can be more difficult.
Therefore, sperm cells go through a process known as the acrosome reaction , which is the reaction that occurs in the acrosome of the sperm as it approaches the egg.
The acrosome is a cap-like structure over the anterior half of the sperm's head. As the sperm approaches the zona pellucida of the egg, which is necessary for initiating the acrosome reaction, the membrane surrounding the acrosome fuses with the plasma membrane of the sperm's head, exposing the contents of the acrosome.
The contents include surface antigens necessary for binding to the egg's cell membrane, and numerous enzymes which are responsible for breaking through the egg's tough coating and allowing fertilization to occur. There are considerable species variations in the morphology and consequences of the acrosome reaction. In several species, the trigger for the acrosome reaction has been identified in a layer that surrounds the egg. In some lower animal species, a protuberance the acrosomal process forms at the apex of the sperm head, supported by a core of actin microfilaments.
The membrane at the tip of the acrosomal process fuses with the egg's plasma membrane. In some echinoderms, including starfish and sea urchins , a significant portion of the exposed acrosomal content contains a protein that temporarily holds the sperm on the egg's surface. In mammals, the acrosome reaction releases hyaluronidase and acrosin ; their role in fertilization is not yet clear. The acrosomal reaction does not begin until the sperm comes into contact with the oocyte's zona pellucida. Upon coming into contact with the zona pellucida, the acrosomal enzymes begin to dissolve, and the actin filament comes into contact with the zona pellucida.
Once the two meet, a calcium influx occurs, causing a signaling cascade. The cortical granules inside the oocyte then fuse to the outer membrane, and a quick fast block reaction occurs. It also alters a patch of pre-existing sperm plasma membrane so that it can fuse with the egg plasma membrane.
A sperm penetration assay includes an acrosome reaction test that assesses how well a sperm can perform during the fertilization process. Sperm that are unable to go through the acrosome reaction properly will not be able to fertilize an egg. This test is rather expensive and provides limited information on a man's fertility. In other cases, such as in the wood mouse Apodemus sylvaticus , premature acrosome reactions have been found to cause increased motility in aggregates of spermatozoa promoting fertilization.
The acrosomal reaction usually takes place in the ampulla of the fallopian tube site of fertilization when the sperm penetrates the secondary oocyte. A few events precede the actual acrosome reaction. The sperm cell acquires a "hyperactive motility pattern" by which its flagellum produces vigorous whip-like movements that propel the sperm through the cervical canal and uterine cavity until it reaches the isthmus of the fallopian tube. The sperm approaches the ovum in the ampulla of the fallopian tube with the help of various mechanisms, including chemotaxis.
Glycoproteins on the outer surface of the sperm then bind with glycoproteins on the zona pellucida of the ovum. Sperm that did not initiate the acrosome reaction prior to reaching to the zona pellucida are unable to penetrate the zona pellucida. Since the acrosome reaction has already occurred, sperm are then able to penetrate the zona pellucida due to mechanical action of the tail, not because of the acrosome reaction itself.
The first stage is the penetration of corona radiata, by releasing hyaluronidase from the acrosome to digest cumulus cells surrounding the oocyte and exposing acrosin 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.
The acrosome reaction must occur before the sperm cell reaches the zona pellucida. 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. This lock-and-key type mechanism is species-specific and prevents the sperm and egg of different species from fusing. The zona pellucida also releases Ca granules to prevent other sperm from binding.
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. A similar mechanism likely occurs in other mammals, but the diversity of zona proteins across species means that the relevant protein and receptor may differ. More recent scientific evidence demonstrates that the acrosomal reaction is necessary to expose a protein called IZUMO1 on the sperm: without the reaction, sperm can still penetrate through the zona pellucida to the egg membrane, but cannot fuse.
Additionally, once the fusion of the sperm and oocyte is complete, phospholipase C zeta is released from the sperm. Upon penetration, if all is normally occurring, the process of egg-activation occurs, and the oocyte is said to have become activated. This is thought to be induced by a specific protein phospholipase c zeta. It undergoes its secondary meiotic division, and the two haploid nuclei paternal and maternal fuse to form a zygote. To prevent polyspermy and minimize the possibility of producing a triploid zygote, several changes to the egg's cell membranes render them impenetrable shortly after the first sperm enters the egg such as the rapid loss of JUNO.
Spermatozoa can initiate the acrosomal reaction well in advance of reaching the zona pellucida, as well as in vitro in an appropriate culture medium. This is referred to as spontaneous acrosome reaction SAR. It is now known that in a certain sense, this phenomenon is physiologically normal across mammalian species. The acrosome reaction is induced by passage through the cumulus oophorus cells, mediated by the hormones they secrete such as progesterone , LPA , LPC.
However, the physiological role of truly spontaneous acrosomal reaction, occurring well before this point in the female reproductive tract, or in vitro , is a separate phenomenon. In mice, it has been well established as physiologically normal and common.
Mouse sperm which have undergone fully spontaneous acrosome reaction are still able to fertilize eggs. In humans, on the other hand, it remains disputed where exactly the acrosome reaction is initiated in physiological fertilization, due to experimental constraints for example, animal studies may make use of transgenic mice with fluorescent sperm, while human studies cannot.
Studies have been done with the intent of linking in vitro SAR rate in human sperm to sperm quality and fertilization rate, but the overall results are mixed, and do not seem to be clinically useful as of The delivery rate per cycle follows the same trend.
The acrosome reaction can be stimulated in vitro by substances a sperm cell may encounter naturally, such as progesterone or follicular fluid , as well as the more commonly used calcium ionophore A Birefringence microscopy,  flow cytometry  or fluorescence microscopy can be used for assessing the shedding of the acrosome or "acrosome reaction" of a sperm sample.
If bound to a fluorescent molecule, regions where these probes have bound can be visualised. Sperm cells with artificially induced acrosome reactions may serve as positive controls. For fluorescence microscopy, a smear of washed sperm cells is made, air-dried, permeabilized, and then stained. Such a slide is then viewed under the light of a wavelength that will cause the probe to fluoresce if it is bound to the acrosomal region.
At least cells are considered arbitrarily and classified as either acrosome intact fluorescing bright green , or acrosome reacted no probe present, or only on the equatorial region. It is then expressed as a percentage of the counted cells. For assessment with flow cytometry, the washed cells are incubated with the chosen probe, possibly passed again, then sampled in a flow cytometer.
After gating the cell population according to forward- and side-scatter, the resulting data can be analyzed E. With this technique, a probe for viability such as propidium iodide PI could also be included in order to exclude dead cells from the acrosome assessment, since many sperm cells will spontaneously lose their acrosome when they die.
From Wikipedia, the free encyclopedia. The discharge, by sperm, of a single, anterior secretory granule following the sperm's attachment to the zona pellucida surrounding the oocyte. The process begins with the fusion of the outer acrosomal membrane with the sperm plasma membrane and ends.
Human Embryology. Retrieved 18 February Proceedings of the National Academy of Sciences. Bibcode : PNAS.. The Journal of Clinical Investigation. International Journal of Molecular Sciences. Reproductive Biology and Endocrinology.
Fertility and Sterility. Archives of Andrology. A; Moran-Verbeek, I. M; Hollanders, J. G Journal of Assisted Reproduction and Genetics. Categories : Andrology Animal reproductive system. Hidden categories: All articles lacking reliable references Articles lacking reliable references from December Articles with short description Articles with long short description Short description matches Wikidata. Namespaces Article Talk. Views Read Edit View history.
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During fertilization , a sperm must first fuse with the plasma membrane and then penetrate the female egg cell to fertilize it. Fusing to the egg cell usually causes little problem, whereas penetrating through the egg's hard shell or extracellular matrix can be more difficult. Therefore, sperm cells go through a process known as the acrosome reaction , which is the reaction that occurs in the acrosome of the sperm as it approaches the egg. The acrosome is a cap-like structure over the anterior half of the sperm's head. As the sperm approaches the zona pellucida of the egg, which is necessary for initiating the acrosome reaction, the membrane surrounding the acrosome fuses with the plasma membrane of the sperm's head, exposing the contents of the acrosome. The contents include surface antigens necessary for binding to the egg's cell membrane, and numerous enzymes which are responsible for breaking through the egg's tough coating and allowing fertilization to occur.
The symposium was organized by D. Because this article reflects the contents of the symposium talks, it is not meant to be a comprehensive review of the topics discussed but is primarily focused on work from the laboratories of the respective investigators. Prudence Talbot, Barry D. Shur, Diana G. Fertilization in mammals requires the successful completion of many steps, starting with the transport of gametes in the reproductive tract and ending with sperm-egg membrane fusion. In this minireview, we focus on three adhesion steps in this multistep process.
that affect the structure, composition and activity of the secre- tory epithelia Key words: fertilization, zygote, gamete fusion, sperm capacitation.
Sperm cells are gametes sex cells that are produced in the testicular organ gonad of male human beings and animals. Like the female gamete oocyte , sperm cells carry a total of 23 chromosomes that are a result of a process known as meiosis. In both animals and human beings, among many other organisms, these cells are involved in the sexual mode of reproduction which involves the interaction of male and female gametes. The general morphology of sperm cells consists of the following parts:. Before looking at the structure and function of sperm cells, it's important to understand the process involved in their production spermatogenesis.
Egg fertilization involves a complex sequence of events that starts with the release of a mature egg from the follicle, continues with the appearance of the two pronuclei after sperm entry, and is completed with the first mitotic division. Understanding the complexities of this process in humans has been limited to a large extent by ethical constraints. However, with the advent of assisted reproductive technologies ARTs , understanding of the various mechanisms involved in successful fertilization has been greatly enhanced. As ART has developed, so has our understanding of the essentials for human reproductive success. This chapter focuses on what is currently known about human egg transport and fertilization.
Sexual reproduction is such a successful way of creating progeny with subtle genetic variations that the vast majority of eukaryotic species use it. In mammals, it involves the formation of highly specialised cells: the sperm in males and the egg in females, each carrying the genetic inheritance of an individual. The interaction of sperm and egg culminates with the fusion of their cell membranes, triggering the molecular events that result in the formation of a new genetically distinct organism. Although we have a good cellular description of fertilisation in mammals, many of the molecules involved remain unknown, and especially the identity and role of cell surface proteins that are responsible for sperm—egg recognition, binding, and fusion.
Fertilization , union of a sperm nucleus , of paternal origin, with an egg nucleus, of maternal origin, to form the primary nucleus of an embryo. In all organisms the essence of fertilization is, in fact, the fusion of the hereditary material of two different sex cells , or gametes , each of which carries half the number of chromosomes typical of the species. The most primitive form of fertilization, found in microorganisms and protozoans, consists of an exchange of genetic material between two cells.
The human sperm head vacuoles and their role in male infertility are still poorly understood. The aim of this study was to identify the clinical and ultrastructural features of human sperm head vacuoles in men included in the in vitro fertilization programme: men with normal normozoospermia and impaired sperm morphology teratozoospermia. The sperm samples were observed under time magnification using motile sperm organelle morphology examination MSOME. The proportion of sperm with head vacuoles was evaluated and related to the outcome of in vitro fertilization. The sperm of men with impaired sperm morphology was characterized by a higher proportion of sperm head vacuoles. The sperm head vacuoles were related to impaired semen quality sperm concentration, motility, and morphology but were not influenced by male factors semen volume, height, age, weight, or body mass index. Moreover, sperm head vacuoles were related to impaired fertilization rate merely after classical in vitro fertilization IVF , while there was no relation to pregnancy.
A mammalian sperm is minute, microscopic, flagellated and motile gamete with no nutritive material, protective envelopes and most of cell- organelles like ribosome, endoplasmic reticulum, etc. The whole body of sperm is enveloped by plasma membrane only. It is small cap-like pointed structure present at the tip of nucleus. It is formed from a part of Golgi body of spermatid.
Figs. 20 and 21 show the sperm axial filament complex encircled by the outer row of nine dense fibers. Since these structures were neither.Sabel T. 11.05.2021 at 15:22
of sperm and egg pronuclei and activation of the zygote. The specific structures of the sperm and egg that are important for fertilization will be discussed and.Ibel C. 13.05.2021 at 15:40
Not a MyNAP member yet?Burrell C. 14.05.2021 at 08:09
). Therefore, many research groups have shown that. mammalian spermatozoa play more important. roles than just deliver their DNA into the ovum.Elita P. 14.05.2021 at 16:49
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