Egg Transport and Fertilization | GLOWM
Fertilization: Sperm meets egg. The mature egg is fertilized Most eggs are fertilized by sperm while still in the fallopian tube. The fertilized egg then travels. One of the two uterine tubes is the pathway down which the ripe ovum travels on its way to Sperm deposited in the female reproductive tract usually reach the. Only 1 in 14 million of the ejaculated sperm will reach the Fallopian tube, but once there the sperm should pick up chemical signals from the egg to help them .
Only 1 in 14 million of the ejaculated sperm will reach the Fallopian tube, but once there the sperm should pick up chemical signals from the egg to help them find their way forward. The sperm finally near the egg and push towards its shell called the zona pellucida.
Many sperm will bind to this shell, but only 1 sperm will be allowed to go all the way through to reach the egg inside. Sperm can survive for a few days in the female reproductive system — hence a sperm ejaculated during intercourse on a Monday could fertilise an egg ovulated on the Tuesday or Wednesday!
How we can help you? The male and female pronuclei move together to the centre of the egg and during IVF this can be seen down the microscope. The egg can now be called a fertilised embryo and would normally be at this stage 1 day after ovulation.
After the egg is released, it moves into the fallopian tube where it stays for about 24 hours. If the egg is not fertilized during that time, the egg disintegrates breaks down and menstruation your period begins 2 weeks later.
Egg meets sperm
Sperm meets egg The mature egg is fertilized when it is joined with a sperm cell. Sperm is contained in the semen which travels up the vagina, through the cervix and uterus and into the fallopian tubes. If an egg is less than 24 hours old, it can be fertilized by a sperm. Fertilization sometimes but rarely happens when semen has been ejaculated outside but near the entrance of the vagina.
How Pregnancy (Conception) Occurs
The fertilized egg attaches to the lining of the uterus and pregnancy begins. Most eggs are fertilized by sperm while still in the fallopian tube.
The fertilized egg then travels down the fallopian tube into the uterus.Sperm swimming in the Fallopian Tube
This can take days. Successful capacitation of the sperm results in a hyperactivated spermatozoon, which is able to bind to the zona pellucida and is susceptible to acrosome reaction induction. The acrosome reaction is an exocytotic process occurring in the sperm head that is essential for penetration of the zona pellucida and fertilization of the oocyte.
The acrosome is a unique organelle, located in the anterior portion of the sperm head analogous to both a lysosome and a regulated secretory vesicle. It exists in a proenzyme form called proacrosin, which is converted to the active form acrosin by changes in acrosomal pH. The binding causes an opening of calcium channels and an influx of calcium and second messengers that result in the acrosome reaction.
Other substances may also induce the acrosome reaction. For example, the addition of periovulatory follicular fluid or progesterone to capacitated spermatozoa stimulates an influx of calcium ions that is coincident with the acrosome reaction. However, other acrosome reaction-stimulating factors e. The zona pellucida plays an important role in species-specific sperm-egg recognition, sperm-egg binding, induction of the acrosome reaction, prevention of polyspermy, and protection of the embryo prior to implantation.
ZP3 is the primary ligand for sperm-zona binding and acrosome reaction induction.
A major breakthrough was made in when researchers identified a protein on the surface of the capacitated sperm named Izumo1 after a Japanese marriage shrine. Sperm that lacked this receptor were unable to fuse with normal eggs. They showed that Juno-deficient eggs were not able to fuse with normal capacitated sperm, which proved that the Juno-Izumo receptor interaction was essential for mammalian fertilization.
Additionally, there is evidence that Juno is undetectable on the oolemma about 40 minutes after fertilization, which suggests that this may be the mechanism for membrane block to polyspermy in mammals. The majority of current data concerning sperm receptors for zona glycoproteins is restricted to nonhuman mammalian and nonmammalian species.
In the human, one of the best described ZP3 receptor candidates is a lectin that binds mannose-containing ligands. Interestingly, both intact zona pellucida and progesterone stimulate tyrosine phosphorylation. The possibility exists that one or more signaling or second-messenger pathways interact to result in the acrosome reaction, and subsequent penetration of the oocyte vestments by the spermatozoon.
Egg meets sperm (article) | Embryology | Khan Academy
In fact, this arrangement could provide sperm with the ability to sense and respond to molecules present in the female reproductive tract that have been shown to initiate the acrosome reaction, such as follicular and oviductal fluids and the cumulus oophorus.
After a spermatozoon passes through the zona pellucida, it must contact, bind to, and fuse with the oocyte plasma membrane. As a result of the prior acrosome reaction, new sperm membrane proteins become exposed that are likely to prove integral for sperm-oocyte fusion. Data indicate that sperm-oocyte fusion is initiated by signal transduction processes that involve adhesion molecules on both sperm and oocyte plasma membranes that belong to the family of integrins.
Fibronectin and vitronectin are glycoproteins that contain functional RGD sequences, and they are present on spermatozoa. These data suggest that a possible mechanism for sperm-oocyte adhesion and fusion involves an integrin-vitronectin receptor-ligand interaction. At some point during or after the fusion process, the oocyte is activated by the spermatozoon.
Extrusion of the second polar body occurs and cortical granules are released into the perivitelline space. The cortical granules modify zona glycoproteins 2 and 3 on the inner aspect of the zona pellucida, resulting in a loss of their ability to stimulate the acrosome reaction and tight binding, so as to prevent polyspermy.
This latter event occurs before or simultaneously with the resumption of meiosis. Failure of the oocyte to synthesize or release the cortical granules in a timely fashion results in polyspermic fertilization.
Calcium is the main intracellular signal responsible for the initiation of oocyte activation. The mechanism by which sperm induce calcium transients is unknown, but there are data that support essentially two models for sperm-induced oocyte activation. During this latent period, a soluble sperm-derived factor diffuses from the sperm into the oocyte's cytoplasm and results in oocyte activation.
Progesterone secreted by the cumulus cells that surround the oocyte stimulates calcium signals that can control hyperactivation and the acrosomal reaction, however, the signaling mechanism has remained unclear.
Recent research has shown that progesterone activates a sperm-specific calcium channel named CatSper, which is primarily associated with hyperactivation of sperm.