For fertilization to occur, sperm must reach the egg within a specific timeframe. Sperm can survive for up to 72 hours after ejaculation, but the egg can survive for no more than 24 hours after ovulation. If sperm reach the fallopian tube too early, they risk dying before the egg shows up. If sperm reach the fallopian tube too late, the egg will be gone. Additionally, the egg is present in only one of your two fallopian tubes in a given month.
Before fertilization, hundreds of sperm will surround your egg while trying to reach the egg's nucleus. Only one sperm will succeed in penetrating the egg's outer membrane. After the sperm penetrates the egg, the egg immediately undergoes a chemical reaction that prevents other sperm from penetrating.
Chromosomes carried by the sperm and the egg then come together, and the egg is officially fertilized. About a week later, a ball of around cells called a blastocyst reaches your uterus and implants into the uterine lining. When it comes to conceiving a baby, timing is everything. To boost your odds, aim to have sex sometime between 72 hours before and 24 hours after you ovulate. The best thing you can do to prepare for conception is to get your body in the best possible shape for making a baby.
You should stop drinking alcohol, smoking and taking drugs, even over-the-counter medications. You should inform your physician of your plans to conceive and ask him or her if you should continue taking prescription medications. Up to three months before you plan to try to conceive, you should begin taking a multivitamin that contains at least micrograms of folic acid to reduce your baby's risk of birth defects.
The anatomy and physiology of the fallopian tube play an important role in egg transport and fertilization. The fallopian tube is a muscular tube with an average length of about 11—12 cm and is composed of four regions. The most distal portion is called the infundibulum, it is approximately 1 cm in length, and it includes the finger-like fimbria.
The epithelial lining of the fimbria is densely ciliated and highly convoluted. This structure, along with the muscle-controlled movements of the fimbria, is thought to be important for capture of the cumulus-oocyte complex. The next portion of the oviduct is called the ampulla. This segment averages 5—8 cm in length. It is within this highly ciliated portion of the oviduct that fertilization and early embryo development occur.
The ampulla is most often also the site for ectopic implantation ectopic pregnancy. The next region, approximately 2—3 cm in length, is the isthmus. Like the ampulla, it too is ciliated yet less densely so. The isthmus is thought to regulate sperm and embryo transport. The last segment of the fallopian tube is called the intramural segment; it is the link between the isthmus of the oviduct and uterine cavity.
The ciliated and non-ciliated cells of the fallopian tube undergo cyclic changes with the menstrual cycle similar to those occurring in the endometrium. Further, each portion of the fallopian tube appears to be preferentially regulated by hormones that cause a distinct regionalization of activities depending on the day in the female reproductive cycle. At day 8 mid-follicular phase , the ampulla has alternating propulsive forces towards and away from the uterus.
At the time of ovulation around cycle day 14 , ipsilateral transport to the ovary increases with increasing follicular diameter. The fallopian tube function is critical for the early stages of fertilization.
At the time of ovulation, the oocyte is surrounded by a mass of specialized granulosa cells called the cumulus oophorus.
Together, the oocyte and granulosa cells are called the cumulus-oocyte complex COC. The innermost cell layers of the cumulus immediately overlying the zona pellucida of the oocyte are called the coronal cells.
These cells have processes that extend through the acellular glycoprotein matrix of the zona to contact the oocyte plasma membrane for a rich metabolic exchange of nutrients via the so-called transzonal projections. The cumulus of the mature COC is sticky and is thought to facilitate the adherence of the COC to the surface of the fimbriae once it is expelled from the follicle at ovulation. The exact mechanism by which the COC is picked up and gains entry into the fallopian tube lumen is unknown.
One possibility is that the fimbriated end of the ipsilateral fallopian tube sweeps over the ovary, picks up the COC, and draws it into the tubular lumen by muscular control. Paradoxically, women have become pregnant who were missing the fallopian tube on the side where ovulation occurred.
Also, oocytes placed in the peritoneal cavity have been picked up by the fallopian tube and resulted in intrauterine pregnancies. Another possibility is that the rhythmic and unidirectional beating of cilia on the fimbriae — where the cilia have adhesive sites — and in the ampullary and isthmic regions of the fallopian tube, draw the COC into the lumen of the fallopian tube.
However, this cannot be the sole mechanism by which the COC is picked up and transported through the fallopian tube because women with immotile cilia syndrome, otherwise known as Kartagener's syndrome, are often fertile.
Another possibility is that muscular contractions of the fallopian tube create negative pressure that helps to aspirate the COC from the surface of the ovary into the lumen. However, capping and suturing of the fimbriated end in women has failed to prevent pregnancy. The pumping frequency increases on the ipsilateral side, in the direction where ovulation will occur, and as the follicular diameter increases.
Therefore, it would seem that at least several mechanisms are involved with COC pickup, the most important of which are ciliary beating, sweeping of the ovarian surface by the fimbria, and peristaltic pumping of the female tract. After ovulation, the fertilizable life span of the mature human oocyte is estimated to be about 24 hours. In contrast, the fertilizable life span of the human spermatozoon is around 72 hours.
Sperm motility can persist for much longer and has been documented in vivo for up to 5 days, but fertilizing ability is lost before motility. Sperm deposited in the proximal vagina can be found in the fallopian tube within 5 minutes. A number of sperm-related events must occur for successful fertilization. The first factor is that a sufficient number of mature, viable spermatozoa must be present in the ejaculate.
Second, the morphology of the sperm must be such that the cervical mucus will allow passage into the uterus. Third, it is essential that a good percentage of the sperm have forwardly progressive motion to propel them through the cervical mucus into the uterine cavity and the fallopian tube for ultimate encounter with the COC. Fourth, sperm must undergo the acrosome reaction and hyperactivation during sperm transport into the female reproductive tract vagina, uterus and tubes to be enabled for cumulus cell penetration and zona pellucida binding.
The term capacitation derives from the observation that sperm must spend time in the female reproductive tract in order to acquire the capacity or ability to fertilize an oocyte.
Sperm can also undergo capacitation in vitro when they are incubated in media containing bovine serum albumin as well as energy substrates and electrolytes. Capacitation begins as sperm swim through the cervical mucus. Proteins absorbed in the plasma membrane are removed and sperm surface molecules are modified.
An efflux of cholesterol from the sperm plasma membrane may be the initiating event for capacitation. The sperm plasma membrane and outer acrosomal membrane have increased permeability and fluidity as a result of these changes.
The more permeable sperm plasma membrane allows for influx of calcium and bicarbonate resulting in activation of second messengers and initiation of signaling events. These unique changes that prepare the spermatozoon for fertilization have collectively been termed capacitation.
Some events that occur to induce capacitation are 1 an increase in membrane fluidity; 8 2 a decrease in net surface charge; 3 an increase in oxidative processes and cyclic adenosine monophosphate cAMP production; 8 , 11 , 12 4 a decrease in the ratio of plasma membrane cholesterol to phospholipid; 8 , 13 , 14 5 expression of mannose binding sites as a consequence of cholesterol removal; 14 6 an increase in tyrosine phosphorylation; 11 , 12 7 an increase in reactive oxygen species; 12 and 8 changes in sperm swimming patterns, termed hyperactivation.
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. When sperm bind to the zona pellucida, intracellular calcium is low.
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 is an acellular glycoprotein matrix that surrounds the mammalian oocyte.
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. The molecular details of sperm-oocyte recognition have remained elusive. 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.
Although ZP3 has been fairly well characterized as a ligand for sperm, such is not the case for ZP3 receptors on the sperm plasma membrane. 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. 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. Another potential ligand for oolemmal integrin is human fertilin. 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. One proposed mechanism for sperm-induced oocyte activation is the binding of the spermatozoon to a receptor on the oolemma, which results in G-protein activation, activation of an amplifying enzyme, and generation of an intracellular second messenger within the oocyte.
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. If you are using contraception you will need to stop using it if you plan to get pregnant. There are no clear guidelines about when to stop using the Pill oral contraception if you are planning to get pregnant. Some health professionals suggest you have three normal menstrual periods, after stopping the Pill, to allow your metabolic function to return to normal.
The length of time that it takes for fertility to return will differ for each woman. It is possible, although rare, for a woman to fall pregnant while on the Pill.
There is no evidence that this causes problems for the baby. Women are encouraged to discuss their health needs with a health practitioner.
If you have concerns about your health, you should seek advice from your health care provider or if you require urgent care you should go to the nearest Emergency Dept. Ovulation and conception Single and lesbian women Optimising conception Section menu. A step-by-step guide to ovulation Every month the pituitary gland, which is in your brain, releases a hormone. This hormone tells the ovaries to produce a number of fluid-filled cysts called follicles.
As the follicles grow they secrete the hormone oestrogen. Oestrogen works to thicken the wall of your uterus in preparation for pregnancy. On day seven of your cycle, the follicles stop growing except for one.
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