Ovulation and conception | The Royal Women's Hospital
Sperm must reach their destination — your egg (which is slowly making its About a week later, a ball of around cells (called a blastocyst). Fertilization: Sperm meets egg. The mature egg is fertilized when it is joined with a sperm cell. This usually happens after a penis* has ejaculated semen inside. Something magical is about to happen! Watch as the ovulation process occurs, and then millions of sperm swim upstream on a quest to fertilize.
The egg is transported to the entrance of the fallopian tube. Once inside the walls of the fallopian tube, muscle contractions push the egg gently towards the uterus.
The egg will either meet sperm on its journey through the fallopian tube and fertilisation will happen, or it will arrive in the uterus unfertilised and be absorbed back into the body. The menstrual cycle A step-by-step guide to conception After ovulation the egg lives for 12 to 24 hours and must be fertilised in that time if a woman is to become pregnant.
The burst of oestrogen just before ovulation also works inside the neck of the uterus the cervix to make protein-rich clear jelly that covers the top of the vagina during sex. This makes the vagina acidic which prevents thrush and other infections.
This is also a suitable environment for sperm survival.
Egg meets sperm (article) | Embryology | Khan Academy
The sperm rapidly swim up and into the cervix, where they can survive in the mucus for up to five days before an egg is released. When the egg is released at ovulation, it is covered in sticky cells, which help the fallopian tube to catch it.
The egg and the sperm meet in the fallopian tube where the sperm start to digest the sticky cells. While it takes only one sperm to make a baby, several need to attach to the outer shell and the membrane of the egg before one can enter and fertilise it.
After fertilisation, the egg and sperm very quickly merge and divide to become an embryo and chemicals are released to stop other sperm from entering. Over the next four or five days the fertilised egg continues to divide and to travel towards the uterus. The hormone progesterone, which is secreted into your blood stream by the burst follicle now called the corpus luteum prepares the uterus for the egg to implant.
The most fertile days will vary depending on your cycle length.
How Fertilization Happens
LH triggers the ovaries to release the egg, while higher blood estrogen levels stimulate the vaginal membrane to secrete glycogen, which is then metabolized to lactate. This lowers vaginal pH to as low as 3. However, this environment can also be toxic to sperm, though the semen a basic fluid can buffer the vaginal acidity to preserve sperm cells.
Only about 1 in 1 million sperm that are ejaculated into the vagina will reach the site of fertilization. Estrogen also relaxes the cervix, causes cervical mucus to become watery and more alkaline, and stimulates uterine contractions — all of which help sperm penetrate and navigate the female reproductive system.
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Relaxing the cervix allows sperm to pass from the vagina into the uterus and reduces a potential physical barrier. Cervical mucus may prevent sperm from passing into the uterus, but during ovulation when the egg is released from the ovaries, the mucus gets thinner and lower in pH. These changes make the mucus a great transport medium for the sperm, and help the sperm continue traveling.
As we can see, the progress of sperm is really influenced by where in the menstrual cycle the female is. The closer to ovulation, the easier it is for sperm to pass.
The vagina and uterus are very susceptible to infection, so the body has to balance on a fine line between protecting these areas and allowing sperm to come through. Diagram showing the female reproductive tract.
Ovulation and conception
The path of the sperm is highlighted via a blue arrow. As the sperm approach the egg, they bind to the zona pellucida in a process known as sperm binding. This triggers the acrosome reaction, in which the enzymes of the acrosome are freed.
When the sperm cell finally reaches the egg cell, the plasma membranes of the two cells fuse together and the sperm releases its genetic material into the egg.
Fusion also triggers the cortical reaction. When the sperm and egg fuse it triggers a release of calcium ions, which cause the cortical granules inside the egg to fuse with the plasma membrane. As they fuse, these granules release their contents outside of the cell, toward the remains of the zona pellucida. The enzymes of the cortical granules further digest the zona pellucida, making it unable to bind more sperm, while other molecules found in the granules create a new protective layer around the fertilized egg.
By creating a new barrier and destroying the initial interface between sperm and egg, the cortical reaction prevents polyspermy, or the fertilization of a single egg by multiple sperm. Other sperm reaching the egg now are just shunted away.