Crosswords1 min ago
How many sperm?
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How many sperm does it take to get pregnant?Some sources say just one, but others say a good few are needed to break down a barrier.tnx
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No..you get twins by division of the egg, not multiple sperm.
It is true only one sperm is needed to get pregnant, however to be considered fertile you need several million in an ejaculation, I believe. Please feel free to correct me if I am wrong!
Apparently quite a few sperm are not viable, hence the need for a fair few in the system..
It is true only one sperm is needed to get pregnant, however to be considered fertile you need several million in an ejaculation, I believe. Please feel free to correct me if I am wrong!
Apparently quite a few sperm are not viable, hence the need for a fair few in the system..
Right. The answer to your question is just one sperm is needed to fertilise the egg. I'll go through the steps that occur to try to explain.
To begin with, there are anything from about 20 million to 600 million sperm present in the ejaculate of a man having normal fertility. However, anything up to around 25% of these sperm are useless as they are dead. Another variable percentage of the remaining 75% go nowhere fast as they literally go around in circles or spirals. The remaining sperm are all capable of reaching the egg in the fallopian tubes albeit at varying speed. A combination of temperature and chemical attraction drives them on towards their goal.
By the time the sperm reach the egg, only a few dozen of them will have survived the journey for various reasons. These reasons include many getting lost or inadvertently trapped themselves within nooks and crannies during their journey or trapping themselves in mucus present in the lower reaches of the uterus. There are other reasons too why their mortality rate is extremely high including capacitation failures.
So what's capacitation? Regardless of the fertility of the male, freshly ejaculated sperm are either incapable or very poorly capable of fertilising an egg. Capacitation in simple terms is the sum total of biochemical changes that occur in the sperm that make it capable of fertilising the egg. These changes include lipids and proteins reorganisation, pH changes and the removal of unnecessary proteins. In general, capacitation doesn't start until the sperm is within the female but there's still ample time for it to occur before the egg is reached.
(continued)
To begin with, there are anything from about 20 million to 600 million sperm present in the ejaculate of a man having normal fertility. However, anything up to around 25% of these sperm are useless as they are dead. Another variable percentage of the remaining 75% go nowhere fast as they literally go around in circles or spirals. The remaining sperm are all capable of reaching the egg in the fallopian tubes albeit at varying speed. A combination of temperature and chemical attraction drives them on towards their goal.
By the time the sperm reach the egg, only a few dozen of them will have survived the journey for various reasons. These reasons include many getting lost or inadvertently trapped themselves within nooks and crannies during their journey or trapping themselves in mucus present in the lower reaches of the uterus. There are other reasons too why their mortality rate is extremely high including capacitation failures.
So what's capacitation? Regardless of the fertility of the male, freshly ejaculated sperm are either incapable or very poorly capable of fertilising an egg. Capacitation in simple terms is the sum total of biochemical changes that occur in the sperm that make it capable of fertilising the egg. These changes include lipids and proteins reorganisation, pH changes and the removal of unnecessary proteins. In general, capacitation doesn't start until the sperm is within the female but there's still ample time for it to occur before the egg is reached.
(continued)
The egg is best visualised as sitting within an outer ring called the Zona Pellucida. Fertilisation starts when the head of, usually, the first sperm to reach the zona pellucida binds with it. The sperm head releases very specialised enzymes which allow it to bore or drill it's way through the zona pellucida. These enzymes are so specialised that they are specific to the species and do not occur elsewhere in the body of the species concerned.
As the drilling of the sperm continues, enzymes and other substances in the head of the sperm leak out, slowly exposing a layer which is the one needed for binding with the egg. In the meantime, the constantly whipping tail of the sperm ensures that it continues on it's journey to the egg.
After the sperm has penetrated the zona pellucida and crosses the gap, the sperm head penetrates the egg and the back of the head binds with the plasma membrane of the egg. The entire contents of the sperm are then drawn into the egg and embryonic development begins.
As the drilling of the sperm continues, enzymes and other substances in the head of the sperm leak out, slowly exposing a layer which is the one needed for binding with the egg. In the meantime, the constantly whipping tail of the sperm ensures that it continues on it's journey to the egg.
After the sperm has penetrated the zona pellucida and crosses the gap, the sperm head penetrates the egg and the back of the head binds with the plasma membrane of the egg. The entire contents of the sperm are then drawn into the egg and embryonic development begins.
Now while that single sperm has been crossing the zona pellucida, changes have been occuring in zona pellucida itself. Granular substances are formed rapidly as a result of the action of enzymes released by the egg and the sperm. Other substances in the zona pellucida play a part too. The result is rapid formation of granular material in the zona pellucida. These granular substances coalesce turning the entire zona pellucida into the biological equivalent of cement.
By this time, our sperm will have joined with the egg. All the same his mates won't be far behind and may even have started their journey through the zona pellucida. When the layer is solidified, they are trapped, can proceed no further. and usually die. The other sperm that have not reached the zona pellucida find that they can't penetrate it and they normally die too.
It's because of this solidification, that only one sperm can join with one egg. So what could happen if two or more sperm could join with the egg? Well, polyspermy as it's known never occurs in nature. Laboratory studies have shown incontrovertibly that polyspermy leads to the death of the majority of embryos within days. Embryonic survival following polyspermy is completely unknown in mammalian species. The hardening of the zona pellucida is a simple, yet ingenious method of preventing polyspermy thus guaranteeing the survival of the species.
By this time, our sperm will have joined with the egg. All the same his mates won't be far behind and may even have started their journey through the zona pellucida. When the layer is solidified, they are trapped, can proceed no further. and usually die. The other sperm that have not reached the zona pellucida find that they can't penetrate it and they normally die too.
It's because of this solidification, that only one sperm can join with one egg. So what could happen if two or more sperm could join with the egg? Well, polyspermy as it's known never occurs in nature. Laboratory studies have shown incontrovertibly that polyspermy leads to the death of the majority of embryos within days. Embryonic survival following polyspermy is completely unknown in mammalian species. The hardening of the zona pellucida is a simple, yet ingenious method of preventing polyspermy thus guaranteeing the survival of the species.
Ice-Maiden, out of politeness I wasn't going to point out that the second sentence of your initial post is incorrect - it's not a "chemical reaction".
Dundurn and Pippa68 also pointed out between them that you were incorrect over the twins.
In the light of this, how can you say you were "basically" correct? You weren't. All the same leaving all that aside, after you've been on here a while, you'll realise that people often require a more comprehensive and detailed answer. Laconic and incorrect replies only invite more questions and sometimes confusion.
Remember, you may not want the lengthy detail but others might.
Dundurn and Pippa68 also pointed out between them that you were incorrect over the twins.
In the light of this, how can you say you were "basically" correct? You weren't. All the same leaving all that aside, after you've been on here a while, you'll realise that people often require a more comprehensive and detailed answer. Laconic and incorrect replies only invite more questions and sometimes confusion.
Remember, you may not want the lengthy detail but others might.
You can get semi-identical twins.
This is where 2 sperm hit the egg at different sides at the exact same time. The half of the egg with one sperm splits away from the other side. So both twins have the same "mum genes" but different "dad genes". It is a very rare thing
http://en.wikipedia.org/wiki/Twin#Semi-identic al
This is where 2 sperm hit the egg at different sides at the exact same time. The half of the egg with one sperm splits away from the other side. So both twins have the same "mum genes" but different "dad genes". It is a very rare thing
http://en.wikipedia.org/wiki/Twin#Semi-identic al
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