Sperms an Eggs

[Supernick]

How does a sperm know that it's encountered the egg, and start burrowing into it? Why aren't they always trying to burrow into the Fallopian tubes etc?

[{Dakota}]

The fallopian tube is where the egg and the sperm meet. In order to ensure the meeting, the fallopian tube performs a two-fold activity; first, it takes the maturated egg cell from the ovary and guides it to the place in the tube where it will meet the sperm. Secondly, it takes the sperm from the cavity of the uterus and brings it to the place where it will meet the egg.

First of all, the fallopian tubes collect all the eggs released from the ovary. The ends of the fallopian tubes are like arms which surround the ovary and are designed to collect the maturated eggs. When the eggs have come to maturity, the arms of the fallopian tubes open and, like the arms of an octopus, they grasp the surface of the egg and begin to move over it with a sweeping motion. Aided by these activities, at the time of ovulation the egg falls into the fallopian tube. The egg, released into the pelvic cavity, enters the fallopian tube which is 10-12 cm. in length. The inside of the fallopian tube is covered with millions of tiny hairs which move in one direction, drawing the egg to where it will meet the sperm.

By this time, the follicle cells surrounding the ovum at the time of ovulation still remain as an outer envelope. The folded mucous membrane of the egg secretes enzymes which gradually cause this cellular envelope to loosen. Thus, the follicle cells are "rinsed away", so that the protective membrane of the egg lies exposed to the sperm.

[Supernick]

But how do the sperm know not to burrow into the Fallopian tube's cells, or the vaginal tract for that matter. How on earth do they know they've encountered the egg, and not just the wall of the tube that they're swimming through?

[{Dakota}]

They don't "know". The egg has to be ready for fertilisation before anything will happen. They could travel the whole female body for all they cared (I know it's not physically possible) but for as long as there is nothing to fertilise then they can go where ever they want.

[Supernick]

So am I right in thinking that they will try and fertilise any obstacle that gets in their way? If they bump into some ordinary tissue cells, they'll frantically try and get inside?

[{Dakota}]

No, the fertilisation is a chemical reaction (for want of a better expression) so it can't try to fertilise anything that doesn't have everything it needs to make the fertilisation happen. For example, if you want to fry an egg, you need to put oil in the pan and switch on the cooker ring, if you don't do that the egg will just float there doing nothing. You need to have the everything in working order in order to fry the egg.

Also, the sperm only lives for up to 24 hours in the female body, so the sperm can't just sit there for 1 month waiting for the next egg to come along that is ready to be fertilised.

Is it making better sense to you?

[{Dakota}]

I can't believe I used frying an egg as an example {blush} LOL

[Scarlett]

Why do we try to have sex with men and not trees?

[{Dakota}]

Sometimes it might as well be a tree given the intelligence level!!

KIDDING BOYS!!

[Supernick]

Very funny ;) Perhaps I wasn't being very clear with my point. I'm very familiar with the fertilisation process, although my A-Level Biology teacher may want to ask for a recount on my A grade. I assumed that the egg must release some sort of chemical that acts as a signal to nearby sperm. As the egg is just an extremely large cell surrounded by millions of others I was curious as to why the sperm only attempt to penetrate the membrane of that 1 cell and not attempt to penetrate the membranes of the millions of cells around it. Obviously the sperm cannot fertilize any of these surrounding cells because it's simply impossible, but I wanted to know what it is about the egg that makes the sperm want (not implying sperm have sentience) to penetrate it before fertilization can take place.

[maxton]

yes, you are right - chemical messengers steer the sperm in the right direction.

If they don't encounter the ova they simply die off over a number of days in the fallopian tubes.