• Question: why do we have periods?

    Asked by siimpleetee to Jen on 15 Jun 2011.
    • Photo: Jen Gupta

      Jen Gupta answered on 15 Jun 2011:

      So that we know when a sentence ends 😉 I assume you’re talking about mestruation though not full stops. If I’m honest I’m not entirely sure about the answer – it’s something to do with the womb creating a lining for the fertilised egg but if the egg doesn’t get fertilised then the body gets rid of this lining and that’s your period. You’d be better off asking someone who didn’t hate biology at school!

      In astronomy when we talk about periods, we normally mean in terms of time so the amount of time it takes a planet to orbit its star, or how often we see a pulse of energy from a spinning neutron star.

Comments

  • Photo: Michael

    Michael commented on :

    I like the humour. On a serious note though, Jen is on the right lines. A woman’s ovaries release an egg into the beginning of the uterus (womb) roughly every 4 weeks (that’s why your menstrual cycle is usually 4 weeks). The egg then spends a few days travelling down the womb and basically waits around to see if a sperm from a male will enter inside it (a sperm will do this a bit like a pin might puncture a tyre on a bike). If a sperm has punctured an egg (which is called fertilisation) then the egg will atach to the uterine wall (something called implantation) and begin to grow. To do this the lining of the uterine wall needs to change during the menstrual cycle to be able to attach the egg. This sends signals to the mothers body to indicate that she is pregnant and this will then prevent the next period happening. If a sperm has not fertilized the egg after a few days, there is no such signal to the mothers body and the lining of the womb – whivh had been preparing to recieve a fertilized egg – now has to revert back to its starting point. To do this means it has to shed some of the lining. This lining is full of blood cells and so the shedding results in a loss of blood associated with the period. Then the whole process starts again.

  • Photo: Joseph

    Joseph commented on :

    “a sperm will do this a bit like a pin might puncture a tyre on a bike”

    I thought the sperm hangs around outside the egg and then the egg envelops the sperm. The view that the sperm ‘penetrates’ the egg is false. At least this is what feminist scientists tell me.

  • Photo: Michael

    Michael commented on :

    Interesting comment Joseph on a number of fronts.
    I can see where you’re coming from so perhaps some detail needs to be added to my simplified answer above before siimpleetee gets completely befuddled by how penetration may be different from envelopment.
    For fertilization of an egg to occur the contents of the sperm somehow need to be introduced to the inside of that egg (oocyte). There are a number of key physical obstacles of the oocyte complex structure that the sperm has to encounter and overcome for this to happen. One is for the sperm to traverse the outer matrix layer of the oocyte complex, the trickiest part of which is the zona pellucida. The sperms acrosomal activation facilitates this. I haven’t previously heard of anyone being worried at this being described as penetration. No penetration of this layer, no fertilization. The next barrier to be encountered is the plasmalemma of the oocyte (oolemma). My understanding is that this presently is thought to involve adhesion of the sperm to the oolemma and subsequent fusion of their membranes. The molecular details surrounding this fusion process and the physical dynamics of it remain, I think, rather unresolved. Granted it’s not going to be a straightforward forced entry of the sperm cell through the oolemma without intercellular cross-talk. One can see why the microvillous nature of the oolemma, and the possibility of controlled release of oocyte exosomes, may give support to the idea for some kind of assimilation of the sperm and oocyte membranes, but it is likely to occur (if it does so this way) once heterocellular tethering has occurred. If not then one needs to think about what the signal for heterocellular fusion might be? What isn’t doubted is that the sperms contents must enter the oocyte to enable delivery of paternal DNA and cell activation for fertilization.

  • Photo: katty

    katty commented on :

    do u have periods

  • Photo: katty

    katty commented on :

    Lol yah so funny!!! :p xxx