# Fertilization ___ **Fertilization** occurs when a [[sperm]] successfully meets up with an [[oocyte]] and they combine to form a diploid [[prenatal development|zygote]]. - 2ndry oocyte - once it has 23 chromosomes, the only has ~24 hours to live, so it needs to be fertilized in that time frame. - The egg just hangs out in the tube for a while after ovulation, usually at the ampulla area of the tube. - sperm travel all the way up the uterine tube to fertilize egg (they can smell which one the egg is in) - 1 egg, millions of sperm enter the vagina, 100-200 sperms reach the egg - "some of you may die...but that is a sacrifice I'm willing to make" - if the woman is not ovulating, the sperm has a hard time getting past the cervix - zygote travels down to uterus - takes 3-4 days - if it doesn't get there in time, and emplants in the tube, it's an **ectopic pregnancy** ![[fertilization.png]] ## Preventing Polyspermy **Polyspermy** is when two or more sperm get into an oocyte—very bad news. The body has some mechanisms to deter this. Upon entry of sperm, there is a [[calcium|Ca++]] surge that cause a cortical reaction. **Zonal inhibiting proteins** or **ZIPs** are released, which destroy sperm receptors. This happens quite fast. A slower method is that spilled fluid binds to water and swells, detaching other sperm trying to get in. ___