The kidney is not one large filter. Each kidney is made up of about a million filtering units called nephrons. Each nephron filters a small amount of blood. The nephron includes a filter, called the glomerulus, and a tubule. The nephrons work through a two-step process.
Generally speaking, first babies tend to engage from about 34 weeks to 36 weeks. However, some babies only engage once labour starts. Try not to worry, though. Even if your baby hasn't engaged by the time labour starts, in most cases, it's not a problem.
If you happen to have sex on the same day as you have ovulates, then you could get pregnant the same day. But if you don't ovulate the same day you have sex, sperm can live for up to three days (some day even longer!). So you can get pregnant 1,2 and even 3 days after you have sex. It all comes down to when you ovulate and if there are sperm hanging around or not! The egg only lives for about a day so it's not hanging around as long as the sperm are. Conception means the day the sperm fertilized the egg.