Hey guys, what's up, it's Jonathan12345 again, here on BioMed with today's topic: the immune system.
Experts in every field like to overestimate how knowledgeable ordinary people are in their field. And I'm definitely NOT an expert (you should not take anything I say as serious medical advice. TALK TO A DOCTOR IF YOU ARE SICK), but it's still pretty easy for me to overestimate how much people know. So we're just going to assume that you know absolutely nothing about the immune system other than "white blood cells eat bacteria".
The first thing you have to know is that "white blood cells" aren't a thing. There are many types of "white blood cells", but the ones we'll be talking about today are the Innate Immune System.
The innate immune system mainly consists of macrophages and neutrophils, both of which are made in the bone marrow. I'll explain them in more detail now.
Macrophages are very big cells that either flow around in your blood or patrol areas in your body. Their job is to detect and consume any bacteria that are found in their regions. If there are too many bacteria to handle, they'll release signals to call for reinforcements, generally in the form of neutrophils.
Neutrophils are a lot more short lived, since they can cause a lot of damage to tissues once they're activated. Generally, they die off naturally shortly after being born (we're talking about shortly in a human scale here), but while they're alive they are kind of on standby, just waiting to reinforce potential battles.
Now, both of these types of cells resemble large white blobs under microscopes, the main difference being that macrophages are larger. They both resemble amoeba and eat similarly---by engulfing their prey with pseudopods and then digesting them alive. Since they don't have eyes, they instead sense chemicals from bacteria to know which direction to attack.
Here's a video of macrophages in action: https://www.youtube.com/watch?v=BlPlgGbb2IU
Sometimes, however, infections can get out of hand. In that case, the body needs a bit more than these cells to defeat invaders...
Here's a bonus video: https://www.youtube.com/watch?v=28FVxYQuLOQ