Picture a ten-year old, blonde hair boy named Timmy. Timmy is home alone this holiday break in a really big mansion outside of Detroit. He's sort of worried about being home alone, but he's a clever little kid. If anything does go wrong, he knows how to respond. Timmy is going to use the concept of physiology, which is the science and study of the functions and processes of living organisms and any respective parts such as physical or chemical factors involved therein to show us how he and the body deal with invading organisms that try to infect us.
One night, Timmy hears two robbers trying to get into the house. These grown men have no idea what's coming to them as they try to enter. The same goes for invading pathogens, disease-causing agents that try to enter our body. As the robbers try to make entry, Timmy throws a vat of acid onto their heads from the second floor, causing the robbers to writhe in pain. This reminds me of the hydrochloric acid produced by the stomach that also kills invading organisms that make it down into the gastrointestinal system.
These robbers are hardy. They are acid-stung, yet they keep moving. Timmy doesn't give up. He throws down a big vat of slimy, sticky goo to try and pin them to the floor. Mucus is produced by the mucus membranes of the body, such as those in the respiratory tract and urinary tract. The mucus is sticky and traps any invading pathogens, preventing them from getting any further into the body.
To top that off, Timmy starts throwing scissors at the robbers to try and cut them apart. This is like enzymes, proteins that speed up biochemical reactions found in the gastrointestinal tract, including the mouth, that cut apart invading pathogens.
All of those defenses, although physiologically produced in some respects, aren't truly an active response to the infection in the sense that the body activates these mechanisms to fight off the infection after it has begun. They are responses that are almost automatic and passive because the mucus, acid, and enzymes are always there, and always killing off the invaders before they enter the tissues and bloodstream of the body. However, some physiological responses are activated after the fact - after the organisms have gotten inside. These responses include inflammation and temperature.
See, the robbers got past and survived the acid, mucus, and enzymes. They have now entered the home - in other words, the invaders have made their way into the tissue cells and vessels of the body. Now, little Timmy and the body have to turn to active defense systems.
First, Timmy tries to set the robbers on fire. This is like the inflammatory process in the body. A process that uses cells and chemicals near the site of infection to try and kill everything in sight. This process is indiscriminate, and generates a lot of redness, pain, and heat to kill the invaders. Think back to the last time you cut a finger. It probably got a bit swollen, hot, painful, and red to the touch. Those are all signs of inflammation. The process of inflammation involves the generation of a fever, an abnormal elevation in body temperature. A fever causes the body temperature to increase to levels that most microorganisms find difficult to live and multiply in. Setting the robbers' hair on fire and burning their hands as they touch hot doorknobs doesn't seem to stop these hardy robbers either.
Timmy is beat. He doesn't know what else to do here, so he calls the cops. The cops come in to target and destroy the robbers with advanced weaponry. Your body does this as well through several means. Two of these include the use of white blood cells and antibodies.
White blood cells are one of any number of cells that fight off infection by either killing the invader directly during inflammation, or by tagging it for destruction by another cell or process. White blood cells are also the cells that produce antibodies, unique and specific protein-based molecules that destroy, or tag for destruction, invading pathogens.
The cops do their job, and destroy the two robbers with their technical know-how and advanced weapons. All that's left for Timmy to do is sweep away the robbers and the mess they made out of the home. Actually, the removal of dirt, debris, dead and dying cells happens by your body in order to help fight off infection, or to clear one away.
While Timmy uses a broom made of horsehair to do this, our body has its own microscopic hairs called cilia, which removes the things I discussed out of the body. One place this occurs in is the respiratory tract, where cilia beats towards the throat, and you cough up a bunch of gunk. This is why when you are sick you cough up that disgusting goo! Your body is trying to sweep away the mess.
Let's sort out this mess by summarizing everything:
All sorts of physiological processes passively and actively respond to pathogens. Physiology is the science and study of the functions and processes of living organisms and any respective parts such as physical or chemical factors involved therein, and pathogens are disease-causing agents. Our body uses hydrochloric acid, a substance that kills invading organisms that make it down into the gastrointestinal system. It also uses mucus, which is a substance produced by the mucus membranes of the body, such as those in the respiratory tract and urinary tract that trap invading pathogens. It can use enzymes to cut them apart. Enzymes are proteins that speed up biochemical reactions.
If all of those fail, our body can set us on fire thanks to the inflammatory process - a process that uses cells and chemicals near the site of infection to try and kill everything in sight. One that can generate a fever, an abnormal elevation in body temperature. And, if all else fails, it uses white blood cells to generate antibodies, unique and specific protein-based molecules that destroy, or tag for destruction, invading pathogens.
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