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Author: Amanda Soderlind

Determine how the human body protects itself from pathogens.

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Source: Video and Images Created by Amanda Soderlind

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Welcome to this lesson today on pathogens. Today we are going to be discussing what a pathogen is and how our body defends us against pathogens. So pathogens are any disease-causing agent. And this could be anything from fungi to bacteria, viruses, parasites, anything that can cause disease in our body.

So these types of pathogens are found almost literally everywhere. So in order for our body to survive and not succumb to the attacks of these pathogens, it has to find ways to defend us against the pathogens. So our body has three lines of defense against pathogens.

And the first line of defense is physical and chemical barriers. So our body has these physical and chemical barriers that try and prevent pathogens from even entering the body at all, or if they do enter the body, trying to immediately get rid of them. So things like mucosal linings, mucus, and our skin are examples of physical barriers that try and keep pathogens out in the first place.

But let's say that a pathogen does get past that. Then our body will attempt to get rid of those pathogens by lysozyme, which is an enzyme, raising or lowering the pH of the body. Diarrhea is a way which our body tries to flush out pathogens. And then good bacteria within our body will also try and get rid of those pathogens as well. So these physical and chemical barriers are the first line of defense against pathogens.

Once those pathogens, though, have entered our body and gotten past those physical or chemical barriers, our innate immunity will kick in. So innate immunity is a general-- it's like a generalized, cure-all response. So it's a very generalized cure-all response. It's very nonspecific.

So what it does is it wipes out many invaders before they can even cause infection. So some examples of responses of innate immunity are phagocytes, inflammation, and fever. So these are some responses of innate immunity that will try and get rid of these pathogens, whatever they are. So cells that are involved in innate immunity don't care what type of pathogen it is. They will just attack any type of pathogen. It's a very generalized, as I mentioned, cure-all response.

And then adaptive immunity is a much more specific type of immunity. So adaptive immunity will also start when innate immunity starts. But the difference between adaptive and innate immunity is that adaptive immunity has specialized cells that fight specific pathogens. So as I mentioned in innate immunity, it's a cure-all response that will try and wipe out any type of invader. But with adaptive immunity, it's fighting specific pathogens. So white blood cells that attack in adaptive immunity have specific receptors for specific types of pathogens. So again, it's a very specific type of immune response.

And this adaptive immunity also changes throughout life as you encounter different sorts of illnesses. And it produces memory cells or immunity. So basically what that means is if you've had a certain type of illness once, your body remembers that illness. It remembers how to fight that illness so that if you come in contact with it again, your body is more well equipped to fight that illness before you even get an onset. So these are the three lines of defense against pathogens, physical barriers, innate immunity, and adaptive immunity. So this lesson has been an overview on pathogens.

Terms to Know
Adaptive Immunity

Also known as specific immunity, adaptive immunity is carried out by T & B lymphocytes and reacts to specific antigens of cells; adaptive immunity also produces memory cells to target the same pathogen if we are ever exposed to it again.


A unique marker on the surface of a cell that can stimulate an immune response.

Innate Immunity

Also known as non-specific immunity, innate immunity consists of general physiologic responses (fever, inflammation, etc.) that can affect the entire body.


Any disease-causing agent that we are exposed to (bacteria, virus, fungus, parasite, etc.)

Physical Barriers

Consists of skin and mucous membranes, physical barriers are our first line of defense against pathogens. Physical barriers are part of our non-specific immunity.