Whenever you catch a cold, cut a finger or skin a knee, your immune system gets to work. But how does this system work? And what organs are involved? This video will teach us about the human immune system and how it keeps us healthy. We'll be going through concepts like transmission of germs, surface barrier responses, internal responses, vaccines, allergies, and blood cells. We'll also be looking at the difference between the immune system as a whole and our body's defenses. To wrap things up, we'll describe a few immune system disorders and provide a few pointers to promote a healthy immune system.