Life Science 6.2

Your Body Defenses

1. Describe how your body keeps out pathogens.

2. Explain how the immune system fights infections.

3. Describe four challenges to the immune system.

Objectives:

Your skin is made of many layers of flat cells. The outermost

layers are dead. As a result, many pathogens that land on your skin have difficulty finding a live cell to infect.

First Lines of Defense

Sometimes, skin is cut or punctured and pathogens can enter the body. Cell parts in the blood called platelets help seal the

open wound so that no more pathogens can enter.Immune system

The cells and tissues that recognize and attack foreign substances in the body.

Failure of First Lines

Macrophages Engulf and digest many

microorganisms or viruses that enter your body.

T cellsCoordinate the immune

system and attack many infected cells.

B cellsMake antibodies.

Antibodies Proteins that attach to

specific antigens.

Cells of the Immune System

If virus particles enter your body, Some of the particles may pass into body cells and

begin to replicate.Other virus particles will be engulfed and broken

up by macrophages. This is just the beginning of the immune response.

Responding to a Virus

A moderate fever of one or two degrees actually helps you get well faster because it slows the growth of some pathogens.

Fevers also help B cells and T cells multiply faster.

Fevers

Memory B cells Cells in your immune system that “remember”

how to make an antibody for a particular pathogen.

If the pathogen shows up again, The memory B cells produce B cells that make

enough antibodies in just 3 or 4 days to protect you.

Memory Cells

Allergies Happen when the immune system overreacts to

antigens that are not dangerous to the body.Autoimmune Disease

Disease in which the immune system attacks the body’s own cells.

Immune-system cells mistake body cells for pathogens.

Challenges to the Immune System

Rheumatoid Arthritis

Bee sting allergy

Cancer Disease in which the cells begin dividing at an

uncontrolled rate and become invasive.AIDS

The human immunodeficiency virus (HIV) causes acquired immune deficiency syndrome (AIDS).

HIV infects the immune system itself, using helper T cells as factories to produce more viruses.