What is the Immune System?

• The immune system is made up of a network of cells, tissues, and organs that work together to protect the body.

• Collectively they protect the body from bacterial, parasitic, fungal, viral infections and from the growth of tumor cells.

• The cells of the immune system can engulf bacteria, kill parasites or tumor cells, or kill viral-infected cells.

• The immune system operates throughout the body.

• There are, however, certain sites where the cells of the immune system are organised into specific structures.

• These are classified as central lymphoid tissue (bone marrow, thymus) and peripheral lymphoid tissue (lymph nodes, spleen, mucosa-associated lymphoid tissue):

How does it work?• The key to a healthy immune system is its remar

kable ability to distinguish between the body’s own cells, recognized as “self,” and foreign cells, or “nonself.”

• When immune defenders encounter foreign cells or organisms carrying markers that say “nonself,” they quickly launch an attack.

• Anything that can trigger this immune response is called an antigen. An antigen can be a microbe such as a virus, or a part of a microbe such as a molecule.

• In abnormal situations, the immune system can mistake self for nonself and launch an attack against the body’s own cells or tissues. The result is called an autoimmune disease for example: some forms of arthritis and diabetes.

• In other cases, the immune system responds to a seemingly harmless foreign substance such as pollen or dust. The result is an allergy, and this kind of antigen is called an allergen.

The Organs of the Immune System• Bone Marrow: is the site of origin of red blood c

ells, white cells (including lymphocytes and phagocytes/ macrophages) and platelets.

• Thymus: T lymphocytes or T cells (“T” stands for “thymus”) mature in the thymus and then migrate to other tissues. B lymphocytes or B cells, become activated and mature into plasma cells, which make and release antibodies.

• Spleen: is an immunologic filter of the blood. It is made up of B cells, T cells, macrophages, dendritic cells, natural killer cells and red blood cells.

• Lymph Nodes: The lymph nodes function as an immunologic filter for the bodily fluid known as lymph.

The Cells of the Immune System• T-Cells: T cells contribute to immune defenses in two m

ajor ways: Some direct and regulate immune responses, whereas others directly attack infected or cancerous cells.

• B Cells: B cells work chiefly by secreting substances called antibodies into the body’s fluids.

• Phagocytes and Macrophages: Phagocytes are large white cells that can swallow and digest microbes and other foreign particles. Macrophages, as scavengers, rid the body of worn-out cells and other debris.

• There are also other lymphocyte cells involved in many of the immune response processes, for example: immunoglobulins, dendritic cells, etc.

Why is it important?• Everyone gets sick sometimes. But your immune system helps you

get well again. • If you've had your shots, your body is extra-prepared to fight off seri

ous illnesses that your immune system alone might not handle very well.

• Sometimes a person has a problem with his or her immune system.• Allergies are one kind of problem — the immune system overreacts

and treats something harmless, like peanuts, as something really dangerous to the body.

• With certain medical conditions, instead of fighting germs, the immune system fights the good cells.

• Other immune system problems may develop due to an illness like HIV/AIDS or cancer.

• You can help your immune system by washing your hands regularly to prevent infections, eating nutritious foods, getting plenty of exercise, and getting regular medical checkups.

http://www.guardian.co.uk/science/video/2010/nov/01/immune-system-viruses-cells

(short video on killing viruses – good)http://vimeo.com/138062 (cool immune system video)

Grade 8 Health Project:• Each student will be required to make a model or poster

related to the work covered in class.• For the model, you can build a skeleton or a working join

t.• For the poster, you can make a poster about a specific a

spect that was covered.• You will need to prepare all your information, pictures, id

eas and materials before the next Health class (which is in one week’s time). You will then create your poster or build your model during the next class. No finished posters or models may be brought to the next class (you will be deducted marks if you do). For the model, all the parts can be prepared before hand, but the model must then be assembled during the class.

• All the information covered in class can be viewed on the PE blog.