Summary

In this lesson, you explored the following essential questions:

• What is the function of the lymphatic system?
• How do the cellular and non-cellular components of the human defence system work together to maintain homeostasis?

The constant battle waged within your body to turn back and destroy foreign invaders is scarcely apparent in your daily life. However, it is this battle that is vital to your survival and the survival of the human species. New and terrifying microbes regularly emerge to challenge your immune system.

The lymphatic system helps to maintain the balance of fluids in your body as well as contain white blood cells that seek and destroy invading pathogens. Your body has three lines of defence.

First, there are physical and chemical barriers, such as skin and stomach acid, that will prevent pathogens from harming healthy cells.

Second, there is a cell-mediated response. This response relies on macrophages, neutrophils, monocytes, and T-cells to recognize and destroy invading pathogens. Antigens, on the surface of the invading cells or on cells that pathogens (such as viruses) have invaded, identify them for destruction.

The third line of defence is the antibody-mediated response. Helper T-cells identify an invading pathogen and stimulate B-cells to produce antibodies. Antibodies are released into the blood and bind to specific antigens. Antibodies for salmonella will only work on the antigens on the surface of salmonella molecules.

Once antibodies have bound to invading antigens, three things can happen. The invading pathogen will be neutralized, the antibody can attract macrophages to destroy the pathogen, and/or the antibody will stimulate granulocytes and killer T-cells to release toxic molecules that will ultimately destroy the pathogen. Any large immune response to pathogens will exhibit a variety of symptoms, such as fever, swelling, pus, and redness.

Lesson Glossary

cell-mediated immunity: involves the activation of white blood cells, specifically macrophages, neutrophils, monocytes, and T-cells rather than the production of antibodies

helper T-cell: arises from the thymus

These T-cells recognize an antigen on the surface of an invading pathogen and stimulate B-cells to produce antibodies.

killer T-cell: also known as a cytotoxic T-cell

It kills other target cells, such as cells infected with viruses, parasites, or cancer. These T-cells monitor all the cells of the body and are ready to destroy any cells that express foreign antigen fragments on the surface.

memory T-cell: a lymphocyte that carries receptors for a specific foreign antigen encountered in an earlier infection or through vaccination; it quickly promotes an immune response if the same antigen is re-encountered in a subsequent infection

suppressor T-cell: slows and suppresses the process of cellular immunity to ensure that normal tissue does not get destroyed