Immune and the lymphatic system

Structure of the immune system

Immunity is best understood as human body's line of defence against foreign agents such as bacteria and viruses also called pathogens.

First line of defence:

1. Mechanical barriers, for example, intact skin and mucous membrane.
2. Chemical barriers, for example, saliva, tears.
3. Reflexes, for example, coughing, sneezing, and vomiting.

Second line of defence:

1. Inflammation and fever
2. Protective proteins that are produced in response to viruses and bacteria.
3. Natural killer cells (lymphocytes).
4. Phagocytes (special white cells that eat pathogens).

Third line of defence:

1. Lymphocytes- T cells and B cells that fight foreign agents.

Immunity can be either natural or active. Natural immunity is an individual’s ability to ward off pathogens and is influenced by the person’s state of health, their nutritional status and their emotional response to stress.

Active immunity occurs as the body builds up a resistance to pathogens that have been introduced through exposure or by immunisation.

Function of the immune system

The immune system is a complex system of cells and responses that recognises something as foreign and acts to remove it. For example micro-organisms, foreign tissue, body cells such as in cancer.

Structure of the lymphatic system

The lymphatic system is comprised of:

• lymphatic capillaries
• lymphatic vessels
• lymphatic nodes
• lymphatic tissue
• lymphatic ducts.

Lymph nodes are found in the axilla (under the arm), in the neck and in the groin. Lymphatic tissue is found in the spleen, the tonsils and the thymus. It is in the lymphatic tissue the lymphocytes are formed.