Question

A virus such as influenza is only one type of pathogen that can invade the human body and cause disease. Different pathogens interact with different components of the immune system in different ways.

(a) Describe the role of skin and mucosae as surface barriers and the mechanisms that enable these anatomical structures to prevent infections.

(b) Discuss three examples of how the lymphatic and immune systems work together both structurally and functionally to fight infections such as influenza.

Answer 1

Defence against infections:

Skin:

Skin is the natural barrier against infections. Only when it is damaged, the infections may enter the body.

• Skin has several layers, outer skin is thick and prevents any pathogen entry.
• Glands present in the skin secrete sweat and oil which prevents the pathogen growth on skin.
• Tiny hairs present in the ears and nose also prevent the pathogen entry.

Mucous membrane:

Pathogens can enter through mouth, nose or eye. Thus to prevent this entry these regions have the mucous membrane.

• Eye secretes tears to prevent the infection.
• Mouth saliva is secreted. Saliva has enzymes that can break the bacterial cell wall and destroy them.
• Nose secretes the mucous which prevents the pathogen entry and destroy them.
• Mucous membrane also lines the respiratory tract, Cilia which is present in the respiratory tract prevent the trapped pathogens and dust in entering the lungs and sends them out of the body.
• If in case these pathogens are swallowed then acid secretions in the stomach further kills the pathogens.

Thus skin and mucous membrane play viral role as surface barriers and protect the body against infections.

Immune System:

Granulocytes and Agranulocytes:

White blood cells contain the granulocytes – neutrophils, eosinophils, basophils, agranulocytes - lymphocytes and monocytes.

When the skin and mucous membrane fails to prevent pathogen entry further these cells engulf the pathogen and destroy them.

Lymphocytes:

• These lymphocytes are synthesized in the lymph node and spleen. There are 2 types of lymphocytes; they are T and B cell.
• B cell synthesise antibodies which binds to the antigen of the pathogen and destroy them
• T cells are synthesised in the thymus gland. T cells along with T helper cells produce immune response against the infections.

How lymphatic and immune system works to fight infections against influenza virus:

WBC

When a pathogen enters the body, the white blood cells engulf the pathogens and destroy them.

B – Cells produce antibodies

But when the infections is large in number when these cells are not enough to protect the body then B cells produce antibodies against the virus antigen and kill them.

T – Cells kill the infected cells

T cells and T helper cells recognise the infected cell and kill them.

T helper cells activate macrophages to engulf the pathogen. The antigen which was present on the virus is then presented on the surface of the macrophage for the T cell to recognise and neutralise.

The T helper cells also secrete NK cells which also fights the infections.

Once the pathogen is completely destroyed, the T suppressor cells turn of the immune system.

• When the body clears all the virus these remain in blood as memory cells that can prevent the infection of the same virus antigen quickly.
• Influenza virus has the ability to change its surface antigens.
• Mutation, recombination or by combining with other virus it forms new surface antigens.
• When this new influenza virus enters, the body no longer will recognize because of the new surface antigen present on the virus.
• This again triggers the body immune system, to produce necessary antibody and T cells to kill the infected cells.