Revision:Defence against infectious disease

State the types of organism that can cause disease

Caused by a variety of organisms.

  • Bacteria
  • Fungi
  • Virii

Explain how skin and mucous membranes act as barriers against microbes

  • The skin, with its tough layer of keratin, is an impregnable barrier as long as it is intact. When it is not, large numbers of micro organisms gain ready entry to the body.
  • Epithelium that forms mucous membranes
    • is more fragile than the skin.
    • is constantly flushed with fluids, such as mucus, saliva and tears, that contain antimicrobial substances.
    • The epithelium lining of the respiratory tract is carpeted with cilia, which sweep away inhaled organisms, dirt and debris trapped in the protective layer of mucous.

Explain how Phagocytic lymphocytes ingest disease causing organisms in the blood and in body tissues


State the difference between antigens and antibodies

  • Antigen
    • a foreign substance, usually a protein or polysaccharide
    • that when bound to a complementary antibody displayed on the surface of a B lymphocyte or to a complementary T-cell receptor, stimulates an immune response.
  • Antibody
    • a globular protein
    • synthesized by a B lymphocyte
    • to a foreign substance (antigen) with which it combines specifically.

Describe Antibody Production

  • B lymphocytes in bone marrow produce during development, clones of identical cells programmed to secrete a specific antibody when recognising one type of antigen (surface recognition sites, humoral immunity and memory cells)
  • Antibody molecules contain an antigen binding site.

Describe AIDS

  • The disease known as AIDS is a complicated illness that may involve several phases. It is caused by a virus called HIV that can be passed from person to person. AIDS impairs the human body's immune system the system responsible for warding off disease and leaves the victim susceptible to various infections. The virus enters the bloodstream and destroys certain white blood cells, called T lymphocytes, that play a key role in the functioning of the immune system.
  • The virus can also infect other types of cells in the body, including the immune-system cells known as macrophages. Unlike T lymphocytes, however, macrophages are not killed by the virus. In fact, research has suggested that macrophages may carry the AIDS virus to healthy brain cells, to the lymphatic system, and to other healthy cells in the body. AIDS is transmitted by direct contamination of the bloodstream with body fluids that contain the AIDS virus, particularly blood and semen from an HIV-infected person. The virus is usually transmitted through various forms of sexual intercourse, the transfusion of virus-contaminated blood, or the sharing of HIV-contaminated intravenous needles.