Disease and Immunity

Health = A state of complete, physical, mental and social well-being and not merely the absence of disease or infirmity.

Good health means you are:

• free from disease,
• able to carry out normal physical and mental tasks expected in modern society,
• well fed, balanced diet,
• usually happy with a positive outlook,
• suitably housed with proper sanitation,
• well integrated into society - able to make and maintain friends,

Disease = A departure from good health. A malfunction of the body or mind, which causes symptoms - either physical, mental or social.

Parasites = organisms that live in (tapeworm), or on (head-lice), a host, cause harm, advantageous for them to live unnoticed - not removed.

Pathogens = microorganisms that cause disease, take nutrition from host, causing damage.

Types of pathogens:

Bacteria = prokaryotic cells, reproduce rapidly, damage cells or release toxic waste products, include tuberculosis, cholera, tonsillitis.

Fungi = lives on skin, send out reproductive hyphae to surface to release spores, cause itching and redness, include athlete's foot and ringworm.

Viruses = invade cells, take over cell and organelles, host cell makes new viruses, host cell bursts releasing them, includes common cold and influenza, HIV and AIDS, plant disease tobacco mosaic virus.

Protoctista = more complex microorganisms, includes malaria parasite plasmodium.

Immunity = being able to resist a particular infectious disease. It can be partial, complete, long lasting or temporary.

First Lines of Defence:

• Skin,
• Eyes,
• Mucous Membranes,
• Ear Canal,
• Reproductive System,
• Stomach,
• Mouth.

Cells of the immune system originate in the BONE MARROW.

• Phagocytes = neutrophils and macrophages,
• Lymphocytes = B and T cells.

Non-specific immunity: second line of defence, immediate attack against a variety of attackers, present from birth, does not distinguish between different pathogens, same response each time, includes phagocytosis and inflammation.

Inflammation:

Histamine is a chemical which dilates capillaries and they become leaky. Area becomes red and swollen as plasma leaks into tissue. Damaged or infected tissue release proteins and other chemicals which attract phagocytes to the area.

Phagocytes engulf and destroy pathogenic cells.

• Pathogen has antigens on surface,
• Antibodies in blood attach to foreign antigens,
• Phagocytes have receptors on cell surface membrane,
• Receptors bind to antibodies that are bound to antigens,
• Phagocytes engulf the pathogen,

Specific immunity: third line of defence, response tailored for a specific attacker, involves lymphocytes and antibodies, slow response when pathogen…