Immunology and Disease (Option A)

The Immune System

Non-specific Defences: This includes physical barriers like skin and mucous membranes, chemical barriers such as stomach acid and lysozyme in tears, and cellular defenses like neutrophils and macrophages that carry out phagocytosis.
Specific Immunity: Lymphocytes operate in the specific immune response. B cells produce antibodies to neutralize specific pathogens, and T cells either directly attack infected cells (T killer cells) or coordinate the immune response (T helper cells).
Immunological Memory: Following an infection, memory B and T cells persist in the body, allowing for quicker and stronger immune response upon subsequent exposure to the same pathogen.

Pathogens: Pathogens such as bacteria, viruses and fungi can cause infectious diseases in host bodies. They invade and damage cells, and can produce toxins.
Non-infectious diseases: These are not caused by pathogens but due to factors like genetic defects, lifestyle choices and environmental elements. These include cancer, heart diseases, diabetes, and genetic disorders.

Active Immunisation: Involves exposing the body to an inactivated or attenuated pathogen or its antigen, generating a protective immune response and creating memory cells.
Passive Immunisation: Involves direct transfer of ready-made antibodies into an individual, providing immediate but short-term protection.

Antibiotics: These are drugs that kill bacteria or inhibit their growth. They do not work against viruses. Overuse may lead to antibiotic resistance.
Antiviral Drugs: These drugs inhibit virus replication within host cells. They do not kill the virus but can limit the severity and duration of viral diseases.

Immunodeficiencies: These are conditions where the immune system’s ability to fight infectious diseases is compromised or entirely absent.
Allergies: These are hypersensitive immune responses to substances that normally are harmless.
Autoimmune Disorders: These occur when the immune system mistakenly attacks and destroys healthy body tissue. Examples include rheumatoid arthritis and lupus.