Health, disease and the immune system
Biology · Key Stage 3 · The School
Two kinds of disease
COMMUNICABLE diseases are caused by pathogens — bacteria, viruses, fungi, protists — and can pass between people. NON-COMMUNICABLE diseases such as most heart disease, type 2 diabetes and many cancers cannot. The distinction matters because it changes what helps: hygiene and vaccination for one, and lifestyle, screening and treatment for the other.
How the body defends itself
The first defences are physical: skin, mucus, stomach acid, and tiny hairs in the airways. If a pathogen gets past them, WHITE BLOOD CELLS respond — some engulf and digest pathogens, others produce ANTIBODIES that lock onto a specific pathogen and mark it for destruction. Antibodies are specific: one shaped for measles does nothing against flu.
Vaccination
A vaccine introduces a harmless form or fragment of a pathogen. The immune system responds as if to the real thing and keeps MEMORY CELLS, so a later real infection meets a fast, large response before the person becomes ill. When enough of a population is vaccinated the pathogen struggles to spread at all, which protects people who cannot be vaccinated themselves.
FIRST exposure: it takes days for the right white blood cells to be found and multiplied, so you feel ill while antibody levels climb slowly. SECOND exposure to the same pathogen: MEMORY cells are already there, so antibodies rise within hours and in far greater numbers, and you may not notice at all. A vaccine gives you the first curve without the illness, so the second one is ready when you need it.