Section B

Body & Disease Mechanisms

How the body keeps balance and what changes in disease.

Homeostasis keeps internal conditions within workable ranges through continuous adjustments that depend on context.

Cells form tissues and organs whose functions depend on constant cooperation across the body.

Circulation connects organs by moving blood that carries gases, nutrients, waste products and chemical signals.

Breathing moves air, while gas exchange and circulation together supply oxygen and remove carbon dioxide.

Immune defence combines barriers, rapid responses and targeted immune memory to limit harmful threats.

Inflammation supports defence and repair, but persistent or misdirected responses can also harm tissues.

Infection occurs when pathogens establish themselves in a host, while transmission describes how they spread between sources and hosts.

Hormones coordinate functions across the body through signals whose effects depend on receptors, timing and feedback.

Metabolism includes the chemical processes that release energy, build body materials and manage stored fuel.

Genetic differences can influence health, but their effects range from minimal to substantial and often depend on other factors.

Cancer develops when altered cells escape normal controls, with different cancers following different biological paths.

Healing coordinates defence, rebuilding and remodelling, with outcomes shaped by the tissue and the conditions surrounding the injury.

Risk factors change the likelihood of an outcome, while evidence of causation asks whether a factor helps produce it.