The four tissue types

Despite the huge diversity of organs in the body, every one of them is built from just four basic tissue types, combined in different amounts and arrangements. Learning these four now means every organ you study for the rest of the course will already feel familiar, because you will recognise its ingredients.

• Epithelial tissue — covers external surfaces (like the outer layer of skin) and lines internal cavities and tubes (like the inside of the gut or the airways). It is often just one or a few cells thick, and it acts as a protective and selective boundary.
• Connective tissue — supports, binds, and cushions other tissues. This is the most varied category by far: it includes bone, cartilage, tendons, fat, and even blood.
• Muscle tissue — contains cells specialised to contract, shortening to create movement or force.
• Nervous tissue — contains cells specialised to generate and carry electrical signals rapidly over distance.

Every organ you will study — the heart, the stomach, a kidney, even the brain — is a specific combination of these four tissue types, arranged for one purpose. The heart, for instance, is mostly muscle tissue (to pump), wrapped in connective tissue (for structure) and lined inside and out with epithelium (as a protective, low-friction surface).