Introduction

In a multicellular organism, cells do not operate independently — instead they specialise and cooperate, forming tight communities that live and work together for the benefit of the whole body. A muscle cell looks and behaves very differently from a skin cell precisely because of this specialisation, which is what lets the body function in a coordinated way. A group of cells that are similar in structure and that perform a common or related function is called a tissue.

Tissues in turn combine, in specific proportions and patterns, to build organs — the lungs, heart, stomach, kidneys, ovaries and testes among them — which is why tissues are sometimes called the body's 'living fabric'. When two or more organs work together toward a shared physical or chemical function, they form an organ system, such as the digestive, respiratory, circulatory or excretory systems. Because most organs are actually built from several different tissue types arranged together, it is the pattern of that arrangement, more than any single tissue alone, that shapes an organ's structure and function. The dedicated study of tissues is called histology, which complements gross anatomy — together the two fields provide the structural basis for understanding how an organ actually works.