Ross and Wilson Anatomy and Physiology in Health and Illness_ With access to Ross & Wilson

Levels of structural complexity Learning outcome After studying this section you should be able to: describe the levels of structural complexity within the body. Within the body are different levels of structural organisation and complexity. The most fundamental level is chemical. Atoms combine to form molecules, of which there are a vast range in the body. The structures, properties and functions of important biological molecules are considered in Chapter 2. Cells are the smallest independent units of living matter and there are trillions of them within the body. They are too small to be seen with the naked eye, but when magnified using a microscope different types can be distinguished by their size, shape and the dyes they absorb when stained in the laboratory. Each cell type has become specialised, and carries out a particular function that contributes to body needs. Figure 1.1 shows some highly magnified nerve cells. In complex organisms such as the human body, cells with similar structures and functions are found together, forming tissues. The structure and functions of cells and tissues are explored in Chapter 3. Figure 1.1 Coloured scanning electron micrograph of some nerve cells (neurones). Organs are made up of a number of different types of tissue and have evolved to carry out a specific function. Figure 1.2 shows that the stomach is lined by a layer of epithelial tissue and that its wall contains layers of smooth muscle tissue. Both tissues contribute to the functions of the stomach, but in different ways. Figure 1.2 The levels of structural complexity. Systems consist of a number of organs and tissues that together contribute to one or more survival needs of the body. For example the stomach is one of several organs of the digestive system, which has its own specific function. The human body has several systems, which work interdependently carrying out specific functions. All are required for health. The structure and functions of body systems are considered in later chapters