In general, a cell represents the smallest living unit of an organism. A body cell is therefore a biological unit in a construct of many cells. There are a total of 200 different cell types, all of which fulfil different functions. The human body is made up of around 3 trillion cells, which can vary greatly in shape and size. A body cell consists of a cell nucleus which has the nucleolus as its centre. The nucleus is enclosed by a nuclear envelope, which in turn is adjacent to the endoplasmic reticulum. The contained cytomal plasma consists of several components such as microbodies, lysosomes, ribosomes and centrioles, among others. All components of the cell are protected and enveloped by a cell membrane. Cells help the human body to protect itself against viruses and bacteria as well as to move or reproduce. The health of body cells can be promoted by treatments such as frequency therapies.