The human body is composed of cells and non-cellular structures which consistently united in tissues, organs, organs' systems and the human body as a whole during the process of philoand ontogenesis. A cell (cellula) is an elementary genetic, structural and functional unit, the main structural element of all living organisms (Fig. 5). A surface apparatus, cytoplasm and nucleus are the components of a human body cell.

The surface apparatus of a cell includes the cell membrane, surface specializations (specialisationes

superficiales) or the supramembrane complex and submembrane structures. The cell membrane, plas-malemma (membrana cellularis, plasmalemma) is composed of the biphospholipid layer and protein molecules which are either on its surface or penetrate it (Fig. 6). Intracellular membranes have a similar structure. A supramembrane layer is termed the glycocalyx (glycocalyx) consisting of carbohydrate molecules (residue) associated with the proteins. This is a receptor unit of a cell. A sub-membrane complex is formed by an ectocytoplasm, cortical cytoplasm (ectocytoplasma) which contains microtubules and microfilaments composed of protein structures that act as the cytoskeleton. The surface apparatus of a cell provides the transmem-brane transport of substances into and out of the

cell.

The cytoplasm (cytoplasma) contains the cytosol (cytosol, matrix cytoplasmatica), organelles and cyto-plasmic inclusions (organella et inclusiones cytoplas-micae). The cytosol is a colloidal solution, the internal environment of the cell where all metabolic reactions occur. The organelles are permanent struc-

tures of a cell; they have a specific structure and perform certain functions. They include the ribo-somes, endoplasmic reticulum, Golgi complex, lysosomes, per-oxysomes, mitochondria, cyto-centre (centrosome).