Cellular Structures Relevant Anatomy and Physiology

Cells are the fundamental building blocks of the human body. On average the human body contains 10 cells, ranging in size from nerve cells with a length of 0.5-1.0 m to red blood cells with a diameter of 7 jam. From a structural perspective, the cell can be subdivided into three major components  

Each one of these components is composed of a complicated array of substituent macromolecules and offers targets suitable for drug design (see figure 7.1). 

MEMBRANE TARGETS Voltage gated ion channels Ligand gated ion channels G-proteins 

The composition of the cell membrane varies from one anatomical location to another. For example, the cell membranes of neurons are 75% lipid and 25% protein, while those of epithelial cells in the intestinal villi are 75% protein and 25% lipid. The mixture of lipids that constitutes the cell membranes of neurons is different from that found in other organ systems the same applies to the membrane proteins of neurons. Cell membranes are dynamic structures the phospholipids and fatty acids are in a state of constant turnover the protein components tend to turnover with a cycle ranging from 9 days to 6 months. 

The cytoplasm is the semi-fluid polyphasic colloid that comprises the bulk of the cell s interior between the cell membrane and the nucleus it contains enzymes responsible for catalyzing the biosynthetic machinery of the cell and organelles responsible for specific tasks within the cell. Cytoplasm must be differentiated from protoplasm protoplasm is the whole material contained within the cell membrane and is further differentiated into the material found within the nucleus (nucleoplasm) and material external to the nucleus (cytoplasm). Organelles are important functional structures within the cytoplasm. Various structures visible by light microscopy are classified as organelles, including mitochondria, endoplasmic reticulum, and lysosomes. 

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