A Trip through the Body

The human body is fantastically intricate. Introduction of a drug into such a complex environment can lead to many outcomes, some of which can be readily anticipated and others that cannot. The complexity of the body stands in stark contrast to the relative simplicity of a biochemical assay for activity determination. 

The body can be defined in a multitude of ways. From a chemical perspective, the simplest analysis is based on elemental composition. Tables 3.1 and 3.2 show the most abundant 

The physiology of the body is assembled from the four hierarchical structures listed in order of increasing complexity cells, tissues, organs, and organ systems. The more complex structures are formed through aggregation of simpler structures. 

The human body consists of approximately 1015 cells. Cells can have a variety of shapes and sizes according to their specialized functions. A typical cell has a rounded shape and is about 10 pm in diameter. Nerve cells can be very long. The nerve cells that run all the way from the tips of one s toes to the base of the spinal cord are about 1 m in length. Epithelial cells that line capillaries are extremely flat to minimize flow resistance. Bone cells (osteocytes) have a star shape to better interlock with neighboring cells and impart strength and rigidity.3 

Tissues are collections of cells with a common function within an organism. Despite the apparent variety of tissues in the body, tissues are classified into just four types connective, epithelium, muscle, and nervous (Table 3.3). 

---