2Humans from a Cellular Perspective
Humans are made up of 60 trillion cells. However, we are more than just a collection of cells. Cells with different functions assemble to form tissues, which are further organized to form organs. Organs and their functions are integrated into systems, which in turn integrate to form individual organisms. In modern medicine, cells (e.g., blood cells) and organs (e.g., internal organs) are transplanted not only from the organ recipients themselves but also from third-party donors as a part of treatment. What kind of existence do cells have in humans? In this chapter, we will survey the behavior of cells—the foundations of individual organisms—and introduce organelles and biological molecules, such as proteins, that constitute cells. We will discuss these topics in relation to humans.