After studying this chapter, you should be able to:
Name the prominent cellular organelles and state their functions in cells.
Name the building blocks of the cellular cytoskeleton and state their contributions to cell structure and function.
Name the intercellular and cellular to extracellular connections.
Define the processes of exocytosis and endocytosis, and describe the contribution of each to normal cell function.
Define proteins that contribute to membrane permeability and transport.
Recognize various forms of intercellular communication and describe ways in which chemical messengers (including second messengers) affect cellular physiology.
The cell is the fundamental working unit of all organisms. In humans, cells can be highly specialized in both structure and function; alternatively, cells from different organs can share features and function. A basic knowledge of cell biology is essential to an understanding of the organ systems and the way they function in the body. The fundamental aspects of cellular and molecular physiology will be reviewed in this chapter.
FUNCTIONAL MORPHOLOGY OF THE CELL
A key tool for examining cellular constituents is the microscope. A light microscope can resolve structures as close as 0.2 μm, while an electron microscope can resolve structures as close as 0.002 μm. The advent of common access to phase contrast, fluorescent, confocal, and many other microscopy techniques along with specialized probes for both static and dynamic cellular structures further expanded the examination of cell structure and function. Equally revolutionary advances in modern biophysical, biochemical, and molecular biological techniques have also greatly contributed to our knowledge of the cell. The specialization of the cells in the various organs is considerable, and no cell can be called “typical” of all cells in the body. However, a number of structures (organelles) are common to most cells. These structures are shown in Figure 2–1.
Cross-sectional diagram of a hypothetical cell as seen with the light microscope. Individual organelles are expanded for closer examination. (Modified with permission from Bloom W, Fawcett DW: A Textbook of Histology, 9th ed. Philadelphia: Saunders; 1968)
The membrane that surrounds the cell, the plasma membrane, is made up of lipids and proteins and is semipermeable, allowing some substances to pass through it while excluding others. Its permeability can also be varied because it contains numerous regulated ion channels and transport proteins that can change the amounts of substances moving across it. The nucleus and other organelles in the cell are bound by similar membranous structures.
General features among the cellular membranes include their size and lipid makeup. They are generally about 7.5 nm (75 angstroms [Å]) thick. The major lipids are phospholipids such as phosphatidylcholine, phosphatidylserine, and phosphatidylethanolamine. The shape of the phospholipid molecule reflects its solubility properties: the “head” ...