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OBJECTIVES

OBJECTIVES

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 connections and intracellular 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 functions.

INTRODUCTION

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. In the previous chapter, some basic principles of biophysics and the catabolism and metabolism of building blocks found in the cell were examined. In some of those discussions, how the building blocks could contribute to basic cell function (eg, DNA replication, transcription, and translation) were discussed. In this chapter, more of the fundamental aspects of cellular and molecular physiology will be reviewed. Additional aspects that concern specialization of cellular and molecular function are considered in the next chapters concerning immune function and excitable cells and within the sections that highlight each physiological system.

FUNCTIONAL MORPHOLOGY OF THE CELL AND HOMEOSTASIS

The actual environment of the cells of the body is the interstitial component of the extracellular fluid (ECF). Because normal cell function depends on the constancy of this fluid, it is not surprising that in multicellular animals, an immense number of regulatory mechanisms have evolved to maintain it. To describe “the various physiologic arrangements which serve to restore the normal state, once it has been disturbed,” W.B. Cannon coined the term homeostasis. The buffering properties of the body fluids and the renal and respiratory adjustments to the presence of excess acid or alkali are examples of homeostatic mechanisms. There are countless other examples, and a large part of physiology is concerned with regulatory mechanisms that act to maintain the constancy of the internal environment. Many of these regulatory mechanisms operate on the principle of negative feedback; deviations from a given normal set point are detected by a sensor, and signals from the sensor trigger compensatory changes that continue until the set point is again reached.

A basic knowledge of cell function and structure is essential to an understanding of the homeostasis, the organ systems and the way they function in the body. 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. Although cell dimensions are quite variable, this resolution can provide a good look at the inner workings of the cell. The advent of common access ...

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