Key Concepts

1. Physiology is the study of the functions of living organisms and how they are regulated and integrated.

2. A stable internal environment is necessary for normal cell function and survival of the organism.

3. Homeostasis is the maintenance of steady states in the body by coordinated physiological mechanisms.

4. Negative and positive feedback are used to modulate the body's responses to changes in the environment.

5. Steady state and equilibrium are distinct conditions. Steady state is a condition that does not change over time, while equilibrium represents a balance between opposing forces.

6. Cellular communication is essential to integrate and coordinate the systems of the body so they can participate in different functions.

7. Different modes of cell communication differ in terms of distance and speed.

8. Chemical signaling molecules (first messengers) provide the major means of intercellular communication; they include ions, gases, small peptides, protein hormones, metabolites, and steroids.

9. Receptors are the receivers and transmitters of signaling molecules; they are located either on the plasma membrane or within the cell.

10. Second messengers are important for amplification of the signal received by plasma membrane receptors.

11. Steroid and thyroid hormone receptors are intracellular receptors that participate in the regulation of gene expression.

Physiology is the study of processes and functions in living organisms. It is a broad field that encompasses many disciplines and has strong roots in physics, chemistry, and mathematics. Physiologists assume that the same chemical and physical laws that apply to the inanimate world govern processes in the body. They attempt to describe functions in chemical, physical, or engineering terms. For example, the distribution of ions across cell membranes is described in thermodynamic terms, muscle contraction is analyzed in terms of forces and velocities, and regulation in the body is described in terms of control systems theory. Because the functions of living systems are carried out by their constituent structures, knowledge of structure from gross anatomy to the molecular level is germane to an understanding of physiology.

The scope of physiology ranges from the activities or functions of individual molecules and cells to the interaction of our bodies with the external world. In recent years, we have seen many advances in our understanding of physiological processes at the molecular and cellular levels. In higher organisms, changes in cell function always occur in the context of a whole organism, and different tissues and organs obviously affect one another. The independent activity of an organism requires the coordination of function at all levels, from molecular and cellular to the organism as a whole. An important part of physiology is understanding how different parts of the body are controlled, how they interact, and how they adapt to changing conditions.

For a person to remain healthy, physiological conditions in the body must be kept at optimal levels and closely regulated. Regulation requires effective communication between cells and tissues. This chapter discusses several topics related to regulation and communication: the internal environment, homeostasis of extracellular fluid, intracellu-lar homeostasis, negative and positive feedback, feedforward control, compartments, steady state and equilibrium, intercellular and intracellular communication, nervous and endocrine systems control, cell membrane transduction, and important signal transduction cascades.

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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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