Notice that the manner of presentation of the material, as well as the content, is part of the study. Therefore, comments on and reactions to either content or pedagogy are desired.

If time permits, those making serious attempts to use these materials as instructional aids will be furnished with a supplement to this guide in the form of a revision, pointing out troublesome matters of pedagogy or content that have come to our attention from other users, as well as bugs that have been uncovered in the laboratory equipment or exercises. It is hoped thereby to overcome some (understandable) instructor reluctance to try materials in the development stage. It should be pointed out, however, at the outset that a considerable amount of testing has already gone into these materials, and we believe them to be quite useable as they are now.

From the physical point of view, heat is transported energy; the body is an engine which transforms chemical energy to mechanical energy, and in doing so produces a residual amount of thermal energy from which the body must continually divest itself in order to maintain within itself a constant thermal environment (temperature). This divesture of thermal energy is accomplished by regulated heat flow (i.e., energy transported to the surroundings by virtue of a body/surroundings temperature difference). The vocabulary related to this viewpoint consists of concepts such as temperature, heat transfer, etc.

Yet another point of view describes the physiological processes by which the body transforms energy and divests itself of the excess. It has its own vocabulary (basal metabolism, sweating, shivering, etc.) as well.

These observations point out that you already have had numerous experiences with heat transport processes used as regulatory mechanisms by your body. The purpose of this module is to discuss the physical character of these heat transport processes. A companion module relates these concepts to the maintainance of a constant body temperature.

Specifically, this module examines thermometry and four fundamental physical processes by which heat exchange occurs between body and surroundings. This discussion, in the context of the human body system, derives physical and physiological correlates to the psychological perceptions of hot and cold. It is hoped that in addition to linking the three vocabularies, this exploration will evolve a basis for understanding your body's methods of temperature regulation.

For example, increase in thermal stimulation of body temperature sensors may result in secretion of water by the sweat glands which in turn cools the skin surface and increases the heat outflow. In another scenario, thermal stimulation can initiate stricturing of certain blood vessels, for example in the extremeties. This shifts the blood flow pattern to levels more removed from the skin's surface, thereby increases the effective thickness of the heat conduction barrier, the body's skin, and maintains interior temperature.

It is by the suitable combination of such unconscious activities, combined with our own efforts which are prompted by consciousness of thermal comfort, that our body temperature is held fixed. The purpose of this module is to explore this regulating system.

After you have completed this module, you will be able to:

a) describe qualitatively the pressure of blood in the human body as a function of location in the circulation system, i.e., aorta, artery, arterioles, ... , vena cava.

b) Discuss in a paragraph (short or long) how the osmotic pressure in the capillaries regulates the water level of the interstitial fluid under normal pressure.

c) Describe how a weak ventricle in the heart creates an edema in the capillaries. Use the terms of this module, i.e., abnormal pressure, water pressure inside and water pressure outside, in this description.

d) Illustrate reverse osmosis by explaining the process of de-salinating sea water.

e) Define osmosis and describe how osmotic pressure is related to the colligative properties of a solution.

NARRATIVE

This story begins in 1748 when J. Abbe Nollet observed and recorded his observation of a solvent passing through a membrane from a dilute solution into a more concentrated one. By applying pressure to the more concentrated solution, the flow of solvent could be slowed, stopped, or reversed. The pressure necessary to stop the flow of solvent from the less concentrated to the more concentrated solution through the membrane is called the osmotic pressure. When considering biological systems the solutions are almost all aqueous solutions, the solvent being water. Consider a container of water. Let the container be separated into two sections by a membrane which only allows water to pass through. Dissolve some solid material in the water on one side of the membrane. The pressure which must now be applied to the solution side, in excess of any pressure applied to the water side, to stop the flow of water through the membrane is called the osmotic pressure. This pressure is the subject of this module.

Of course, these cells are not completely independent. They share in a society, but especially in an economy, of the whole organism. This economy does not trade dollars of differing currencies; rather, its commerce is in energy of differing forms.

A particularly important asset is thermal energy. It is the natural by-product of the various energy conversion processes, the biochemical reactions within the body. But, additionally, its average level of distribution throughout the body (i.e., the body's temperature) is significant in the maintenance of the proper rate of these same biochemical reactions.

The purpose of this module is to characterize and evaluate the energy management of the body, with special emphasis on relating the physical processes of thermal energy transport (i.e., heat flow) to the body·s temperature regulation process.

Note: pages 22 & 35 are intentionally omitted.