a. Pressure Gradient. Consider a situation in which there are two separate but
connected spaces. If the concentration or pressure of that substance is greater in one
space than the other, then there is a pressure gradient for that substance. As a result,
the substance will move from the area of higher pressure to the area of lower pressure.
b. Boyle's Law. Assume that we have a container and we can change the
volume of the container without allowing a gas to escape. Boyle's law tells us that if we
increase the volume, the pressure inside will decrease. Likewise, if we decrease the
volume, the pressure inside will increase.
c. Pascal's Law. If a closed container is filled with a fluid, a pressure applied to
the fluid will produce an equal pressure at each and every point on the inner surface.
d. Surface Area. Most phenomena in breathing and respiration take place at
one surface or another. As surface area increases, more gases can be exchanged or
7-4. GENERAL ANATOMY AND CONSTRUCTION OF THE HUMAN TRUNK
The human trunk (Figure 7-1) can be considered a hollow cylinder. A muscular
membrane, the thoracic diaphragm, extends across this hollow and divides the trunk
into upper and lower cavities.
Figure 7-1. Schematic frontal section of the human trunk.