2 The Circulatory System in the Human Body

The primary functions of the cardiovascular system are: (i) to pick up oxygen and nutrients from the lungs and the intestine, respectively, and deliver them to tissues (cells) of various parts, (ii) to remove waste and carbon dioxide from the body for excretion through the kidneys and the lungs, respectively, and (iii) to regulate body temperature by convecting the heat generated and dissipating it through transport across the skin. The circulatory system in the normal human body (as in all vertebrates and some other select group of species) can be considered as a closed system, meaning that the blood never leaves the system of blood vessels. The driving potential for blood flow is the prevailing pressure gradient.

The circulations associated with the cardiovascular system may be considered under three subsystems. These are the (i) systemic circulation, (ii) pulmonary circulation, and (iii) coronory circulation. (See Fig. 17.1.) In the systemic circulation, blood flows to all of the tissues in the body except the lungs. Contraction of the left ventricle of the heart pumps oxygen-rich blood to a relatively high pressure and ejects it through the aortic valve into the aorta. Branches from the aorta supply blood to the various organs via systemic arteries and arterioles. These, in turn, carry blood to the capillaries in the tissues of various organs. Oxygen and nutrients are transported by diffusion across the walls of the capillaries to the tissues. Cellular metabolism in the tissues generates carbon dioxide...