The Blood Vascular System

The blood vascular system comprises the heart and blood vessel with their contained fluid, the blood. The composition of the blood and the minute anatomy of the blood vessels will be considered in the section on Histology.

The Heart of is the central organ of the entire system, and consists of a hollow muscle; by its contraction the blood is pumped to all parts of the body through a complicated series of tubes, termed arteries. The arteries undergo enormous ramification in their course throughout the body, and end in very minute vessels, called arterioles, which in their turn open into a close meshed network of microcapilaries it is collected into a series of larger vessels, called veines, by which it is again returned to the heart. The passage of the blood through the heart and blood vessel constitutes what is termed the circulation of the blood, of which the following is on outline.

The human heart is divided by a septum into two halves, right and left, each half being further constricted into two cavities, the upper of the two being termed the auricle and the lower the ventricle. The heart therefore consists of four chamber or cavities, two forming the right half, the right article and right ventricle, and two forming the right half, the right auricle and right ventricle, and two the left half, the left auricle and left ventricle. The right half of the heart contains venous or impure blood; the left article or pure blood. From the cavity of the left ventricle the pure blood is carried into a large artery, the aorta, through the numerous branches of which it is distributed to all parts of the body, with the exception of the lungs. In its passage through the capillaries of the body the blood gives up to the tissues the materials necessary for their growth and nourishment, and at the same time receives from the tissues the waste product resulting from their metabolism, and in doing so becomes changed from arterial or pure blood into venous or impure blood, which is collected by the vein and through them returned to the right auricle of the heart. From this cavity the impure blood passes into the right ventricle, from which it is conveyed through the pulmonary arteries to the lungs. In the capillaries of the lungs it again becomes arterialized, and is then carried to the left auricle by the pulmonary veins. From this cavity it passes into that of the left ventricle, from which the cycle once more begins.