The circulatory system, composed of the heart, blood, and blood vessels, circulates a transport fluid throughout the body, providing the cells with a steady supply of oxygen and nutrients and carrying away waste products such as carbon dioxide and toxic nitrogen compounds.
It is a closed tubular system in which the blood is propelled by a muscular heart. Two circuits, the pulmonary and the systemic, consist of arterial, capillary, and venous components.
THE HEART:
The primary function of the heart is to serve as a muscular pump
It propels blood into and through vessels to and from all parts of the body.
The adult human heart is normally slightly larger than a clenched fist.
It average dimensions is about 13 × 9 × 6 cm (5 × 3.5 × 2.5 inches).
It weight is approximately 10.5 ounces (300 grams).
It is cone-shaped, with the broad base directed upward and to the right and the apex pointing downward and to the left.
It is located in the chest (thoracic) cavity behind the breastbone (sternum), in front of the windpipe (trachea), the
esophagus, and the descending aorta, between the lungs, and above the diaphragm (the muscular partition between the chest and abdominal cavities).
About two-thirds of the heart lies to the left of the mid line
THE ARTERIES:
The arteries, which receive this blood at high pressure and velocity and conduct it throughout the body.
It has thick walls that are composed of elastic fibrous tissue and muscle cells.
The arterial tree—the branching system of arteries—terminates in short, narrow, muscular vessels called arterioles, from which blood enters simple endothelial tubes (i.e., tubes formed of endothelial, or lining, cells) known as capillaries.
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