The cardiovascular system is the best known of the heart-centered processes in the body. Its actual functions are sometimes confused with other cardiac systems, and thus may be misunderstood. While sometimes characterized as including all of the organs involved in the entire relationship between the heart and the body, the cardiovascular system is the circulatory system, composed of the heart and the network of blood vessels that it anchors. The cardiovascular is the body's distributor of oxygen and nutrients, as well as the mechanism for waste transport.
Consistent with its primary function, the efficient circulation of blood, the cardiovascular system is interconnected with two other heart-centered systems: the cardiopulmonary system, which controls the relationship between the heart and the lungs, and the cardiorespiratory system, the interrelationship between the heart and the general breathing mechanisms in the body, including the exchange of oxygen and carbon dioxide that occurs within the lungs.
The cardiovascular system is a complex and extensive network. The circulatory process begins with a pump action in the heart muscle, known familiarly as the heart beat. Each beat is a two-part action, the timing of which is regulated by the heart component known as the SA node, whose function is in turn tied to brain signals. The first part of each beat is the longer diastole, and the second is the shorter systole. Blood pressure in the circulatory system is calculated as a function of the two components of the pulse and the resistance of the arterial wall.
Each beat sends a quantity of nutrient-rich, oxygenated blood into the channels known as arteries. The arteries are relatively thick walled and highly flexible cylinders, encased in a ring of muscle. As the pumping action of the heart creates pressure in the artery through the flow of blood, the arterial walls are constructed to contract and thus slow the rate of blood as it travels through the artery.
The arteries ultimately narrow into arterioles. These become the tiny capillaries, which are the system's exchange point for actual transfer of oxygen and nutrients to individual muscle and organ cells, and the corresponding receipt of waste carbon dioxide. The carbon dioxide is then transferred into small veins known as venules. The venules lead to larger veins; as the vein is not constructed with any muscle to regulate propulsion of blood through it, the blood travels more slowly on its return to the heart. Near the heart, the blood enters the pulmonary artery, located on the right side of the heart, which directs the blood to the lungs to be recharged with oxygen. The blood is then pumped back into the cardiovascular system from the left side of the heart.
The fluid components of blood is called plasma and is comprised of more than 90% water. The erythrocytes, or red blood cells, are the organisms in the blood that carry the chemical hemoglobin, and are thus able to transport oxygen. Red blood cells are manufactured at a rate of two million per second from the bodily stores of bone marrow. Fluid replacement during exercise has the important effect of maintaining proper blood volume, which permits the efficient transport of oxygen.
Approximately 25% of the body's blood is filtered through the kidneys, the organs that purify the blood as it is directed through the cardiovascular system. Some fluid waste products and toxins are extracted by the kidneys and secreted into the bladder as urine, which is passed from the body.
The cardiovascular system is generally the most important of the heart-centered physical systems to athletic performance. While athletes can often significantly improve muscular strength and endurance in every form of athletic activity through rigorous training, the level of improvement in cardiac output will dictate the ultimate level of the athlete's success. Cardiac output is defined as the amount of blood that the heart can pump per minute. The greater the cardiac output, the greater the number of red blood cells available to transport oxygen to working muscles, essential to the generation of muscle energy.
Diet and physical activity are the crucial factors to general cardiovascular health. The heart, like any muscle, requires the stimulation and muscle building of exercise to maintain heart health. The walls of the heart will grow as a result of exercise. Diets that are not a healthy mix of carbohydrates, proteins, and fats (usually consumed in the general ratio of (60-65% carbohydrates, 15-20% proteins, and 25% fats) typically lead to excess weight, which puts a strain on heart function. Diet, especially if it is high in fats, or the athlete smokes cigarettes, can cause a buildup of plaque in the arteries. This causes both a narrowing of the channel, known as stenosis, or the hardening and thickening of the artery, the condition known as arteriosclerosis. The unhealthy artery also presents the risk that the plaque material may break off and cause a clotting of the vessel, which blocks the flow of blood to the heart. This condition is known as a stroke, and it is often fatal. If heart function loss occurs from the stroke, the result may be damage to vital organs such as the brain.