Circulatory System of the Human Body

The human circulatory system, also called the human cardiovascular system, functions as the delivery truck and the garbage truck. The word cardiovascular comes from the Greek word "kardia," meaning heart, and the Latin word "vasculum," meaning small vessel. The heart, blood and blood vessels make up the cardiovascular system, with help from the lungs and kidneys.

  1. Blood

    • Blood consists of red and white blood cells sitting in plasma (the liquid portion). Around 91.5 percent water, plasma helps conduct heat through the body. The blood cells carry oxygen and nutrients to the body's cells and then remove carbon dioxide and waste. An average human male has about 1.5 gallons of blood, while an average female has only 1.2 gallons. Blood makes up roughly 8 percent of the body's weight.

    The Heart and Coronary Circulation

    • Coronary circulation refers to blood flow inside the heart. This cone-shaped muscular organ is responsible for pumping blood to the entire body. The heart weighs about 10.5 oz. and pumps over 100,000 times a day. The heart has two sides (left and right), each having two chambers, an atrium on top and a ventricle on bottom. The right side handles incoming carbon dioxide-rich blood, and the left handles outgoing oxygenated blood.

    Blood Vessels and Systemic Circulation

    • Blood vessels form a tube system that carries blood to all parts of the body, called systemic circulation. This system consists of veins, capillaries and arteries. Arteries move oxygen-rich blood away from the heart, while veins move carbon dioxide-rich blood to the heart. Arteries leave the heart and branch into smaller vessels called arterioles. Arterioles split into microscopic capillaries inside muscle tissue. The blood exchanges substances with cells through the capillary walls. After depositing nutrients and picking up waste, blood collects into venules (small veins) then into larger veins before returning to the heart.

    The Lungs and Pulmonary Circulation

    • Pulmonary circulation refers to the movement of blood from the heart to the lungs and back. Waste-rich blood fills the right atrium, then the atrium contracts, sending the blood to the right ventricle. When the right ventricle fills up, it contracts, pushing the blood into the pulmonary artery toward the lungs. The blood flows into capillaries in the lung tissue where cells give up carbon dioxide and pick up oxygen. The newly oxygen-rich blood returns through pulmonary veins to the left atrium of the heart. The full left atrium contracts, pushing the blood into the left ventricle, then the left ventricle contracts pushing the blood into the aorta and out into the body.

    Kidneys, Liver and Systemic Circulation

    • A renal circulation is the path of the blood through the kidneys. The kidneys remove waste elements, other than carbon dioxide, from the blood. Portal circulation means the path of the blood through the small intestine, where it collects in the portal vein and passes to the liver. The liver filters sugars from the blood and keeps them stored for later.

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