What Is the Cardiovascular System? - dummies

What Is the Cardiovascular System?

By David Terfera, Shereen Jegtvig

The cardiovascular system is part of the larger circulatory system, which circulates fluids throughout the body. The circulatory system includes both the cardiovascular system and the lymphatic system. The cardiovascular system moves blood throughout the body, and the lymphatic system moves lymph, which is a clear fluid that’s similar to the plasma in blood.

Blood contains nutrients from the foods you eat and oxygen from the air you breathe. It also contains hormones and cells that fight infection. The blood also transports waste products to various places that then promptly remove the waste from the body.

The parts of the cardiovascular system include the heart, which is the organ that pumps the blood, and a network of blood vessels:

  • Arteries: The blood vessels that take blood away from the heart

  • Veins: Blood vessels that return blood to the heart

  • Capillaries: Very small vessels that lie between the arteries and veins

The portal vein and its tributaries carry blood from parts of the digestive system to the liver before reaching the heart.

The heart is a muscular pump with four chambers inside: the right and left atria and the right and left ventricles. Those four chambers allow the heart to pump blood through the following two circulatory pathways:

  • Systemic circulation: Takes oxygen-rich blood to the tissues and organs of the body

  • Pulmonary circulation: Takes oxygen-depleted blood to the lungs and oxygen-rich blood back to the heart again

Here’s the pathway taken by the blood while it’s in systemic circulation, delivering oxygen-rich blood throughout the body:


  1. The left ventricle of the heart receives oxygenated blood from the left atrium.

  2. Blood is ejected from the left ventricle into the aorta, a large artery.

    The ascending aorta sends blood to the upper thorax, upper extremities, neck, and head.

    The descending aorta sends blood to the lower thorax, the abdomen, the pelvis, and the lower extremities.

  3. The blood leaves the ascending and descending parts of the aorta and enters a network of systemic arteries that run to all places of the body.

  4. Blood passes from the smallest arteries (called arterioles) into the capillary beds. In the capillary beds, blood exchanges oxygen, nutrients, and waste products with the tissues.

  5. The oxygen-poor blood leaves the capillary beds via small veins (called venules) and drains into a network of systemic veins that eventually lead to the venae cavae (either of the two large veins leading into the heart).

    The superior vena cava receives blood from the upper thorax, head, neck, and upper extremities.

    The inferior vena cava receives blood from the lower thorax, the abdomen, the pelvis, and the lower extremities.

  6. The venae cavae empty the oxygen-poor blood into the right atrium of the heart.

After systemic circulation, the blood in the right atrium is depleted of oxygen, so it needs to go to the lungs to exchange carbon dioxide for oxygen. The pathway from the heart to the lungs and back to the heart is called pulmonary circulation, and it takes the following path:

  1. The right ventricle receives the oxygen-depleted blood from the right atrium.

  2. The blood leaves the right ventricle and enters the pulmonary trunk, which splits into two pulmonary arteries.

  3. The pulmonary arteries lead to the lungs, where exchange of gases takes place. Carbon dioxide is removed from the blood, and oxygen enters the blood.

  4. Blood leaves the lungs via the pulmonary veins.

    The pulmonary veins carry freshly oxygenated blood to the heart while the systemic veins carry oxygen-poor blood to the heart.

  5. The oxygenated blood enters the left atrium of the heart.

    The blood in the left atrium moves into the left ventricle and enters the systemic circulation.

A number of problems can be classified as cardiovascular disease. The problems can occur after a person has developed atherosclerosis, also known as “hardening of the arteries,” which results in decreased blood flow because the blood vessels are plugged. It occurs when fat, cholesterol, and calcium build up within the walls of the arteries. These build-ups, called plaques, can block the arteries and reduce the flexibility of the arterial walls. Atherosclerosis is common in older people, especially in those who have high blood pressure, are diabetic, have high cholesterol, eat too much saturated fat, drink too much alcohol, smoke, don’t get enough exercise, and are overweight or obese. Blood clots can also form in the diseased vessels and stop blood flow completely, depriving tissues of oxygen.

Heart attacks (myocardial infarcts) occur when blood flow to some part of the heart is blocked, causing damage to part of the heart. Arrhythmia is a problem with the heart rhythm; the heart may beat too slow, too fast, or irregularly.

Cardiovascular disease can affect the brain as well. Ischemic strokes happen when a blood vessel in the brain is blocked. Hemorrhagic strokes occur when a blood vessel in the brain breaks open. Either type of stroke can result in damage to a part of the brain.