Path of Blood Through the Heart

Path of Blood Through the Heart
Path of Blood Through the Heart (image: Zoofari, CC 3.0)

The heart is the large muscular organ that pumps deoxygenated blood to the lungs and oxygenated blood to the brain and rest of the body. But, what is the path of blood through the heart? The short answer is that deoxygenated blood from the body enters the right atrium of the heart and the right ventricle pumps it to the lungs. The oxygenated blood returns to the heart, entering the left atrium, while the left ventricle pumps it to the body.

  • The right side of the heart receive deoxygenated blood and sends it to the lungs.
  • The left side of the heart receives oxygenated blood from the lungs and pumps it to the body. This is a big task, which is why the left ventricle is the largest and strongest heart chamber.
  • The valves between the chambers control the flow of blood and prevent it from flowing backwards.

Step-by-Step Path of Blood Through the Heart

Here is the step-by-step flow of blood, including the chambers and valves:

  1. Deoxygenated blood from the body flows to the heart via the superior vena cava and inferior vena cava.
  2. Right atrium
  3. Tricuspid valve
  4. Right ventricle
  5. Pulmonary arteries
  6. The lungs receive deoxygenated blood from the pulmonary arteries and return oxygenated blood to the heart via the pulmonary veins. Remember, arteries carry blood away from the heart, while veins return it to the heart. The blood flow to and from the heart is the only time when arteries carry deoxygenated blood and veins carry oxygenated blood.
  7. Pulmonary veins
  8. Left atrium
  9. Mitral valve
  10. Left ventricle
  11. Aortic valve
  12. The aorta carries oxygenated blood to major arteries that supply the body (and heart itself).

Most diagrams indicated deoxygenated blood in blue and oxygenated blood in red. This makes the flow of blood easier to understand, but keep in mind even deoxygenated blood is actually red.

The Chambers of the Heart

The heart has four chambers. Remember that the right side of the heart deals with deoxygenated blood, while the left side handles oxygenated blood:

  1. Right Atrium:
    • Function: Receives deoxygenated blood from the body through the superior and inferior venae cavae.
    • Significant Details: The right atrium also receives blood from the coronary sinus, which drains deoxygenated blood from the heart muscle. It has a thinner wall compared to the left atrium because the pressure of blood inflow is relatively low.
  2. Right Ventricle:
    • Function: Pumps deoxygenated blood to the lungs for oxygenation via the pulmonary artery.
    • Significant Details: The right ventricle has a shape somewhat like a crescent or a triangular pouch, with a wall thicker than the right atrium but thinner than the left ventricle. This is because it only needs to pump blood to the lungs, not the entire body.
  3. Left Atrium:
    • Function: Receives oxygenated blood returning from the lungs via the pulmonary veins.
    • Significant Details: The left atrium, like the right, has a relatively thin wall. It acts as a holding chamber for blood before it moves to the left ventricle.
  4. Left Ventricle:
    • Function: Pumps oxygenated blood through the aorta to the systemic circulation, supplying organs and tissues throughout the body.
    • Significant Details: The left ventricle has the thickest wall of all heart chambers because it propels blood throughout the entire body. Each pump has to overcome the high systemic arterial pressure. Its circular shape helps it generate powerful contractions.

A Closer Look at the Valves

Just as there are four chambers, there are also four valves. The valves let blood in and then close so it doesn’t go the wrong direction when a chamber contracts.

  • Tricuspid Valve: This valve prevents backflow of blood into the atrium when the ventricle contracts.
  • Pulmonary Valve: This valve prevents backflow of blood into the right ventricle from the pulmonary artery.
  • Mitral Valve: Another name for the mitral valve is the bicuspid valve. This valve also prevents backflow of blood into the atrium.
  • Aortic Valve: This valve prevents the backflow of blood from the aorta into the left ventricle.

Pulmonary, Coronary, and Systemic Circulation

The cardiovascular system includes three types of blood circulation: pulmonary, systemic, and coronary. The phrase “heart circulation” is ambiguous. The path of blood flow through the heart and lungs is pulmonary circulation, while the blood supply to the heart itself is coronary circulation.

  1. Pulmonary Circulation:
    • Purpose: Pulmonary circulation is responsible for oxygenating the blood. It involves the movement of deoxygenated blood from the right side of the heart to the lungs and then returning oxygenated blood to the left side of the heart.
    • Pathway: Blood flows from the right ventricle through the pulmonary artery to the lungs. In the lungs, blood releases carbon dioxide and absorbs oxygen. The oxygenated blood then returns to the left atrium via the pulmonary veins.
  2. Systemic Circulation:
    • Purpose: Systemic circulation distributes oxygenated blood from the heart to all parts of the body and returns deoxygenated blood back to the heart. It provides oxygen and nutrients to tissues and organs and carries away waste products.
    • Pathway: The left ventricle pumps oxygenated blood through the aorta. The aorta branches into many smaller arteries which spread throughout the body. Blood delivers oxygen and collects carbon dioxide, becomes deoxygenated, and returns to the right atrium of the heart via the venae cavae (superior and inferior).
  3. Coronary Circulation:
    • Purpose: Coronary circulation supplies blood to the heart muscle (myocardium) itself. This is crucial because the heart needs a continuous supply of oxygen and nutrients.
    • Pathway: The coronary arteries branch off from the aorta near the point where it exits the heart. These arteries encircle the heart muscle, providing oxygenated blood. The coronary veins collect deoxygenated blood from the heart and drain into the coronary sinus and then back into the right atrium.