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.
Key Takeaways: Path of Blood Through the Heart
- Blood flows through the heart in a loop from body → heart → lungs → heart → body.
- The right heart pumps deoxygenated blood to the lungs.
- The left heart pumps oxygenated blood to the body.
- Valves ensure one-way blood flow through the heart.
- Pulmonary, systemic, and coronary circulation describe different parts of blood flow.
Step-by-Step Path of Blood Through the Heart
Here is the step-by-step flow of blood, including the chambers and valves:
- Deoxygenated blood from the body flows to the heart via the superior vena cava and inferior vena cava.
- Right atrium
- Tricuspid valve
- Right ventricle
- Pulmonary arteries
- 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.
- Pulmonary veins
- Left atrium
- Mitral valve
- Left ventricle
- Aortic valve
- 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.
| Feature | Right Side (Pulmonary) | Left Side (Systemic) |
|---|---|---|
| Receives Blood From | Body (Venae cavae) | Lungs (Pulmonary veins) |
| Type of Blood | Deoxygenated | Oxygenated |
| Sends Blood To | Lungs (via pulmonary arteries) | Body (via aorta) |
| Valve | Tricuspid → Pulmonary | Mitral → Aortic |
| Chamber Thickness | Thinner walls | Thickest walls |
Tips for Remembering the Order
Mnemonic devices help make remembering the order easier:
Mnemonic: Try Pulling My Aorta
T – Tricuspid
P – Pulmonary
M – Mitral
A – Aortic
(Order of valves in the blood flow path)
Or:
“RA → RV → Lungs → LA → LV → Body” (Right Atrium to Right Ventricle to Lungs…)
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:
- 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.
- 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.
- 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.
- 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.
- 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.
- 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).
- 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.
Frequently Asked Questions (FAQs)
Q: Which side of the heart has oxygenated blood?
A: The left side of the heart contains oxygenated blood. It receives blood from the lungs and pumps it to the rest of the body.
Q: Why is the left ventricle thicker than the right ventricle?
A: The left ventricle has the thickest muscular wall because it must pump blood throughout the entire body, requiring greater force and pressure than the right ventricle, which only pumps blood to the lungs.
Q: What keeps blood from flowing backward in the heart?
A: Four heart valves (tricuspid, pulmonary, mitral (bicuspid), and aortic) act as one-way gates, ensuring that blood flows in the correct direction and does not move backward during heart contractions.
Q: Do arteries always carry oxygenated blood?
A: No. Arteries carry blood away from the heart, while veins carry it toward the heart. The pulmonary arteries carry deoxygenated blood to the lungs, and the pulmonary veins carry oxygenated blood to the heart. This is opposite of the usual pattern.
Q: Where does blood go after it leaves the aorta?
A: Blood leaving the aorta enters systemic circulation, traveling through arteries that branch into arterioles and capillaries to deliver oxygen and nutrients to the entire body.
Q: What is the first chamber of the heart that blood enters?
A: Blood returning from the body enters the right atrium first, through the superior and inferior vena cava.
Q: How does the heart get its own blood supply?
A: The heart receives oxygenated blood through the coronary arteries, which branch off from the base of the aorta. Deoxygenated blood from the heart muscle returns via coronary veins into the right atrium.
Q: Is all blood red?
A: Yes, all human blood is red due to hemoglobin. Oxygenated blood is bright red, while deoxygenated blood is darker red. Diagrams use blue to represent deoxygenated blood for clarity, but it’s not actually blue in the body.
References
- Fuster, V; Alexander RW; O’Rourke RA (2001). Hurst’s The Heart (10th ed.). McGraw-Hill. ISBN 0-07-135694-0.
- Guyton, Arthur; Hall, John (2000). Guyton Textbook of Medical Physiology (10th ed.). ISBN 978-0-7216-8677-6.
- Iaizzo, Paul A (2015). Handbook of Cardiac Anatomy, Physiology, and Devices. Springer. ISBN 978-3-31919464-6.
- Mcconnell, Thomas H.; Hull, Kerry L. (2020). Human Form, Human Function: Essentials of Anatomy & Physiology (Enhanced ed.). Jones & Bartlett Learning. ISBN 978-1-28-421805-3.