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How the Heart Pumps Blood
the Heart Pumps Blood
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The heart is a muscular pump that keeps blood moving through the body every minute of life. It sends oxygen-poor blood to the lungs and oxygen-rich blood to the organs, tissues, and brain. This circulation delivers oxygen and nutrients while carrying away carbon dioxide and wastes. Understanding how the heart pumps helps explain blood pressure, pulse, exercise response, and many common medical conditions.
The pumping cycle depends on four chambers, four valves, and an electrical timing system. Blood moves from atria to ventricles, then out through major arteries because pressure changes open and close valves in one direction. The right side of the heart pumps blood to the lungs, while the left side pumps blood to the entire body. Each heartbeat is a coordinated cycle of filling, contraction, and relaxation called the cardiac cycle.
Key Facts
- The right atrium receives oxygen-poor blood from the body through the superior and inferior vena cava.
- The right ventricle pumps oxygen-poor blood to the lungs through the pulmonary artery.
- The left atrium receives oxygen-rich blood from the lungs through the pulmonary veins.
- The left ventricle pumps oxygen-rich blood to the body through the aorta.
- Cardiac output = heart rate x stroke volume.
- Blood pressure is commonly written as systolic pressure over diastolic pressure, such as 120/80 mmHg.
Vocabulary
- Atrium
- An atrium is one of the two upper heart chambers that receives blood returning to the heart.
- Ventricle
- A ventricle is one of the two lower heart chambers that pumps blood out of the heart.
- Valve
- A valve is a flap-like structure that keeps blood flowing in one direction through the heart.
- Systole
- Systole is the phase of the heartbeat when the ventricles contract and push blood into the arteries.
- Diastole
- Diastole is the phase of the heartbeat when the heart muscle relaxes and the chambers fill with blood.
Common Mistakes to Avoid
- Thinking arteries always carry oxygen-rich blood. This is wrong because pulmonary arteries carry oxygen-poor blood from the heart to the lungs.
- Confusing the right and left sides of the heart in a diagram. This is wrong because diagrams often show the patient’s right side on the viewer’s left.
- Saying valves actively pump blood. This is wrong because valves open and close due to pressure differences, while the heart muscle provides the pumping force.
- Treating the heart as one simple pump. This is wrong because the right and left sides are separate pumps connected in series through the lungs and body.
Practice Questions
- 1 A student has a heart rate of 75 beats per minute and a stroke volume of 70 mL per beat. Calculate the cardiac output in mL per minute and L per minute.
- 2 During exercise, a person’s heart rate rises to 150 beats per minute and stroke volume rises to 100 mL per beat. What is the cardiac output in L per minute?
- 3 Explain why the wall of the left ventricle is thicker than the wall of the right ventricle, even though both chambers pump the same amount of blood per heartbeat.