Blood Flow in the Heart – MCAT Biology | MedSchoolCoach

Blood Flow in the Heart

MCAT Biology - Chapter 7 - Section 4.3 - Organ Systems - Circulatory System
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Sample MCAT Question - Blood Flow in the Hearth

Blood entering the right ventricle from the right atrium goes through which valve?

a) Tricuspid valve

b) Aortic valve

c) Mitral valve

d) Pulmonary valve

A is correct. The tricuspid valve.


The blood enters the heart from the superior and inferior vena cava, into the right atrium. From the right atrium, blood travels through the tricuspid valve, into the right ventricle, and heads towards the lungs. From the lungs, blood travels back into the left atrium through the mitral valve, and into the left ventricle. After this, it is expelled into the rest of the body, eventually returning by venous circulation back into the heart.

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Blood Flow in the Heart Intro

The heart is responsible for pumping blood throughout the body. For the MCAT exam, understanding the pathway of blood through the heart is important. Figure 1 illustrates the structure of the heart, its significant anatomy, and the pathway of blood flow. Briefly put, blood flow through the heart follows this path: systemic circulation → right atrium → right ventricle → pulmonary circulation (where it is re-oxygenated) → left atrium → left ventricle → systemic circulation.

Circulation of blood through the heart's right atrium, right ventricle, left atrium, and left ventricle
Figure 1. Blood Flow through the Heart

Systemic Circulation → Right Atrium

Blood first enters the heart through the superior and inferior vena cava. These blood vessels carry deoxygenated blood from the systemic circulation to the heart. Both the inferior and superior vena cava empty into the right atrium

Right Atrium → Right Ventricle

From the right atrium, the blood is pumped into the right ventricles, passing through the right atrioventricular valve, aka the tricuspid valve. The heart has a number of these valves to prevent the backflow of blood. For example, when the right ventricle contracts, the tricuspid valve prevents the blood from shooting back into the right atrium. 

Right Ventricle → Pulmonary Circulation → Left Atrium

With the tricuspid valve closed, the blood can move into the pulmonary artery. Once again, the pulmonary artery has a valve called the pulmonary valve that prevents the backflow of blood back into the right ventricle. From the pulmonary artery, the deoxygenated blood will reach the lungs where gas exchange occurs. At this point, the blood becomes oxygenated. Afterward, it will move through the pulmonary veins into the left atrium of the heart.

Left Atrium → Left Ventricle

 From the left atrium, the oxygenated blood will travel to the left ventricle, passing through the left atrioventricular valve. This valve is also known as the bicuspid or mitral valve. Like the tricuspid valve, the bicuspid valve also prevents the backflow of blood from the ventricle to the atrium. 

Left Ventricle → Systemic Circulation

When the left ventricle contracts, blood is pushed into the aorta and then to the rest of the body. Similar to the pulmonary artery, the aorta has a valve, called the aortic valve, that prevents the backflow of blood.

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