Every day, you walk or do some physical activity. But have you ever wondered how all your cells get oxygen?

Your heart is one of the most important organs in your body. The heart pumps about five liters of blood per minute (about the total amount of blood in your body). How? What pathway does the blood take throughout the heart? Well, you’re about to find out!

The heart has two upper atria and two lower ventricles (a total of four chambers).

Right Atrium (First Chamber)

Blood that needs oxygen arrives at the right atrium through large blood vessels which are the superior and inferior vena cavas (these blood vessels are veins because they carry deoxygenated blood to the heart so the blood can get oxygenated via the lungs, while arteries carry oxygenated blood away from the heart and to the rest of the body).

Right Ventricle (Second Chamber)

The right atrium then contracts and squeezes the deoxygenated blood through the tricuspid valve and into the right ventricle.

How Does the Deoxygenated Blood Get Oxygenated?

After the right atrium contracts and squeezes the blood into the right ventricle through the tricuspid valve, the right ventricle contracts and squeezes (with about 25 mmHg of pressure) the deoxygenated blood through the pulmonic valve (also called pulmonary valve) and into the pulmonary artery.

The blood then travels down the pulmonary artery and arrives at the lungs, near the alveoli (small sacs present in the lungs that are responsible for storing oxygen for the body and at the same time taking in carbon dioxide from the blood to release it every time we breathe out), “picking up” oxygen molecules, making the deoxygenated blood oxygenated.

So now, our deoxygenated blood finally has oxygen, thanks to our lungs and alveolar sacs. Hurray! But how does the rest of our body receive the oxygenated blood? To answer this question, lets talk about the left side of our heart.

Left Atrium (Third Chamber)

The oxygenated blood now leaves the pulmonary artery and enters the pulmonary vein, arriving at the left atrium (this is the only time where blood travels away from the heart to get oxygen through an artery and travels back to the heart with oxygen through a vein).

Left Ventricle (Fourth Chamber)

The left atrium then contracts and squeezes the oxygenated blood through the mitral valve (also called bicuspid valve) and into the last chamber of the heart called the left ventricle.



How Does the Left Ventricle Deliver the Oxygen Rich Blood to the Rest of the Body?

The left ventricle will now contract and squeeze at a high pressure (around 120 mmHg, the systolic number, which is the top number of your resting blood pressure). The oxygenated blood will rush through the aortic valve and will exit via the aorta, causing the oxygenated blood to travel throughout the body and to provide all your oxygen depleted cells with oxygen and other important nutrients. Again, once the oxygenated blood is “out of oxygen” after delivering its oxygen throughout the body, the once oxygenated and now deoxygenated blood will arrive at the right atrium through the superior/inferior vena cavas to get oxygenated and this ongoing cycle will continue.

How Does the Heart Get Oxygen Rich Blood?

That’s a good question. Your heart is a muscle and it needs oxygen just like any other cell in your body to function efficiently.

When the oxygenated blood gets pumped via the left ventricle and aorta, some of the oxygen rich blood also gets pumped and enters into the coronary arteries (arteries present in the heart) which deliver the oxygenated blood to the myocardium (heart muscle cells) and other cardiac cells that need oxygen and other important nutrients.

Once the oxygenated blood delivers its oxygen to different parts of the heart, the blood now becomes deoxygenated and enters the coronary sinus (veins present in the heart), which delivers the deoxygenated blood to the right atrium to get oxygenated again and this fascinating cycle repeats itself.

When Do the Atria and Ventricles Contract?

Keep in mind that the left and right atria contract together and the left and right ventricles contract together via the internal pacemaker (sinoatrial node, bundle of nerve cells that serve as the starting point of the internal pacemaker) which starts at the right atrium. So, as explained above, the deoxygenated blood “sits” in the right atrium and oxygenated blood “sits” in the left atrium. Then, both the left and right atria squeeze together sending the blood to the left and right ventricles. Now the right ventricle contains deoxygenated blood and the left ventricle contains oxygenated blood. Together, both ventricles contract. The right ventricle sends the deoxygenated blood through the pulmonary artery and to the lungs so the deoxygenated blood can get oxygenated. At the same time, the left ventricle sends the oxygenated blood to the aorta and out to the the rest of the body.

So What Controls the Blood Flow Between the Chambers of the Heart?

Now that you have read about the pathway our blood takes throughout the heart and to the body, you are probably wondering what controls the back flow of blood into other chambers of the heart. Our cardiac valves control the direction of blood flow within our heart. Our papillary muscles and chordae tendineae, (the papillary muscles and chordae tendineae are located in the left and right ventricles since both the ventricles, especially the left ventricle, contract at relatively high pressures) make sure that both the mitral valve and the tricuspid valve open and close in a proper and uniform manner, preventing any back flow of blood into the left and right atria when the ventricles contract. The pulmonic and aortic valve, however, open and close when blood leaves the ventricles, preventing regurgitation back into the ventricles (for example when the ventricles contract, the pulmonic valve and the aortic valve open to let the blood through and then close tightly, so no regurgitation of blood occurs into the ventricles). All four cardiac valves respond to changes in pressure between the four chambers of the heart. Just before the ventricles contract, the pressure rises. This rise in pressure causes the tricuspid and mitral valves to “shut” immediately so no blood would “sneak” back into the left and right atria.

Let’s Look at an Example

For instance, when blood sits in the bottom two ventricles (left and right ventricles), the tricuspid valve (the valve that allows deoxygenated blood through and into the right ventricle when the right atrium contracts) and the mitral valve (the valve that allows oxygenated blood through and into the left ventricle when the left atrium contracts) “slam” shut, right before the left and right ventricles contract, thanks to our papillary muscles and chordae tendineae present in both our left and right ventricles (if you need to, refer to the first picture to remind yourself where the heart chambers and valves are located). The closing and opening of these valves (tricuspid and mitral valves) at certain vital moments prevent the regurgitation (backflow of blood into certain chambers of the heart due to a certain valve or even more than one valve not functioning properly) of blood into the left and right atria.

This extremely important system of the closing and opening of our atrioventricular (tricuspid and mitral) and semilunar (pulmonic and aortic) valves and the proper, discipline function of our papillary muscles/chordae tendineae is necessary for normal heart function.

The heart is phenomenal and extremely efficient. And of course, your heart is vital for survival. The heart has many more important functions that are necessary for human survival. So make sure to love your heart by making healthy lifestyle choices such as exercise and choosing a heart-healthy diet! Obviously, genetics plays a role in heart health and in thousands of other important factors, but you can make a big difference by committing too many healthy lifestyle choices.

Author: Rishav Sinha