How the Heart and Lungs Work Together

by John Bottrell Health Professional

Pulmonary (lung) and cardiovascular (heart and circulation) health are closely tied because they work as a team to oxygenate the cells and tissues of your body. This is why it’s so important for people with chronic obstructive pulmonary disease (COPD) to understand how both systems work.

Your lungs, as you probably know, are a pair of highly elastic and spongy organs that sit inside your chest on either side of your heart. They are the main organs of respiration, or breathing. They allow you to take in air from the atmosphere, and provide a platform for which oxygen can get from the air into your bloodstream.

You have two lungs:

  • Right Lung: Consists of an upper, middle and lower lobe

  • Left Lung: Consists of an upper and lower lobe. It has only two lobes in order to make room for the heart.

Your heart is a muscle the size of your fist that sits in the center of your chest, although it’s skewed toward the left. It has four chambers:

  • Left Atria

  • Left Ventricle

  • Right Atria

  • Right Ventricle

Just as you have two lungs, you have two hearts:

  • Left Heart: Consists of the Left Atria and Left Ventricle

  • Right Heart: Consists of Right Atria and Right Ventricle

How Breathing Oxygen Works

To help me show how these two systems work together to keep you alive, pretend that you are an oxygen molecule. Here, let me shrink you down to size. There Now you are smaller than a speck of dust.

The wind catches you, and you are inhaled by a person (you don’t know who), and you make your way to the lungs as I describe in my post Your Journey Down the Respiratory Tract.

Once in the lungs, you make your way to the bloodstream. Here, you catch a ride on a cell that looks kind of like a purplish-blue inner-tube called a red blood cell (RBC), or an erythrocyte. On this RBC is a hemoglobin molecule, and it attracts you to it, attaching you securely like a seat belt. When this happens, the RBC turns from a purplish-blue color to bright red.

Looking around, you watch as many oxygen molecules cross over from the lungs to RBCs, turning the blood red. But you are moving fast, and quickly find yourself in a pulmonary vein that takes you inside the heart.

You are now inside the left atrium. In this chamber blood collects quickly. The walls appear very relaxed, and as more blood pools these walls expand. When they contract, you shoot through a valve called the Mitral Valve. Now you find yourself inside the left ventricle.

The left Ventricle is the largest chamber in the heart, and it is also the strongest. This is necessary because it’s job is to send freshly oxygenated blood to every part of the body except through the lungs. A ton of blood pools up around you, and all of a sudden… WHOOSH! You are shot like a bullet through the Aortic Valve into the Aorta.

The aorta is a large artery, the largest in the body. This is necessary because a lot of blood is forced through this vessel with a very strong force by the left ventricle. You now travel through a series of vessels called arteries. Arteries are strong vessels that carry oxygenated blood to the various tissues of the body, including all the major organs: heart, lungs, brain, kidneys, stomach, intestines, and liver.

While other oxygen molecules jump off along the way, you travel through a series of arteries that take you all the way up to the brain. The hemoglobin lets go of you, turning the RBC to a bluish-purple color again. That RBC will head back to the right heart, along with the rest of the unoxygenated blood, to pick up another oxygen molecule, and the cycle will continue.

In the meantime, you enter a brain cell. Here you participate in cellular respiration, a complex series of chemical reactions that allows the cell to release energy from food. This energy is needed for that cell to do its job to keep the brain thinking.

If you look at this on a larger scale, millions of oxygen molecules enter your body every time you breathe in. It keeps your brain thinking, heart pumping, intestines digesting, and kidneys filtering and removing waste. It’s used by all the cells of your body to keep you alive.

How the Body Removes Carbon Dioxide

Cellular respiration also produces a waste product called carbon dioxide, or CO2. It must be removed from the cell, and then exhaled by the lungs. The heart also plays a role in removing this waste product from your body. To help me explain this, I want you to pretend you are a CO2 molecule.

As an RBC passes the cell, an empty hemoglobin molecule attracts and attaches you to it. You are now riding through the venous system, which contains unoxygenated blood on its way back to the right heart and then to the lungs to pick up oxygen.

You are a long way from the mighty force of the left ventricle, so the blood pressure here is low, so you are moving along slowly. You have time to observe the blood around you is a purplish-blue color, the color of RBCs not carrying oxygen (if you look at your hands and arms you should see veins).

As you get close to the heart you see the tricuspid valve. It opens and you enter the heart once again, only this time you are in the right atrium, or the smallest chamber of the heart. As blood collects the walls of the right atria expand, and then contract, forcing you through a valve called the pulmonary valve.

You are now inside the fourth chamber of the heart, this one is called the right ventricle. This ventricle is smaller than the left ventricle because it only has to push blood through the lungs. In a healthy person, not much force, or pressure, is needed for this job.

As blood continues to enter the right ventricle, the walls expand, and then the walls contract, and -- SWOOSH! -- you are shot into the lungs. Here, you exit the bloodstream and into an alveolar air sac, through a series of pipes in the lungs that get larger and larger until (voila) you are exhaled through the mouth or nose.

There! Now you can be the full size you are again.

How the Heart Works

If you place your ear, or your stethoscope, on a person’s chest over the heart, you will hear the sounds of the heart. The sound is normally described as lub dub. The lub is heard when the atria expand and contract, and the dub when the ventricles expand and contract. You should hear a lub dup (a heartbeat) about once a second.

So, on your journey you saw that the heart is a muscle that relaxes and contracts. When the heart relaxes it’s called diastole, and this is when blood enters the heart. During this time the walls expand as more and more blood enters.

When the walls contract, this is called systole. During systole, blood in the atria is forced into the ventricles (lub), and blood in the ventricles is forced through the entire body (dup).

Another neat thing about the heart is it works completely independent of your brain. In fact, you could actually be brain dead and your heart will keep beating. This is because your heart has its own pacemaker, specialized cells in the upper part of the right atria called the Sinoatrial Node (SA Node).

When these cells fire, they set off an electrical charge. It causes the right atria to contract first, and then the left atria a split second later. The charge then travels to the ventricles, which contract at about the same time. A normal heart beats 60-100 times every minute.

So, now you have an understanding of how the heart and pulmonary system work together to oxygenate the body and keep it working.

In my next post I will describe how the natural progression of a disease like COPD might damage this system.

If you'd like more informaion, The Mayo Clinic has a great video showing how the heart and circulatory system work together: “Heart and Circulatory System.”

John Bottrell
Meet Our Writer
John Bottrell

John Bottrell is a registered Respiratory Therapist. He wrote for HealthCentral as a health professional for Asthma and Chronic Obstructive Pulmonary Disease (COPD).