a submarine searches with spotlights in the dark of a lung

Let’s Discuss Lung Anatomy

Heart failure is primarily a heart disease, yet it can sometimes affect your lungs too. Plus, lung diseases can also affect your heart. So I thought it would be neat to discuss a little lung anatomy. So, let's begin!


In the air around us are molecules of oxygen. They are the essential molecules of life. They are inhaled into your lungs and are then transported to all the tissues of your body by your arteries.

Oxygen is then used by all the cells of your body to make energy. This energy allows your cells to do whatever their jobs are which is how we stay alive. This process of cells using oxygen to make energy is called cellular respiration.1-2

What next?

Take a deep breath. There! You just inhaled a lot of air, which includes lots of oxygen molecules. So what happens to these oxygen molecules? Let’s just take a second here to attach the smallest camera in the world to one oxygen molecule. We’ll go in slow motion here as this molecule travels through your airway.

It passes the opening in your nostril. It passes through tiny hairs (that look huge by the view from our fake camera). These hairs are important in that they filter the air you inhale. This is the immune system's first line of defense to keep inhaled germs and particles out of your lungs.3-5

Traveling on

Now our molecule travels by turbinates. These are the bony structures we now see on the lateral walls inside our nasal passages. These are neat structures in that they act as humidifiers and heaters. This is important because cool and dry air can be harmful to your lungs. So, they humidify and warm inhaled air to body temperature (98.6 degrees F. and 36 degrees C).3,4

Mouth breathing

The passage behind the nasal cavity is called the nasal pharynx. It meets up with the oral pharynx, which collects air you inhale through your mouth. Note, the air you breathe in through your mouth is still warmed and humidified, but this effect is much enhanced if you inhale through your nose. The mouth generally should only be used for breathing when we are talking or exercising. I suppose another reason is if you have a stuffy nose.3-4

Trachea and windpipe

The pharynx carries are to your trachea. Surrounding the trachea are c-shaped rings made of cartilage. These rings prevent the trachea from collapsing when you breathe out. If you feel your neck, you can feel these rings.3-4

Inside the trachea, our molecule travels through your vocal cords. Another term for this is windpipe. Along with the rest of your upper airway, it is lined by mucus membranes. These produce mucus to trap and kill harmful substances. This is part of an ongoing defense mechanism to keep your lungs clean and sterile.3-6

Inside your lungs

At the end of the trachea there is a fork in the road, so to speak. Our molecule can either go right or left. This fork is called the carina. It is where our molecule can take a path to your right lung or your left lung.3-5

Our molecule travels right, toward your right lung. Inside your lungs are many passages (of course, the same is true of your left lung). After the carina, our molecule travels through the largest airways. These are called bronchi (bronchus). They are also surrounded by cartilage. These branch out into smaller and smaller airways, kind of like the branches of a tree.

From here, airways get smaller and smaller. After the bronchus, airways are no longer surrounded by cartilage. Instead, wrapped around airways are smooth muscles. Sometimes these muscles can spasm and cause an illness called asthma.


Our molecules travel to the smallest airways which are called bronchioles. These get smaller and smaller and like branch-like too. The smallest bronchioles are called terminal bronchioles. To put this into perspective, there are over 16,000 terminal bronchioles. The opening inside these airways is very tight, although our oxygen molecule flows easily through them. The internal diameter of these passages is only 700 μm.4

These get even smaller and turn into respiratory bronchioles. To put them into perspective, they are only .04 mm in diameter. Both terminal and respiratory bronchioles come into contact with alveoli.4


Now we enter the alveoli. Respiratory bronchioles attach to alveoli. These are small balloon-like structures that expand when you inhale. They naturally recoil when you exhale. In a sense, they are kind of like tiny balloons. When you look from the outside you can see alveoli are clumped together and look like grapes.3-5

So our molecule enters alveoli. This is where gas exchange occurs. As we look at the surfaces of the alveoli, we can see carbon dioxide (CO2) molecules entering the alveoli. CO2 is a waste product of cellular metabolism. We watch as it goes up the way our molecule came.3-5

Into the bloodstream

Our molecule then travels through the walls of the alveoli and we enter into the bloodstream. Here our molecule hops onto what looks like a purple inner tube. This inner tube is actually a hemoglobin molecule. Once we hop onto it, the inner tube turns to a bright red color. As you can see, it is oxygen that turns blood that bright red color.3

The smallest blood vessels are called capillaries. Tiny blood vessels attach to all the alveoli inside your lungs. From capillaries, we watch as our molecule travels through your arterial system. Arteries are blood vessels that carry oxygen molecules to all the tissues of your body. Our oxygen molecule will travel through this arterial blood until it finds a cell.3-4

Wrapping it all up

COPD causes airways to become abnormally narrow. Pulmonary fibrosis causes alveolar walls to become stiff.  Both can make it hard to breathe. And, over time, both may contribute to heart failure.

Heart failure flare-ups may cause pulmonary edema. This is where fluid seeps from your capillaries into your alveoli which makes it hard to breathe. I think it’s nice to know a little about lung anatomy - any questions?

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