How the Lungs Work

Our cells get oxygen through a process called respiration. The process is carried out by specialized organs, tissues, and cells in our bodies. These parts, working together, make up the respiratory system. In the respiratory system, air becomes the oxygen that fuels the body’s cells. Our cells, which are the body’s building blocks, need this oxygen for energy and growth. Without it, the cells would die.

The stars of the respiratory system are the lungs. In the lungs, air from outside the body gets filtered, and oxygen gets passed on to the body.

Healthy lungs are important for your overall health. In 2022, lung cancer was the leading cause of death worldwide. According to the Lung Cancer Research Foundation, lung cancer kills almost three times as many men as prostate cancer, and almost three times as many women as breast cancer.

A Closer Look at Your Lungs

Think about an empty plastic two-liter soda bottle. Now imagine 7,500 of those bottles. That’s 15,000 liters. According to the American Lung Association, that’s how much air our lungs take in each day. It breaks down to about 6 to 10 liters of air per minute.

Lungs have a very delicate, spongy texture. They weigh between about 1.25 and 1.37 pounds (between 567 and 625 g). Lungs are not dense; they are the only organs in your body that float on water.

Lungs are not dense, but they are relatively large. Your two lungs take up most of the space in your thoracic cavity (chest). Your left lung is slightly smaller than your right lung. Your left lung lies within the chest cavity, just to the left of your heart. Your right lung is just to the right of the heart. Your heart and its major blood vessels are separated from your lungs by protective tissue called the pericardium.

The Lungs View Larger Image © Superstock, Inc.

Each lung is divided into lobes, or sections, by deep, rounded grooves called fissures. The right lung has three lobes, while the left has only two. The top part of each lung is referred to as the apex. The apex is located just behind your collarbone. The flat bottom of the lung is referred to as the base. The bases of your lungs sit on your diaphragm, an important muscle used in breathing.

Surrounding the lungs on their outer surfaces are two layers of tissue called pleurae. The innermost layer of tissue, which attaches to the lungs, is known as the visceral pleura. The outer layer, which lines the internal chest walls, is called the parietal pleura. A narrow open region called the interpleural space separates the two pleural layers. The space is filled with a slippery fluid, which acts like a lubricant, allowing the pleural layers to slide over each other. At the same time, this pleural fluid causes the two layers to cling to each other. This means the lungs essentially cling to the internal walls of the chest. When your chest expands, such as when you begin to take a breath of air, your lungs expand, too.

Air Moving In and Out

In order for air to get to your lungs, it travels through a passageway that starts at your nose and mouth, travels through your neck and chest, and then splits into each lung. The passageway filters, moistens, and warms the air before it reaches your lungs.

When entering through the nose, air must pass through the external nares, more commonly called the nostrils. Behind the nostrils lies your nasal cavity. The walls of the nasal cavity are lined with mucous membranes, which have glands that produce a sticky substance called mucus. Mucus moistens the air as it passes by and traps a lot of microscopic dirt and bacteria that is in it. Directly behind the mucous membrane is a web of veins. Warm blood rushing through these veins heats the mucus and warms the air as well.

Your nasal cavity is surrounded by several sinuses, hollow spaces within your skull. Your sinuses serve several purposes, one of which is to secrete more mucus, which leaks into your nasal cavities to join the mucus created there.

The passageways from your nose and mouth join at the pharynx, or throat. Your pharynx has three main parts. The uppermost part is called the nasopharynx. This is the nasal connector—where air from the nasal cavity enters. Below the nasopharynx is the oropharynx, which is the oral part of the pharynx.

Air and food from the mouth travel through the oropharynx, as does air from the nose that has already passed through the nasopharynx. The bottom part of the pharynx, located below the oropharynx, is the laryngopharynx. Your entire pharynx, including all three of its parts, is about 5 inches (12.7 cm) long when you are a full-grown adult.

Delving Deeper

The next part of the passageway, below the pharynx, is your larynx, or voice box. It houses your vocal cords, which are used in speaking. The larynx is formed by eight pieces of rigid cartilage. Its most obvious feature is the shieldlike thyroid cartilage, or Adam’s apple. The larynx is the “gatekeeper” for the rest of the passageway to your lungs. Its main job is to make sure that only air—not food or liquids—enters your air passageway. This is made possible by the epiglottis, a flap of elastic cartilage at the top end of the larynx.

When you swallow, your larynx moves upward, and your epiglottis tips to form a protective lid over the opening of the larynx. When you’re breathing, the epiglottis remains open, allowing air to pass to the larynx. When you’re eating, the lid closes, forcing the food and liquids to travel toward the stomach instead. If you swallow a little food that sneaks past the epiglottis, you immediately cough and gasp for air. This forces the food back up and clears the passageway to the lungs.

Air from the larynx travels into the trachea, also called the windpipe. Your trachea, which is a little less than 4 inches (10.2 cm) long, is rigid and reinforced with sixteen to twenty C-shaped rings of cartilage. You can feel these rings by tilting your head back and rubbing the front of your neck. Muscle tissue called the tracheal membrane, covers the open ends of the C-shaped rings. The rigid rings help keep the trachea at least partially open all of the time. Within your trachea are small hairlike structures, called cilia. These gently move back and forth, collecting dirt, debris, and mucus, and keeping these things out of your lungs.

Branching Passageways

At the bottom of the trachea, the passageway branches into two major tubes. These are called the left and right main bronchi. Your right bronchus (singular of bronchi) leads to your right lung, and your left bronchus leads to your left lung. Within your lungs, the main bronchi branch into smaller bronchi. These branch into yet smaller tubes called bronchioles. The air that goes into your lung through the bronchi will split and split and split into smaller passageways many times.

The last of the smooth-surfaced bronchioles are called terminal bronchioles. There are thousands of these passageways in each of your lungs. They, in turn, split into even smaller passageways called respiratory bronchioles. Air that passes into the respiratory bronchioles is cleaned of most impurities.

At the end of the respiratory bronchioles are microscopic tubes called alveolar ducts, which are made up of individual air chambers. These air chambers are called alveoli. (A single one is called an alveolus.) Alveoli are round and hollow. Each lung has about 120 to 160 million alveoli. If you laid all of them out on the ground, they would cover a tennis court!

At the bottom end of the alveolar duct, the alveoli bunch together like a cluster of grapes. The cluster—called an alveolar sac—is the final destination of the oxygen in the lungs. It is here that oxygen makes its way into our blood, or circulatory system.