Breathing

We need to breathe to stay alive.

Breathing moves air in and out of our lungs. This brings in the air we breathe. It also takes away waste air.

Your nose warms up the air you take in. It also makes the air wet. When you breathe out, you might see a mist. This happens in cold weather. Breathing also helps us talk and laugh.

It is a busy job for our bodies!

Breathing is the way we move air in and out of our lungs.

This process helps us take in oxygen. We also need to get rid of carbon dioxide. This is a waste gas our bodies make.

Air travels through a system of tubes. These tubes branch out like a tree. They lead to tiny parts called alveoli. This is where the gases move into our blood.

Our lungs do not move on their own. Muscles help them work. A large muscle called the diaphragm sits below the lungs. It pulls down to let air in. This is called inhalation. When the muscle relaxes, air moves out. This is called exhalation.

Your nose also helps. It warms and wets the air you breathe.

Your brain controls your breathing. It works on its own most of the time. But you can also choose to breathe deeply. This can help you relax. Breathing also lets us speak and laugh. It is a vital part of staying healthy.

Breathing is a rhythmic process that keeps us alive. It is the way we move air into our lungs, called inhalation, and out of them, called exhalation.

We need this to perform gas exchange with our bodies. Living things that use oxygen, called aerobic organisms, need it for cellular respiration. This is how they get energy from food. During this process, they also create carbon dioxide as a waste product. Breathing helps remove that waste while bringing in fresh oxygen.

How does this work step by step? First, air enters through the nose or mouth. The nasal cavities warm and moisten the air using a wet surface.

Then, the air travels down a system of tubes called the tracheobronchial tree. This tree branches many times, about 23 generations in humans. Finally, the air reaches the alveoli, which are tiny, blind-ended sacs.

At the alveoli, oxygen moves into the blood through a thin membrane. At the same time, carbon dioxide moves from the blood into the lungs to be breathed out. This movement of gases is called diffusion.

Our lungs cannot inflate themselves. Instead, they rely on muscles to change the space inside our chest. The main muscle is the diaphragm, which sits below the lungs. When the diaphragm contracts, it expands the chest cavity and pulls air in.

To help, the intercostal muscles lift the rib cage. At rest, breathing out is often passive. The lungs and chest wall simply snap back to their original shape. This is called elastic recoil. During heavy exercise, we use extra muscles in our abdomen to push air out faster.

Your brain is the boss of your breathing. It uses special sensors called chemoreceptors to check your blood. These sensors live in places like the medulla and the carotid bodies.

They monitor levels of carbon dioxide, oxygen, and the pH of your blood. If levels change, the brain sends signals through nerves like the phrenic nerve. This tells the muscles to change how fast or deep you breathe. This automatic system keeps your internal environment steady and safe. You can also control your breath on purpose to sing or swim.

Breathing changes depending on where you are. At sea level, the air pressure is about 100 kPa. But at the summit of Mount Everest, the pressure is only 33.7 kPa. Even though the percentage of oxygen stays the same, there is less pressure to push it into your lungs. This means you must breathe more air to get enough oxygen. You can also see your breath on a cold day. This happens because the warm water vapor from your lungs hits the cold air and turns into a mist.

Breathing, also known as respiration or ventilation, is the rhythmic process of moving air into and out of the lungs. This movement allows for gas exchange with the internal environment of an organism. The primary goal is to take in oxygen and remove carbon dioxide. All aerobic organisms require oxygen for cellular respiration. This is the process that extracts energy from food. Carbon dioxide is produced as a waste product during this energy extraction.

The mechanism of breathing relies on changing the volume of the thoracic cavity. The lungs are not self-inflating organs. In mammals, expansion is driven mainly by the contraction of the diaphragm. This is a large muscle located below the lungs. The intercostal muscles also help by lifting the rib cage. During forceful inhalation, accessory muscles can further increase chest volume. At rest, exhalation is largely a passive process. This happens because of the elastic recoil of the lungs and chest wall. As these muscles relax, the chest returns to its resting position.

Air travels through a complex system of airways known as the tracheobronchial tree. In humans, these airways branch about 23 times. The process begins in the upper airways, such as the nasal cavities. The nasal septum divides these cavities, which are lined with convoluted conchae. These structures expose inhaled air to a large mucosal surface. This surface warms and humidifies the air. It also traps particulate matter in mucus. Below the upper airways, the larger conducting airways branch into smaller bronchi and bronchioles. These eventually lead to the terminal divisions. These include respiratory bronchioles, alveolar ducts, and the alveoli. The alveoli are tiny, blind-ended sacs where gas exchange occurs.

Gas exchange occurs at the alveoli through a process called diffusion. This movement happens across a thin respiratory membrane. This membrane is composed of the alveolar epithelium and the capillary endothelium. It also includes the basement membrane, which forms a blood-gas barrier. As air moves through the airways, it leaves behind a volume called anatomical dead space. In an adult, this volume is about 150 ml. This space consists of conducting airways that do not participate in gas exchange. Even after a maximum exhalation, mammals retain residual air. In an adult human, the functional residual capacity is about 2.5 to 3.0 L.

The brainstem regulates the rate and depth of breathing through homeostatic mechanisms. These mechanisms maintain the arterial partial pressures of oxygen and carbon dioxide. Central chemoreceptors in the medulla are very sensitive to pH and carbon dioxide levels. Peripheral chemoreceptors in the aortic and carotid bodies sense arterial oxygen. The brain integrates this information in the pons and medulla. It then sends signals through motor nerves, such as the phrenic nerves. These nerves control the muscles of breathing, like the diaphragm. While breathing is mostly automatic, humans can voluntarily modify it. This is necessary for activities like singing, swimming, or speaking.

The composition of the air we breathe changes during the respiratory cycle. Inhaled air is roughly 78% nitrogen and 20.95% oxygen. It contains small amounts of argon, carbon dioxide, and other gases. When we exhale, the concentration of carbon dioxide increases significantly. Exhaled air contains 4% to 5% carbon dioxide. This is about a hundredfold increase over the amount inhaled. The volume of oxygen is reduced by about a quarter. You can sometimes see this change in cold weather. Warm water vapor from the lungs condenses into a visible mist in cold air.

Environmental factors like altitude greatly affect how we breathe. Atmospheric pressure decreases exponentially as you rise in altitude. At sea level, the ambient pressure is about 100 kPa. At the summit of Mount Everest, the pressure drops to 33.7 kPa. While the percentage of oxygen remains at 21%, the partial pressure of oxygen decreases. On Everest, the partial pressure of oxygen is only 7.1 kPa. This means a person must inhale a greater volume of air to get enough oxygen. To compensate, the body automatically increases the respiratory minute volume. This helps maintain the necessary levels of gases in the blood.