With each breath you take you are participating in a grand recycling system that sustains life on earth. You are drawing in air that is shared with every respiring being in existence. From your first gasping inhale at birth to the last sighing exhale at the end of life, your respiratory system is an engine driving every moment.  

Your lungs work tirelessly day and night breathing around 25,000 times a day. They function to extract life-giving oxygen and exchange it for waste carbon dioxide from the blood. In this blog we introduce you to the mysteries of the respiratory system so you can understand its anatomy and physiology and see how this vital system powers your every moment.  

Anatomy of the Respiratory System 

The respiratory system is made up of all the organs involved in gas exchange. It is separated into the Upper Respiratory Tract and the Lower Respiratory Tract.

Upper Respiratory Tract: Located outside of the chest cavity. These organs allow air to move into the system and warm and humidify it, so it doesn’t shock the lungs. 

 

• Nostrils and Nasal Cavity: Air enters the nostrils and passes into the nasal cavity which is separated down the middle by the septum. The mucus membranes of the nasal cavity trap small particulate matter, bacteria, and other foreign material so it can be sneezed or blown out. The small hairs (cilia) on the mucus membrane move sticky mucus towards the pharynx where it gets swallowed to be killed by stomach acids. The nasal cavity also contains chemoreceptors for smell.  

• Sinuses: Air-filled pockets under the cheek bones that help make the skull lighter and act as resonance chambers for speech.  

• Pharynx: The part of the throat where both air and food are taken in before reaching their separate destinations. The pharynx also plays a role in speech.  

• Larynx: Also known as the voice box as it contains the vocal cords. The epiglottis covers the larynx when food is swallowed to prevent it entering the lungs.  

Lower Respiratory Tract: Located within the chest cavity. This is where gas exchange occurs.  

• Trachea: Also known as the windpipe, is the airway to the lungs situated just below the larynx. It is made up of smooth muscle that allows for flexibility when large bites of food are swallowed and has rings of cartilage that prevent it from collapsing. The inside of the trachea is covered in cilia that moves mucus away from the lungs to the pharynx where it can be swallowed.

• Bronchi: Branch from the trachea inside the lungs to carry air to each lung. The bronchi continue to branch into the secondary bronchi, the tertiary bronchi, and finally into the bronchioles.  

• Bronchioles: The smallest, many-branched tubules are called bronchioles. The branches of the bronchi and bronchioles are compared to the branching of an upside-down tree. The entire bronchial tree is lined with mucus that purifies the air entering from the outside world. Each lung has up to 30,000 bronchioles.  

• Alveoli: Tiny air sacs found at the end of the bronchioles where gas exchange occurs. There are around 600 million alveoli in the lungs. They give the lungs a massive amount of surface area for gas exchange. The alveoli are surrounded by a network of capillaries.  

• Diaphragm: The largest respiratory muscle that expands and contracts to allow air into the chest cavity.  

• Lungs: A pair of sac-like spongy organs that fill up most of the chest cavity. They provide oxygen to the capillaries and exhale carbon dioxide. The right lung has three lobes, and the left lung has only two lobes to make space for the heart. Each lung is surrounded by a membrane known as the pleural membrane. The pleura produces a fluid that allows the lungs to slide smoothly against the interior of the chest cavity with each breath. The lungs are separated by the mediastinum.  

Physiology of the Respiratory System 

The respiratory system provides oxygen to the blood and disposes of carbon dioxide. There are four different actions that make up respiration.  

1. Pulmonary Ventilation: Also known as breathing. The process of air moving in and out of the lungs continuously. Inspiration and expiration.  

1. External Respiration: The gas exchange between the pulmonary blood and the alveoli.  

1. Respiratory gas transport: The process of oxygen and carbon dioxide being transported to and from the lungs and the cells of the body in the bloodstream.  

1. Internal respiration: The gas exchange that occurs between the blood and tissue cells at the capillary beds.  

The Mechanics of Breathing  

The fluid filling the pleural space between the lungs and the thoracic wall creates a seal between the two structures. This seal ensures that the lungs expand and contract with the expansion and contraction of the thoracic wall. When you breathe, the contraction and relaxation of the respiratory muscles changes the volume of the thoracic cavity. This in turn changes the volume of the lungs. With changing volume within the lungs there is a change in pressure.  

Physicists Robert Boyle and Edme Marriotte independently discovered the Boyle-Mariotte Law. This law states that if temperature remains constant, the volume of gas is inversely proportional to pressure. This means that as the volume of the thoracic cavity increases, and the volume of the lungs also increases the pressure within the lungs decreases out of necessity. When the volume of the thoracic cavity decreases along with a decrease in volume in the lungs the pressure within the lungs increases.  

During inspiration/inhalation, the muscles of respiration contract and air enters the lungs. The diaphragm flattens, increasing the size of the chest cavity at the top and bottom. The intercostal muscles (muscles between the ribs) lift the ribs and sternum increasing the front/back dimension of the chest cavity. This causes an overall increase in the volume of the chest cavity. As the lungs are sealed to the inner surface of the thoracic cavity they also increase in volume. This increase in volume causes a decrease in pressure inside of the lungs. The external pressure of the air is now greater than the air pressure within the lungs. Air moves into the lungs down this pressure gradient.  

During exhalation, or expiration, air is pushed out of the lungs. This is caused by the relaxation of the respiratory muscles. The diaphragm relaxes, decreasing the upper and lower dimensions of the chest cavity. The intercostal muscles relax, bringing the ribs and sternum downwards, decreasing the dimensions of the chest cavity from front to back. This relaxation causes a decrease in the overall volume of the thoracic cavity and of the lungs. The decrease in volume leads to an increase of pressure within the lungs. The air pressure within the lungs is now greater than that of the external environment and air moves down this pressure gradient in an exhale.  

Forced breathing occurs when air is moved rapidly in and out of the lungs more quickly than normal due to rapid expansion and contraction of the thoracic cavity. This most often occurs during exercise. Active inspiration requires the use of five accessory muscles in addition to the diaphragm and the intercostals. The scalene muscles lift the upper ribs, the sternocleidomastoid lifts the sternum, the pectoralis major and minor pull the ribs downwards, the serratus anterior lifts the ribs, and the latissimus dorsi lifts the lower ribs.  

Active expiration or exhalation requires the contraction of additional thoracic and abdominal muscles to decrease the volume of the thoracic cavity more quickly than normal. The anterolateral abdominal wall increases the pressure in the abdominal cavity which pushes the diaphragm upwards into the chest cavity. The internal intercostal and the innermost intercostal both depress the ribs.  

The Pathway of a Breath Through the Respiratory Tract  

As you inhale, oxygen rich air enters your nose or mouth and travels down the trachea. It moves into the lungs through the left and right bronchi. Continues into the smaller branches of the bronchi into the bronchioles. From the bronchioles air moves into the alveoli. Each alveolus is surrounded by a network of capillaries. The capillaries contain blood that has traveled through your body feeding your tissues. The veins deliver it to the heart in a deoxygenated state and the heart pumps it to the lungs for gas exchange.  

Both the alveoli and the capillary walls are very thin. They are each made up of a single layer of squamous epithelial cells. Their wall’s basement membranes are fused, creating a respiratory membrane with blood flowing on one side and air on the other. Oxygen passes from the air in the alveoli to the blood within the capillaries, where it attaches to hemoglobin. Carbon dioxide travels from the blood within the capillaries into the alveoli. The oxygen enriched blood is sent to the heart and is then pumped out to the entire body. Carbon dioxide is exhaled from the lungs into the external environment via the nose or mouth. 

How the Lungs Stay Healthy 

The lungs are self-cleaning, producing mucus that collects particulate matter and pathogens. The mucus is then swept out of the lungs by tiny hairlike cilia that line the branches of your airways. This mucus is normally swallowed without you noticing. If you have an infection or irritation your body may produce more mucus than normal. The coughing reflex brings up this mucus. The alveoli also contain macrophages (immune cells) that ‘eat’ pathogens and irritants to prevent lung infections.  

Blood Homeostasis 

The amount of oxygen and carbon dioxide in the blood must be carefully maintained within a specific range for survival. The respiratory system works with the nervous system and the cardiovascular system to maintain homeostasis in blood gases and pH. Levels of carbon dioxide determine blood pH; Too much carbon dioxide, and blood becomes acidic, too little and it becomes too basic.  

Cells cannot survive for long without oxygen, but it is carbon dioxide levels that are monitored more closely by the body. Your breath rate is sped up or slowed down by the autonomic nervous system depending on carbon dioxide levels. If carbon dioxide levels are too high, your breath rate will speed up, raising pH and oxygen levels in the blood. If carbon dioxide levels are too low your breathing will slow until pH and oxygen levels go down.  

The Lungs as a Detox Organ 

Often overlooked in discussions centered around the liver and kidneys, the lungs play a crucial role in detoxification. With every breath, the lungs not only supply oxygen to the bloodstream but also expel carbon dioxide—a byproduct of cellular metabolism. This process of gas exchange is vital for maintaining the body's pH balance and eliminating volatile toxins.  

Additionally, the lungs filter and remove inhaled pollutants, pathogens, and particulate matter, trapping these harmful substances in mucus, which is then expelled from the body through coughing or swallowing. Supporting lung health through deep breathing exercises, clean air environments, and herbal remedies can significantly enhance your body's natural detoxification pathways, ensuring that your respiratory system efficiently performs its role in keeping you healthy. Stay tuned for our article 10 Herbs for the Lungs and Respiratory System.  

Conclusion 

The respiratory system is essential for sustaining life, providing the oxygen our bodies need and expelling carbon dioxide. Maintaining the health of your airways is one of the most immediately important things you can do. You can survive three to four weeks without food, three to four days without water, and only three to four minutes without air.  

The proper functioning of the respiratory system is crucial for overall health as it can affect everything from energy levels to the efficiency of other body systems. Some of the things you can do to support your respiratory system include avoiding pollutants, the inhalation of fine particulates, and smoke exposure, and staying active.  

Dr. Morse also stresses that the lungs are one of your four major eliminative organs. The byproduct of respiration is carbon dioxide, which, along with other gases, acts as a filter for other toxins and particulates you inhale. These potentially harmful substances are coughed out, killed by stomach acids, or cleaned up in the lymph system. A healthy respiratory system prevents your other eliminative organs from becoming over-taxed. We hope further knowledge of the workings of this vital system encourages you to seek out greater respiratory health and care.