- The respiratory system is a vital biological system responsible for the exchange of gases, primarily oxygen and carbon dioxide, between the body and the environment. Its main function is to supply oxygen (O₂) to the bloodstream for delivery to the body’s tissues and to remove carbon dioxide (CO₂), a metabolic waste product, from the body. This exchange is critical for cellular respiration, the process by which cells generate energy in the form of ATP (adenosine triphosphate). The respiratory system works in close coordination with the circulatory system to maintain homeostasis and metabolic balance.
- Structurally, the respiratory system is divided into two main parts: the upper respiratory tract and the lower respiratory tract. The upper respiratory tract includes the nose, nasal cavity, pharynx, and larynx. Air enters the body through the nose or mouth, where it is filtered, warmed, and humidified. The nasal passages contain cilia and mucus to trap dust, microbes, and other particles. The air then passes through the pharynx (throat) and larynx (voice box) before entering the lower respiratory tract.
- The lower respiratory tract includes the trachea (windpipe), bronchi, bronchioles, and lungs. The trachea branches into two primary bronchi, each leading to a lung. Within the lungs, the bronchi divide into smaller bronchioles that terminate in alveoli, which are tiny air sacs surrounded by capillaries. These alveoli are the primary sites of gas exchange. The walls of the alveoli and capillaries are extremely thin, allowing oxygen to diffuse from the air into the blood and carbon dioxide to diffuse from the blood into the alveolar space for exhalation.
- The lungs are spongy, elastic organs housed within the thoracic cavity and protected by the rib cage. The diaphragm, a dome-shaped skeletal muscle located below the lungs, plays a central role in ventilation—the physical movement of air in and out of the lungs. During inhalation, the diaphragm contracts and flattens, increasing thoracic volume and causing air to be drawn into the lungs. During exhalation, the diaphragm relaxes, and the lungs recoil, expelling air.
- Breathing is regulated by the respiratory centers in the brainstem—specifically the medulla oblongata and pons—which respond to changes in blood levels of CO₂, O₂, and pH. Chemoreceptors in the aortic arch and carotid bodies monitor these levels and send feedback to the brain to adjust the rate and depth of respiration. This automatic control ensures that gas exchange remains efficient even during changes in activity or metabolic demand.
- The respiratory system also performs several secondary functions. It facilitates vocalization through the vibration of the vocal cords in the larynx, supports olfaction (sense of smell) through receptors in the nasal cavity, and helps regulate blood pH by controlling CO₂ levels. It also plays a role in immune defense, as the respiratory tract is lined with mucosa-associated lymphoid tissue (MALT) and contains immune cells that protect against inhaled pathogens.
- Diseases of the respiratory system are common and can significantly impact quality of life. These include asthma (inflammatory airway narrowing), chronic obstructive pulmonary disease (COPD), pneumonia (lung infection), tuberculosis, pulmonary fibrosis, and lung cancer. Environmental factors such as air pollution, smoking, and occupational exposures, as well as infections and genetic predispositions, influence respiratory health.
