The respiratory system (or ventilatory system) is a biological system consisting of specific organs and structures used for the process of respiration in an organism. The respiratory system is involved in the intake and exchange of oxygen and carbon dioxide between an organism and the environment.
In human respiration takes place in the respiratory organs called lungs. The passage of air into the lungs to supply the body with oxygen is known as inhalation, and the passage of air out of the lungs to expel carbon dioxide is known as exhalation; this process is collectively called breathing or ventilation. In humans and other mammals, the anatomical features of the respiratory system include trachea, bronchi, bronchioles, lungs, and diaphragm. Molecules of oxygen and carbon dioxide are passively exchanged, by diffusion, between the gaseous external environment and the blood. This exchange process occurs in the alveoli air sacs in the lungs.
As we breathe, oxygen enters the nose or mouth and passes the sinuses, which are hollow spaces in the skull. Sinuses help regulate the temperature and humidity of the air we breathe. The trachea, also called the windpipe, filters the air that is inhaled, according to the American Lung Association. It branches into the bronchi, which are two tubes that carry air into each lung. The bronchial tubes are lined with tiny hairs called cilia. Cilia move back and forth, carrying mucus up and out. Mucus, a sticky fluid, collects dust, germs and other matter that has invaded the lungs. We expel mucus when we sneeze, cough, spit or swallow.
The bronchial tubes lead to the lobes of the lungs. The right lung has three lobes; the left lung has two, according to the American Lung Association. The left lung is smaller to allow room for the heart, according to the National Heart, Lung and Blood Institute (NHLBI). Lobes are filled with small, spongy sacs called alveoli, and this is where the exchange of oxygen and carbon dioxide occurs.
The alveolar walls are extremely thin (about 0.2 micrometers). These walls are composed of a single layer of tissues called epithelial cells and tiny blood vessels called pulmonary capillaries.
Blood passes through the capillaries. The pulmonary artery carries blood containing carbon dioxide to the air sacs, where the gas moves from the blood to the air, according to the NHLBI. Oxygenated blood goes to the heart through the pulmonary vein, and the heart pumps it throughout the body.
The diaphragm, a dome-shaped muscle at the bottom of the lungs, controls breathing and separates the chest cavity from the abdominal cavity, the American Lung Association noted. When a breath it taken, it flattens out and pulls forward, making more space for the lungs. During exhalation, the diaphragm expands and forces air out.
Some of the many diseases that can affect the respiratory system include:
Laryngitis - Swelling and irritation of the larynx
Bronchitis - An infection in your bronchial tubes
Tonsillitis - Inflammation of the tonsils
Pneumonia - An infection deep in your lungs
Bronchiectasis - Widening and destruction of the airways, often caused by recurrent infection or inflammation
Influenza (the flu) - A virus that enters your body through your nose and mouth and causes fever, headaches, muscle aches and sore throat
Asthma - A chronic disease in which your airway walls become sore and swollen, narrowing so that your lungs get less air
Tuberculosis (TB) - A bacterial infection that attacks the lungs and other parts of the body and can be deadly if not treated correctly
Lung cancer - One of the most common cancers in the world, usually caused by cigarette smoke
Chronic obstructive pulmonary disease (COPD) - Damage of the airways and air sacs from cigarette smoke and other pollutants that prevents airflow in and out of your lungs
Emphysema - A type of COPD, usually caused by cigarette smoke, which makes it hard to catch your breath
Pulmonary embolism (PE) - A blood clot that blocks a lung artery because of surgery or long periods of inactivity