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The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies greatly, depending on the size of the organism, the environment in which it lives and its evolutionary ...
In physiology, respiration is the transport of oxygen from the outside environment to the cells within tissues, and the removal of carbon dioxide in the opposite direction to the environment by a respiratory system. [1]
The upper respiratory tract can refer to the parts of the respiratory system lying above the vocal folds, or above the cricoid cartilage. [4] [5] The larynx is sometimes included in both the upper and lower airways. [6] The larynx is also called the voice box and has the associated cartilage that produces sound.
The respiratory tract is lined by respiratory epithelium or respiratory mucosa, with hair-like projections called cilia that beat rhythmically and carry mucus. This mucociliary clearance is an important defence system against air-borne infection. [ 34 ]
The breathing of all vertebrates with lungs consists of repetitive cycles of inhalation and exhalation through a highly branched system of tubes or airways which lead from the nose to the alveoli. [4] The number of respiratory cycles per minute is the breathing or respiratory rate, and is one of the four primary vital signs of life. [5]
The average total lung capacity of an adult human male is about 6 litres of air. [1] Tidal breathing is normal, resting breathing; the tidal volume is the volume of air that is inhaled or exhaled in only a single such breath. The average human respiratory rate is 30–60 breaths per minute at birth, [2] decreasing to 12–20 breaths per minute ...
For the respiratory system to function properly, there need to be as few impediments as possible to the movement of air within the lungs. Inflammation of the lungs and excess mucus are common sources of breathing difficulties. [50] In asthma, the respiratory system is persistently inflamed, causing wheezing or shortness of breath.
Along with the diaphragm, the intercostal muscles are one of the most important groups of respiratory muscles. These muscles are attached between the ribs and are important in manipulating the width of the rib cage. There are three layers of intercostal muscles. The external intercostal muscles are most important in respiration.