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The respiratory system consists of the lungs, airways, diaphragm, trachea (windpipe) and pharynx (throat) and its primary function is the exchange of oxygen and carbon dioxide- breathing in and out. Between 6 and 10 liters of air are brought in and out of the lungs and 0.3 liters of oxygen are transferred from the alveoli to the blood per minute.
Inhalation and exhalation is accomplished by respiratory muscles, namely the diaphragm and intercostal, neck and abdominal muscles. The diaphragm contracts and increases the volume of the chest cavity, expanding the lungs and contracting the intercostal muscles to expand the ribcage. This occurs during inhalation. Upon inhalation, oxygenated air travels down the trachea which separates into 2 bronchi, one leading to each lung. From here the air travels through smaller bronchioles to the alveoli which are the location for exchange of oxygen and CO2 to and from the bloodstream and the pulmonary circulation. Exhalation is a passive process whereby the muscles relax, the volume of the chest cavity decreases and air containing CO2 for excretion is forced out.
Disorders of the respiratory system can be divided into four main areas:
In total there are more than 40 conditions which affect the lungs and airways, ranging from mild and self-limiting, such as the common cold, to life-threatening occurrences such as bacterial pneumonia and cancer. They are a common and important cause of illness and death and the incidence of asthma and allergy has almost trebled in the last 20 years, making it an increasingly important target for medical research.