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An alveolus (plural: alveoli, from Latin alveus, "little cavity"), is an anatomical structure that has the form of a hollow cavity. Mainly found in the lung, the pulmonary alveoli are spherical outcroppings of the respiratory bronchioles and are the primary sites of gas exchange with the blood. Date: December 2007: Source: Own work using:
Almost any type of lung tumor or lung cancer can compress the alveoli and reduce gas exchange capacity. In some cases the tumor will fill the alveoli. [33] Cavitary pneumonia is a process in which the alveoli are destroyed and produce a cavity. As the alveoli are destroyed, the surface area for gas exchange to occur becomes reduced.
This typical mammalian anatomy combined with the fact that the lungs are not emptied and re-inflated with each breath (leaving a substantial volume of air, of about 2.5–3.0 liters, in the alveoli after exhalation), ensures that the composition of the alveolar air is only minimally disturbed when the 350 ml of fresh air is mixed into it with ...
Each respiratory bronchiole supplies the alveoli held in each acinus accompanied by a pulmonary artery branch. The pulmonary lobule is the portion of the lung ventilated by one bronchiole. Bronchioles are approximately 1 mm or less in diameter and their walls consist of ciliated cuboidal epithelium and a layer of smooth muscle .
The lungs are not capable of expanding to breathe on their own, and will only do so when there is an increase in the volume of the thoracic cavity. [71] This is achieved by the muscles of respiration, through the contraction of the diaphragm, and the intercostal muscles which pull the rib cage upwards as shown in the diagram. [72]
The alveoli are tiny air sacs in the lungs where gas exchange takes place. The mean number of alveoli in a human lung is 480 million. [11] When the diaphragm contracts, a negative pressure is generated in the thorax and air rushes in to fill the cavity. When that happens, these sacs fill with air, making the lung expand.
Diagram of alveoli with emphysema. Emphysema is a respiratory disease of the lower respiratory tract. [7] It is commonly caused by tobacco smoking but some people are affected who have never smoked. [14] The presence of emphysema is a clear risk factor for lung cancer, made stronger in those who smoke. [20] Early symptoms of emphysema vary.
The zones of the lung divide the lung into four vertical regions, based upon the relationship between the pressure in the alveoli (PA), in the arteries (Pa), in the veins (Pv) and the pulmonary interstitial pressure (Pi): Zone 1: PA > Pa > Pv; Zone 2: Pa > PA > Pv; Zone 3: Pa > Pv > PA; Zone 4: Pa > Pi > Pv > PA