Each day we breathe about 20,000 times. All of this breathing couldn't happen
without help from the respiratory system, which includes the nose, throat, voice
box, windpipe, and lungs. With each breath, you take in air through your
nostrils and mouth, and your lungs fill up and empty out. As air is inhaled, the
mucous membranes of the nose and mouth warm and humidify the air.
Although we can't see it, the air we breathe is made up of several gases. Oxygen is the
most important for keeping us alive because body cells need it for energy and
growth. Without oxygen, the body's cells would die.
Carbon dioxide is the waste gas that is produced when carbon is combined with
oxygen as part of the body's energy-making processes. The lungs and respiratory
system allow oxygen in the air to be taken into the body, while also enabling
the body to get rid of carbon dioxide in the air breathed out.The lungs follow the first airways that have the function of heating the air
and freeing it from atmospheric dust and pollutants, thanks to the vibratile
eyelash system; also in the first airways there is the organ of vocalization (larynx);
vice versa, the lung is the organ responsible for gaseous exchanges, the main
organ of respiration which consists precisely in introducing oxygenated air into
the lung and releasing carbon dioxide from the blood of the periphery. To ensure
the blood circulation through the lung we have the small circulation, by the
heart pump and, precisely, the right sections of the heart, those working at low
pressure. On the contrary, the heart, received the oxygenated blood in the left
atrium, through the pulmonary veins, pushes it into the left ventricle and from
there into the great circulation, that is in the body.
They occupy the two halves of the rib cage but leave a median space free, called the "mediastinum" in which are located important organs: the heart, the cardiac nerves, the azygos vein, the phrenic nerves, the pulmonary veins, the esophagus and numerous mediastinal lymph node stations, the thymus, internal mammary arteries and internal mammary veins, lymphatic vessels from the liver, lymph nodes, adipose tissue.
The lungs are covered by the parietal and visceral pleura and have the appearance of two semi-conical spongy and elastic masses with a smooth surface of a color that varies from pink to gray depending on age. They rest on the diaphragm which is the muscle, along with the intercostal muscles, deputed to the expansion of the thoracic cavity in the respiration field. Some deep furrows affect the lung surface: the right lung is divided by these furrows into three lobes (the lobe is the part of an organ delimited by incisura, ie depressions with sharp limits placed on the margin of the organ itself) and the left one in two.
Their structure is formed by the set of alveoli and bronchial branches. In fact,
the trachea, a fibrocartilaginous organ consisting of consecutive rings, arrived
in the mediastinum, is divided into the two main bronchi, which branch several
times, up to constitute the bronchioles. The trachea dividing into two canals
from the bronchi, these branch several times, up to the terminal part which are
the so-called terminal bronchioles, of limited caliber, less than a millimeter
and end with a kind of bunch, called infundibulo, which resembles to a bunch of
grapes, of which each grape is called "alveolus". The alveolus is the true
functional unit of the lung, since it has such thin walls where practically the
blood capillaries are in close contact with the oxygen contained in its interior.
The surface of all the alveoli, if unraveled, reaches 200 square meters, then as a soccer field. The blood is separated from the alveolar air only from the endothelium of the capillary and from the epithelium that internally covers the alveolus: the blood bypasses the nucleus of the cells of the epithelium (which is the densest part of the cell) and comes into contact with the oxygen to detect it through the oxidation of the iron contained in the hemoglobin molecule (hematosis process). Vice versa the blood binds the carbon dioxide and the water vapor that comes from the endocellular respiratory processes that, in essence, derive in turn from the metabolism of glucose
The lungs and the chest wall are elastic structures.
When the diaphragm lowers,
the lungs find themselves in a cavity where the intrapleural pressure is lowered,
because the diaphragm, like a sort of syringe plunger, going down, creates
depression, a sort of "suction" ". Therefore the lungs are also obliged to
follow the diaphragm and expand, allowing the entry of air into them. After
inhalation, the lungs return to the initial position, essentially "deflate" and
the air escapes along with the waste gases. This obviously happens in a healthy
lung, since in chronic bronchial pneumopathies obstructive, this process is
prevented, up to the established pictures of fibrothorax or interstitiopathy (cf.
pulmonary fibrosis), in which the lung is a fibrous mass.In addition, the
presence of kyphosis or costal rigidity are other elements that hinder good lung
ventilation. Intrinsic lung diseases (of the pulmonary parenchyma) are
characterized by inflammatory or scarring processes of pulmonary tissue (interstitial
lung disease) or involve filling the air spaces with exudate and other materials
(pneumonia). They include fibrotic idiopathic diseases, connective tissue
diseases, iatrogenic (from drugs) pneumonia and primary lung diseases.
The extrinsic disorders (extra-pulmonary diseases) are characterized instead by
an involvement of one or more respiratory pump components (chest wall, pleura,
respiratory muscles), which to achieve effective ventilation must be intact and
function normally. The involvement of these structures involves lung restriction
(think of kypho-scoliosis), alteration of the ventilatory function and, in the
more advanced cases, respiratory insufficiency (for example in the case of
neuromuscular disorders). In adult men, the
frequency of expiratory acts (inhalation, exhalation, pause) is 16-20 per
minute. The respiratory rhythm can be more or less frequent. We can voluntarily
control only part of the frequency and amount of air we breathe in; we can
voluntarily block respiration for some time, but when the amount of carbon
dioxide in the blood is in excess, we are obliged to breathe even independently
of our will.