33.Respiration. Mechanics of pulmonary ventilation.
The respiratory system supplies oxygen to the tissues and removes carbon dioxide. The
major functional events of respiration include:
● pulmonary ventilation,which is the movement of air in and out of the alveoli
● diffusion of oxygen and carbon dioxide between the blood and alveoli
● transport of oxygen and carbon dioxide to and from the peripheral tissues
● regulation of respiration.
Normal quiet breathing is accomplished with the diaphragm. During inspiration,
contraction of the diaphragm pulls the lower surfaces of the lungs downward. During
expiration, the diaphragm relaxes, and the elastic recoil of the lungs, chest wall, and
abdominal structures compresses the lungs.
During heavy breathing, the elastic forces are not sufficiently powerful to cause rapid
expiration. The extra force is achieved mainly through contraction of the abdominal
muscles, which pushes the abdominal contents upward against the diaphragm.
Muscles that raise the rib cage are muscles of inspiration. Contraction of the external
intercostals causes the ribs to move upward and forward in a “bucket handle” motion.
Muscles that depress the rib cage are muscles of expiration, including the internal
intercostals and the abdominal recti. Other abdominal muscles compress the abdominal
contents upward toward the diaphragm.
Pleural pressure is the pressure of the fluid in the space between the lung pleura and
chest wall pleura.
When the glottis is open and there is no movement of air, the pressures in all parts of
the respiratory tree are equal to the atmospheric pressure, which is considered to be 0
cm of water.
During inspiration, the pressure in the alveoli decreases to about 1 cm of water, which is
sufficient to move about 0.5 L of air into the lungs within the 2 seconds required for
inspiration.
During expiration, opposite changes occur: The alveolar pressure rises to about +1 cm
of water, which forces the 0.5 L of inspired air out of the lungs during the 2 to 3 seconds
of expiration.
The water surface lining the alveoli attempts to contract as the water molecules pull
toward one another. This attempts to force air out of the alveoli, causing the alveoli to
The respiratory system supplies oxygen to the tissues and removes carbon dioxide. The
major functional events of respiration include:
● pulmonary ventilation,which is the movement of air in and out of the alveoli
● diffusion of oxygen and carbon dioxide between the blood and alveoli
● transport of oxygen and carbon dioxide to and from the peripheral tissues
● regulation of respiration.
Normal quiet breathing is accomplished with the diaphragm. During inspiration,
contraction of the diaphragm pulls the lower surfaces of the lungs downward. During
expiration, the diaphragm relaxes, and the elastic recoil of the lungs, chest wall, and
abdominal structures compresses the lungs.
During heavy breathing, the elastic forces are not sufficiently powerful to cause rapid
expiration. The extra force is achieved mainly through contraction of the abdominal
muscles, which pushes the abdominal contents upward against the diaphragm.
Muscles that raise the rib cage are muscles of inspiration. Contraction of the external
intercostals causes the ribs to move upward and forward in a “bucket handle” motion.
Muscles that depress the rib cage are muscles of expiration, including the internal
intercostals and the abdominal recti. Other abdominal muscles compress the abdominal
contents upward toward the diaphragm.
Pleural pressure is the pressure of the fluid in the space between the lung pleura and
chest wall pleura.
When the glottis is open and there is no movement of air, the pressures in all parts of
the respiratory tree are equal to the atmospheric pressure, which is considered to be 0
cm of water.
During inspiration, the pressure in the alveoli decreases to about 1 cm of water, which is
sufficient to move about 0.5 L of air into the lungs within the 2 seconds required for
inspiration.
During expiration, opposite changes occur: The alveolar pressure rises to about +1 cm
of water, which forces the 0.5 L of inspired air out of the lungs during the 2 to 3 seconds
of expiration.
The water surface lining the alveoli attempts to contract as the water molecules pull
toward one another. This attempts to force air out of the alveoli, causing the alveoli to
