Respiratory System Flashcards
MUSCLES THAT CAUSE LUNG
EXPANSION AND CONTRACTION.
The lungs can be expanded and contracted in two ways:
(1) by downward and upward movement of the diaphragm to lengthen or shorten the chest cavity, for normal breathing and (2) by elevation and depression of the ribs to increase and decrease the anteroposterior diameter of the chest cavity.
Muscles that raise the rib cage
are the external intercostals, but others that help are the
(1) sternocleidomastoid muscles (2) anterior serrati (3) scaleni,
Muscles that pull the rib cage downward during expiration are abdominal recti and internal intercostal muscles.
Pleural Pressure and Its Changes during Respiration
Pleural pressure is the pressure of the fluid in the thin space between the lung pleura and the chest wall pleura.
The normal pleural pressure at the beginning of inspiration is about −5 centimeters of water, which is the amount of suction required to hold the lungs open to their resting level.
During normal inspiration, expansion of the chest cage pulls outward on the lungs with greater force and creates more negative pressure, to an average of about −7.5 centimeters of water.
Increasing negativity of the pleural pressure from −5 to −7.5 during inspiration and in the upper panel an increase in lung volume of 0.5 liter. Then, during expiration, the events are essentially reversed.
Alveolar Pressure—The Air Pressure Inside the Lung Alveoli
When the glottis is open and no air is flowing into or out of the lungs, the pressures in all parts of the
respiratory tree, all the way to the alveoli, are equal to atmospheric pressure, which is considered to be zero reference pressure.
During normal inspiration, alveolar pressure decreases to about −1 centimeters of water. This slight negative pressure is enough to pull
0.5 liter of air into the lungs in the 2 seconds required for normal quiet inspiration.
During expiration, alveolar pressure rises to about +1 centimeter of water, which forces the 0.5 liter of inspired air out of the lungs during the 2 to 3 seconds of expiration.
Transpulmonary Pressure—The Difference between Alveolar and Pleural Pressures.
Transpulmonary pressure is the pressure difference between that in the alveoli and that on the outer
surfaces of the lungs (pleural pressure).
It is a measure of the elastic forces in the lungs that tend to collapse the lungs at each instant of respiration, called the recoil pressure.
Compliance of the Lungs
The extent to which the lungs will expand for each unit increase in transpulmonary pressure is called the lung compliance. The total compliance of both lungs together in the normal adult human averages about 200 milliliters of air per centimeter of water transpulmonary pressure.
Compliance diagram are determined by the elastic forces of the lungs. These forces
can be divided into two parts: (1) elastic forces of the lungs and (2) elastic forces caused by surface tension of the fluid that lines the inside walls of the alveoli.
Surfactant and Its Effect on Surface Tension.
Surfactant is a surface active agent in water, which means that it greatly reduces the surface tension of water. It is secreted by special surfactant -secreting epithelial cells called type II alveolar epithelial cells, which constitute about 10 percent of the surface area of the alveoli.
The most important components
are the phospholipid dipalmitoyl phosphatidylcholine, surfactant apoproteins, and calcium ions.
Alveolar ventilation and dead space
The rate at which new air reaches alveoli, alveolar sacs, alveolar ducts, and respiratory bronchioles is called alveolar ventilation.
Some of the air a person breathes never reaches the gas exchange areas but simply fills respiratory passages where gas exchange does not occur, such as the nose, pharynx, and trachea. This air is called anatomical dead space air because it is not useful for gas exchange.
The normal dead space air in a young adult man is about 150 milliliters. Dead space air increases slightly with age.
Some of the alveoli are nonfunctional
or only partially functional because of absent or poor blood flow through the adjacent pulmonary capillaries called as alveolar dead space.
When the alveolar dead space is
included in the total measurement of dead space, this is called the physiological dead space,
