Respiratory Physiology Flashcards
Click on Answer for some relevant diagrams on internal lung anatomy.
4 major components of respiration
(1) pulmonary ventilation
(2) alveolar gaseous exchange
(3) transport of carbon dioxide and oxygen in the blood
(4) exchange of gases at tissue level
the lungs can be expanded and contracted in two ways …
(1) downward or upward movement of the diaphragm to lengthen or shorten the chest cavity
(2) elevation or depression of the ribs to increase or decrease the anteroposterior diameter of the chest cavity
(a) discuss the mechanism of normal quiet breathing
(b) compare expiration in normal quiet breathing and heavy breathing
(a) Normal quiet breathing is achieved almost entirely by movement of the diaphragm. During inspiration, contraction of the diaphragm pulls the lower surfaces of the lung downward. During expiration, the diaphragm simply relaxes and the elastic recoil of the lungs, chest wall and abdominal structures compresses the lungs to expel air.
(b) During heavy breathing, elastic recoil is not powerful enough to cause the necessary rapid expiration, so extra force is achieved through contraction of abdominal muscles, which pushes the abdominal contents upward against the bottom of the diaphragm, thereby compressing the lungs.
muscles that raise the rib cage
external intercostals, anterior serrati, sternocleidomastoid, scaleni
muscles that pull the rib cage downwards
abdominal recti, internal intercostals
“Continual suction of excess fluid into ________ channels maintains a slight suction between the visceral surface of the lung pleura and the parietal pleural surface of the thoracic cavity. Therefore the lungs are held to the thoracic wall as if glued there, except that they are well lubricated and can slide freely as the chest expands and contracts.”
lymphatic
What is transpulmonary pressure?
This 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 recoil pressure.]
Comment on alveolar pressure.
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 in the airways, i.e. 0 cm H2O pressure. To cause inward flow of air into the alveoli during inspiration, the pressure in the alveoli must fall to a value slightly below atmospheric pressure.
What is lung compliance?
This refers to the extent to which the lungs will expand for each unit increase in transpulmonary pressure.
[The total compliance of both lungs together in the normal adult averages about 200 ml of air/cm H2O transpulmonary pressure.]
elastic forces of the lungs which determine lung compliance can be divided into two …
(1) elastic forces of the lung tissue
(2) elastic forces caused by surface tension of the fluid that lines inside the walls of the alveoli
________ cells are cells that secrete surfactant in the lung alveoli.
type II alveolar epithelial cells/type II pneumocytes
What is the effect of surfactant on surface tension?
surfactants reduce surface tension
What is the physiological basis of Respiratory Distress Syndrome of the Newborn?
This syndrome is characterized by breathing difficulties and cyanosis in premature newborn. The primary cause is insufficient or lack of surfactant in the lungs. Surfactant production usually starts around 24 weeks of pregnancy and is sufficient by 34 - 36 weeks. Babies born before 28 weeks are particularly at risk.
Explain each of the following pulmonary volumes.
(a) Tidal volume
(b) Inspiratory reserve volume
(c) Expiratory reserve volume
(d) Residual volume
(a) Tidal volume: This is the volume of air inspired or expired with each normal breath; it amounts to about 500 ml in the average healthy man.
(b) Inspiratory reserve volume: This is the extra volume of air that can be inspired over and above the normal tidal volume when the person inspires with full force; it is usually equal to about 3000 ml.
(c) Expiratory reserve volume: This is the maximum extra volume of air that can be expired forcefully after the end of a normal tidal expiration; this volume normally amounts to about 1100 ml in men.
(d) Residual volume: This is the volume of air remaining in the lungs after the most forceful expiration; this volume averages about 1200 ml.
[8-minute video]: Lung Volumes and Capacities
Explain the following pulmonary capacities:
(a) Inspiratory capacity
(b) Functional residual capacity
(c) Vital capacity
(d) Total lung capacity
(a) Inspiratory capacity: the amount of air that a person can breathe in, beginning at the normal expiratory level and distending the lungs to the maximum amount. It equals tidal volume plus the inspiratory reserve volume.
(b) Functional residual capacity is the amount of air that remains in the lungs at the end of normal expiration. It equals the expiratory reserve volume plus the residual volume.
(c) Vital capacity: the maximum amount of air a person can expel from the lungs after first filling the lungs to their maximum extent and then expiring to the maximum extent. It equals the inspiratory reserve volume plus the tidal volume plus the expiratory reserve volume.
(d) Total lung capacity: The maximum volume to which the lungs can be expanded with the greatest possible effort. It is equal to the vital capacity plus the residual volume.
[8-minute video]: Lung Volumes and Capacities
Distinguish between anatomical and physiological dead space.
Anatomical dead space refers to the volume of air in the respiratory system that does not participate in gaseous exchange. It includes airways from the nose or mouth down to the terminal bronchioles [conducting airways].
Physiological dead space includes the anatomical dead space plus any alveoli that are ventilated but not perfused with blood, meaning they do not participate in gaseous exchange. It is roughly equivalent to the anatomical dead space, but can be larger in individuals with lung disease.
How is the rate of alveolar ventilation calculated?
VA = Freq × (VT −VD)
Where:
VA is the volume of alveolar ventilation per minute,
Freq is the frequency of respiration per minute
VT is the tidal volume, and VD is the physiological dead space volume.
Discuss autonomic innervation of the bronchioles.
Sympathetic dilation of bronchioles is brought about by stimulation of beta-adrenergic receptors upon binding with epinephrine or norepinephrine.
Parasympathetic constriction of the bronchioles is mediated by acetylcholine.
Bronchial arteries which supply the lung tissue are branches of ________.
the thoracic aorta
[Diagram]
Compare anatomical differences between systemic and pulmonary arteries.
(1) Systemic arteries have thicker walls with more smooth muscle and elastic tissue. This is necessary to withstand the higher pressure required to pump blood throughout the entire body. Pulmonary arteries on the other hand, have thinner walls with less smooth muscle and elastic tissue. This is because they operate under lower pressure compared to systemic arteries.
(2) Systemic arteries have narrower diameters compared to pulmonary arteries which helps to maintain the high pressure needed for systemic circulation.
(3) The walls of systemic arteries are highly elastic to accommodate the pulsatile flow of blood from the heart and to help maintain pressure during diastole, whereas the walls of pulmonary arteries are less elastic reflecting the lower pressure and shorter distance the blood needs to travel to reach the lungs.
“For adequate aeration of blood to occur, the blood must be distributed to the segments of the lungs where the alveoli are best oxygenated.” Explain the mechanism behind this distribution.
When the concentration of oxygen in the alveolar air falls below normal [about 70%], the adjacent blood vessels constrict. This effect is opposite to the effect observed in systemic vessels, which dilate rather than constrict in response to low oxygen levels.
Further notes:
Although the mechanisms that promote pulmonary vasoconstriction duirng hypoxia are not completely understood, low oxygen concentration may have the following effects:
(1) stimulate release of, or increase sensitivity to, vasoconstrictor substances such as endothelin or reactive oxygen species; or
(2) decrease release of vasodilator, such as nitric oxide from the lung tissue.
(a) What causes the capillaries in the alveolar walls to distend?
(b) What compresses the capillaries in the alveolar walls from the outside?
(c) What happens when the lung alveolar air pressure becomes greater than the capillary blood pressure?
(a) The blood pressure inside them.
(b) The alveolar air pressure.
(c) The capillaries close and there is no blood flow.
Explain Zone 1 of pulmonary blood flow.
This zone of pulmonary blood flow only exists in pathological conditions. In this zone, there is no blood flow at all in all phases of the cardiac cycle. This is because the alveolar capillary pressure fails to rise above the alveolar air pressure during any part of the cardiac cycle.
The pulmonary systolic arterial pressure may be too low, or the alveolar air pressure may be too high.
[5-minute video]: Zones of Pulmonary Blood Flow - Osmosis from Elsevier
