Respiratory Physiology I: Guyton Chapter 38 - 41 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.]
[Diagram 1] [Diagram 2]
[6-minute video]: Alveolar Pressure and Pleural Pressure
Further notes:
✔ TPP = Palv − Ppl
✔ This pressure difference is crucial because it represents the distending pressure that keeps the lungs expanded. Under normal physiological conditions, the transpulmonary pressure is always positive, which helps prevent lung collapse.
✔ It is an outward acting 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
What is the law of Laplace and what are its implications in the sizes of alveoli?
The law of Laplace describes the relationship between the pressure inside a spherical structure, the surface tension of the walls, and the radius of the structure. The law is mathematically expressed as:
P = 2T/r
The law of Laplace explains that smaller alveoli have a higher internal pressure compared to larger alveoli if the surface tension is constant. This would theoretically cause smaller alveoli to collapse and larger alveoli to expand further, leading to instability.
________ 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 during 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
Explain Zone 2 of pulmonary blood flow.
In this zone, there is intermittent blood flow only during the peaks of the pulmonary arterial pressure because the systolic pressure is greater than the alveolar air pressure, but the diastolic pressure is lower than the alveolar air pressure.
The apical parts of the lung experience this type of blood flow.
[5-minute video]: Zones of Pulmonary Blood Flow - Osmosis from Elsevier
Explain Zone 3 of pulmonary blood flow.
In zone 3 there is continuous blood flow because the alveolar capillary pressure remains greater than the alveolar air pressure during the entire cardiac cycle.
Lower regions of the lungs from about 10 cm above the level of the heart all the way to the bottom of the lungs experience continuous flow through alveolar capillaries.
[5-minute video]: Zones of Pulmonary Blood Flow - Osmosis from Elsevier
What happens to bood flow in the lungs when a person is lying down?
When a person is lying down, no part of the lung is more than a few centimeters above the level of the heart. In this case, the blood flow in a normal person is entirely zone 3 blood flow, including the lung apices.
Explain why exercise increases blood flow to the apices of the lungs.
Exercise necessitates increased pulmonary vascular pressures, converting the apices of the lung from zone 2 regions to zone 3 regions.
Regarding the length of time blood stays in the pulmonary capillaries …
(a) How long does blood stay in the pulmonary capillaries when cardiac output is normal?
(b) How long does blood stay in the pulmonary capillaries when the cardiac output increases?
(c) What mechanism helps accommodate increased blood flow in the pulmonary capillaries when the cardiac output is higher?
(a) about 0.8 seconds
(b) as little as 0.3 seconds
(c) additional capillaries which are normally closed, open up
Further notes:
Capillary Recruitment
💨 At rest, not all pulmonary capillaries are open. Some remain closed or underutilized because the demand for oxygen and the need to remove carbon dioxide is relatively low.
💨 During exercise or other activities that increase cardiac output, the heart pumps more blood through the pulmonary circulation. This increased blood flow requires the lungs to accomodate a higher volume of blood.
💨 To handle the increased blood flow, previously closed or underutilized capillaries in the lungs open up. This process is known as capillary recruitment. Capillary recruitment increases the surface area available for gas exchange, allowing more oxygen to enter the blood and more carbon dioxide to be expelled.
💨 Mechanism: The increased blood flow raises the hydrostatic pressure in the pulmonary arteries, which helps to open the previously closed capillaries. The smooth muscles in the walls of the pulmonary arterioles relax, allowing more blood to flow through the capillaries.
What keeps the alveoli from filling with fluid under normal conditions?
The pulmonary capillaries and pulmonary lymphatic system maintain a slight negative pressure in the interstitial spaces, which prevents fluid accumulation in the alveoli.
How is extra fluid in the alveoli managed?
Extra fluid is mechanically sucked into the lung interstitium through small openings between the alveolar epithelial cells and then carried away through the pulmonary lymphatics [negative pressure].
What is pulmonary edema?
This refers to the acculumation of excess fluid in the lung alveoli and interstitial spaces.
What are two most common causes of pulmonary edema?
(a) Left-sided heart failure or mitral valve disease, with consequent great increases in pulmonary venous pressure and pulmonary capillary pressure and flooding of the interstitial spaces and alveoli.
(b) Damage to the pulmonary blood capillary membranes caused by infections such as pneumonia or by breathing noxious substances such as chlorine gas or sulfur dioxide gas.
[Diagram]: Pulmonary Edema
A negative force is always required on the outside of the lungs to keep them expanded. This negative force is provided by the negative pressure in the normal pleural space. What is the basic cause of the negative pressure in the pleural space?
The pumping of fluid from the space by lymphatics.
(1) What is the usual pleural fluid pressure measured in the lungs?
(2) What is the minimum pleural fluid pressure required to keep the lungs expanded?
(1) - 7 mm Hg
(2) - 4 mm Hg
What is the partial pressure of a gas?
This is the pressure that a single gas in a mixture of gases would exert if it occupied the entire volume by itself.
What is Dalton’s law of partial pressures?
This law states that the total pressure of a mixture of gases is equal to the sum of the partial pressures of each individual gas in the mixture.
[Diagram]
What is Henry’s law?
Henry’s law states that the amount of gas that dissolves in a liquid is directly proportional to the partial pressure of that gas above the liquid, provided the temperature remains constant. [Diagram]
What is a compositional change that happens to atmospheric air as it enters the respiratory passages?
It becomes almost totally humidified by the fluids covering the respiratory surfaces.
What is the partial pressure of water vapor at normal body temperature (37°C)?
47 mm Hg
Why is the slow replacement of alveolar air important?
The slow replacement of alveolar air is crucial in preventing sudden changes in gas concentrations in the blood. This stabilizes the respiratory control mechanism, helping to prevent excessive fluctuations in tissue oxygenation, CO₂ concentration, and pH when respiration is temporarily interrupted.
What two factors control the oxygen concentration and partial pressure in the alveoli?
(1) The rate of absorption of oxygen into the blood.
(2) The rate of entry of new oxygen into the lungs by the ventilatory process.
