Respiratory Physiology I: Guyton Chapter 38 - 41 Flashcards
5
Q
Click on Answer for some relevant diagrams on internal lung anatomy.
6
Q
4 major components of respiration
A
(1) pulmonary ventilation
(2) alveolar gaseous exchange
(3) transport of carbon dioxide and oxygen in the blood
(4) exchange of gases at tissue level
7
Q
the lungs can be expanded and contracted in two ways …
A
(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
8
Q
(a) discuss the mechanism of normal quiet breathing
(b) compare expiration in normal quiet breathing and heavy breathing
A
(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.
9
Q
muscles that raise the rib cage
A
external intercostals, anterior serrati, sternocleidomastoid, scaleni
10
Q
muscles that pull the rib cage downwards
A
abdominal recti, internal intercostals
11
Q
“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.”
A
lymphatic
12
Q
What is transpulmonary pressure?
A
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.
13
Q
Comment on alveolar pressure.
A
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.
14
Q
What is lung compliance?
A
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.]
15
Q
elastic forces of the lungs which determine lung compliance can be divided into two …
A
(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
16
Q
What is the law of Laplace and what are its implications in the sizes of alveoli?
A
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.
17
Q
________ cells are cells that secrete surfactant in the lung alveoli.
A
type II alveolar epithelial cells/type II pneumocytes
18
Q
What is the effect of surfactant on surface tension?
A
surfactants reduce surface tension
19
Q
What is the physiological basis of Respiratory Distress Syndrome of the Newborn?
A
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.
20
Q
Explain each of the following pulmonary volumes.
(a) Tidal volume
(b) Inspiratory reserve volume
(c) Expiratory reserve volume
(d) Residual volume
A
(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
21
Q
Explain the following pulmonary capacities:
(a) Inspiratory capacity
(b) Functional residual capacity
(c) Vital capacity
(d) Total lung capacity
A
(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
22
Q
Distinguish between anatomical and physiological dead space.
A
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.
23
Q
How is the rate of alveolar ventilation calculated?
A
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.
24
Q
Discuss autonomic innervation of the bronchioles.
A
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.
25
Bronchial arteries which supply the lung tissue are branches of ________.
the thoracic aorta
[**[Diagram](https://radiologykey.com/wp-content/uploads/2018/10/9783132004818_c006_f001.jpg)**]
26
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.
27
"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.
28
(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.
29
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](https://youtu.be/uLtueVyNJ9Y?si=NV6fokk9OlyMXqTW)**]: Zones of Pulmonary Blood Flow - Osmosis from Elsevier
30
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](https://youtu.be/uLtueVyNJ9Y?si=NV6fokk9OlyMXqTW)**]: Zones of Pulmonary Blood Flow - Osmosis from Elsevier
31
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](https://youtu.be/uLtueVyNJ9Y?si=NV6fokk9OlyMXqTW)**]: Zones of Pulmonary Blood Flow - Osmosis from Elsevier
32
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.
33
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.
34
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.
35
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.
36
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].
37
What is pulmonary edema?
This refers to the acculumation of excess fluid in the lung alveoli and interstitial spaces.
38
What are two most common causes of pulmonary edema?
(a) **Left-sided heart failure** or **[mitral valve disease](https://www.mayoclinic.org/-/media/kcms/gbs/patient-consumer/images/2013/08/26/10/53/hb7_mitralprolapsethu_jpg.jpg)**, 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](https://my.clevelandclinic.org/-/scassets/images/org/health/articles/24218-pulmonary-edema)**]: Pulmonary Edema
39
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.
40
(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 mmHg
(2) - 4 mmHg
41
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.
42
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](https://cdn1.byjus.com/wp-content/uploads/2018/07/Dalton%E2%80%99s-Law.png)**]
43
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](https://cdn1.byjus.com/wp-content/uploads/2016/10/Henrys-Law-700x327.png)**]
44
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.
45
What is the partial pressure of water vapor at normal body temperature (37°C)?
47 mmHg
46
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.
47
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.
48
What are the six layers of the respiratory membrane?
(1) A layer of fluid containing surfactant that lines the alveolus and reduces the surface tension of alveolar fluid
(2) The alveolar epithelium, composed of thin epithelial cells
(3) An epithelial basement membrane
(4) A thin interstitial space between the alveolar epithelium and capillary membrane
(5) A capillary basement membrane that in many places fuses with the alveolar epithelial basement membrane
(6) The capillary endothelial membrane
[**[Diagram](https://i.pinimg.com/564x/c6/c9/47/c6c947c4b802be8ca41e3431f692510f.jpg)**]
49
(a) How much blood is in the capillaries of the lungs at any given instant?
(b) What is the estimated total surface area of the respiratory membrane in healthy men?
(a) The total quantity of blood in the capillaries of the lungs at any given instant is 60 to 140 ml.
(b) about 70 square meters
*Further notes:*
"Now, imagine this small amount of blood spread over the entire surface of a 25 × 30-foot floor (70 square meters), and it is easy to understand the rapidity of the respiratory exchange of O2 and CO2."
50
The average diameter of the pulmonary capillaries is only about 5 micrometers, which means that the red blood cells must squeeze through them. **How does the close contact between red blood cells and the capillary wall affect gas exchange?**
The close contact between red blood cells and the capillary wall means that O2 and CO2 need not pass through significant amounts of plasma, increasing the rapidity of diffusion between the alveolus and red blood cell.
51
List four factors that will determine how rapidly a gas will pass through the respiratory membrane.
(1) the thickness of the membrane
(2) the surface area of the membrane
(3) the diffusion coefficient of the gas in the substance of the membrane
(4) the partial pressure difference of the gas between the two sides of the membrane.
52
What can cause an increase in the thickness of the respiratory membrane?
**Edema** fluid in the interstitial space and alveoli, as well as **pulmonary diseases like fibrosis**, can increase the thickness of the respiratory membrane.
53
What conditions can decrease the surface area of the respiratory membrane?
Conditions such as the **removal of an entire lung** and diseases like **[emphysema](https://cdn.britannica.com/04/100104-050-9C3C04EB/Emphysema-walls-alveoli-oxygen-intake-loss-lungs.jpg)**, where alveoli coalesce and alveolar walls dissolve, can greatly decrease the surface area of the respiratory membrane.
54
What factors determine the diffusion coefficient for gas transfer through the respiratory membrane?
The diffusion coefficient depends on the **gas’s solubility in the membrane** and **inversely on the square root of the gas’s molecular weight**.
55
What determines the pressure difference of a gas across the respiratory membrane?
The pressure difference is the difference between the partial pressure of the gas in the alveoli and the partial pressure of the gas in the pulmonary capillary blood.
56
# *Measurement of Diffusing Capacity - The Carbon Monoxide Method*
How is the CO diffusing capacity measured (DLCO)?
(1) The patient inhales a small amount of a harmless gas mixture, usually containing a very low concentration of carbon monoxide.
(2) The patient holds their breath for about 10 seconds to allow the gases to diffuse across the alveolar-capillary membrane.
(3) The patient then exhales, and the concentration of carbon monoxide in the exhaled breath is measured.
(4) The difference in the concentration of carbon monoxide between the inhaled and exhaled air is used to calculate the DLCO. This measurement reflects the efficiency of gas transfer from the alveoli into the blood.
[**[10-minute video](https://youtu.be/oOkNS-vvnhQ?si=moCFX3MuNcImx3kn)**]: Diffusing capacity of the lung for carbon monoxide (DLCO)
57
# *Measurement of Diffusing Capacity - The Carbon Monoxide Method*
How is the CO diffusing capacity converted to O2 diffusing capacity?
The CO diffusing capacity value is multiplied by a factor of 1.23 because the diffusion coefficient for O2 is 1.23 times that for CO.
58
# *Measurement of Diffusing Capacity - The Carbon Monoxide Method*
What is the average diffusing capacity for CO in healthy young men at rest?
The average diffusing capacity for CO in healthy young men at rest is 17 ml/min per mmHg.
59
# *Measurement of Diffusing Capacity - The Carbon Monoxide Method*
What is the average diffusing capacity for O2 in healthy young men at rest?
The average diffusing capacity for O2 is 1.23 times the CO diffusing capacity, which is 21 ml/min per mmHg.
60
(a) What is V/Q ratio?
(b) What is the ideal V/Q ratio?
(a) ventilation/perfusion ratio
(b) 0.8 [meaning that for every litre of blood flowing through the pulmonary capillaries, there is about 0.8 litres of air reaching the alveoli]
61
# *Transport of Oxygen and Carbon Dioxide in Blood and Tissue Fluids*
What effect does increasing blood flow have on interstitial fluid PO2?
It increases interstitial fluid PO2.
*Further notes:*
"Howerver, the upper limit to which the PO2 can rise, even with maximal blood flow, is 95 mmHg because this is the O2 pressure in the arterial blood. Conversely, if blood flow through the tissue decreases, the tissue PO2 also decreases."
62
# *Transport of Oxygen and Carbon Dioxide in Blood and Tissue Fluids*
Define utilization coefficient.
This refers to the percentage of oxygen that is extracted from the blood by the tissues as it passes through the capillaries.
*Further notes:*
It is calculated as the difference between the oxygen content of arterial blood and venous blood, divided by the oxygen content of arterial blood, and then multiplied by 100.
63
# *Transport of Oxygen and Carbon Dioxide in Blood and Tissue Fluids*
What is the role of hemoglobin in maintaining PO2 in tissues under basal conditions?
Hemoglobin helps maintain a nearly constant PO2 in tissues by releasing about 5 ml of O2 per 100 ml of blood, keeping tissue PO2 around 40 mmHg.
64
# *Transport of Oxygen and Carbon Dioxide in Blood and Tissue Fluids*
How does hemoglobin respond during heavy exercise?
During heavy exercise, **hemoglobin delivers up to 20 times more O2** to tissues with little decrease in tissue PO2 due to the steep slope of the dissociation curve and increased blood flow.
65
# *Transport of Oxygen and Carbon Dioxide in Blood and Tissue Fluids*
What happens to tissue PO2 when atmospheric oxygen concentration changes markedly?
**Hemoglobin buffers tissue PO2** effectively, keeping it relatively stable despite significant changes in alveolar PO2 from 60 to over 500 mmHg.
66
# *Transport of Oxygen and Carbon Dioxide in Blood and Tissue Fluids*
What are four factors that can shift the oxygen-haemoglobin dissociation curve to the right?
(1) a lower than normal blood pH value (e.g. 7.2)
(2) increased CO2 concentration
(3) increased blood temperature
(4) increased 2,3-biphosphoglycerate (BPG)
*Further notes:*
2,3-bisphosphoglycerate increases the ability of haemoglobin to release oxygen.
67
What are some conditions that may increase blood 2,3-BPG levels?
(a) High altitude
(b) Chronic hypoxia
(c) Anemia
(d) Hyperthyroidism [can increase metabolic rate and oxygen consumption, leading to elevated BPG levels to meet the higher oxygen demands of tissues.]
68
# *Transport of Oxygen and Carbon Dioxide in Blood and Tissue Fluids*
What is the Bohr effect?
The Bohr effect is a physiological phenomenon where an increase in carbon dioxide (CO2) levels or a decrease in pH (increased acidity) in the blood reduces hemoglobin’s affinity for oxygen (O2).
69
# *Transport of Oxygen and Carbon Dioxide in Blood and Tissue Fluids*
What happens to the oxygen-hemoglobin dissociation curve in the lungs?
In the lungs, CO2 diffuses from the blood into alveoli, reducing blood PCO2 and H+ concentration, shifting the dissociation curve to the left and upward.
70
# *Transport of Oxygen and Carbon Dioxide in Blood and Tissue Fluids*
What is the result of the dissociation curve shifting to the left in the lungs?
The quantity of O2 that binds with hemoglobin at any given alveolar PO2 increases, allowing greater O2 transport to the tissues.
71
# *Transport of Oxygen and Carbon Dioxide in Blood and Tissue Fluids*
Why does a small fall in PO2 cause large amounts of extra O2 to be released from hemoglobin?
Due to the **steep slope of the dissociation curve** and **increased tissue blood flow** caused by decreased PO2. [**[Diagram](https://rk.md/wp-content/uploads/2017/04/oxyhemoglobin-dissociation-curve-rk.webp)**]
72
Why is CO poisoning particularly dangerous despite normal PO2 levels in the blood?
CO poisoning is dangerous because the **blood remains bright red**, **masking signs of hypoxemia like cyanosis**, and the normal PO2 **levels do not trigger the feedback mechanism** to increase respiration rate.
73
What are the initial symptoms of CO poisoning affecting the brain?
The initial symptoms include **disorientation** and **unconsciousness** due to the brain being one of the first organs affected by lack of oxygen.
74
How can a patient severely poisoned with CO be treated?
Treatment includes **administering pure O2 to displace CO from hemoglobin** and **simultaneous administration of 5% CO2 to stimulate the respiratory center**, increasing alveolar ventilation and reducing alveolar CO.
75
State three ways in which carbon dioxide is transported in the blood.
(a) in its dissolved state
(b) as bicarbonate ion
(c) in combination with haemoglobin; carbaminohaemoglobin
76
What enzyme catalyzes the reaction between CO2 and water in red blood cells?
carbonic anhydrase
77
As soon as H₂CO₃ is formed, it dissociates into H⁺ and HCO₃⁻ ions. Briefly discuss the fate of each.
💨 Most of the **H⁺ ions combine with haemoglobin** in the red blood cells because **haemoglobin is a powerful acid-base buffer**.
💨 In turn, many of the **HCO₃⁻ ions diffuse from the red blood cells into the plasma** while **chloride ions diffuse into the red blood cells** to take their place. This diffusion is made possible by the presence of a special *bicarbonate-chloride carrier protein* in the red blood cell membrane that shuttles these two ions in opposite directions at rapid velocities. [Thus, the chloride content of venous red blood cells is greater than that of arterial red blood cells, a phenomenon called the *chloride shift*.]
78
What is the Haldane effect?
The Haldane effect is a property of haemoglobin where oxygenation of blood in the lungs displaces carbon dioxide from haemoglobin, thereby increasing the removal of carbon dioxide. [**[Diagram](https://ars.els-cdn.com/content/image/3-s2.0-B9780128012383116320-f11632-02-9780081027233.jpg)**]
*Further notes:*
💨 The Haldane effect results from the simple fact that the combination of O2 with hemoglobin in the lungs causes the hemoglobin to become a stronger acid.
💨 When oxygen binds to haemoglobin in the lungs, it causes haemoglobin to release hydrogen ions, making it a stronger acid. This increase in acidity promotes the release of carbon dioxide from haemoglobin.
79
How is respiratory quotient calculated?
Rate of carbon dioxide output / Rate of oxygen uptake
80
With respect to regional gas exchange in the upright lung, which of the following is true?
(a) Perfusion is much greater at the top of the lungs compared with the bases
(b) Both ventilation and perfusion are greater at the base of the lung
(c) Ventilation/perfusion ratio is abnormally high at the top of the lungs
(d) Ventilation is greater at the top of the lungs
(e) Perfusion without ventilation leads to absolute physiologic dead space
(b) Both ventilation and perfusion are greater at the base of the lung
and
(c) Ventilation/perfusion ratio is abnormally high at the top of the lungs
*Further notes:*
With regards to choice (e):
**Absolute physiologic dead space** refers to areas of the lung **where there is ventilation but no perfusion**, meaning air reaches the alveoli, but no blood flow is available for gas exchange.
81
Which of these does not affect diffusion rate?
(a) Humidity of gas
(b) Thickness of respiratory membrane
(c) Surface area for diffusion
(d) Molecular weight of gas
(e) Concentration gradient
(a) Humidity of gas
82
If a patient has increased resistance in his or her lungs, how can this be detected by a doctor?
(a) This can be detected using a nebulizer. By detecting the rate at which air can be taken into the lung, a diagnosis of a restrictive disease can be made.
(b) This can be detected using spirometry. By detecting the rate at which air can be expelled from the lung, a diagnosis of a restrictive disease can be made.
(c) This can be detected using spirometry. By detecting the rate at which air can be taken into the lung, a diagnosis of a restrictive disease can be made.
(d) This can be detected using a nebulizer. By detecting the rate at which air can be expelled from the lung, a diagnosis of a restrictive disease can be made.
(e) All of the above.
(b) This can be detected using spirometry. By detecting the rate at which air can be expelled from the lung, a diagnosis of a restrictive disease can be made.
*Further notes:*
💨 Increased resistance in the lungs is typically associated with obstructive lung diseases (such as asthma or chronic obstructive pulmonary disease - COPD), rather than restrictive diseases. However, spirometry can help detect both types of conditions.
💨 Nebulizers are used to deliver medication directly to the lungs and are not diagnostic tools for measuring lung function.
💨 Spirometry primarily measures the volume of air that is exhaled and the speed at which it is exhaled.
83
Airway resistance to air flow ____________.
(a) is decreased at high altitude
(b) varies directly with the fourth power of the radius
(c) is increased in asthma
(d) is reduced when breathing helium – oxygen gas mixture
(e) varies directly with the velocity of flow
(c) is increased in asthma
84
Intra-pleural pressure ____________.
(a) is subatmospheric throughout normal inspiration and expiration
(b) becomes less subatmospheric during inspiration with a high airway resistance
(c) rises above atmospheric pressure with a forced expiration against resistance
(d) becomes more subatmospheric with inspiration
(e) can be assessed by measuring intragastric pressure
Both of the following answers are correct:
(a) is subatmospheric throughout normal inspiration and expiration
(d) becomes more subatmospheric with inspiration
*Further notes:*
Intra-pleural pressure is the pressure within the pleural cavity. It is typically subatmospheric (negative) during normal breathing to keep the lungs inflated.
85
How does the administration of 100% oxygen save a patient from carbon monoxide poisoning? Why wouldn't giving carbon dioxide work?
(a) At that concentration, oxygen will be transported in the body at a high rate by dissolving in blood. Carbon dioxide has more affinity for haemoglobin than oxygen.
(b) At that concentration, oxygen will displace the carbon monoxide from the haemoglobin. Carbon dioxide has more affinity for haemoglobin than oxygen.
(c) At that concentration, oxygen will displace the carbon monoxide from the haemoglobin. Oxygen has more affinity for haemoglobin than carbon dioxide.
(d) At that concentration, oxygen will be transported in the body at a high rate by dissolving in blood. Oxygen has more affinity for haemoglobin than carbon dioxide.
(e) None of the above.
(c) At that concentration, oxygen will displace the carbon monoxide from the haemoglobin. Oxygen has more affinity for haemoglobin than carbon dioxide.
86
Compare the partial pressure of oxygen between venous blood and air in an alveolus, and between arterial blood and body tissues.
(a) lower in the blood than in the air and higher in the blood than in the body tissues
(b) higher in the blood than in the air and higher in the blood than in the body tissues
(c) higher in the blood than in the air and lower in the blood than in the body tissues
(d) lower in the blood than in the air and lower in the blood than in the body tissues
(e) none of the above
(a) lower in the blood than in the air and higher in the blood than in the body tissues
87
When someone is standing, gravity stretches the bottom of the lung down toward the floor to a greater extent than the top of the lung. What implication could this have on ventilation in the lungs?
(a) concentration gradient leads to decreased ventilation further down in the lung
(b) pleural pressure gradient leads to decreased ventilation further down in the lung
(c) posture has no effect on ventilation
(d) concentration gradient leads to increased ventilation further down in the lung
(e) pleural pressure gradient leads to increased ventilation further down in the lung
(e) pleural pressure gradient leads to increased ventilation further down in the lung
88
During maximal inspiration in a healthy adult ________.
(a) heart rate is reduced
(b) skeletal muscles of the diaphragm relax
(c) intra-pleural pressure rises to about 2 mmHg
(d) venous return is decreased
(e) alveolar ventilation increases
(e) alveolar ventilation increases
89
Amphibians such as frogs breathe by collecting air in a pouch below their throat. Muscles then contract the pouch and force air into their lungs. How does this differ from inhalation in humans and other mammals?
(a) Inhalation in humans and other mammals involves contracting the thoracic cavity by creating negative pressure in the lungs, which causes air to diffuse into the lungs.
(b) Inhalation in humans and other mammals involves expanding the thoracic cavity by creating negative pressure in the lungs, which causes air to diffuse into the lungs.
(c) Inhalation in humans and other mammals involves openings called spiracles, which connect to the tubular network to allow the oxygen to pass into the body.
(d) Inhalation in humans and other mammals involve direct diffusion across the outer membrane to meet oxygen requirements. Gases can diffuse quickly through direct diffusion.
(e) None of the above.
(b) Inhalation in humans and other mammals involves expanding the thoracic cavity by creating negative pressure in the lungs, which causes air to diffuse into the lungs.
90
A patient has a dead space of 150 ml, functional residual capacity of 3 L, tidal volume of 650 ml, expiratory reserve volume of 1.5 L, total lung capacity of 8 L, and respiratory rate of 15 breaths/min. What is the residual volume?
(a) 500 ml
(b) 1500 ml
(c) 6500 ml
(d) 2500 ml
(e) 1000 ml
(b) 1500 ml
91
If you were travelling in a miniaturized ship through the respiratory system from the pharynx to the alveolus, which structures would you pass along the way, and in what order?
(a) bronchioles, trachea, bronchi, and larynx
(b) larynx, trachea, bronchi, and the bronchioles
(c) bronchioles, bronchi, trachea and larynx
(d) trachea, larynx, bronchi, and bronchioles
(e) trachea, bronchioles, bronchi and larynx
(b) larynx, trachea, bronchi, and the bronchioles
92
The volume of air that can be exhaled after normal exhalation is the ________.
(a) inspiratory reserve volume
(b) expiratory reserve volume
(c) residual volume
(d) forced expiratory volume
(e) none of the above
(c) expiratory reserve volume
93
During inspiration there is an increase in ________.
(a) intra-pleural pressure
(b) intra-oesophageal pressure
(c) intra-thoracic pressure
(d) intra-pulmonary pressure
(e) intra-abdominal pressure
(e) intra-abdominal pressure
94
After inspiration commences, the ________.
(a) intra-pleural pressure falls and venous return decreases
(b) intra-pulmonary pressure rises and volume of the alveoli is momentarily unchanged
(c) intra-pleural pressure falls and intra-pulmonary pressure rises
(d) intra-pleural pressure and intra-pulmonary pressure both fall
(e) intra-pleural pressure rises and venous return to heart decreases
(d) intra-pleural pressure and intra-pulmonary pressure both fall
95
Regarding oxygen transport
(a) 1 gram of pure Hb can combine with 1.34 - 1.39 ml of oxygen
(b) Carbon dioxide is 200 times more soluble than oxygen
(c) The CO2 dissociation curve is less steep than that of oxygen
(d) An anaemic patient has a lowered arterial PO2 because the Hb is low
(e) The predominant way oxygen is transported in the blood is as dissolved oxygen
(a) 1 gram of pure Hb can combine with 1.34 - 1.39 ml of oxygen
(c) The CO2 dissociation curve is less steep than that of oxygen
*Further notes:*
Regarding (c): The CO2 dissociation curve is generally more linear and less steep compared to the sigmoid shape of the oxygen dissociation curve.
96
Alveolar ventilation in a male with a respiratory rate of 10 breath/min and tidal volume of 600 ml is ________.
(a) 1000 ml
(b) 4500 ml
(c) 3000 ml
(d) 1750 ml
(e) 6000 ml
(b) 4500 ml
97
During quiet respiration
(a) Intra-alveolar pressure is always subatmospheric
(b) External intercostal muscles contract in the inspiratory phase
(c) Intra-pleural pressure is always subatmospheric
(d) Volume of air left in the lungs at the end of inspiration constitutes the vital capacity
(e) Volume of air left in the lungs at the end of expiration constitutes the residual volume
(c) Intra-pleural pressure is always subatmospheric
98
How does the structure of alveoli maximize gas exchange?
(a) Their direct connection to the bronchi maximizes their access to air.
(b) They are spheres that fully fill with blood, which will come in contact with air.
(c) Their sac-like structure increases their surface area.
(d) They actively transport the gases between the air and blood.
(e) None of the above.
(c) Their sac-like structure increases their surface area.
99
Spirometry can measure all the following except ________.
(a) IC
(b) ERV
(c) FRC
(d) Vital capacity
(e) TV
(c) FRC
*Explanation*:
**Functional residual capacity (FRC)**: The volume remaining in the lungs after a normal exhalation. FRC includes expiratory reserve volume and residual volume. Since spirometry cannot measure residual volume (RV), it cannot measure FRC directly either.
100
Which statement is false about anatomical dead space?
(a) anatomical dead space varies with age
(b) can be estimated by the Fowler's method
(c) significantly large in shallow breathing
(d) measured by plotting N2 concentration against expired volume as in Bohr's method
(e) estimated at around 150 ml in a 75 kg man with TV 500 ml
(c) significantly large in shallow breathing
(d) measured by plotting N2 concentration against expired volume as in Bohr's method
*Explanation:*
**Regarding (c)**: Anatomical dead space is a fixed volume (approximately 150 ml in a healthy adult), and it does not change with the depth of breathing. However, the proportion of tidal volume taken up by dead space increases with shallow breathing, making it less efficient.
**Regarding (d)**: The Bohr method is used to measure **physiologic dead space**, which includes both anatomical and alveolar dead space. It involves analyzing the partial pressures of gases in the expired air.
101
Surfactant is produced by ________ and acts to ________ alveolar surface tension.
(a) Type II alveolar cells, increase
(b) Type II alveolar cells, decrease
(c) Dust cells, increase
(d) Hepatic cells, decrease
(e) Carbonic anhydrase, decrease
(b) Type II alveolar cells, decrease
102
Which of these values would normally be the highest?
(a) tidal volume
(b) inspiratory reserve volume
(c) expiratory reserve volume
(d) residual volume
(e) vital capacity
(e) vital capacity
103
Which of the following is true?
(a) the elastic recoil of the lungs assists quiet respiration
(b) plasma levels of chloride will be higher in systemic veins than in systemic arteries
(c) approximately 20% of the oxygen in the bloodstream is dissolved in plasma
(d) approximately 80% of the carbon dioxide in the bloodstream is bound to haemoglobin and referred to as carbaminohaemoglobin
(e) an inability to generate carbonic anhydrase is the cause of infant respiratory distress syndrome
(a) the elastic recoil of the lungs assists quiet respiration
(b) plasma levels of chloride will be higher in systemic veins than in systemic arteries
104
Select the correct statement about O2 transport in blood.
(a) During normal activity, a molecule of haemoglobin returning to the lungs contains one molecule of oxygen.
(b) As pH decreases, oxygen's affinity for haemoglobin increases.
(c) Increased BPG levels in the RBC enhance oxygen loading.
(d) A 50% oxygen saturation level of blood returning to the lungs might indicate a higher activity level than normal.
(e) As pH increases, oxygen's affinity for haemoglobin decreases.
(d) A 50% oxygen saturation level of blood returning to the lungs might indicate a higher activity level than normal.
105
Why is it more difficult to breathe in when the stomach is full?
(a) Because the full stomach impedes the downward motion of the contracting diaphragm.
(b) Because the full stomach impedes the downward motion of the relaxing diaphragm.
(c) Because the full stomach prompts a decrease in gastric juice secretion.
(d) Because the full stomach prompts an increase in gastric juice secretion.
(e) Because the full stomach stimulates increased activity in the ventral respiratory group.
(a) Because the full stomach impedes the downward motion of the contracting diaphragm.
106
During inspiration, pressure will be lowest in which of the following?
(a) Alvelolar duct
(b) Trachea
(c) Secondary bronchus
(d) Laryngopharynx
(e) Nasal cavity
(a) Alvelolar duct
107
The respiratory membrane is composed of which structures?
1. Pulmonary capillary endothelium
2. Type 1 alveolar cell membrane
3. Respiratory epithelium
(a) 1, 2 and 3
(b) 1 and 2
(c) 2 and 3
(d) 1 and 3
(e) 3 only
(b) 1 and 2
108
All of these statements about surfactant are true except
(a) Promote stability of alveoli
(b) Reduce surface tension of alveoli
(c) Larger alveoli have lower surface tension than small alveoli according to the law of Laplace
(d) Assist in avoiding transudation of fluid into capillary
(e) Produced by Type II pneumocytes
(d) Assist in avoiding transudation of fluid into capillary
109
The oxygen dissociation curve is shifted to the right by all of the following except
(a) increase [H+]
(b) pCO2
(c) increase in temperature
(d) carbon monoxide
(e) 2,3-DPG
(d) carbon monoxide
110
Alveolar surfactant acts to increase pulmonary
(a) surface tension
(b) compliance
(c) airway resistance
(d) blood flow
(e) both (b) and (d) above
(b) compliance
111
An individual who breathes through a hose or tube while keeping his tidal volume normal would be expected to have an increased (compared to normal) ________.
(a) dead space
(b) wasted ventilation
(c) systemic arterial carbon dioxide content
(d) all of the above
(e) only A and B above
(d) all of the above
112
Regarding the oxygen-haemoglobin dissociation curve, which of the following statements is incorrect?
(a) Shifted to the right by 2,3-diphospholgycerate in erythrocytes
(b) Shifted to the right by carbon dioxide
(c) Shifted to the right by increased temperature
(d) Shifted to the left by biphosphoglycerate
(e) Shifted to the right by lowering pH
(d) Shifted to the left by biphosphoglycerate
113
A healthy, 25-year-old medical student participates in a 10 km charity run for the American Heart Association. Which of the following muscles does the student use during expiration?
(a) diaphragm only
(b) internal intercostals and abdominal recti
(c) scaleni
(d) diaphragm and internal intercostals
(e) diaphragm and external intercostals
(b) internal intercostals and abdominal recti
114
Most of the carbon dioxide in the blood is transported as ________.
(a) solute dissolved in the plasma
(b) carbaminohaemoglobin
(c) bicarbonate ions
(d) solute dissolved in the cytoplasm of red blood cells
(e) carbonic acid
(c) bicarbonate ions
115
The partial pressure of oxygen in the arterial blood is approximately ________ mmHg.
(a) 40
(b) 45
(c) 50
(d) 80
(e) 100
(e) 100
116
The partial pressure of carbon dioxide in the cells of the peripheral tissues is approximately ________ mmHg.
(a) 60
(b) 45
(c) 50
(d) 70
(e) 100
(b) 45
117
The respiratory rate times the tidal volume corrected for dead space is the ________.
(a) vital capacity
(b) inspiratory ventilation rate
(c) pulmonary ventilation rate
(d) alveolar ventilation rate
(e) external respiration rate
(d) alveolar ventilation rate
118
When CO2 diffuses into blood in systemic capillaries most of it ________.
(a) remains in solution as CO2
(b) converts to bicarbonate ions in RBC
(c) converts to carbamino compounds
(d) combines with Hb directly
(e) combines with H2O in plasma to form carbonic acid
(b) converts to bicarbonate ions in RBC
119
What would happen if no carbonic anhydrase was present in red blood cells?
(a) Carbon dioxide would be hydrolyzed into carbonic acid or bicarbonate. The maximum amount of carbon dioxide would be transported in the blood away from the tissues.
(b) Carbon dioxide would not be hydrolyzed into carbonic acid or bicarbonate. The maximum amount of carbon dioxide would be transported in the blood away from the tissues.
(c) Carbon dioxide would not be hydrolyzed into carbonic acid or bicarbonate. Only 15 percent of carbon dioxide would be transported in the blood away from the tissues.
(d) Oxygen would not be hydrolyzed into carbonic acid or bicarbonate. Only 15 percent of carbon dioxide would be transported in the blood away from the tissues.
(e) None of the above.
(c) Carbon dioxide would not be hydrolyzed into carbonic acid or bicarbonate. Only 15 percent of carbon dioxide would be transported in the blood away from the tissues.
120
The alveolar ventilation in a normal adult at rest would be ________.
(a) 7500 ml
(b) 3000 ml
(c) 4500 ml
(d) 6150 ml
(e) 5250 ml
(e) 5250 ml
121
Pulmonary vascular resistance ________.
(a) is greater in the lung during maximal inspiration rather than expiration
(b) is about 1/10 that of systemic circulation
(c) is decreased by recruitment but increased by distension
(d) will decrease in poorly ventilated areas
(e) is not affected by sympathetic nervous system
(b) is about 1/10 that of systemic circulation
*Further notes:*
Regarding choice (c):
✔ Recruitment refers to the opening of previously collapsed capillaries, which **decreases resistance**.
✔ Distension refers to the stretching and widening of capillaries, which **also decreases resistance**.
122
Ventilation and perfusion relationships vary in the upright lung:
(a) ventilation is greater at the apex than base
(b) perfusion is greater at the apex than at the base
(c) variation in ventilation is greater than the variation in perfusion
(d) V/Q is more than 3x greater at the apex than at the base
(e) V/Q approaches infinity at the apex
(d) V/Q is more than 3x greater at the apex than at the base
*Explanation:*
For answer (e), V/Q approaches infinity only when ventilation is present with no perfusion at all, which is not a typical physiological condition at the apex in a healthy individual.
Therefore, the V/Q ratio being more than 3 times greater at the apex than at the base is a more accurate statement to describe the ventilation-perfusion relationship in the upright lung.
122
Carbon dioxide is ________.
(a) carried mostly as carbamino compounds in the blood
(b) carried more effectively by oxygen saturated Hb
(c) is converted to bicarbonate primarily by plasma carbonic anhydrase in the periphery
(d) carried by blood according to a much steeper dissociation curve than oxygen
(e) mostly carried as bicarbonate in the blood, but the arteriovenous difference is mostly due to carbamino compounds
(e) mostly carried as bicarbonate in the blood, but the arteriovenous difference is mostly due to carbamino compounds
*Further notes:*
**Regarding choice (c)**: Carbon dioxide is converted to bicarbonate in the red blood cells rather than in the plasma.
123
(1) The transfer of gas across the pulmonary capillary membrane is ________.
(a) diffusion limited for nitrous oxide
(b) perfusion limited for carbon monoxide
(c) said to be diffusion limited if it is dependent on blood flow
(d) perfusion limited for oxygen under normal conditions
(e) occurs in less than 0.2 seconds for oxygen in normal circumstances
(2) Explain your answer.
(1) (d) perfusion limited for oxygen under normal conditions
(2) **Explanation**:
◾ _Perfusion limitation_ means that **the transfer of a gas across the alveolar-capillary membrane is primarily limited by the amount of blood flow (perfusion) through the pulmonary capillaries rather than by the properties of the gas or the membrane**.
◾ Under normal conditions, oxygen is perfusion limited because it diffuses rapidly across the alveolar-capillary membrane.
◾ The blood becomes almost fully saturated with oxygen very quickly as it passes through the pulmonary capillaries.
◾ Once the blood is saturated, **the only way to increase oxygen uptake is to increase blood flow (perfusion)**.
124
The total lung capacity consists of ________.
(a) vital capacity and tidal volume
(b) residual volume and vital capacity
(c) functional residual capacity and vital capacity
(d) tidal volume and functional residual capacity
(e) tidal volume and residual volume
(b) residual volume and vital capacity
125
Which of the following statements is true?
(a) Surfactant acts to keep alveoli dry.
(b) The base of the lung has small resting volume and expands well on inspiration.
(c) Medium sized bronchi are the chief site of airway resistance.
(d) Intra-pleural pressures reduce during inspiration.
(e) All of the above.
(e) All of the above.
125
The following will reduce lung compliance except ________.
(a) pulmonary congestion
(b) pulmonary fibrosis
(c) alveolar oedema
(d) emphysema
(e) atelectasis
(d) emphysema
126
Pulmonary vasoconstriction occurs in the following circumstances except ________.
(a) hypoxia
(b) sympathetic outflow
(c) high altitude
(d) alkalosis
(e) all of the above
(d) alkalosis
127
Choose the correct expression regarding Zone 2 of the lung.
(a) PA > Pa > Pv
(b) PA > Pv > Pa
(c) Pa > Pv > PA
(d) Pv > Pa > PA
(e) Pa > PA > Pv
(e) Pa > PA > Pv
*Further notes:*
Pa = arterial pressure
PA = alveolar air pressure
128
(1) Which of the following gases is diffusion limited under normal conditions?
(a) nitrous oxide
(b) carbon monoxide
(c) carbon dioxide
(d) oxygen
(e) all of the above
(2) Explain your answer.
(1) (b) carbon monoxide
(2) **Explanation**:
✔ Diffusion limitation occurs when the transfer of a gas across the alveolar-capillary membrane is restricted by the diffusion properties of the gas or the membrane itself.
✔ CO is diffusion limited because it binds very tightly to haemoglobin and hence its transfer across the membrane is dependent on the diffusion capacity of the lung.
✔ The rest of the gases are perfusion limited.
129
At which of the following sites is the partial pressure of oxygen highest?
(a) exhaled gas
(b) anatomical dead space at the end of expiration
(c) anatomical dead space at the end of inspiration
(d) alveolar gas
(e) about the same in all of the above (100 mmHg)
(c) anatomical dead space at the end of inspiration
130
At which of the following sites is the partial pressure of carbon dioxide highest?
(a) exhaled gas
(b) alveolar gas
(c) systemic arterial blood
(d) systemic venous blood
(e) about the same in all of the above (40 mmHg)
(d) systemic venous blood
*Further notes:*
Exhaled gas (a): Contains a mixture of alveolar air and dead space air, with lower PCO2 than venous blood.
131
What would be the expected effect of pulmonary edema on the pulmonary diffusing capacity for oxygen (DO2) and carbon dioxide (DCO2)?
(a) reduce DO2 and reduce DCO2
(b) reduce DO2 but no effect on DCO2
(c) reduce DCO2 but no effect on DO2
(d) no effect on either DO2 or DCO2
(e) no effect on either DO2 or DCO2 unless diffusing area is reduced also
(a) reduce DO2 and reduce DCO2
132
(1) When is the resistance to blood flow of the pulmonary vascular bed lowest?
(a) When a person is at rest sitting up.
(b) When a person is at rest lying down.
(c) When a person is breathing air at high altitude.
(d) When a person is exercising maximally.
(e) None of the above because pulmonary vascular resistance is constant.
(2) Explain your answer.
(1) (d) When a person is exercising maximally.
(2) **Explanation**:
◾ During maximal exercise, the cardiac output increases significantly, leading to higher pulmonary arterial pressure.
◾ This increase in pressure causes recruitment and distension of pulmonary capillaries, which reduces the pulmonary vascular resistance to accommodate the increased blood flow.
133
Compared with pulmonary arterial blood, systemic arterial blood has a higher ________.
(a) oxygen content
(b) pH
(c) bicarbonate ion concentration
(d) chloride concentration
(e) sodium concentration
(a) oxygen content
134
Which of the following concerning average lung volumes and capacities of a person at rest is true?
(a) TLC > VC > TV > FRC
(b) TLC > FRC > VC > TV
(c) TLC > VC > FRC > TV
(d) TLC > FRC > TV > VC
(e) None of the above
(c) TLC > VC > FRC > TV
135
In human beings, partial pressure of carbon dioxide in the inspired and expired air are respectively ________.
(a) 0.3 and 40 mmHg
(b) 0.3 and 32 mmHg
(c) 40 and 46 mmHg
(d) 40 and 0.3 mmHg
(e) 46 and 40 mmHg
(a) 0.3 and 40 mmHg
136
Which one of the following describes the functional residual capacity?
(a) tidal volume + inspiratory reserve volume
(b) tidal volume + inspiratory reserve volume + expiratory reserve volume
(c) residual volume + expiratory reserve volume
(d) total lung capacity - residual volume
(e) vital capacity + residual volume
(c) residual volume + expiratory reserve volume
137
If tidal volume is 500 ml, dead space = 150 ml and frequence of breathing is 15, what is the alveolar minute ventilation?
(a) 7.35 L/min
(b) 2.75 L/min
(c) 5.25 L/min
(d) 9.75 L/min
(e) 2.25 L/min
(c) 5.25 L/min
138
If tidal volume is 500 ml, dead space = 150 ml and frequence of breathing is 12, what is the alveolar minute ventilation?
(a) 6.0 L/min
(b) 7.8 L/min
(c) 1.8 L/min
(d) 4.2 L/min
(e) None of the above
(d) 4.2 L/min
139
Which one of the following represents the pressure difference that acts to distend the lung?
(a) alvelolar pressure
(b) airway opening pressure
(c) transthoracic pressure
(d) transpulmonary pressure
(e) esophageal pressure
(d) transpulmonary pressure
140
The volume of air left in the lungs at the end of passive expiration is known as ________.
(a) expiratory reserve volume
(b) residual volume
(c) tidal volume
(d) functional residual capacity
(e) total lung capacity
(d) functional residual capacity
141
Which of the following is **not true** regarding the alveolar capillary membrane?
(a) Oxygen and carbon dioxide actively diffuse across the membrane barrier.
(b) The gas exchange barrier is about 1 - 2 micrometers in thickness.
(c) The membrane contains type I alveolar epithelial cells, capillary endothelial cells and their basement membranes.
(d) Gas exchange occurs through a mesh-like network of capillaries and alveoli.
(e) RBCs pass through the network in less than one second.
(a) Oxygen and carbon dioxide actively diffuse across the membrane barrier.
142
Which one of the following occurs during inspiration?
(a) Diaphragm contracts, pleural pressure increases, alveolar pressure decreases
(b) Diaphragm relaxes, external intercostals contract, pleural pressure increases
(c) Diaphragm relaxes, pleural pressure decreases, internal intercostals relax
(d) External and internal intercostals contract, pleural and alveolar pressure increases
(e) Diaphragm and external intercostals contract, pleural and alveolar pressure decreases
(e) Diaphragm and external intercostals contract, pleural and alveolar pressure decreases
143
The anatomical dead space in the respiratory system
(a) Is reduced in chronic obstructive pulmonary disease.
(b) Can be measured using "rapidly recording nitrogen metre" technique.
(c) Can be measured through "helium dilution method".
(d) Of adult females is 50% smaller than that of adult males.
(e) In each breath has a volume that is larger than the volume of the alveolar ventilation.
(b) Can be measured using "rapidly recording nitrogen metre" technique.
144
Which one of the following statements is **false** concerning the V/Q ratio?
(a) Absolute physiologic dead space is when V/Q equals infinity.
(b) Wasted ventilation is associated with the apices of the lungs.
(c) Alveoli are smaller in size at the apex of the lung than at the base.
(d) Wasted perfusion is associated with the bases of the lung.
(e) Absolute physiologic shunt is when V/Q equals zero.
(c) Alveoli are smaller in size at the apex of the lung than at the base.
145
Increased respiratory minute volume occurs with ________.
(a) rise in body temperature
(b) renal tubula acidosis
(c) lowered barometric pressure
(d) brain damage
(e) arterial PO2 of 100 mmHg
(a) rise in body temperature
*Explanation:*
An increase in body temperature leads to an increased respiratory minute volume. This is because higher temperatures enhance the sensitivity of peripheral chemoreceptors to oxygen and central chemoreceptors to changes in pH, resulting in increased respiratory rate and tidal volume.
146
The thickness of the gas-exchange membrane separating alveolar air from blood capillaries is typically ________.
(a) 1 micron or less
(b) 5 to 10 microns
(c) 50 to 100 microns
(d) 500 to 1000 microns
(e) greater than 5 mm
(a) 1 micron or less
147
Which one of the following is false concerning the relationship between the variables of oxygen across the respiratory membrane?
(a) Doubling the thickness of the membrane would reduce the total flow of the oxygen by half.
(b) Doubling the area of the membrane would double the total flow of oxygen.
(c) Increasing the alveolar concentration of oxygen would increase the total flow of oxygen across the respiratory membrane.
(d) The lower the diffusion coefficient, the higher the total flow.
(e) Increasing the arterial concentration of oxygen would decrease the total flow of oxygen.
(d) The lower the diffusion coefficient, the higher the total flow.
147
