Guyton and Hall Physiology Chapter 40 - Principles of Gas Exchange; Diffusion of Oxygen and Carbon Dioxide Through the Respiratory Membrane

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Questions and Answers

What is the average thickness of the respiratory membrane in most areas?

0.2 micrometers

1.0 micrometers

0.6 micrometers (correct)

1.5 micrometers

What is the approximate total surface area of the respiratory membrane in healthy men?

35 square meters

70 square meters (correct)

100 square meters

150 square meters

What is the function of the surfactant layer in the alveoli?

Reduce surface tension (correct)

Enhance blood flow

Facilitate gas exchange

Increase airway resistance

What happens to dead space air during respiration?

It is gradually washed out of the alveoli Signup and view all the answers

What are the capillary blood volume levels in the lungs at a given instant?

60 to 140 ml Signup and view all the answers

How does the interconnecting network of capillaries in the alveoli benefit gas exchange?

Reduces gas diffusion distance Signup and view all the answers

What is significant about the capillary basement membrane in relation to the alveolar membrane?

It fuses with the alveolar epithelial basement membrane in many areas Signup and view all the answers

Which measurement can be used to describe the efficiency of gas exchange across the respiratory membrane?

Partial pressures of gases Signup and view all the answers

What is the primary function of the surfactant in the alveolar fluid?

To reduce surface tension of alveolar fluid Signup and view all the answers

How does increased thickness of the respiratory membrane affect gas exchange?

It interferes significantly with normal respiratory exchange Signup and view all the answers

What condition can lead to the greatest decrease in surface area of the respiratory membrane?

Removal of an entire lung Signup and view all the answers

What occurs during the diffusion of gases between the alveolus and the blood?

Oxygen diffuses from the alveolus into the red blood cell Signup and view all the answers

Which pulmonary condition might lead to fibrosis and increase the thickness of the respiratory membrane?

Pulmonary fibrosis Signup and view all the answers

What is primarily collected when studying alveolar air?

The last portion of the expired air Signup and view all the answers

What determines the overall composition of expired air?

The amount of expired air that is dead space air and alveolar air Signup and view all the answers

Which structure is NOT part of the respiratory unit?

Trachea Signup and view all the answers

What is the average diameter of an alveolus?

0.2 millimeter Signup and view all the answers

Which gas concentrations are typically found in expired air?

Concentrations between those of alveolar and humidiﬁed atmospheric air Signup and view all the answers

What does dead space air refer to?

Air in the respiratory passages that does not participate in gas exchange Signup and view all the answers

During expiration, how do O2 and CO2 partial pressures change?

O2 decreases while CO2 increases Signup and view all the answers

What is the role of the respiratory membrane in gas exchange?

It allows for the diffusion of gases between alveoli and blood Signup and view all the answers

How many alveoli are commonly estimated to be in the two lungs?

300 million Signup and view all the answers

Which part of the respiratory anatomy primarily participates in gas exchange?

Alveoli Signup and view all the answers

What is the primary factor that determines the amount of gas exchange occurring in the alveoli?

Partial pressure gradient Signup and view all the answers

Which component is NOT typically considered part of the physiological dead space?

Tidal volume Signup and view all the answers

How does the aging process affect lung structure and function based on current understanding?

Decreases lung volume and elasticity Signup and view all the answers

Which of the following best describes the role of the pulmonary blood-gas barrier?

Acts as a selective filter for gas exchange Signup and view all the answers

What is the expected effect on arterial blood gas levels if there is increased physiological dead space?

Increased PaCO2 and decreased PaO2 Signup and view all the answers

Which mechanism primarily drives the diffusion of gases across the alveolar-capillary membrane?

Concentration gradient Signup and view all the answers

In terms of respiratory anatomy, what is the main function of airways in relation to gas exchange?

Transporting air to the alveoli Signup and view all the answers

Which statement accurately describes the relationship between ventilation and perfusion in the lungs?

Proper gas exchange requires optimal matching of both Signup and view all the answers

What happens to the diffusion capacity for carbon monoxide during exercise in a healthy individual?

It increases due to improved blood flow Signup and view all the answers

Which parameter is critical in evaluating a patient's ventilatory status?

V̇T and PaCO2 levels Signup and view all the answers

What is the primary role of alveoli in the respiratory system?

Facilitate gas exchange between air and blood Signup and view all the answers

Which mechanism primarily drives gas exchange in the alveoli?

Diffusion due to partial pressure differences Signup and view all the answers

During breathing, which gas has a higher partial pressure in the alveolus compared to the blood?

Oxygen (O2) Signup and view all the answers

What is meant by 'dead space air' in the context of respiratory anatomy?

Air trapped in alveoli that cannot participate in gas exchange Signup and view all the answers

Which component of the alveoli helps maintain their structure and prevent collapse?

Elastic fibers Signup and view all the answers

What type of cells primarily line the alveoli and facilitate gas exchange?

Type I alveolar cells Signup and view all the answers

Which structure is NOT part of the respiratory division of the bronchial tree?

Terminal bronchiole Signup and view all the answers

Which vascular structures are directly associated with the alveoli for gas exchange?

Capillaries Signup and view all the answers

What primarily prevents excess fluid from accumulating in the interstitial space of the lungs?

Lymphatic vessels Signup and view all the answers

How does the structure of alveolar walls facilitate their function?

Thin walls that allow rapid diffusion of gases Signup and view all the answers

How does an increase in the rate of O2 absorption into the blood affect O2 concentration in the alveoli?

It decreases O2 concentration in the alveoli. Signup and view all the answers

What is the relationship between the rate of entry of new O2 into the lungs and its concentration in the alveoli?

Higher entry rate usually leads to higher O2 concentration in the alveoli. Signup and view all the answers

What are the two main factors that control O2 concentration in the alveoli?

O2 absorption rate and ventilatory entry rate. Signup and view all the answers

What happens to the alveolar Po2 when 1000 ml of O2 is being absorbed each minute during moderate exercise?

It increases to a maximum of 149 mm Hg. Signup and view all the answers

How does the alveolar Pco2 respond to an increase in the rate of CO2 excretion?

It increases directly in proportion to the rate of CO2 excretion. Signup and view all the answers

At what normal ventilatory rate and O2 consumption does the normal operating point occur?

4.2 L/min ventilation and 250 ml/min O2 consumption. Signup and view all the answers

What is the effect of carbon dioxide excretion rates on the partial pressure of carbon dioxide in the alveoli?

Higher excretion rates maintain lower partial pressure of carbon dioxide. Signup and view all the answers

What must happen to alveolar ventilation when the absorption of O2 increases to 1000 ml/min?

It must increase fourfold. Signup and view all the answers

What is the relationship between extreme increases in alveolar ventilation and the maximum alveolar Po2?

Alveolar Po2 can be significantly elevated. Signup and view all the answers

What change occurs to the alveolar Pco2 when alveolar ventilation is significantly increased?

It decreases in inverse proportion to ventilation. Signup and view all the answers

What is the estimated total surface area of the respiratory membrane in healthy men?

70 square meters Signup and view all the answers

What is the average thickness of the respiratory membrane in some areas?

0.6 micrometers Signup and view all the answers

What is the approximate range of blood volume in the capillaries of the lungs at any given time?

60 to 140 ml Signup and view all the answers

Which layer is NOT typically considered part of the respiratory membrane?

Bronchial epithelial layer Signup and view all the answers

Which component of the alveoli helps reduce surface tension?

Pulmonary surfactant Signup and view all the answers

What is the functional significance of the interconnecting capillaries in the alveoli?

To facilitate gas exchange Signup and view all the answers

In which condition might the thickness of the respiratory membrane increase?

Pulmonary fibrosis Signup and view all the answers

What structural feature of alveolar walls facilitates gas exchange?

Thin, permeable membranes Signup and view all the answers

What is the composition of air in the dead space compared to the alveoli?

Lower in oxygen than alveolar air Signup and view all the answers

What is the main purpose of the alveolar epithelial and capillary basement membranes fusing?

To decrease diffusion distance Signup and view all the answers

The molecular weight of a gas influence its diffusion coefficients.

True Signup and view all the answers

The diffusion coefficient for O2 is equal to 20.3.

False Signup and view all the answers

Water vapor has a lower relative diffusion coefficient compared to oxygen.

False Signup and view all the answers

The partial pressures of gases are unchanged during the expiration of air.

False Signup and view all the answers

At sea level, the total atmospheric pressure is 760 mm Hg.

True Signup and view all the answers

Each normal inspiration brings around 350 ml of new air into the lungs.

True Signup and view all the answers

The total pressure in the alveoli can exceed the atmospheric pressure of 760 mm Hg.

False Signup and view all the answers

It takes approximately 34 seconds to remove half of the gas in the alveoli when ventilation is half-normal.

True Signup and view all the answers

The composition of atmospheric air includes significant amounts of CO2.

False Signup and view all the answers

Half of the excess gas in the alveoli can be removed in about 8 seconds with double the normal ventilation rate.

True Signup and view all the answers

The maximum ventilation limit is set at 150 ml O2/min.

False Signup and view all the answers

Normal alveolar partial pressure of oxygen is around 100 mm Hg.

True Signup and view all the answers

An increase in tidal volume automatically increases the alveolar PO2 level.

False Signup and view all the answers

If 1000 ml of O2 is absorbed, the alveolar PO2 will decrease significantly during moderate exercise.

True Signup and view all the answers

Alveolar ventilation refers specifically to the total ventilation rate during resting conditions.

False Signup and view all the answers

Dead space air refers to the portion of tidal volume that does not participate in gas exchange.

True Signup and view all the answers

The average thickness of the respiratory membrane is critical for efficient gas exchange.

True Signup and view all the answers

Alveolar ventilation will decrease if the tidal volume decreases with constant breathing rate.

True Signup and view all the answers

The relationship between the rate of O2 consumption and alveolar PO2 is direct and linear.

False Signup and view all the answers

Alveolar Pco2 generally rises when there is an increase in the rate of CO2 excretion.

False Signup and view all the answers

Match the following gases with their corresponding partial pressures at sea level:

Nitrogen = 600 mm Hg Oxygen = 160 mm Hg Total pressure = 760 mm Hg Carbon dioxide = 0.3 mm Hg Signup and view all the answers

Match the following terms with their descriptions:

Kinetic energy = Energy of motion that facilitates gas diffusion Partial pressure = Pressure exerted by a single gas in a mixture Gas chamber = A space containing gases that can diffuse Concentration gradient = Difference in concentration of gas between two areas Signup and view all the answers

Match the following processes with their definitions:

Diffusion = Movement of molecules from high to low concentration Dissolved gas pressure = Pressure exerted by gas molecules in liquid Gas molecule motion = Random linear movement until colliding with others Cell membrane interaction = Exchange of gases at the cellular level Signup and view all the answers

Match the following types of movement with their contexts:

Linear movement = High velocity movement of free molecules Random movement = Unpredictable motion of gas molecules Bouncing movement = Redirection of gas molecules upon collision Directional movement = Net diffusion towards lower concentration areas Signup and view all the answers

Match the following symbols with the gases they represent:

Pco2 = Partial pressure of carbon dioxide Po2 = Partial pressure of oxygen Pn2 = Partial pressure of nitrogen Phe = Partial pressure of inert gases Signup and view all the answers

Match the following terms related to lung physiology with their definitions:

Physiological shunt = Blood that fails to become normally oxygenated Ventilation-perfusion ratio = Balance of airflow and blood flow in the lungs Emphysema = Condition characterized by the destruction of alveolar walls Chronic Obstructive Lung Disease = Long-term bronchial obstruction leading to reduced airflow Signup and view all the answers

Match the following components of blood oxygen measurement with their descriptions:

CiO2 = Concentration of oxygen in ideal ventilation CaO2 = Measured concentration of oxygen in arterial blood CvO2 = Concentration of oxygen in mixed venous blood Q̇T = Total cardiac output per minute Signup and view all the answers

Match the following effects of exercise on lung blood flow with their outcomes:

Increased blood flow to upper lung = Decreases physiological dead space Optimal gas exchange = Increased efficiency during exercise Ventilation disparities = Inequalities in exchanging O2 and CO2 Excessive shunting = Reduced effectiveness of respiration Signup and view all the answers

Match the following physiological concepts with the corresponding descriptions:

Physiological dead space = Inefficient regions of the lung for gas exchange Alveolar air trapping = Retention of air due to obstructive conditions Bronchial vessels = Vessels supplying blood to lung tissue without gas exchange Cardiac output = Amount of blood pumped by the heart per minute Signup and view all the answers

Match the conditions affecting O2 concentration in the alveoli with their triggers:

Increased O2 absorption = Decrease in alveolar O2 concentration Increased CO2 excretion = Effect on alveolar Pco2 levels Bronchial obstruction = Impairs airflow and gas exchange Ideal ventilation = Maximizes O2 delivery to the blood Signup and view all the answers

Study Notes

Expired Air

Expired air is a mixture of dead space air and alveolar air.
Dead space air comes from the respiratory passageways, and is typical humidiﬁed air.
Alveolar air is expired at the end of expiration after forceful expiration removes all the dead space air.

Respiratory Unit

The respiratory unit is also called the respiratory lobule.
The respiratory unit is composed of a respiratory bronchiole, alveolar ducts, atria, and alveoli.
There are about 300 million alveoli in the lungs, each with an average diameter of about 0.2 millimeter.

Respiratory Membrane

The respiratory membrane is the collective term for the membranes of all terminal portions of the lungs, including the alveoli.
The respiratory membrane is also called the pulmonary membrane.
The respiratory membrane is extremely thin, consisting of:
- a layer of ﬂuid containing surfactant
- alveolar epithelium
- epithelial basement membrane
- interstitial space
- capillary basement membrane
- capillary endothelial membrane
The total surface area of the respiratory membrane in healthy men is about 70 square meters.
The total quantity of blood in the capillaries of the lungs at any given instant is 60 to 140 ml.

Diffusion of Gases

Gas exchange between the alveolar air and pulmonary blood occurs through the respiratory membrane.
The thickness of the respiratory membrane occasionally increases, for example, as a result of edema ﬂuid.
Increased thickness of the respiratory membrane can interfere with respiratory gas exchange.
The surface area of the respiratory membrane can be greatly decreased by conditions like emphysema which cause many of the alveoli to coalesce, with dissolution of many alveolar walls.

Factors Affecting Alveolar O2 Concentration

The rate at which O2 is absorbed into the blood
The rate at which new O2 enters the lungs via ventilation

Normal Operating Point of Alveolar Po2

A normal ventilatory rate of 4.2 L/min and an O2 consumption of 250 ml/min is the normal operating point for a young man

Moderate Exercise

The rate of alveolar ventilation must increase fourfold to maintain alveolar Po2 at 104 mm Hg during moderate exercise

Maximum Alveolar Po2

Extreme increases in alveolar ventilation cannot increase alveolar Po2 above 149 mm Hg when breathing normal atmospheric air at sea level because 149 mm Hg is the maximum Po2 in humidified air at this pressure

Factors Affecting Alveolar CO2 Concentration

Rate of CO2 excretion from the blood
Rate of alveolar ventilation

Effect of Increased CO2 Excretion on Alveolar Pco2

Alveolar Pco2 increases directly with the rate of CO2 excretion
Example: A fourfold increase in CO2 excretion elevates the alveolar Pco2 curve by four

Effect of Increased Ventilation on Alveolar Pco2

Alveolar Pco2 decreases inversely with alveolar ventilation

Respiratory Membrane Composition

Alveolar epithelium
Epithelial basement membrane
Interstitial space with connective tissue fibers
Capillary basement membrane
Capillary endothelial membrane

Respiratory Membrane Characteristics

It's extremely thin, averaging approximately 0.6 micrometer in thickness, except where cell nuclei are present
The total surface area is about 70 square meters in healthy men
Contains 60 to 140 ml of blood

Diﬀusing Capacity for Oxygen

Average diﬀusing capacity for O2 in a young man at rest is 21 ml/min per mm Hg
During normal quiet breathing, the average O2 pressure difference across the respiratory membrane is about 11 mm Hg
The diﬀusion capacity multiplied by the pressure difference equals approximately 230 ml of oxygen diffusing through the respiratory membrane each minute, which is the rate at which the resting body uses O2

Increased Oxygen Diffusing Capacity During Exercise

Increased diﬀusing capacity for O2 during exercise is a result of:
- Opening up of previously dormant pulmonary capillaries
- Increased pulmonary blood flow
- Increased alveolar ventilation

Diﬀusing Capacity of other Gases

The diﬀusing capacity varies directly with the diffusion coefficient of the gas.
The diffusion coefficient for CO2 is slightly more than 20 times that of O2

Measurement of Diﬀusing Capacity - Carbon Monoxide Method

A small amount of CO is breathed into the alveoli
The partial pressure of CO in the alveoli is measured from appropriate alveolar air samples
The CO pressure in the blood is essentially zero because hemoglobin combines with it rapidly, preventing its pressure from building up
The pressure difference of CO across the respiratory membrane is equal to its partial pressure in the alveolar air sample
The volume of CO absorbed over a short period is divided by the alveolar CO partial pressure to determine the CO diﬀusing capacity
The CO diﬀusing capacity is multiplied by 1.23 to convert it to O2 diﬀusing capacity, accounting for the difference in their diffusion coefficients
The average diﬀusing capacity for CO in healthy young men at rest is 17 ml/min per mm Hg, while the diﬀusing capacity for O2 is 1.23 times this, or 21 ml/min per mm Hg

Venous Blood and Alveolar Gas Equilibration

Venous blood returning from the systemic circulation perfuses the lungs' capillaries
The gases in this venous blood equilibrate with the alveolar gases, influencing the alveolar partial pressures.
Venous blood typically has a Po2 of 40 mm Hg and a Pco2 of 45 mm Hg.

Respiratory Gas Diffusion and Exchange

Diffusion of gases across a membrane depends on several factors such as the difference in partial pressure between the two sides, the surface area of the membrane, the thickness of the membrane, and the solubility and molecular weight of the diffusing gas.
The diffusion coefficient, a measure of how easily a gas diffuses, is proportional to the square root of its solubility divided by its molecular weight.
Respiratory gases, including oxygen and carbon dioxide, are exchanged across the respiratory membrane, composed of multiple layers including the alveolar fluid, the alveolar epithelium, the interstitial space, the capillary endothelium, and the red blood cell membrane.

Factors Affecting Respiratory Gas Exchange

The partial pressure difference between the alveolar air and the pulmonary capillary blood drives the diffusion of gases.
The thickness of the respiratory membrane can be increased by various factors like interstitial edema or fibrosis, leading to increased diffusion distance and decreased gas exchange.
Increased surface area of the respiratory membrane improves gas exchange. This surface area can be decreased by conditions like lung removal or emphysema, which can impair gas exchange.
Ventilation-perfusion ratio, the ratio of airflow to blood flow, can influence gas exchange.

Diffusing Capacity of the Respiratory Membrane

The diffusing capacity of the respiratory membrane refers to the volume of a gas that can diffuse across the membrane per minute for a given pressure difference.
Increased ventilation during exercise enhances the diffusion of oxygen across the respiratory membrane.
The diffusion capacity for carbon dioxide is not measurable due to its extremely rapid diffusion rate.

Physiological Shunt

A small portion of blood flows through bronchial vessels, bypassing alveolar capillaries, representing 2% of cardiac output.
This unoxygenated blood contributes to the physiological shunt.
The physiological shunt is measured by analyzing oxygen concentrations in mixed venous blood and arterial blood, alongside cardiac output.
The equation for calculating physiological shunt is: Q̇PS = (CiO2 - CaO2) / (CiO2 - CvO2), where Q̇PS is the shunt blood flow, Q̇T is cardiac output, and CiO2, CaO2, and CvO2 are oxygen concentrations in ideal arterial blood, measured arterial blood, and mixed venous blood, respectively.

Molecular Basis of Gas Diffusion

Gases involved in respiratory physiology are simple molecules that move freely by diffusion.
Diffusion requires energy, sourced from the kinetic motion of molecules.
Molecules move randomly and continuously, colliding with each other, leading to a net diffusion from areas of higher concentration to lower concentration.
Partial pressure of a gas in a mixture is proportional to its concentration.
Partial pressures of nitrogen and oxygen in atmospheric air are 600 mm Hg and 160 mm Hg, respectively, totaling 760 mm Hg.

Pressures of Gases Dissolved in Water and Tissues

Dissolved gases in water or tissues exert pressure due to their kinetic energy and random movement.
When dissolved gas encounters a surface, it exerts its partial pressure, similar to gas in the gas phase.

Factors Affecting Rate of Gas Diffusion Through the Respiratory Membrane

Rate of gas diffusion through the respiratory membrane is influenced by:
- Thickness of the membrane
- Surface area of the membrane
- Diffusion coefficient of the gas in the membrane
- Partial pressure difference of the gas across the membrane

Effects of Alveolar Ventilation on Alveolar Oxygen and Carbon Dioxide Concentrations

Oxygen concentration in alveoli is controlled by rate of oxygen absorption into blood and rate of new oxygen entry from ventilation.
Carbon dioxide is constantly formed in the body, transported to the alveoli by blood, and removed by ventilation.
The alveolar partial pressure of carbon dioxide (PCO2) is affected by alveolar ventilation and the rate of carbon dioxide excretion from blood.

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Description

This quiz covers the fundamental aspects of the respiratory system, including expired air, the structure of the respiratory unit, and the composition of the respiratory membrane. Test your understanding of these critical components of human physiology.