Egan’s Ch. 12 Gas Exchange and Transport Quiz

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Questions and Answers

What is the primary purpose of respiration?

To increase CO2 levels in the tissues

To take O2 into the body for tissue utilization (correct)

To transport CO2 out of the lungs

To remove O2 from the body

How does gas movement between the lungs and tissues primarily occur?

Facilitated diffusion

Active transport

Endocytosis

Simple diffusion (correct)

Which gas has the highest partial pressure in human cells?

CO2 (correct)

In which direction does CO2 move between the cells and venous blood?

From tissues to venous blood Signup and view all the answers

What happens to PaCO2 levels if CO2 production increases while VA remains constant?

PaCO2 increases Signup and view all the answers

What is the normal range for PACO2?

35 mmHg - 45 mmHg Signup and view all the answers

What does the alveolar air equation account for?

The partial pressures of O2 and CO2 in alveolar air Signup and view all the answers

What determines the partial pressure of N2 in alveolar gas?

Dalton's law Signup and view all the answers

What is the normal ratio of CO2 compared to oxygen in the lungs?

0.8 Signup and view all the answers

Which gas has no role in gas exchange but occupies space and exerts pressure in the lungs?

Nitrogen Signup and view all the answers

What is the prime determinant of partial pressure of CO2 (PACO2) in the lungs?

Volume of alveolar ventilation (VA) Signup and view all the answers

What is the main barrier to gaseous diffusion in the lung?

Alveolar-capillary membrane Signup and view all the answers

Which of the following is required for gases like CO2 or O2 to move between alveoli and the pulmonary capillary blood?

Alveolar epithelium Signup and view all the answers

According to Fick's law, what factors contribute to more diffusion occurring?

Greater surface area, diffusion constant, and pressure gradient Signup and view all the answers

In a normal lung, what does diffusion primarily depend on?

Gas pressure gradients Signup and view all the answers

When will PaO2 not be any higher than 120 mmHg during hyperventilation?

At sea level when breathing room air Signup and view all the answers

What occurs along pressure gradients in terms of pulmonary diffusion gradients?

Diffusion occurs Signup and view all the answers

What accounts for 3/4 of the normal difference between PAO2 and PaO2?

Regional inequalities in V/Q Signup and view all the answers

Which condition arises when venous blood enters areas with V/Q ratios of 0?

Alveolar shunts Signup and view all the answers

What mainly causes regional variations in V/Q in the normal lung?

Gravity Signup and view all the answers

Where do exchange units with V/Q values of 0 occur?

Alveolar shunts Signup and view all the answers

Which part of the lung has a high V/Q ratio typically above 1?

Apices Signup and view all the answers

What does mixing of well-oxygenated arterial blood with poorly oxygenated blood cause?

Dilution of O2 contents Signup and view all the answers

Which gas has a higher solubility in plasma, leading to faster diffusion across the alveolar-capillary membrane?

Carbon dioxide (CO2) Signup and view all the answers

What is the approximate time that blood leaving the lungs is normally exposed to alveolar gas for proper equilibration?

0.75 second Signup and view all the answers

What is the typical PO2 of blood leaving the tissue capillaries after equilibration?

40 mmHg Signup and view all the answers

What causes carbon dioxide to diffuse in the opposite direction, from blood into the alveolus?

Higher PCO2 in venous blood compared to alveolar gas Signup and view all the answers

What is the primary cause of anatomic shunts that lead to a lower PaO2 than calculated PAO2?

Right-to-left anatomic shunts Signup and view all the answers

Why does blood move from the tissue capillaries back into the cells after equilibration?

To release oxygen to the cells Signup and view all the answers

Study Notes

Purpose and Mechanics of Respiration

Primary purpose of respiration is to exchange gases: oxygen intake and carbon dioxide removal.
Gas movement between lungs and tissues mainly occurs through diffusion driven by concentration gradients.

Gaseous Composition and Movement

Oxygen has the highest partial pressure in human cells.
Carbon dioxide (CO2) moves from cells into venous blood, balancing internal production and arterial release.

CO2 Production and Levels

If CO2 production increases while alveolar ventilation (VA) remains constant, PaCO2 levels rise.
Normal range for arterial PACO2 is typically 35-45 mmHg.

Alveolar Air Equation and Composition

Alveolar air equation accounts for the partial pressures of gases in alveoli, reflecting discrepancy between alveolar and arterial oxygen tensions.
Partial pressure of nitrogen (N2) in alveolar gas is determined by its concentration in inspired air and the total atmospheric pressure.

Gas Ratios and Roles

Normal CO2 to oxygen ratio in the lungs is around 1:4.
Nitrogen has no role in gas exchange but occupies space and exerts pressure in the lungs.

Determinants of Gas Exchange

Prime determinant of PACO2 in the lungs is the rate of CO2 production relative to its elimination.
Main barrier to gaseous diffusion in the lung is the alveolar-capillary membrane.

Requirements and Influencing Factors

Gases like CO2 or O2 require a concentration gradient and sufficient membrane surface area for diffusion between alveoli and pulmonary capillary blood.
According to Fick's law, diffusion increases with larger surface area, steeper gradients, and lower molecular weight gases.

Diffusion Dependence and Limits

In normal lungs, diffusion primarily depends on the surface area and distance across the alveolar-capillary membrane.
During hyperventilation, PaO2 may not exceed 120 mmHg due to limitations in oxygen solubility and transport.

Pressure Gradients and V/Q Relationships

Pulmonary diffusion occurs along pressure gradients between alveolar gas and blood.
Approximately three-quarters of the normal difference between PAO2 (alveolar oxygen pressure) and PaO2 (arterial oxygen pressure) is attributed to shunting and ventilation-perfusion ratios.

Ventilation-Perfusion Ratios

Conditions arise when venous blood enters areas with ventilation-perfusion (V/Q) ratios of 0, leading to hypoxemia.
Regional variations in V/Q in the normal lung are mainly caused by gravity, affecting blood flow distribution.
Exchange units with V/Q values of 0 primarily occur in dependent lung regions.

High V/Q Ratios and Effects

The apex of the lungs typically exhibits high V/Q ratios, often above 1.
Mixing of well-oxygenated arterial blood with poorly oxygenated blood causes dilution of oxygen content in the arteries.

Gas Solubility and Diffusion

Carbon dioxide has a higher solubility in plasma than oxygen, facilitating faster diffusion across the alveolar-capillary membrane.
Blood normally spends around 0.75 to 1 second in pulmonary capillaries to allow for gas equilibration with alveolar gas.

Equilibration Dynamics

Typical PO2 of blood leaving tissue capillaries after equilibration is around 40 mmHg.
Carbon dioxide diffuses from blood into the alveolus due to higher concentration in the blood relative to the alveolar air.

Anatomic Shunts and Cellular Dynamics

Primary cause of anatomic shunts leading to lower PaO2 than calculated PAO2 is blood bypassing ventilated alveoli.
Blood returns from tissue capillaries into cells after equilibration due to concentration gradients favoring nutrient and gas exchange.

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Description

Test your knowledge on gas exchange, transport of O2 and CO2, and the process of respiration in the context of Egan’s Chapter 12. Explore concepts such as diffusion of gases between tissues and blood, as well as the movement of O2 from the lungs to the tissues.