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Questions and Answers
What is the primary component of the work required to expand the lungs against elastic forces?
What is the primary component of the work required to expand the lungs against elastic forces?
Which mechanism primarily causes bronchoconstriction under parasympathetic stimulation?
Which mechanism primarily causes bronchoconstriction under parasympathetic stimulation?
Which law describes the relationship between the pressure and volume of a gas at constant temperature?
Which law describes the relationship between the pressure and volume of a gas at constant temperature?
What factor significantly affects the resistance offered by the respiratory airways?
What factor significantly affects the resistance offered by the respiratory airways?
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What triggers the cough reflex in the respiratory system?
What triggers the cough reflex in the respiratory system?
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What is the effect of excessive mucus secretion on airway resistance?
What is the effect of excessive mucus secretion on airway resistance?
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During which condition does positive intrapleural pressure increase airway resistance?
During which condition does positive intrapleural pressure increase airway resistance?
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Which of the following gases has a partial pressure of 149 mm Hg in the alveoli at sea level?
Which of the following gases has a partial pressure of 149 mm Hg in the alveoli at sea level?
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What role do beta-adrenergic receptors play in airway resistance?
What role do beta-adrenergic receptors play in airway resistance?
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How is gas diffusion across the respiratory membrane primarily affected?
How is gas diffusion across the respiratory membrane primarily affected?
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Which factor does NOT contribute to the diffusion capacity of a gas across the respiratory membrane?
Which factor does NOT contribute to the diffusion capacity of a gas across the respiratory membrane?
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What is the primary effect of increased thickness of the respiratory membrane on diffusion?
What is the primary effect of increased thickness of the respiratory membrane on diffusion?
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During exercise, which change enhances the diffusion of oxygen in the lungs?
During exercise, which change enhances the diffusion of oxygen in the lungs?
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Which of the following statements about gas diffusion is incorrect?
Which of the following statements about gas diffusion is incorrect?
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Which factor is most critical for enhancing the diffusion rate of gases across the respiratory membrane?
Which factor is most critical for enhancing the diffusion rate of gases across the respiratory membrane?
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What impact does the cough reflex primarily have on airway resistance?
What impact does the cough reflex primarily have on airway resistance?
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Bronchodilation primarily occurs through which mechanism?
Bronchodilation primarily occurs through which mechanism?
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Which of the following best defines airway resistance?
Which of the following best defines airway resistance?
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Which gas law is primarily responsible for explaining how pressure differences drive gas diffusion in the respiratory system?
Which gas law is primarily responsible for explaining how pressure differences drive gas diffusion in the respiratory system?
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What physiological change occurs during bronchoconstriction?
What physiological change occurs during bronchoconstriction?
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Study Notes
Work of Breathing
- Breathing involves the contraction of respiratory muscles, specifically to stretch the elastic tissues of the chest wall and lungs
- This work can be categorized as compliance work, tissue resistance work and airway resistance work.
- Compliance work is responsible for expanding the lungs against elastic forces of the lungs and chest wall.
- These forces are generated by elastin and collagen fibers as well as surface tension
- Tissue resistance work is required to overcome the viscosity of the lung and chest wall structures
- Airway resistance work requires overcoming the resistance in the airways.
- Airway resistance increases during bronchial constriction
Factors Affecting Airflow Resistance
- Parasympathetic nervous system constricts bronchioles
- Ach acts on target cells via M1, M2, and M3 receptors
- This process increases intracellular Ca2+ and causes smooth muscle contraction
- Sympathetic nervous system dilates bronchioles
- Norepinephrine and epinephrine are the primary mediators
- Stimulation of beta-adrenergic receptors cause bronchodilation
- Cough reflex triggered by irritants in airways
- Stimulates the vago-vagal reflex
- Leads to bronchoconstriction, a rapid inspiration, and forceful expiratory contractions
Airway Resistance: Effect of Airway Radius
- Airway resistance is mainly determined by the radius of the airway.
- Poiseuille’s formula: R = 8 v l / π r4 (R = peripheral resistance, v = viscosity, r = radius of tube, l = length of tube)
- Under normal conditions, viscosity and length of the airways remain constant
- A slight change in radius causes a marked change in airway resistance.
Airway Resistance: Other Factors
- Negative intrapleural pressure helps keep the airway open during inspiration, reducing resistance.
- Positive intrapleural pressure can collapse smaller airways during forced expiration, increasing resistance.
- The presence of excessive mucus secretion also increases resistance.
- In exercise, due to faster breathing, airway resistance increases.
Gas Laws Applicable to Pulmonary Diffusion
- Charles law: The volume of a gas at constant pressure is directly proportional to its temperature.
- Boyle’s law: The pressure exerted by a gas at constant temperature is inversely proportional to its volume.
Partial Pressures of Gases
- Partial pressure: the amount of pressure exerted by a specific gas in a mixture.
- Dry air is: 21% oxygen, 78% Nitrogen, 0.04% Carbon Dioxide and 0.096% other inert gases.
- The partial pressure of gases in alveoli: PO2 is 149 mm Hg, PN2 is 564 mm Hg and PCO2 is 0.3 mm Hg
Respiratory Membrane
- Total surface area of the respiratory membrane is 70 square meters.
- It is comprised of the walls of the alveolar epithelium and the capillary endothelium.
- The respiratory membrane is comprised of these layers:
- Thin layer of fluid & surfactant
- Alveolar wall
- Basement membrane of alveoli
- Interstitial space
- Basement membrane of capillary
- Wall of capillary endothelium
- The average thickness of the respiratory membrane is 0.6 microns
Factors Affecting Diffusion: Diffusion Coefficient
- Diffusion depends on:
- Pressure gradient (P1 - P2): Higher gradient, higher diffusion
- Total surface area (A): Larger surface area, higher diffusion
- Thickness of the membrane (d): Thinner membrane, higher diffusion
- Solubility of the gas (S): More soluble, higher diffusion
- Molecular weight of the gas (Mol wt): Lower weight, higher diffusion
- Diffusing capacity: The volume of gas that diffuses across the respiratory membrane per minute for a pressure difference of 1 mm Hg.
- Diffusing capacity for O2: 23 ml / min/ mm Hg
- CO2 diffuses 20 times faster than O2
Changes in O2 Diffusion During Exercise
- During exercise, increased blood flow in pulmonary capillaries prolongs the time for PO2 equilibrium.
- The total surface area of the respiratory membrane increases due to stretching of alveolar and capillary walls, as well as opening dormant capillaries.
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Description
This quiz explores the mechanisms of breathing, focusing on the work involved in lung expansion and the resistance encountered during airflow. It also covers the roles of the sympathetic and parasympathetic nervous systems in regulating bronchial constriction and dilation. Understand the different types of work required for effective respiration.
