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Questions and Answers
Which of the following best describes the alveolar pressure (PA) at rest?
Which of the following best describes the alveolar pressure (PA) at rest?
- -5 cmH2O (relative)
- 755 mmHg (absolute)
- 760 mmHg (absolute) (correct)
- 0 mmHg (relative)
What is the main muscle of ventilation?
What is the main muscle of ventilation?
- External intercostals
- Internal intercostals
- Diaphragm (correct)
- Scalenes and SCM
Which muscles are considered accessory muscles of inspiration?
Which muscles are considered accessory muscles of inspiration?
- Scalenes and SCM (correct)
- Internal intercostals
- External intercostals
- Abdominal muscles
What is the definition of airway resistance?
What is the definition of airway resistance?
Which muscles are considered passive at rest during expiration?
Which muscles are considered passive at rest during expiration?
What is the pleural pressure at rest, relative to barometric pressure?
What is the pleural pressure at rest, relative to barometric pressure?
What keeps the lung adhered to the chest wall?
What keeps the lung adhered to the chest wall?
What causes the lung to collapse inward?
What causes the lung to collapse inward?
What does a pneumothorax cause in the intrapleural space?
What does a pneumothorax cause in the intrapleural space?
In which condition does emphysema cause a change in compliance?
In which condition does emphysema cause a change in compliance?
What leads to a reduced functional residual capacity (FRC) in fibrosis?
What leads to a reduced functional residual capacity (FRC) in fibrosis?
What is responsible for reducing surface tension in the lung?
What is responsible for reducing surface tension in the lung?
What is compliance a measure of?
What is compliance a measure of?
What is the role of surfactant in the lungs?
What is the role of surfactant in the lungs?
Why are the compliance curves different during expiration and inspiration?
Why are the compliance curves different during expiration and inspiration?
What reduces as lung volume increases, leading to lower compliance at the beginning of expiration?
What reduces as lung volume increases, leading to lower compliance at the beginning of expiration?
How does lung volume affect surface tension?
How does lung volume affect surface tension?
According to Poiseuille's law, what has the biggest effect on airway resistance?
According to Poiseuille's law, what has the biggest effect on airway resistance?
What eliminates the air-fluid interface and significantly reduces surface tension?
What eliminates the air-fluid interface and significantly reduces surface tension?
What factor contributes to increased airway resistance in healthy individuals?
What factor contributes to increased airway resistance in healthy individuals?
Why is compliance greater in saline inflated lungs?
Why is compliance greater in saline inflated lungs?
Which neurohumoral factor decreases airway resistance by increasing diameter?
Which neurohumoral factor decreases airway resistance by increasing diameter?
What is responsible for decreasing surface tension as lung volume increases?
What is responsible for decreasing surface tension as lung volume increases?
What causes an increase in airway resistance and bronchoconstriction?
What causes an increase in airway resistance and bronchoconstriction?
What contributes to airway resistance across the lung according to Poiseuille's law?
What contributes to airway resistance across the lung according to Poiseuille's law?
How does total cross-sectional area change as we progress deeper into the lung?
How does total cross-sectional area change as we progress deeper into the lung?
What happens to intrapleural pressure during inspiration?
What happens to intrapleural pressure during inspiration?
What is the role of alveolar pressure (PA) at rest?
What is the role of alveolar pressure (PA) at rest?
How does elastic recoil pressure change at higher lung volumes?
How does elastic recoil pressure change at higher lung volumes?
What happens to alveolar pressure during expiration?
What happens to alveolar pressure during expiration?
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Study Notes
Respiratory System
- Alveolar pressure (PA) at rest is approximately equal to atmospheric pressure.
- The main muscle of ventilation is the diaphragm.
- Accessory muscles of inspiration include sternocleidomastoid, scalene, and intercostal muscles.
Airway Resistance and Pressure
- Airway resistance is the opposition to airflow in the lungs.
- Pleural pressure at rest is negative, approximately -5 cmH2O relative to barometric pressure.
- The lung is kept adhered to the chest wall by the negative pleural pressure.
- A pneumothorax causes air to enter the intrapleural space, leading to lung collapse.
- Pleural pressure becomes positive during expiration.
Lung Compliance and Surface Tension
- Compliance is a measure of the lung's ability to stretch and expand.
- Surfactant reduces surface tension in the lung, allowing for easier expansion.
- Compliance curves are different during expiration and inspiration due to changes in surfactant activity.
- As lung volume increases, surface tension decreases, leading to increased compliance.
Factors Affecting Airway Resistance and Lung Function
- According to Poiseuille's law, airway resistance is most affected by radius, with smaller radii resulting in higher resistance.
- Increased airway resistance is contributed to by factors such as bronchoconstriction and decreased diameter.
- Neurohumoral factors, such as acetylcholine, increase airway resistance by constricting airways.
- Saline-inflated lungs have greater compliance due to the elimination of the air-fluid interface and reduced surface tension.
Changes in Pressure and Volume
- During inspiration, intrapleural pressure becomes more negative, and alveolar pressure decreases.
- Elastic recoil pressure increases at higher lung volumes, contributing to decreased compliance.
- During expiration, alveolar pressure increases, and intrapleural pressure becomes less negative.
- Passive muscles during expiration include the diaphragm and intercostal muscles, which relax to allow lung recoil.
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