18 Questions
What is the primary function of lung surfactant?
To prevent alveolar collapse by reducing surface tension
Which of the following is NOT a factor affecting ventilation?
Blood pressure
What is the role of compliance in the respiratory system?
To aid in the expansion of the lung
What happens to the lungs when the stretching force is removed?
They collapse
What is Laplace's law related to in the context of the respiratory system?
Surface tension of the alveoli
What is the main reason why inspiration is an active process?
Because it requires energy to overcome both airway resistance and stretch the lung
What is the main factor that drives airflow in healthy individuals?
Modest differences in pressure between the atmosphere and alveoli
During which phase of respiration is airway resistance the lowest?
Inspiration
What is the mathematical formula for airway resistance?
R = 8ηL/πr4
What is the effect of lung expansion on airway resistance?
Decreases airway resistance
What is the result of increased tension within lung tissue during inspiration?
Increased diameter of airways and blood vessels
What is the location of the highest resistance to airflow?
Airways
What is the primary mechanism by which the lungs expand during inhalation?
Radial traction on airways due to stretch of elastic fibers
What is the purpose of hypoxic vasoconstriction in the pulmonary arteries?
To decrease blood flow to poorly ventilated regions of the lung
What percentage of total energy metabolism is accounted for by respiratory work at rest?
1-2%
What is the main component of respiratory work?
Work required to overcome elastic forces of the lungs and thoracic cage
What is the effect of salbutamol on the airways?
Dilation of airways
What is the primary function of pulmonary surfactant?
To reduce alveolar surface tension
Study Notes
Respiratory Physiology Introduction
- The work of breathing is an active process that requires energy to expand the lungs and overcome airway resistance.
The Work of Breathing
- Factors affecting ventilation include:
- Resistance to flow in the airways
- Elastic properties of the lung
- Surface tension of the alveoli
- Inspiration is an active process that requires energy to:
- Stretch the lung (collagen, elastin, and surface tension)
- Overcome the resistance of the airways (RAW)
- Lungs must collapse when the stretching force is removed, aided by elasticity.
Resistance to Airflow in Airways
- In health, flow resistance in the airways is small, and modest differences in pressure drive a lot of airflow.
- In disease, airway resistance can increase, and must be overcome by the action of inspiratory muscles.
- Airway resistance is lowest during inspiration and highest during expiration.
- The formula for airway resistance is: R = 8ηL / πr4
Elasticity of Lung Tissue
- Elasticity of lung tissue affects the work of breathing.
- Stretching the lung increases tension within lung tissue.
- Tension pulls on airways and blood vessels, increasing their diameter and reducing pulmonary vascular resistance and airway resistance.
Regulation of Airway Resistance
- SNS release of adrenaline acts on β2 receptors, causing bronchodilation (during exercise and stress).
- Airway dilation reduces airway resistance.
Resistance to Blood Flow (Perfusion)
- Regulation of resistance is a key concept in pulmonary blood flow.
- Pulmonary Hypoxic Vasoconstriction (HPV) occurs when alveolar PO2 is low, leading to increased pulmonary arterial resistance and diversion of blood away from poorly ventilated regions of the lung.
The Metabolic Cost of Breathing
- At rest, respiratory work accounts for 1-2% of total energy metabolism.
- During exercise, respiratory work can be up to 10% of total energy metabolism.
- The majority of respiratory work (90%) is due to overcoming alveolar surface tension and the elastic forces of the lungs, while frictional work due to airway resistance accounts for 10%.
This lecture covers the fundamentals of respiratory physiology, focusing on the work of breathing, ventilation, perfusion, gas exchange, and central control of ventilation. Learn about the physical properties of the lung and the forcing mechanisms behind breathing.
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