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Questions and Answers
What happens during normal expiration when the diaphragm and external intercostals stop contracting?
What happens during normal expiration when the diaphragm and external intercostals stop contracting?
- Lung volume decreases, returning to pre-inspiration size. (correct)
- Air flows into the lungs due to decreased pressure.
- Lung volume increases significantly.
- Recoil causes the thoracic cavity volume to increase.
What role do accessory muscles of expiration play during forceful breathing?
What role do accessory muscles of expiration play during forceful breathing?
- They assist with inward and downward movement of the chest wall. (correct)
- They prevent any movement of the chest wall.
- They primarily increase lung volume.
- They only compress the alveoli during exhalation.
What characterizes eupnea in terms of breathing effort?
What characterizes eupnea in terms of breathing effort?
- Eupnea is only present during exercise.
- Eupnea requires the use of accessory muscles.
- Eupnea is characterized by resting and unlaboured breathing. (correct)
- Eupnea involves rapid and forceful inhalations.
What occurs to the pressure in the thoracic cavity during a forceful expiration?
What occurs to the pressure in the thoracic cavity during a forceful expiration?
Which components contribute to the recoil process during expiration?
Which components contribute to the recoil process during expiration?
What is the primary role of intrapleural pressure during ventilation?
What is the primary role of intrapleural pressure during ventilation?
During forceful inspiration, what is the effect of anterior contraction of the external intercostals?
During forceful inspiration, what is the effect of anterior contraction of the external intercostals?
Which muscle is primarily responsible for the majority of lung expansion during quiet breathing?
Which muscle is primarily responsible for the majority of lung expansion during quiet breathing?
What happens to alveolar pressure during the process of inhalation?
What happens to alveolar pressure during the process of inhalation?
What is eupnea?
What is eupnea?
Which of the following correctly describes the role of accessory muscles in forced breathing?
Which of the following correctly describes the role of accessory muscles in forced breathing?
What primarily opposes the inward pressure created by the chest wall during ventilation?
What primarily opposes the inward pressure created by the chest wall during ventilation?
What is the result of stronger contraction of the diaphragm during inspiration?
What is the result of stronger contraction of the diaphragm during inspiration?
What drives the process of ventilation in the respiratory system?
What drives the process of ventilation in the respiratory system?
What occurs during the process of inspiration?
What occurs during the process of inspiration?
Which statement accurately describes Boyle's Law in the context of ventilation?
Which statement accurately describes Boyle's Law in the context of ventilation?
What is the typical atmospheric pressure at sea level?
What is the typical atmospheric pressure at sea level?
What primarily facilitates gas exchange in external respiration?
What primarily facilitates gas exchange in external respiration?
How does the body create the necessary pressure gradient for ventilation?
How does the body create the necessary pressure gradient for ventilation?
How does expiration differ from inspiration in terms of air pressure?
How does expiration differ from inspiration in terms of air pressure?
What would happen if the volume of the thoracic cavity increases during respiration?
What would happen if the volume of the thoracic cavity increases during respiration?
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Study Notes
Respiratory System Overview
- Focus on ventilation: air movement between the atmosphere and alveoli.
- Gas exchange:
- External respiration: exchange between alveoli and pulmonary capillaries.
- Internal respiration: exchange between tissue capillaries and interstitial fluid/tissue cells.
- Gas transport: movement by pulmonary and systemic circulations between gas exchange locations.
Ventilation - General Principles
- Atmospheric pressure at sea level is approximately 760 mmHg.
- Pressure changes are often reported relative to atmospheric pressure.
- Ventilation is driven by an air pressure gradient, moving from high to low pressure.
- Inspiration: air moves from the atmosphere (high pressure) to the alveoli (low pressure).
- Expiration: air moves from the alveoli (high pressure) to the atmosphere (low pressure).
- Between breaths, pressures equalize, resulting in no air movement.
- To create a pressure gradient for ventilation, the pressure at the alveolar level must be manipulated.
Ventilation - Boyle's Law
- In a closed system at constant temperature, pressure (P) and volume (V) are inversely related.
- Increasing volume decreases pressure.
- Decreasing volume increases pressure.
- Changing volume changes pressure, creating a pressure gradient, and producing ventilation.
Ventilation - Three Pressures
- Atmospheric pressure (Patm): pressure of the surrounding environment.
- Alveolar pressure (Palv): pressure within the alveoli.
- Intrapleural pressure (Pip): pressure within the intrapleural space between visceral and parietal pleura.
Ventilation - Intrapleural Pressure
- Intrapleural pressure is always subatmospheric (lower than Patm).
- It creates a pressure gradient:
- Between alveolar and intrapleural: outward pressure opposing lung elastic recoil (prevents lung collapse).
- Between atmospheric and intrapleural: inward pressure opposing chest wall elastic recoil (prevents chest wall expansion).
- These pressures work together to link the lung and chest wall, allowing them to move as a unit.
Ventilation - Inspiration
-
Eupnea (quiet, resting, unlaboured breathing):
- Diaphragm: 75% contribution, contraction flattens it, increasing thoracic cavity volume by ~2 cm.
- External intercostals: 25% contribution, contraction moves chest wall outward and upward, increasing lung volume.
- Intrapleural pressure becomes subatmospheric, drawing air into the lungs.
-
More forceful breathing:
- Increased diaphragm contraction (up to 10 cm flattening).
- Increased external intercostals contraction.
- Recruitment of accessory muscles of inspiration (scalenes, sternocleidomastoid, pectoralis minor) further increases chest wall movement.
- Greater increase in lung volume.
- Intrapleural pressure decreases further below atmospheric, creating a larger pressure gradient.
- More air flows into the lungs.
Ventilation - Expiration
-
Eupnea:
- Diaphragm and external intercostals stop contracting, allowing recoil to pre-inspiration positions.
- Thoracic cavity volume decreases.
- Alveolar pressure increases, exceeding atmospheric pressure, forcing air out of the lungs.
-
More forceful breathing:
- Increased recoil of the diaphragm and external intercostals.
- Recruitment of accessory muscles of expiration (internal intercostals, abdominals) further decreases chest wall movement.
- Greater decrease in lung volume, compressing the alveoli more.
- Intrapleural pressure increases beyond atmospheric, creating a larger pressure gradient.
- More air flows out of the lungs.
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