Anatomy of Pleural cavity, mechanics of breathing, surfactant and compliance Flashcards
What is tidal volume (TV)?
Tidal volume is the amount of air that is inhaled or exhaled during normal breathing.
Typical value: ~500 mL per breath in an average adult.
What is inspiratory reserve volume (IRV)?
Inspiratory reserve volume is the maximum amount of air that can be inhaled after a normal inspiration.
Typical value: ~3000 mL in an average adult.
What is expiratory reserve volume (ERV)?
Expiratory reserve volume is the maximum amount of air that can be exhaled after a normal exhalation.
Typical value: ~1100 mL in an average adult.
What is residual volume (RV)?
Residual volume is the amount of air that remains in the lungs after a forceful exhalation.
This volume prevents the lungs from collapsing completely.
What is vital capacity (VC)?
Vital capacity is the maximum amount of air that can be exhaled after a maximum inhalation.
It includes tidal volume, inspiratory reserve volume, and expiratory reserve volume.
Typical value: ~4600 mL in an average adult.
What is total lung capacity (TLC)?
Total lung capacity is the maximum amount of air the lungs can hold, combining all lung volumes (TLC = TV + IRV + ERV + RV).
Typical value: ~5800 mL in an average adult.
What is inspiratory capacity (IC)?
Inspiratory capacity is the maximum amount of air that can be inhaled after a normal exhalation (IC = TV + IRV).
Typical value: ~3500 mL in an average adult.
What is functional residual capacity (FRC)?
Functional residual capacity is the amount of air that remains in the lungs after a normal exhalation (FRC = ERV + RV).
Typical value: ~2300 mL in an average adult.
How are lung volumes used clinically?
Lung volumes are measured to assess lung function, diagnose respiratory diseases, and monitor recovery or progression of conditions such as asthma, COPD, or restrictive lung disease.
What is the pleural cavity?
The pleural cavity is the space between the two layers of the pleura (the membranes surrounding the lungs).
It contains a small amount of pleural fluid, which helps reduce friction during breathing.
What are the two layers of the pleura?
Visceral pleura:
The inner layer that covers the surface of the lungs.
Parietal pleura:
The outer layer that lines the chest wall, diaphragm, and mediastinum.
What is the function of pleural fluid?
The pleural fluid reduces friction between the visceral and parietal pleurae during breathing.
It allows smooth movement of the lungs as they expand and contract during respiration.
What is the pleural space or pleural cavity filled with?
The pleural cavity is filled with a thin layer of pleural fluid, which acts as a lubricant for the lungs to move smoothly within the thoracic cavity.
What is the role of the pleura in breathing?
The pleura helps maintain the negative pressure within the pleural cavity, which is essential for the expansion of the lungs during inhalation.
The pleura prevents the lungs from collapsing by creating surface tension between the visceral and parietal layers.
What happens if there is fluid accumulation in the pleural cavity?
If excessive fluid builds up in the pleural cavity, it leads to a condition called pleural effusion, which can impair lung expansion and breathing.
What is the costodiaphragmatic recess?
The costodiaphragmatic recess is a potential space at the lower part of the pleural cavity, between the diaphragm and the ribs, where pleural fluid can accumulate in certain conditions.
How is the pleural cavity clinically relevant?
The pleural cavity is important in the diagnosis of conditions like pleuritis, pneumothorax (air in the pleural cavity), and pleural effusion (fluid accumulation).
What is a pneumothorax?
A pneumothorax is a condition where air enters the pleural cavity, disrupting the negative pressure and causing the lung to collapse. This can occur due to trauma or spontaneously.
What are the parietal and visceral pleura?
Visceral pleura: The inner layer of the pleura that covers the surface of the lungs.
Parietal pleura: The outer layer that lines the chest wall, diaphragm, and mediastinum.
How are the parietal and visceral pleura connected?
The parietal and visceral pleura are continuous with each other at the hilum of the lung, where structures like blood vessels and airways enter and exit the lung.
What is the pleural cavity?
The pleural cavity is the space between the parietal and visceral pleura, which contains a small amount of pleural fluid that reduces friction during breathing movements.
How does the pleural cavity assist in lung inflation and deflation?
The pleural cavity maintains negative pressure relative to the atmospheric pressure, which helps the lungs expand during inhalation and recoil during exhalation.
Why is the relationship between the parietal and visceral pleura important for lung inflation?
The surface tension created by the pleural fluid between the parietal and visceral pleurae ensures that the lungs are “pulled” along with the chest wall during inhalation, allowing the lungs to expand and fill with air.
What happens to the visceral pleura during lung inflation?
During inhalation, the diaphragm and chest wall expand, which pulls the parietal pleura. The visceral pleura moves with the parietal pleura because of the adhesion created by the pleural fluid, causing the lungs to expand as well.
Why is negative pressure in the pleural cavity critical for lung deflation?
The negative pressure between the parietal and visceral pleurae helps to keep the lungs slightly expanded even during exhalation. When the chest wall relaxes, the lungs recoil to their resting state, aided by the elasticity of the lung tissue.
What would happen if the pleural layers were separated (e.g., pneumothorax)?
If air or fluid enters the pleural cavity (e.g., in pneumothorax), the negative pressure is lost, causing the visceral pleura (and the lung) to collapse. This impairs lung inflation and reduces the ability to breathe properly.
What is the importance of the pleural fluid between the parietal and visceral pleura?
Pleural fluid creates surface tension, allowing the visceral and parietal pleura to stick together while also reducing friction, enabling smooth lung movement during inflation and deflation.
How does the parietal pleura contribute to lung deflation?
The parietal pleura is attached to the chest wall and diaphragm. As the chest wall contracts during exhalation, the parietal pleura moves inward, pulling the visceral pleura and causing the lung to recoil and expel air.
What is the main function of the muscles of respiration?
The muscles of respiration are responsible for changing the volume of the thoracic cavity, which in turn affects lung volume and allows for inhalation (inspiration) and exhalation (expiration).
Which muscles are involved in inspiration (inhalation)?
Diaphragm:
The primary muscle of inspiration. When it contracts, it flattens, increasing the vertical volume of the thoracic cavity.
External intercostal muscles:
These muscles contract to elevate the ribs, expanding the lateral and anterior-posterior dimensions of the thoracic cavity.
How does the diaphragm act during inspiration?
When the diaphragm contracts, it moves downward (flattens), increasing the vertical volume of the thoracic cavity, which causes a decrease in pressure inside the lungs. This pressure difference causes air to flow into the lungs.
How do the external intercostal muscles help in inhalation?
The external intercostal muscles contract, causing the ribs to elevate and expand, increasing the lateral and front-to-back dimensions of the thoracic cavity. This further reduces intrathoracic pressure and allows air to enter the lungs.
What is the role of accessory muscles during heavy or forced inhalation?
During deep or forced inhalation (e.g., exercise), accessory muscles like the sternocleidomastoid and scalene muscles help elevate the rib cage further, enhancing thoracic volume expansion.
Which muscles are involved in exhalation (expiration)?
Diaphragm:
The diaphragm relaxes and moves upward, decreasing the vertical volume of the thoracic cavity.
Internal intercostal muscles:
These muscles contract to depress the ribs, decreasing the lateral and front-to-back dimensions of the thoracic cavity.
How does the diaphragm act during expiration?
During normal exhalation, the diaphragm relaxes and moves upward, reducing the vertical volume of the thoracic cavity. This increases the pressure in the lungs, forcing air out.
How do the internal intercostal muscles contribute to exhalation?
The internal intercostal muscles contract, causing the ribs to depress, which decreases the lateral and anterior-posterior dimensions of the thoracic cavity, increasing pressure within the lungs and pushing air out.
What role do abdominal muscles play in forced exhalation?
The abdominal muscles (e.g., rectus abdominis, external obliques) contract during forced exhalation, pushing the diaphragm upward further and increasing intra-abdominal pressure, which further aids in expelling air from the lungs.
What is the overall mechanism by which thoracic volume is altered during breathing?
Inhalation: The diaphragm and external intercostals increase thoracic volume, lowering pressure in the lungs, causing air to flow in.
Exhalation: The diaphragm and internal intercostals decrease thoracic volume, raising pressure in the lungs, causing air to flow out.
What is Boyle’s Law?
Boyle’s Law states that the pressure of a gas is inversely proportional to its volume when the temperature is constant.
Mathematically: P ∝ 1/V, meaning as the volume of a container increases, the pressure decreases, and vice versa.
How does Boyle’s Law apply to breathing mechanics?
Boyle’s Law explains how the pressure and volume of the thoracic cavity are related during inspiration and expiration, driving air movement into and out of the lungs.
How does Boyle’s Law explain inspiration (inhalation)?
During inspiration, the diaphragm contracts and the intercostal muscles elevate the ribs, causing the volume of the thoracic cavity to increase.
According to Boyle’s Law, as the volume of the thoracic cavity increases, the pressure inside the lungs decreases (since the lungs expand), creating a pressure difference between the lungs and the external environment.
This pressure gradient causes air to flow into the lungs from the atmosphere.
How does Boyle’s Law explain expiration (exhalation)?
During expiration, the diaphragm relaxes and the rib cage contracts, decreasing the volume of the thoracic cavity.
According to Boyle’s Law, as the volume of the thoracic cavity decreases, the pressure inside the lungs increases.
This increase in pressure forces air out of the lungs and into the atmosphere to equalize the pressure difference.
What happens to pressure and volume in the lungs during deep inspiration?
During deep inspiration, the volume of the thoracic cavity increases more significantly, causing the pressure in the lungs to decrease even further.
This large decrease in pressure allows more air to flow into the lungs to fill the larger volume.
What happens to pressure and volume in the lungs during forced expiration?
During forced expiration, the volume of the thoracic cavity decreases rapidly, which leads to a sharp increase in pressure inside the lungs.
This high pressure forces air out of the lungs quickly and with greater force to expel air efficiently.
How does Boyle’s Law explain the movement of air in and out of the lungs?
Inhalation: Increased lung volume (due to diaphragm and rib cage movement) decreases lung pressure, causing air to flow into the lungs.
Exhalation: Decreased lung volume (due to diaphragm and rib cage relaxation) increases lung pressure, causing air to flow out of the lungs.
How does Boyle’s Law help explain lung compliance and resistance?
Lung compliance refers to the lung’s ability to expand (increase volume), and Boyle’s Law shows that for air to flow into the lungs, the volume must increase enough to reduce pressure inside the lungs.
Resistance to airflow occurs when the lungs are not able to expand efficiently or when the airway diameter is restricted (e.g., in asthma), making it harder to change the lung volume and lower the pressure.
What is respiratory minute volume (RMV)?
Respiratory minute volume (RMV) is the total amount of air inhaled or exhaled per minute.
It is calculated as:
RMV = Tidal Volume (TV) × Respiratory Rate (RR)
What are the mechanical factors that affect respiratory minute volume?
Tidal volume (TV)
Respiratory rate (RR)
Lung compliance
Airway resistance
Elastic recoil of the lungs
How does tidal volume (TV) affect respiratory minute volume?
Tidal volume is the amount of air moved in and out of the lungs with each breath.
An increase in tidal volume increases respiratory minute volume (RMV), as more air is moved per breath. Conversely, a decrease in tidal volume reduces RMV.
How does respiratory rate (RR) affect respiratory minute volume?
Respiratory rate is the number of breaths taken per minute.
An increase in respiratory rate (breaths per minute) increases RMV, as more air is ventilated per minute.
Conversely, a decrease in respiratory rate reduces RMV.
How does lung compliance affect respiratory minute volume?
Lung compliance refers to the ability of the lungs to stretch and expand during inhalation.
Higher compliance (lungs are more easily stretched) allows greater tidal volumes with less effort, increasing RMV.
Lower compliance (stiff lungs) reduces the tidal volume and may require more effort to achieve the same RMV.
How does airway resistance affect respiratory minute volume?
Airway resistance is the opposition to airflow in the airways.
Increased airway resistance (e.g., due to bronchoconstriction in asthma) makes it harder to move air in and out of the lungs, decreasing tidal volume and/or respiratory rate, which can reduce RMV.
How does the elastic recoil of the lungs affect respiratory minute volume?
Elastic recoil is the ability of the lungs to return to their resting volume after being stretched during inspiration.
Higher elastic recoil aids in forceful exhalation, allowing for faster exhalations and more effective ventilation.
Reduced elastic recoil (e.g., in emphysema) impairs expiration and can lead to reduced RMV.
How does thoracic cage mobility influence respiratory minute volume?
The mobility of the thoracic cage (rib cage and diaphragm movement) affects the ability of the lungs to expand.
Restricted thoracic cage movement (e.g., due to injury or obesity) limits lung expansion, which can reduce tidal volume and thus decrease RMV.
What impact does lung disease have on respiratory minute volume?
Diseases such as chronic obstructive pulmonary disease (COPD) or pulmonary fibrosis can reduce lung compliance, increase airway resistance, or decrease elastic recoil.
These changes make it harder to move air efficiently, leading to reduced RMV.
What is intrapleural pressure?
Intrapleural pressure is the pressure within the pleural cavity (the space between the visceral and parietal pleura).
It is typically negative relative to atmospheric pressure.
What is alveolar pressure?
Alveolar pressure (also called intrapulmonary pressure) is the pressure within the alveoli (air sacs of the lungs).
It fluctuates with breathing, becoming negative during inspiration and positive during expiration.
Why is intrapleural pressure always less than alveolar pressure?
The intrapleural pressure is always less than alveolar pressure due to the elastic recoil of the lungs and the chest wall.
The lungs have a natural tendency to collapse inward (due to elastic recoil), while the chest wall tends to expand outward.
This opposing forces create a negative pressure within the pleural cavity, pulling the lungs outward and ensuring that intrapleural pressure stays lower than alveolar pressure.
How does negative intrapleural pressure help in lung expansion?
The negative intrapleural pressure creates a pressure gradient that keeps the lungs expanded.
This negative pressure causes the lungs to be pulled outward during inspiration, allowing them to expand and fill with air when the alveolar pressure drops below atmospheric pressure.
What happens if the intrapleural pressure becomes equal to or greater than alveolar pressure?
If intrapleural pressure equals or exceeds alveolar pressure, the lungs would collapse (a condition known as pneumothorax).
The negative pressure that normally keeps the lungs inflated would be lost, preventing normal lung expansion and airflow.
How does Boyle’s Law relate to intrapleural and alveolar pressure during breathing?
During inhalation, as the thoracic cavity volume increases, alveolar pressure drops below atmospheric pressure (creating a pressure gradient).
The intrapleural pressure remains negative due to the opposing forces of lung recoil and chest wall expansion, ensuring that the lungs expand efficiently as air flows in.
Why is maintaining a negative intrapleural pressure important for breathing?
A negative intrapleural pressure is critical for keeping the lungs inflated and preventing lung collapse.
It ensures that alveolar pressure can drive air into the lungs during inhalation, while exhalation occurs when the lungs recoil to expel air, with the pressure gradients maintained for effective ventilation.
What is pulmonary surfactant?
Pulmonary surfactant is a mixture of lipids and proteins secreted by type II alveolar cells in the lungs.
Its primary function is to reduce surface tension within the alveoli, helping to maintain lung stability during breathing.
What is the role of pulmonary surfactant?
Pulmonary surfactant decreases the surface tension at the air-liquid interface in the alveoli, preventing the alveoli from collapsing.
It allows the alveoli to expand more easily during inhalation, making breathing more efficient by reducing the effort needed to inflate the lungs.
Surfactant also helps maintain equilibrium between alveoli of different sizes, preventing smaller alveoli from collapsing into larger ones.
What is the Law of Laplace?
The Law of Laplace describes the relationship between pressure (P), surface tension (T), and radius (r) in a sphere.
Mathematically:
P = 2T / r
This means that the pressure required to keep a spherical structure open is directly proportional to the surface tension and inversely proportional to its radius.
How does the Law of Laplace apply to the lungs?
In the lungs, the alveoli are essentially spherical structures where the Law of Laplace applies.
According to the law, smaller alveoli would naturally require higher pressure to remain open due to their smaller radius, making them more prone to collapse.
This is where pulmonary surfactant plays a crucial role in reducing surface tension in smaller alveoli, allowing them to stay open with less pressure and preventing collapse.
How does pulmonary surfactant affect the Law of Laplace in the lungs?
Pulmonary surfactant reduces the surface tension in the alveoli, which lowers the pressure needed to keep the alveoli open, especially in smaller ones.
By reducing surface tension, surfactant allows for equalization of pressure in alveoli of different sizes, preventing smaller alveoli from collapsing and improving lung compliance.
Why is the production of pulmonary surfactant critical in newborns?
Pulmonary surfactant is essential for lung function, and premature infants often lack sufficient surfactant, leading to respiratory distress syndrome (RDS).
Without adequate surfactant, the surface tension in the alveoli remains high, making it difficult to keep the alveoli inflated, leading to atelectasis (collapse of the alveoli) and impaired gas exchange.
What happens if there is insufficient pulmonary surfactant in the lungs?
Insufficient surfactant results in increased surface tension in the alveoli, which leads to lung collapse and reduced lung compliance.
This increases the work of breathing, making it harder for the lungs to expand, which can lead to hypoxemia (low oxygen levels) and respiratory failure.
What is the definition of compliance in the context of the lungs?
Compliance refers to the ability of the lungs and thoracic cage to expand and stretch in response to changes in pressure.
It is a measure of how easily the lungs can be inflated.
Mathematically:
Compliance = Change in volume / Change in pressure
What does high compliance in the lungs indicate?
High compliance means the lungs are easily expandable, requiring less pressure to achieve a given change in volume.
This is typically seen in conditions where the lung tissue is less stiff or more elastic.
What does low compliance in the lungs indicate?
Low compliance means the lungs are stiff and require more pressure to achieve the same increase in volume.
This can occur in conditions where lung tissue is fibrotic or scarred, making it harder to expand the lungs.
What are the factors that affect lung compliance?
Elasticity of the lung tissue
Surface tension in the alveoli
Chest wall stiffness
Lung volume
Age and lung health
How does elasticity of the lung tissue affect compliance?
Elasticity refers to the lung tissue’s ability to return to its original shape after being stretched.
Increased elasticity improves compliance, as the lungs expand more easily.
Decreased elasticity, as seen in diseases like pulmonary fibrosis, reduces compliance, making lung expansion more difficult.
How does surface tension in the alveoli affect lung compliance?
Surface tension in the alveoli creates an inward pull that resists lung expansion.
Pulmonary surfactant reduces surface tension, improving compliance by making it easier for the alveoli to expand during inhalation.
How does chest wall stiffness affect lung compliance?
The stiffness of the chest wall, including the ribs and diaphragm, can affect lung compliance.
If the chest wall is stiff (e.g., due to rib deformities or muscle weakness), it becomes harder to expand the lungs, leading to reduced compliance.
How does lung volume affect compliance?
Compliance varies with lung volume.
At very low lung volumes (e.g., during forced exhalation), the lungs are more compliant and easier to expand.
At higher lung volumes, compliance decreases as the lungs approach their total lung capacity, and it becomes harder to stretch the lungs further.
How does age affect lung compliance?
As a person ages, lung tissue becomes less elastic and more fibrotic, reducing compliance.
Older individuals typically have a decrease in lung compliance, meaning their lungs become stiffer and more difficult to expand.
How do diseases like emphysema and pulmonary fibrosis affect lung compliance?
Emphysema (a form of COPD) causes the destruction of alveolar walls, leading to increased compliance (lungs become overly distensible, but less able to recoil).
Pulmonary fibrosis leads to decreased compliance due to scar tissue formation, making the lungs stiff and difficult to expand.
