Respiratory Physiology - Pulmonary Mechanisms

Lung compliance refers to the ability of the lungs to expand and contract in response to changes in pressure.

During inspiration, the alveolar pressure decreases below atmospheric pressure, while the intrapleural pressure becomes more negative. This creates a pressure gradient that drives air into the lungs. During expiration, the reverse occurs, causing air to move out of the lungs.

<p>Surface tension is a force that exists at the interface of the fluid lining the alveoli and the air inside. It helps to maintain the shape and stability of the alveoli, but also creates a tendency for them to collapse.</p> Signup and view all the answers

<p>Factors affecting lung compliance include the elastic properties of lung tissue, the surface tension of the fluid lining the alveoli, and the presence of any restrictive lung diseases or disorders.</p> Signup and view all the answers

<p>Surfactant reduces surface tension in the alveoli, which prevents their collapse, particularly at lower lung volumes. This ensures efficient gas exchange and reduces the work of breathing.</p> Signup and view all the answers

<p>Airway resistance is primarily determined by the radius of the airways. The largest resistance is found in the medium-sized bronchi, and it is affected by factors such as bronchoconstriction and turbulent airflow.</p> Signup and view all the answers

<p>Emphysema causes destruction of lung tissue, leading to decreased elastic recoil and increased airway resistance. Fibrosis, on the other hand, causes scarring and stiffening of the lung tissue, making it difficult for the lungs to expand.</p> Signup and view all the answers

<p>Atmospheric pressure is the pressure exerted by the weight of the air surrounding the earth. At sea level, atmospheric pressure is approximately 760 mmHg.</p> Signup and view all the answers

<p>False</p> Signup and view all the answers

<p>Intra-alveolar pressure is the pressure within the alveoli, while transpulmonary pressure is the difference between intra-alveolar pressure and intrapleural pressure. Transpulmonary pressure represents the distending pressure that keeps the alveoli open.</p> Signup and view all the answers

<p>Boyle's Law states that the volume of a gas is inversely proportional to its pressure at a constant temperature. This means that as lung volume increases during inspiration, intra-alveolar pressure decreases, and vice versa.</p> Signup and view all the answers

<p>Intrapleural pressure is negative due to the opposing recoil tendencies of the lungs and chest wall. The lungs tend to collapse inward, while the chest wall tends to expand outward. This creates a vacuum in the pleural space, resulting in a sub-atmospheric pressure.</p> Signup and view all the answers

<p>Intrapleural pressure serves two key functions: it helps to keep the alveoli open and facilitates venous return. The negative intrapleural pressure creates a suction that prevents the lungs from collapsing and also assists in the return of blood to the heart.</p> Signup and view all the answers

<p>Transpulmonary pressure is the pressure difference between intra-alveolar pressure and intrapleural pressure. During inspiration, the chest wall expands, making intrapleural pressure more negative. This increases transpulmonary pressure, which acts as a distending force that opens up the alveoli.</p> Signup and view all the answers

<p>A pneumothorax is a condition where air enters the pleural space, disrupting the negative pressure and causing the lung to collapse. There are two main types: open pneumothorax, where air enters from outside through an opening in the chest wall, and closed pneumothorax, where air leaks from the lung itself.</p> Signup and view all the answers

<p>A pneumothorax leads to a loss of negative intrapleural pressure, causing the affected lung to collapse. This can result in breathing difficulties and other symptoms, such as chest pain and shortness of breath.</p> Signup and view all the answers

<p>Recoil tendency refers to the ability of the lungs and chest wall to return to their original resting volume after being stretched or compressed.</p> Signup and view all the answers

<p>The recoil tendency of the chest wall is primarily due to the elastic properties of the muscles, tendons, and ligaments that make up the chest wall.</p> Signup and view all the answers

<p>Both A and B</p> Signup and view all the answers

<p>Surfactant is a substance that reduces surface tension in the alveoli. This helps to prevent the alveoli from collapsing, particularly at lower lung volumes, which is when surface tension would normally be greatest.</p> Signup and view all the answers

<p>Airway resistance is the opposition to airflow in the airways, caused by friction between the air and the walls of the airways. It is measured as the change in pressure required to change the airflow rate by one unit.</p> Signup and view all the answers

<p>There are two types of airflow in the airways: laminar flow, which is smooth and streamlined, and turbulent flow, which is chaotic and irregular. Laminar flow results in lower airway resistance, while turbulent flow increases resistance.</p> Signup and view all the answers

<p>The radius of the airways is inversely proportional to the fourth power of airway resistance. This means that a small change in airway diameter can have a significant impact on resistance.</p> Signup and view all the answers

<p>Airway diameter is mainly affected by physical factors, including the negative intrapleural pressure that keeps the alveoli open and radial traction provided by the elastic recoil of surrounding alveoli. Changes in these factors can cause bronchodilation or bronchoconstriction, which affect airway resistance.</p> Signup and view all the answers

<p>The nervous system plays a crucial role in regulating airway resistance. Sympathetic stimulation through beta-2 adrenergic receptors causes bronchodilation (relaxation of airways), while parasympathetic stimulation through cholinergic receptors causes bronchoconstriction (narrowing of airways). Chemical factors such as histamine, leukotrienes, and environmental factors like plant pollens can also trigger bronchoconstriction. CO2 in the airways, however, acts as a bronchodilator.</p> Signup and view all the answers

<p>Emphysema reduces lung elasticity and leads to a loss of radial traction in the small airways. This causes the airways to collapse during forced expiration, making it difficult for air to escape from the lungs. This is known as air trapping.</p> Signup and view all the answers

<p>Bronchial asthma is an inflammatory disease characterized by attacks of bronchoconstriction caused by the hyperreactivity of bronchial smooth muscles to allergens. This leads to thickening of the bronchial walls, edema, and increased mucus production. All these factors contribute to increased airway resistance, making it harder to breathe, especially during expiration.</p> Signup and view all the answers

<p>PEFR represents the maximum speed of air that can be forced out of the lungs during a forced expiration, starting from a position of full lung inflation.</p> Signup and view all the answers

<p>Challenge tests, also known as bronchoprovocation tests, are used to assess airway sensitivity, which is a characteristic of asthma. They involve exposing the airways to a specific trigger, such as methacholine (a bronchoconstrictor) or exercise, and measuring the resulting changes in airway resistance by spirometry.</p> Signup and view all the answers

<p>Pulmonary compliance refers to the stretchability or expandability of the lungs. It reflects how easily the lungs can expand and contract in response to pressure changes.</p> Signup and view all the answers

<p>Pulmonary compliance is calculated as the change in lung volume divided by the change in transpulmonary pressure (the pressure difference between the alveoli and the pleural space).</p> Signup and view all the answers

<p>Elastance is the opposite of compliance and represents the stiffness or resistance of the lungs to expansion. Elastance is inversely proportional to compliance. A lung with high compliance will have low elastance and vice versa.</p> Signup and view all the answers

<p>Pulmonary compliance can be calculated by dividing the change in lung volume (ΔV) by the change in transpulmonary pressure ΔP.</p> Signup and view all the answers

<p>Static lung compliance can be affected by factors such as the elasticity of lung tissue, the surface tension of the fluid lining the alveoli, and the presence of any lung diseases or disorders that affect lung tissue elasticity or surface tension.</p> Signup and view all the answers

<p>Static lung compliance is measured when the lung is allowed to stabilize at each volume step, without any airflow. Dynamic lung compliance is measured during actual breathing and airflow, where the lung is not allowed to fully stabilize. Dynamic compliance is influenced by airway frictional resistance, which is not a factor in static compliance.</p> Signup and view all the answers

<p>The work of breathing refers to the energy expended by the respiratory muscles to move air in and out of the lungs, overcoming various resistance forces.</p> Signup and view all the answers

<p>The work of breathing can be divided into three main components: compliance work (related to the elastic properties of the lungs), tissue resistance work (related to the resistance of non-elastic tissue in the chest wall), and airway resistance work (related to the resistance to airflow in the airways).</p> Signup and view all the answers

<p>The work of breathing can be represented on a dynamic P-V curve by the area enclosed within the curve. Compliance work is represented by the area under the curve during inspiration and expiration. Tissue resistance work is represented by the area between the compliance curve and a horizontal line representing atmospheric pressure. Airway resistance work is represented by the area between the compliance curve and the tissue resistance curve.</p> Signup and view all the answers