Lung Physiology Flashcards
What is the primary function of the respiratory system?
The respiratory system’s main role is to deliver oxygen (O₂) to the body and remove carbon dioxide (CO₂) produced during metabolism. This gas exchange occurs in the alveoli.
Outline the pathway that air takes from entry to the site of gas exchange.
Air enters via the nose or mouth, moves through the pharynx and larynx, travels down the trachea, divides into the bronchi, continues into the bronchioles, and finally reaches the alveoli where gas exchange occurs.
What causes air to flow into and out of the lungs?
Air movement (ventilation) is driven by pressure differences created by changes in lung volume. When lung volume increases, pressure drops, drawing air in; when lung volume decreases, pressure rises, expelling air.
Describe the process of inhalation (inspiration).
Inhalation is an active process where the diaphragm contracts (moves downward) and the external intercostal muscles elevate the ribs. This expands the chest cavity, increases lung volume, decreases intrapulmonary pressure, and causes air to flow into the lungs.
What is the mechanism behind quiet (passive) exhalation?
During quiet exhalation, the diaphragm and intercostal muscles relax. The lungs return to their resting state with the help of elastic recoil, which decreases lung volume, increases intrapulmonary pressure, and pushes air out.
How does forced exhalation differ from quiet exhalation?
Forced exhalation is an active process that involves the contraction of accessory muscles (e.g., abdominal muscles and quadratus lumborum) to further reduce lung volume and expel air more rapidly than during passive exhalation.
What is spirometry, and why is it used?
Spirometry is a common lung function test that measures the volume and flow of air during inhalation and exhalation. It is used to assess lung health, diagnose respiratory conditions, and monitor disease progression or response to treatment.
List three key measurements obtained from spirometry.
- Tidal Volume (TV): The amount of air inhaled or exhaled during normal breathing (∼500 mL).
- Forced Vital Capacity (FVC): The maximum volume of air that can be forcefully exhaled after a full inhalation. 3. Forced Expiratory Volume in 1 Second (FEV₁): The volume of air exhaled in the first second of the FVC maneuver.
What does the FEV₁/FVC ratio indicate, and what is a normal value?
The FEV₁/FVC ratio is the percentage of the forced vital capacity exhaled in the first second. Normal values are generally above 70–80%. A reduced ratio indicates airflow obstruction, as seen in conditions like asthma and COPD.
Describe the appearance of a flow-volume loop in healthy lungs.
In healthy lungs, the flow-volume loop shows a rapid rise to a high peak expiratory flow followed by a smooth, continuous decline during expiration and an appropriate curve during inspiration.
How does a flow-volume loop typically differ in a patient with asthma?
In asthma, the flow-volume loop shows a reduced peak expiratory flow and a ‘scooped-out’ or concave appearance during expiration due to airway narrowing. Improvement may be seen after administration of a bronchodilator.
What role do central chemoreceptors play in breathing control?
Central chemoreceptors, located in the medulla, detect changes in CO₂ and the resulting hydrogen ion (H⁺) concentration in the cerebrospinal fluid. They primarily regulate the rate and depth of breathing based on these changes.
What is the function of peripheral chemoreceptors in respiratory control?
Peripheral chemoreceptors, found in the carotid and aortic bodies, primarily sense low oxygen (O₂) levels. They also respond to changes in CO₂ and pH, especially during hypoxic conditions, thereby supporting the regulation of breathing.
Why does the urge to breathe occur during breath holding?
When you hold your breath, CO₂ builds up in the blood. The central chemoreceptors detect the increased CO₂ (and resultant lower pH), triggering an urge to breathe to restore normal gas exchange.
Which muscles are primarily involved in quiet inspiration?
The diaphragm is the primary muscle of inspiration, assisted by the external intercostal muscles, which work together to increase the thoracic cavity’s volume.
Name the muscles involved in forced breathing (both inspiration and expiration).
Forced Inspiration: Diaphragm, external intercostal muscles, and accessory muscles (e.g., pectoralis major/minor, serratus anterior).
Forced Expiration: Abdominal muscles (rectus abdominis, internal and external obliques) and sometimes the quadratus lumborum.
What is alveolar ventilation, and why is it important?
Alveolar ventilation is the portion of the total ventilation that reaches the alveoli, where gas exchange occurs. It is crucial because only this air can participate in oxygen uptake and carbon dioxide removal.
Provide the formula for calculating alveolar ventilation.
Alveolar Ventilation = (Tidal Volume - Dead Space) × Respiratory Rate
Give an example calculation of alveolar ventilation using TV = 500 mL, dead space = 150 mL, and respiratory rate = 12 breaths/min.
(500 mL - 150 mL) × 12 = 350 mL × 12 = 4200 mL/min (or 4.2 L/min)
Define anatomical dead space.
Anatomical dead space is the volume of air in the conducting airways (nose, pharynx, trachea, bronchi, and bronchioles) that does not reach the alveoli and therefore does not participate in gas exchange. In adults, it is typically about 150 mL.
What is alveolar (physiological) dead space, and how does it differ from anatomical dead space?
Alveolar (physiological) dead space refers to alveoli that are ventilated but not perfused (due to insufficient blood supply), meaning they do not effectively participate in gas exchange. This can occur in certain diseases, such as pulmonary embolism.
How is oxygen transported from the alveoli to body tissues?
Oxygen diffuses across the alveolar-capillary membrane into the blood, where it binds to hemoglobin in red blood cells for delivery to tissues.
How is carbon dioxide eliminated from the body?
Carbon dioxide, produced as a metabolic waste, diffuses from the blood into the alveoli and is exhaled. It is also transported in the blood as bicarbonate (HCO₃⁻) or dissolved directly in the plasma.
What does a reduced FEV₁/FVC ratio indicate about lung function?
A reduced FEV₁/FVC ratio indicates airflow obstruction, which is characteristic of obstructive lung diseases such as asthma and COPD.
Summarize how the respiratory system maintains gas exchange during both quiet and forced breathing.
Quiet Breathing: The diaphragm and external intercostal muscles create pressure changes via passive expansion and elastic recoil, allowing efficient gas exchange.
Forced Breathing: Accessory muscles augment the process to increase airflow during increased respiratory demands. Respiratory centers and chemoreceptors adjust the breathing rate and depth based on metabolic needs.
