Physiology Flashcards
(48 cards)
Define Boyle’s Law.
At any constant temp, the pressure exerted by a gas varies inversely with the volume of the gas i.e. as the volume of the gas increases, the pressure exerted by the gas decreases
What are the two forces that hold the thoracic wall and the lungs in close opposition?
The intrapleural fluid cohesivenes - water molecules in the intrapleural fluid are attached to each other and resist being pulled apart.
The negative intrapleural pressure - the sub-atmospheric intrapleural pressure creates a transmural pressure gradient across the lung wall and across the chest wall, therefore the lungs are forced to expand outwards while the chest is squeezed inwards.
What are the three important forces of ventilation?
Atmospheric pressure.
Intra-alveolar pressure.
Intrapleural pressure.
Explain what is meant by the terms “internal respiration” and “external respiration”.
Internal respiration - refers to the intracellular mechanisms which consume O2 (required to produce energy and function) and produce CO2 (produced by cellular reactions and must be continuously removed from the body).
External respiration - refers to the sequence of events that lead to the exchange between O2 and CO2 between the external environment and the cells of the body.
Identify the four steps of external respiration.
1 - VENTILATION or gas exchange between the atmosphere and air sacs (alveoli) in the lungs. The mechanical process of moving gas in and out of the lungs
2 - GAS EXCHANGE of O2 and CO2 between air in the alveoli and the blood in the pulmonary capillaries
3 - GAS TRANSPORT of O2 and CO2 between the lungs and tissues
4 - GAS EXCHANGE of O2 and CO2 between the blood in the systemic capillaries and the body cells
Explain ventilation - the first step of external respiration
The mechanical process of moving air between the atmosphere and the alveolar sacs. Air flows down a pressure gradient from a region of high pressure to a region of low pressure.
The intra-alveolar pressure must be LESS than atmospheric pressure for air to flow into the lungs. The Thorax and Lungs expand as a result of contraction of the inspiratory muscles.
What is a pneumothorax?
Air in the pleural space - abolishes the transmural pressure gradient meaning the lungs cannot expand.
Can be caused by stab wound (puncture), car accidents (hole in the lung, collapsed lung etc.)
Explain the difference between Inspiration and Expiration
Inspiration is an active process depending on muscle contraction (whereas resting expiration is a passive process).
What are the inspiratory muscles used during normal resting breathing? How do they function?
The Diaphragm (major inspiratory muscle) - volume of the thorax is increased vertically by contraction. Done by the phrenic nerve at C3, 4 and 5
The external intercostal muscle - contraction lifts the ribs and moves out the sternum.
Explain how the lungs recoil.
Elastic connective tissue - allows the whole structure to bounce back into shape
Alveolar surface tension - attraction between water molecules at liquid air interface that produces a force in the alveoli which allows them to resist the stretching of the lungs.
Describe the role and importance of pulmonary surfactant, with the Law of LaPlace and alveolar stability.
Surfactant (complex mix of lipids and proteins secreted by type II alveoli) REDUCES the alveolar surface tension by interspersing between water molecules lining the alveoli.
Law of LaPlace - smaller alveoli have a higher tendency to collapse (P=2T/r, where P is the inward directed collapsing pressure, T is surface tension and r is the radius of the bubble).
Surfactant lowers the surface tension of smaller alveoli more than that of larger alveoli.
Describe the opposing forces acting on the lungs.
Forces keeping the alveoli open:
- Transmural pressure gradient
- Pulmonary surfactant
- Alveolar interdependence
Forces promoting alveolar collapse:
- elasticity of stretched pulmonary connective tissue fibres
- alveolar surface tension
Describe alveolar interdependence.
If an alveolus starts to collapse, the surrounding alveoli are stretched and then recoil, exerting expanding forces in the collapsing alveolus to reopen it.
Explain the lung volumes and capacities.
Tidal Volume (TV) - Volume of air entering or leaving the lungs during a single breath - 500 ml avg value
Inspiratory Reserve Volume (IRV) - Extra volume of air that can be maximally inspired over and above the typical resting tidal volume - 3000 ml avg value
Inspiratory Capacity (IC) - Maximum volume of air that can be inspired at the end of a normal quiet expiration (IC-IRV+TV) - 3500 ml avg value
Expiratory Reserve Volume (ERV) - Extra volume of air that can be actively expired by maximal contraction beyond the normal volume of air after a resting tidal volume - 1000 ml avg value
Residual Volume (RV) - Minimum volume of air remaining in the lung even after a maximal expiration - 1200 ml avg value
Functional Residual Capacity (FRC) - Volume of air in lungs at the end of normal passive expiration (FRC=ERV+RV) - 2200 ml avg value
Vital Capacity (VC) - Maximum volume of air that can be moved out during a single breath following a maximal inspiration (VC=IRV+TV+ERV) - 4500 ml avg value
Illustrate the changes in dynamic lung volumes in obstructive and restrictive lung disease
Airway obstruction - FVC=low or normal, FEV1=low, FEV1/FVC%=low
Lung restriction - FVC=low, FEV1=low, FEV1/FVC%=normal
Combination of obstruction and restriction - FVC=low, FEV1=low, FEV1/FVC %=low
How is Spirometry used for Dynamic Lung Volumes?
Allows us to determine:
FVC=Forced Vital Capacity - max volume that can be forcibly expelled from the lungs following a maximum inspiration
FEV1=Forced Expiratory Volume in one second - Volume of air that can be expired during the first second of expiration
FEV1/FVC ratio - the proportion of the FVC that can be expired in the first second. Normally more than 70%
These dynamic lung volumes are useful in the diagnosis of Obstructive and Restrictive lung disease.
Identify the factors which influence airway resistance.
Primary determinant is the radius of the conducting airway.
Parasympathetic stimulation causes bronchoconstriction
Sympathetic stimulation causes bronchodilatation
Disease states can lead to significant increases in airflow resistance.
Explain Dynamic Airway Compression.
The rising pleural pressure during active expiration compresses the alveoli and airway. This pressure applied to the alveolus helps to push air out of the lungs.
The increased airway resistance causes an increase in airway pressure upstream. This helps open the airways by increasing the driving pressure between the alveolus and airway.
This causes no problems in normal people.
How does Dynamic Airway Compression affect expiration in patients with airway obstruction?
If there’s an obstruction, the driving pressure between the alveolus and airway is lost over the obstructed segment.
This causes a fall in airway pressure along the airway downstream, resulting in airway compression by the rising pleural pressure during active expiration.
Define Pulmonary Compliance.
Compliance is the measure of effort that has to go into stretching or distending the lungs.
The LESS compliant the lungs are, the MORE work is required to produce a degree of inflation.
What factors can lead to decreased Pulmonary Compliance?
Pulmonary fibrosis, pulmonary oedema, lung collapse, pneumonia, absence of surfactant.
Decrease in compliance means greater pressure is required to produce a change in volume (lungs are “stiffer”). This causes SOB, especially on exertion.
What factors can lead to increased Pulmonary Compliance?
Abnormal increase could be due to a loss in elastic recoil of the lungs.
This occurs in emphysema - patients have to work harder to get air out of the lungs, leading to hyperinflation of the lungs (“Desperate Dan chest”).
Compliance also increases with age.
Explain “Work of Breathing”
Normal quite breathing requires 3% of total energy expenditure, and lungs typically operate at “half full”.
Work of breathing is increased…
- when pulmonary compliance is decreased
- when airway resistance is increased
- when elastic recoil is decreased
- when there is a need for increased ventilation
Explain the difference between pulmonary ventilation and alveolar ventilation.
Pulmonary ventilation is the volume of air breathed in and out per minute. = tidal volume (L/breath) x respiratory rate (breath/min) = 6L/min under resting conditions.
Alveolar ventilation the volume of air exchanged between the atmosphere and alveoli per minute, and is less than pulmonary ventilation because of the presence of anatomical dead space. 4.2 L/min
