Physiology Flashcards
What is internal respiration?
The intra-cellular mechanisms which consume oxygen and produce carbon dioxide
What is external Respiration?
The sequence of events that lead to the exchange of oxygen and carbon dioxide between the external environment and the cells of the body
What are the 4 steps of external respiration?
1) VENTELATION: The mechanical process of moving air into and out of the lungs
2) GAS EXCHANGE BETWEEN ALVIOLI AND BLOOD: The exchange of oxygen and carbon dioxide between the air in alvioli and blood in pulmonary capillaries
3) GAS TRANSPORT IN THE BLOOD: The binding and transport of oxygen and carbon dioxide in the circulating blood
4) GAS EXCHANGE AT THE TISSUE LEVEL: The exchange of carbon dioxide and oxygen between blood in the systemic capillaries and body cells.
What is Boyles Law?
At any constant temperature the pressure exerted by a gas varies inversely with the volume of the gas
Before inspiration, what can be said about atmospheric and intra alviolar pressure?
They are equal
There is no physical connection between the lungs and the chest wall. What 2 forces hold the thoracic wall and lungs in close opposition?
1) Intrapleural fluid cohesiveness: the water molecules in the intra pleural fluid are attached to each other and resist being pulled apart.
2) Negative intra pleural pressure: the sub atmospheric intrapleural pressure creates a transmural pressure gradient across the lung wall and chest wall. The lungs are forced to expand outwards while the chest is forced to squeeze inwards.
What are the 3 important pressures in ventilation?
1) Atmospheric pressure
2) Intra-alveolar pressure
3) Intra pleural pressure
What is atmospheric pressure?
Pressure caused by the weight of gas in the atmosphere on the earths surface. 760mmHg or 101kPa at sea level
What is intra-alveolar pressure?
Pressure within the lung alvioli. 760mmHg or 101kPa when equilibriated with atmospheric pressure.
What is Intra-pleural pressure?
Pressure exerted outside the lungs within the pleural cavity. Usually less than atmospheric pressure.
What is the nerve supply to the diaphragm?
Cervical nerves 3, 4 and 5
Which muscles contract during inspiration?
Diaphragm contracts flattening its dome shape
External intercostal muscles contract to lift the ribs and move the sternum out (bucket handle mechanism.
Is inspiration passive or active process?
Active
Is expiration a passive or an active process?
Passive
Why do the chest wall and stretched muscles recoil to their pre-inspiratory size during expiration?
They have elastic properties
What is a pneumothorax?
Air within the pleural space either from outside or from the lung. It can be spontaneous, traumatic or iatrogenic
What are the physical signs of a pneumothorax?
Hyper-resonant percussion note and decreased or absent breath sounds
What is surface tension?
The attraction between water molecules at a liquid/air interface
What is the role of alveolar surface tension in the alvioli?
It produces a force that resists the stretching of the lungs. If the alvioli were lined with water alone the surface tension would be so strong the lungs would collapse
What reduces alviolar surface tension, to prevent lung collapse?
Surfactant
What is La Place’s law?
P = 2T/r
where P = inward collapsing pressure, T = Surface tension and r= radius of bubble (alvioli)
Do smaller or larger alvioli have a greater tendency to collapse?
Smaller
What is pulmonary surfactant?
Mixture of lipids and proteins secreted by type 2 alviolar cells
What is the function of pulmonary surfactant?
Lower the surface tension by interspersing between water molecules lining the alvioli. It has a greater effect on smaller alvioli.
What is Respiratory Distress Syndrome of the new born?
Lack of surfactant produced by premature babies leading to an inability or difficulty to inflate the lungs.
WHat is alviolar interdependence?
If an alvioli starts to collapse, the surrounding alvioli are stretched and then recoil, exerting expanding forces in the collapsing alvioli to open it.
List 3 forces keeping alvioli open.
Transmural pressure gradient
Pulmonary Surfactant
Alviolar interdependance
List 2 forces promoting alviolar collapse.
Elasticity of lung connective tissue
Alviolar surface tension
What are the major inspiratory muscles?
Diaphragm and external intercostal muscles
What are the accessory muscles of inspiration
Sternocleidomastoid, scalenus and pectoral muscles
What are the muscles of ACTIVE expiration?
Abdominal muscles and internal intercostal muscles
What is the tidal volume?
The volume of air entering and leaving the lungs in a single breath. ~0.5L
What is the inspiratory reserve volume?
The extra volume of air that can be inspired above the typical resting tidal volume. ~3L
What is the expiratory reserve volume?
The extra volume of air that can be expired by maximal contraction beyond the normal volume of air after a resting tidal volume. ~1L
What is the residual volume?
The minimum volume of air remaining in the lungs after maximal expiration. ~1.2L
What is the inspiratory capacity?
Maximum volume of air that can be inspired after the end of a normal quiet expiration. ~3.5L. IC = TV + IRV
WHat is the functional residual capacity?
The volume of air left in the lungs following normal quiet expiration. ~2.2L. FRC = ERV + RV
What is vital capacity?
The maximum volume of air that can be moved out during a single breath following maximal inspiration. ~4.5L. VC = TV + IRV + ERV
What is the total lung capacity?
The total volume of air the lungs can hold. ~5.7L TLC = VC + RV
Which 2 lung volumes/capacities cannot be measured by spirometry?
Total lung capacity and residual volume
Which medical conditions would increase the residual volume?
Any condition where the elastic recoil of the lungs is lost or the lungs become hyper-inflated. Eg Emphysema
What is the FVC?
Forced vital capacity: the maximal volume that can be expelled from the lungs following maximal inspiration.
What is FEV1?
Forced expiratory volume in 1 second: the volume of air that can be expired during the first second of expiration in FVC determination.
What is the FEV1/FVC ratio?
The proportion of the FVC that can be expired in the first second.
What does an FEV1/FVC ration of <70% imply?
Obstructive lung disease
What does a normal FEV1/FVC ratio but a low FVC imply?
Restrictive lung disease
What is spirometry used for?
Determining between obstructive and restrictive lung disease.
What is the primary determinant of airways disease?
radius of the airway
Parasympathetic stimulation causes bronchoconstriction/bronchodilation?
Bronchoconstriction
Sympathetic stimulation causes bronchoconstriction/bronchodilation?
Bronchodilation
What happens to intraplueral pressure during inspiration and expiration?
Inspiration- pressure falls
Expiration- pressure rises
What is dynamic airway compression during expiration?
As the pleural pressure rises, it compresses the alvioli and airways. The pressure applied to the alvioli helps to push air out of the lungs. Pressure applied to the airway is not desirable.
Normal: increased pressure in alvioli causes and increase in airway pressure upstream- keeps airways open
Diseased airways: more compressible. Any driving pressure is lost over a obstructed segment which causes a fall in airway pressure above leading to airway compression as the intrapleural pressure rises
What is a peak flow meter used for?
Measures the velocity in which you bring air out of the lungs. It gives an estimate of peak flow rate. Assesses airway function and is useful in obstructive disease.
What is pulmonary compliance?
Compliance is a measure of the effort that goes into stretching the lungs. Volume change per unit of pressure change across the lungs. The less complient the lungs are, the more effort is needed to produce a given degree of inflation
What are the causes of decreased pulmonary compliance?
Pulmonary fibrosis, pulmonary oedema, lung collapse, pneumonia, loss of surfactant.
Decreased pulmonary compliance will show what pattern on spirometry?
Restrictive pattern
What are the causes of increased pulmonary compliance?
Emphysema, when the elastic recoil of the lungs is lost. Patients must work harder to exhale.
Does pulmonary compliance increase with age?
Yes
When is the work of breathing increased?
Pulmonary compliance decreased
Airway resistance increased
Elastic recoil decreased
Need for increased ventilation
How much of total energy is used for breathing at rest?
What level of capacity do the lungs function at rest?
3%
50%
What is the pulmonary ventilation rate?
The volume of air breathed in and out per minute
What is the alveolar ventilation rate?
The volume of air exchanged between the atmosphere and the alveoli per minute. ~350ml per breath so about 4.2L/min
What is ventilation?
What is perfusion?
What conditions are ideal?
Ventilation: the rate at which gas is passing through the lungs. Worse at the bottom of the lungs
Perfusion: the rate at which blood is passing through the lungs. Worse at the top of the lungs
When ventilation and perfusion are matched
What is alveolar dead space?
Ventilated alveoli not sufficiently perfused with blood
What controls ventilation/perfusion matching?
Vasodilation/vasoconstriction of the local blood vessels
Dilation/constriction of local blood vessels
What are the 4 factors that influence gas exchange?
Partial pressure gradients of oxygen and carbon dioxide
Diffusion coefficient for oxygen and carbon dioxide
Surface area of alveolar membranes
Thickness of alveolar membranes
What is Dalton’s Law?
The total pressure exerted by a gas mixture is the sum of the partial pressures of each individual component in the gas mixture
What is the alveolar gas equation?
PAO2 = PiO2 - (PaCO2/0.8)
0.8 is the respiratory exchange ratio
What is the diffusion coefficient?
The solubility of a gas in a membrane. The diffusion coefficient for CO2 is 20x greater than O2
What would cause and increase or decrease in alveolar surface area?
Increase- exercise
Decrease- emphysema and lung collapse
What would cause and increase in alveolar membrane thickness?
Oedema, Fibrosis, Pneumonia
What is Fick’s Law?
The amount of gas that moves across a sheet of tissue in a unit time is proportional to the surface area and inversely proportional to the thickness of the tissue
Respiratory tree
What are the conducting zones?
What are the respiratory zones?
Conducting = trachea, bronchi, bronchioles and terminal bronchioles Respiratory = respiratory bronchioles, alveolar ducts and alveolar sacs
What are the non respiratory functions of the airways and lungs?
Water loss and heat elimination, enhances venous return, helps maintain acid/base balance, enables speech, defends against inhaled matter, removes modifies or activate materials passing through the pulmonary circulation
What is Henry’s Law?
The amount of a given gas dissolved in a given type and volume of liquid at a constant temperature is proportional to the partial pressure of the gas in equilibrium with the liquid.
If the partial pressure of the gas increases the concentration of gas dissolved in the liquid would increase proportionately.
How much oxygen is dissolved in a litre of blood at PO2 13.3kPa?
3ml
At rest, cardiac output is ~5L/min =>15ml of oxygen, but the consumption of oxygen by body cells at rest is 250ml
How is oxygen carried in the blood?
- 5% dissolved
98. 5% bound to haemoglobin
How many haem groups in haemoglobin? How much oxygen can one haem group carry?
4 haem groups which can each carry one oxygen molocule
What is the primary factor which determines the saturation of haemoglobin with oxygen?
PO2
What shape is the oxygen haemoglobin dissociation curve and why?
Sigmoid because the binding of one oxygen molocule to haemoglobin increases the affinity of haemoglobin for oxygen. The graph will flattern when all the sites are occupied.
What is the oxygen delivery index?
The product of the oxygen content of arterial blood and the cardiac output.
How does foetal haemoglobin differ from adult haemoglobin?
Foetal haemoglobin has 2 alpha and 2 gamma subunits.
Adult haemoglobin has 2 alpha and 2 beta subunits.
Foetal haemoglobin interacts less with 2,3- bisphosphogylcerate in the blood and has a higher affinity for oxygen.
Foetal haemoglobin curve is to the left of the adult haemoglobin curve allowing oxygen to be transferred to the foetus even when PO2 is low
What is myoglobin?
The short term oxygen store in skeletal muscles. Each myoglobin molocule has one haem group. There is no cooperative binding of oxygen and the dissociation curve is hyperbolic because myoglobin releases oxygen at very low concentrations
What does the presence of myoglobin in blood indicate?
Muscle damage
How is carbon dioxide transported in the blood?
In solution ~10%
Bicarbonate ions ~60%
Carbon amino compounds ~30%
Where does the bicarbonate reaction take place and what enzyme is involved?
Red blood cells
Carbonic anhydrase
What prevents the build up of CO2 in the red blood cells?
What do H+ ions bind to in the red blood cells?
The chloride shift. When the bicarbonate ion moves out of the red blood cell, Cl- moves in.
Haemoglobin
What is the bohr effect?
The shift of the oxygen dissociation curve to the right in response to:
Increase carbon dioxide, Increased H+, increased temp, increased 2,3, bisphosphoglycerate.
Leads to increased release of oxygen at the tissues
What is the haldane effect?
Removing oxygen from haemoglobin increase the ability of haemoglobin to pick up carbon dioxide and carbon dioxide generated ions.
What are carbon amino compounds?
Molecules formed by the combination of carbon dioxide with terminal amine groups in blood proteins
What is the purpose of the bohr and haldane effects?
To work together to facilitate oxygen liberation and uptake of carbon dioxide and carbon dioxide generated H+ ions at the tissues.
