Physiology Flashcards
What is internal respiration?
Internal respiration refers to the intracellular mechanism which consumes O2 and produces CO2
What is external respiration?
External respiration refers to the sequence of events that lead to the exchange of O2 and CO2 between the external environment and the cells of the body
What are the four steps of external respiration?
Ventilation, Gas exchange between alveoli and blood, Gas transport in the blood and Gas exchange at the tissue level
What is Boyle’s law?
Boyle’s law is that at any constant temperature, the pressure exerted by a gas varies inversely with the volume of the gas. Gases move from higher to lower pressure
What is ventilation?
Ventilation is the mechanical process of moving gas in and out of the lungs
What is atmospheric pressure?
Atmospheric pressure is caused by the weight of the gas in the atmosphere on the Earth’s surface
What is intra-alveolar pressure?
Intra-alveolar pressure is the pressure within the lung alveoli when equilibrated with atmospheric pressure
What is intrapleural pressure?
Intrapleural pressure is the pressure exerted outside the lungs within the pleural cavity
What is the transmural pressure gradient?
The difference between the intra-pleural and intra-alveolar pressure (a pneumothorax abolishes this gradient)
What are the normal muscles of inspiration and is this an active or passive process?
The muscles are the diaphragm and the external intercostal muscles and the process is active
Explain the recoil of the lungs and if normal resting expiration is passive or active?
Normal resting expiration is passive due to the alveolar recoil of the lungs caused by elastic connective tissue and the alveolar surface tension
What is pulmonary surfactant and why is it important?
Surfactant reduces alveolar surface tension by interspersing between the water molecules and so decreases the energy required to expand the lungs
What is the Law of La Place?
The Law of La Place says that the smaller alveoli are less likely to collapse because surfactant has a greater effect on the smaller alveoli, adding surfactant reduces the chance of alveolar collapse
Where does alveolar stability come from?
Alveolar interdependence is when surrounding alveoli stretch and recoil to expand the collapsing alveoli and stop it closing
What are the forces opening the lungs?
transmural pressure gradient, pulmonary surfactant, alveolar interdependence
What are the forces closing the lungs?
alveolar surface tension and elasticity of stretched lung connective tissue
What are the accessory muscles of inspiration?
sternocleidomastoid, scalenus and pectoral
What are the muscles of active expiration?
abdominal muscles and internal intercostal muscles
What is tidal volume?
tidal volume is the volume of air inhaled and exhaled during a normal breath
What is inspiratory reserve volume?
IRV is the volume of air that can be recruited to increase resting tidal volume
What is the residual volume?
RV is the remaining air in the lungs after a complete forced exhalation
What is the functional residual capacity?
FRC is the volume of air left in the lung after expiration of a normal tidal volume breath
What is the vital capacity?
VC is the greatest volume of air that can be inhaled and exhaled
What is total lung capacity and why can’t this be measured using spirometry?
TLC is the maximum volume of air that the lungs can hold, this can’t be measured by spirometry because the RV can’t
What is the equation linking IC, TV and TRV
IC = IRV + TV
What is the equation linking ERV, RV and FRC
FRC = ERV + RV
What is the equation linking IRV, TV, ERV and VC
VC = IRV + TV + ERV
What is the equation linking VC, TLC and RV
TLC = VC + RV
How does obstructive lung disease change FVC and FEV1/FVC ratio?
low or normal FVC and low FEV1/FVC ratio
How does restrictive lung disease change FVC and FEV1/FVC ratio?
low FVC and normal FEV1/FVC ratio
What are the factors that influence airway resistance?
Pressure and resistance
Does sympathetic cause bronchoconstriction or bronchodilation?
sympathetic causes bronchodilation
Does parasympathetic cause bronchoconstriction or bronchodilation?
parasympathetic causes bronchoconstriction
What is dynamic airway compression and why does this cause problems in patients with airway obstruction?
Dynamic airway compression is the pressure applied to the airways and alveoli during active expiration and is harmful in patients with airway obstruction because there is no air moving through the airway so the outside pressure overcomes the inside pressure and the airway can collapse
What is a peak expiratory flow meter used for?
A PEFR meter is used to identify reversible airway obstruction and to asses the severity of acute airways obstruction
What is lung compliance?
Lung compliance is a measure of the effort that goes into stretching the lungs
What diseases could decrease pulmonary compliance?
pulmonary fibrosis, pulmonary oedema, lung collapse, pneumonia and the absence of surfactant
What could cause an increase in pulmonary compliance?
emphysema because there is loss of elastic recoil of the lungs
What is meant by the term ‘work of breathing’?
work of breathing is the energy expended to inhale or exhale a gas
What factors could increase the work of breathing?
a decreased pulmonary compliance, an increased airway resistance, a decreased elastic recoil and when there is an increased need for ventilation
What is the difference between pulmonary ventilation and alveolar ventilation?
pulmonary ventilation is the volume of air breathed in and out per minute but alveolar is the volume of air exchanged between the atmosphere and the alveoli per minute
What is anatomical dead space?
Anatomical dead space is the volume of the airways that gets filled with air but the air will be exhaled without having undergone gas exchange with the tissues
What is ventilation perfusion matching?
ventilation is the rate at which gas is passing through the lungs and perfusion if the rate at which blood is passing through the lungs, in a healthy human this is matched
What is alveolar dead space?
alveolar dead space is the alveoli which are ventilated but are not adequately perfused with blood, this is increased in disease
What does physiological dead space equal?
physiological dead space = anatomical dead space + alveolar dead space
What will be the response in the airways to alveolar CO2 accumulation?
the airway resistance will be decreased so there will be increased airflow to remove the CO2
What will be the response in the airways to increased alveolar O2?
there will be pulmonary vasodilation so that blood flow is increased to match the larger airflow
What are the four factors that influence gas transfer across the alveolar membranes?
- partial pressure gradients of O2 and CO2
- diffusion coefficient for O2 and CO2
- surface area of alveolar membrane
- thickness of alveolar membrane
What is Dalton’s law of partial pressures?
Dalton’s law of partial pressures is that the total pressure exerted by a gaseous picture is the sum of all the individual partial pressures
What factor influences how gases move?
gases move down their partial pressure gradient
What is the alveolar gas equation?
PaO2 = PiO2 - (PaCO2/0.8)
What does a big gradient between the partial pressure oxygen in the alveolar air and the partial pressure of oxygen in the arterial blood mean?
there could be problems with gas exchange or a high to left shift in the heart
Why is the diffusion coefficient for CO2 larger than that of O2?
because CO2 is far more soluble in membrane than O2 so the coefficient is 20x larger
What is Fick’s law of diffusion in relation to membrane surface area and membrane thickness?
Fick’s law states that the amount of gas that moves across a sheet is proportional to the area of the sheet but inversely proportional to its thickness
What are some of the non-respiratory functions of the respiratory system?
- route for water and heat loss
- enhances venous return
- maintains normal acid-base balance
- enables speech
- defends against foreign matter
- nose is organ of smell and removes, modifies and activates material passing through the pulmonary circulation
What is Henry’s law in relation to partial pressure in gas solubility?
Henry’s law is that the amount of a given gas dissolved 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
How is oxygen carried in the blood?
mostly by haemoglobin but a very small amount is physically dissolved
What shape is the oxygen-haemoglobin dissociation curve and why is it this shape?
sigmoidal shape due to the cooperative binding of oxygen so as one o2 binds it makes it easier for other to bind too
What is the equation linking oxygen content of the arterial blood, cardiac index and oxygen delivery index?
oxygen delivery index = oxygen content of the arterial blood * cardiac index
What is the oxygen content of the arterial blood determined by?
the concentration of haemoglobin in the blood and the percentage saturation of haemoglobin with oxygen
What is oxygen delivery to the tissues affected by and why?
respiratory disease (arterial pO2 is decreased so Hb saturation and O2 is too), heart failure (cardiac output decreased) and anaemia (Hb concentration and O2 content are decreased)
What is the significance of the Bohr effect in relation to O2 liberation at tissues and what conditions is this in response to?
a rightward shift allows quick offloading of oxygen at tissues in response to increased CO2, pH , temp or 2,3-biphosphoglycerate
How does foetal haemoglobin differ from adult haemoglobin?
HbF has two gamma subunits instead of beta and has a higher affinity for oxygen and it interacts less with 2,3-biphosphoglycerate
Why is the higher affinity for oxygen in foetal haemoglobin important?
oxygen transfer can happen from mother to foetus even when PO2 is low
What is the shape of the oxygen-myoglobin curve and what is its significance?
the myoglobin curve is hyperbolic because there is only one haem group and there is no cooperative binding of oxygen so myoglobin releases O2 at very low PO2
How is CO2 carried in the blood and what are the percentages?
10% in solution
60% as bicarbonate (HCO3-)
30% as carbamino compounds
How is most of CO2 transported in the blood?
as bicarbonate (HCO3-)
How is bicarbonate formed?
the addition of CO2 and H2O with the enzyme carbonic anhydrase
What is the chloride shift?
the chloride shift is the exchange of chloride ions with carbonate ions in bicarbonate formation
What is the role of Hb in blood buffering?
Hb joins with hydrogen ions to form HbH which is an important buffering mechanism
What does the CO2 dissociation curve look like?
a diagonally upwards line
What does an increase in oxygen concentration do to a Co2 dissociation curve?
rightward shift
What is the Haldane effect?
removing O2 from Hb increased the ability of Hb to pickup CO2 and CO2 generated H+
What do the Bohr effect and the Haldane effect work together to do?
to facilitate the liberation of O2 and uptake of CO2 and Co2 generated H+
What does the picking up of O2 weaken the ability of Hb to do?
it weakens its ability to bond CO2 and H+
Which respiratory centre generates rhythm and where is it?
the medulla sits below the peons and above the spinal cord
What is the name of the network of neurones that generate breathing rhythm?
the Pre-Botzinger complex which are found near the upper end of the medullary respiratory centre
Where is the generated breathing rhythm modified? How does it do this?
it is modified by the pneumotaxic centre in the pons, it does this by stimulating termination of inspiration by firing dorsal neurons
What does the apneustic centre do?
the apneustic centre excites the inspiratory area of the medulla to prolong inspiration
Where are the peripheral chemoreceptors found?
the peripheral chemoreceptors are found in the carotid and aortic bodies
What do the peripheral chemoreceptors sense?
- O2
- CO2
- [H+]
Where are the central chemoreceptors?
central chemoreceptors are near the surface of the medulla of the brainstem
What are the central chemoreceptors stimulated by?
the [H+] of the cerebrospinal fluid
What is the chemoreceptor system particularly responsive to?
hypercapnia so ventilation will increase as soon as an increase in CO2 levels is detected
What happens when there is a fall in arterial pO2?
increase in ventilation
What happens in response to a rise in arterial [H+]?
detected by the peripheral chemoreceptors so hyperventilation so that CO2 goes so it can’t generate [H+]
What factor plays a dominant role in the control of ventilation?
the arterial pCO2
What is hypoxic drive and in which patients is it particularly important?
hypoxic drive is stimulated when arterial oxygen drops very low, it is important in patients with chronic CO2 retention (peripheral chemoreceptors)
What are the acute adaptations to hypoxia?
hyperventilation and increased cardiac output
What are chronic adaptations to hypoxia?
- increased RBC production
- increased 2,3 BPG in RBC
- increased number of capillaries
- increased mitochondria
- conservation of acid in the kidneys
