Respiration Flashcards
Ficks law of diffusion?
Smaller the distance and greater the surface area = greater rate of diffusion
Type 1 alveoli cells?
Make up the wall of the alveoli
Type 2 alveoli cells?
Secrete pulmonary surfactant
Law of LaPlace?
(2 x surface tension) / radius = inward pressure
Therefore, smaller radius = higher inwards pressure
What causes the lungs to return to their pre-inspiration size?
Alveolar surface tension - elastic recoil
Role of pulmonary surfactant?
Decreases alveolar surface tension
- reduces recoil / prevents smaller alveoli from collapsing into larger ones
Why does pulmonary surfactant decrease surface tension in smaller alveoli more compared to larger ones?
Because the surfactant molecules are more crowded
Define the transmural pressure gradient
The pressure gradient between the alveolar pressure (same as atmospheric) and the intrapleural pressure (4 mmHg less than atmospheric). Means there is more pressure pushing out from inside than pressure pushing in from outside
Role of transmural pressure gradient?
Keeps the alveoli open and forces the lungs to expand with expansion of the thoracic cavity
Explain how pneumothorax occurs
Hole in the lung or chest pierces the pleural sac, causing the pressure to equilibriate with atmospheric pressure. Abolishes the transmural pressure gradient, causing it to collapse. Rib cage will spring out
Define newborn respiratory distress syndrome
Insufficient pulmonary surfactant cause by premature birth. Results in poorly compliant lungs due to increased alveoli surface tension + increased transmural pressure gradient. Would need massive effort to inflate the lungs
Boyle’s law? + application
P = 1 / V
As chest volume increases, pressure decreases - allowing air to enter lungs as the alveolar pressure is now less than atmospheric
Muscles involved in active expiration?
Internal intercostal muscles and abdominal muscles
Name 2 factors keeping alveoli open
- pulmonary surfactant
- transmural pressure gradient
Name 2 forces promoting alveolar collapse
- alveolar surface tension
- elasticity of pulmonary connective tissue
Define tidal volume
The volume entering and leaving the lungs during a single breath
Define residual volume
Minimal volume of air remaining in lungs after maximal expiration
Cannot be measured using spirometer
Compare pulmonary and alveolar ventilation
Alveolar excludes the ‘dead space’ volume and reveals how much air is actually reaching alveoli. Pulmonary is the total volume of air inspired and expired
If V/Q = more than 1, what are the control mechanisms?
- increase in Oxygen causes local vessel dilation to increase blood flow
- decrease in CO2 causes contraction of smooth muscle = more airway resistance = reduced airflow
What can increased CO2 cause?
Respiratory acidosis
CO2 in blood forms carbonic acid. Reduced CO2 would make blood alkaline
What could cause V / Q to be less than 1?
Asthma attack.
More perfusion than ventilation
V / Q < 1 control mechanisms?
Want to increase air flow by dilating airways and decrease blood flow by constructing vessels
Would too much CO2 in the blood cause alkalosis or acidosis? Explain.
Acidosis. There would be more CO2 induced H+ ions in blood
Which part of the brainstem houses the respiratory control centre?
Medulla (+ pons)
Compare the dorsal and ventral respiratory groups?
Dorsal = in control during quiet breathing - innervates the diaphragm
Ventral = takes over control during increased ventilation. Innervates both inspiratory and expiratory muscles
Where does the respiratory control centre receive input from?
Central chemo receptors
What do central chemoreceptors detect?
The pH of the extra cellular fluid in the brain
What do peripheral chemoreceptors detect?
Oxygen partial pressure + pH of blood
Where are peripheral chemoreceptors located
In aortic arch and carotid bodies
Which chemoreceptors will detect hypoxia
Peripheral
The hypoxic urge to breathe occurs when?
Partial pressure of O2 below 60
Describe the hypoxic urge to breathe mechanism.
When pO2 <60, the peripheral chemoreceptors send messages to medullary respiratory centre to increase ventilation
What does an increase in PCO2 do to the brain?
Increases carbonic acid = lowers the pH. This is recognised by the central chemoreceptors which respond by innervating the respiratory centre causing an increase in ventilation
Consequence of CO2’s high diffusion coefficient?
Diffuses faster than O2, does not require as high of a concentration gradient, and is removed by exhalation much easier
Explain renal compensation of respiratory acidosis
With chronic elevation of CO2, the kidneys respond by retaining bicarbonate ions which neutralise the excess H+ to bring the pH back to normal levels
Explain how renal compensation of respiratory acidosis knocks out central chemoreceptors? What impact does this have
The kidneys increase bicarbonate concentration to neutralise the blood pH. The bicarbonate can eventually diffuse across the BBB to also neutralise the excess H+ there. As a result, the central chemoreceptors are not detecting an abnormal pH, so they do not innervate the respiratory centre. Causes respiration to slow down. Eventually slows so much that the pO2 drops to a point where the hypoxic urge to breathe kicks in
Which chemoreceptors are responsible for mediating non-CO2 induced alkalosis or acidosis?
Peripheral
How long does it take for renal compensatory mechanisms to kick in?
Hours to days
Compare apnea and dyspnea
Apnea = subconsciously ‘forgets’ to breathe - e.g. sleep apnea
Dypsnea = consciously feels that their ventilation is inadequate
How can you tell if a person is hyperventilating based on a blood gas report?
CO2 will be low
If bicarb levels are within the normal range, what does this indicate?
The acidosis must be acute, because the kidney’s compensatory mechanisms have not kicked in yet
What is a condition where the PA-aO2 might be above 10?
Asthma - indicates a physiological shunt
With prolonged renal compensation, patients might become dependent on…?
The hypoxic drive to breathe
If the CO2 is low but the pH is acidic, what could this indicate?
Acidity is not due to the respiratory system. Could be metabolic acidosis
Compensatory mechanism for metabolic acidosis?
Low pH recognised by peripheral chemoreceptors only (bc ions cannot cross BBB), causing innervation of medullary respiratory centre, causing increased ventilation
