Respiratory Physiology Flashcards
Main anatomical divisions of the respiratory tract.
Key points:
- conducting zone
- transitional and respiratory zones
- acinus
How do the epithelial cell types change as one progresses through the airways within the lung?
Columnar –> cuboidal –> squamous
More cilia ———————– less to no cilia
Which pneumocyte type is responsible for secretion of surfactant?
Type II
What is the thickness of the thickest portion of the blood-gas barrier?
3 micrometers
What collagen type makes up the pulmonary epithelial barrier?
Type IV
Fick’s law
Diffusion of gas through a tissue is proportional to surface area and partial pressures of gas on either side but inversely proportional to thickness of the membrane that diffusion must occur across.
D = directly proportional to the solubility of gas but inversely proportional to its molecular weight.
Define the following:
- Tidal volume
- Vital capacity
- Residual volume
- Functional residual capacity
- Total ventillation
- Alveolar ventillation
- Tidal volume = the volume inspired during normal respiration
- Vital capacity = the amount of air that can be inhaled/exhaled during maximal inhalation/exhalation
- Residual volume = air left in the lunds following maximal inhalation/exhalation
- Functional residual capacity = the volume remaining in the lungs after normal expiration.
- Total ventillation = the total volume of air leaving the lung per minute
What is the normal ratio of pulmonary capillary perfusion to air flow?
Normally it is equal giving a V/Q ratio of 1.
How can alveolar ventillation be estimated clinically?
Using ETCO2:
All expired CO2 should come from the alveolus and therefore CO2 concentration is inversely proportional to alveolar ventillation.
How does air move through the different parts of the lung?
In the conducting airways it is by convection/bulk flow. In the respiratory zone diffusion of gas becomes much more important.
Compare anatomic dead space vs. physiologic dead space
Anatomic = the physical space that is not ventillated in the lung
Physiologic = the proportion of the lung that is not being ventillated.
This should be relatively equal in health.
What is the difference in how fast CO2 and O2 can diffuse?
CO2 diffuses 20x faster due to its higher solubility.
Define a diffusion limited gas vs. perfusion limited (give examples)
Diffusion Limited
This refers to a gas that is rapidly taken up by haemoglobin therefore the partial pressure in the blood never rises to opose diffusion. So other properties of fick’s law come in to play e.g. membrane thickenss. An example is carbon monoxide as it binds rapidly and strongly to haemoglobin.
Perfusion Limited
This is where the partial pressures will equate so the the gas needs to be cleared from that area of the capillary to achieve further transfer of the gas into the blood. An example is NO.
O2 has properties of both of these. Initially diffusion limiting is the only issue as the oxygen binds to haemoglobin. Once fully bound (about 1/3 of the way through the capillary) it becomes a perfusion limited gas.
How does NO form in the capillary to allow vasodilation?
L-arginine is synthesised to NO by endothelial nitrogen oxide synthase (eNOS).
How is fluid cleared from the alveolar space in a normally functioning lung?
Via the Na/KATPase on the epithelial cells.
What are the four mechanisms of hypoxaemia?
Hypoventillation
Diffusion impairment
Shunt
V/Q mismatch
Why will a patient with V/Q mismatch (or shunt) hyperventillate but not increase their PaO2?
The hyperventillation occurs due to the chemoreceptor response to increased CO2 levels in the circulation. Therefore, ventillatory drive increases and the alveoli that are functional will blow off the CO2.
What is the normal adult haemoglobin variant?
Haemoglobin A
What product of red blood cell metabolism is produced in greater amounts during conditions of chronic hypoxaemia?
2,3-diphosphoglycerate - this shifts the HbO2 curve to the right.
What is the result of shifting the HbO2 curve to the right?
Oxygen binds less strongly to haemoglobin and so is offloaded in greater amounts in the tissues. However, it is then harder to saturate the haemoglobin under conditions of lower oxygen tension.
What is the result of carbon monoxide on the HbO2 curve?
Shifts to the left making it harder for haemoglobin to offload its oxygen.
What is the haldane effect?
That H+ binds more readily to Hb in deoxygenated blood.
What are the three forms in which Co2 can be carried in the blood?
- Dissolved
- As HCO3
- Carboxyhaemoglobin
What is the action of the external and internal intercostal muscles?
External = pull the ribs up and out
Internal = Pul the ribs down and inwards
What is the main component of surfactant?
Dipalmitoyl phosphatidylcholine
Which airways present the most airway resistance?
The medium sized bronchi
Which nerve acts as the effector for respiration?
The phrenic nerve.
What is the mechanism by which central chemoreceptors affect ventillation?
They detect changes in blood PCo2 indirectly by responding to changes in H+ concentration in the CSF. This concentration is a result of the diffusion of Co2 into the CSF.
Where are the central chemoreceptors located?
In the ventral medulla.
Where are peripheral chemoreceptors located?
Carotid and aortic bodies
What do the peripheral chemoreceptors detect, which is the most important?
- O2 (has most profound effect)
- CO2
- pH (carotid bodies only in humans)
Hering-Breuer inflation reflex
Slowing of respiration with increased airway stretch.
Cheyne-Stokes respitation
Phenomenon where in chronic hypoxaemia patients have 10-20s apnoic pauses and then suddently hyperventillate for a similar period of time.
Law of laplace and relevance to respiratory physiology.
One can see that with a sphere of decreasing radius inward pressure increases markedly. Also, with decreased surface tension the pressure is reduced (which is what surfactant does).
Pouiselle’s law and its relevance to respiratory physiology
Can be used to look at flow rates, pressure and resistance during laminar flow. It can also be re-arranged to tell you about resistance. The most important point is that decreasing airway diameter causes a marked increase in resistance.
Reynaulds number (and calculation) that results in turbulant flow
> 2000
