Respiratory Physiology- Gas Exchange Flashcards
Pulmonary ventilation
Pulmonary Ventilation (L/min (resting conditions))= TV (L/breath) x RR (breath/min)
Vol of air breathed in and out every minute
How to increase pulmonary ventilation?
Increase depth (TV) (more advantageous due to dead space) Increase rate of breathing (RR)
Alveolar ventilation
Vol of air exchanged between atmosphere and alveoli per minute
(TV-dead space)xRR
Less than pulmonary ventilation due to dead space being deducted
Factors affecting transfer of gas between body and atmosphere
Ventilation: rate gas passes through lungs
Perfusion: rate at which blood passes through lungs
Alveolar dead space
ventilated alveoli which aren’t sufficiently perfused with blood
Anatomical dead space
Volume of air that is inhaled that does not take part in the gas exchange, because it either:
- remains in the conducting airways or
- reaches alveoli that are not perfused or poorly perfused
Physiological dead space
alveolar and anatomical dead space
What happens when perfusion>ventilation?
- CO2 increases; O2 decreases
- local airways dilate; local blood vessels constrict
- airflow increases; blood flow decreases
Effect of increased O2 conc on pulmonary arterioles?
Vasodilation (opposite for systemic arterioles)
Factors affecting the rate of gas exchange across alveolar membrane?
- partial pressure gradient
- diffusion coefficient for O2 and CO2
- surface area of alveolar membrane
- thickness of alveolar membrane
Partial pressure
The pressure which one gas in a mixture would exert if it were the only gas present in the volume that the whole mixture occupies at a given temp
Dalton’s law of partial pressures
Total pressure exerted by a gaseous mixture= the sum of partial pressure of each individual component in the gas mixture
Respiratory Exchange Ratio
CO2 produced/ O2 consumed
0.8 for a person eating a mixed diet
Partial Pressure of O2 in alveolar air (equation)
PAO2=PiO2-[PaCO2/0.8]
Partial pressure gradient for PaO2
Gases move from lungs to tissue (for PaCO2 tissue to lung)
Why is the PP gradient for CO2 smaller than that of O2?
CO2 is twenty times O2 diffusion coefficient ie it is much more soluble in membranes
Fick’s Law
The amount of gas to move across a sheet of tissue in unit time is proportional to the area of the sheet and inversely proportional to its thickness
Respiratory tree
Trachea-> bronchi-> bronchioles-> terminal bronchioles-> respiratory bronchioles-> alveolar ducts-> alveolar sacs
Components of the conducting zone of the respiratory tree
Trachea-> bronchi-> bronchioles-> terminal bronchioles
Components of the transport and respiratory zone go the respiratory tree
Respiratory bronchioles-> alveolar ducts-> alveolar sacs
Alveolus
Thin walled, inflatable sac
Wall made of type 1 alveolar cells
Function in gas exchange
Surrounded by pulmonary capillary
When partial pressure increases, rate of transfer across alveolar membrane…
Increases
When diffusion coefficient increases, rate of transfer across alveolar membrane…
Increases
When surface area increases, rate of transfer across alveolar membrane…
Increases
Can be achieved via exercise (deeper breathing-> alveoli expand and pulmonary capillaries open up when cardiac output increases)
SA decreases with emphysema etc.
When tissue thickness increases, rate of transfer across alveolar membrane…
Decreases
Thickness increases with pulmonary oedema, fibrosis, pneumonia etc.
Non respiratory functions of the respiratory system
- Route for water loss and heat elimination
- Increases venous return (cardio)
- LPS helps maintain acid-base balance (respiratory and renal)
- Speech, singing etc.
- Defence against foreign particles
- Nose- organ of smell
- removes/ modifies/ (in)activates materials passing through pulmonary circulation
How does air flow match blood flow?
Local controls work on smooth muscle of airways and arterioles
What happens when perfusion in alveoli is increased?
Decreased airway resistance-> increases air flow-> CO2 accumulates
What happens when ventilation is increased?
Pulmonary vasodilation-> increases blood flow to match larger airflow-> Increased alveolar O2 conc
Which pressure of a gas determines the pressure gradient?
Partial pressure
