Physiology 3 - Gas exchange Flashcards
Anatomical dead space
some inspired air that remains in the airway where is is NOT AVAILABLE for GAS EXCHANGE
What is pulmonary ventilation
volume of air breathed in and out per minute
= tidal volume x respiratory rate
what is alveolar ventilation
volume of air exchange between atmosphere and alveoli per minute
= (tidal volume - dead space volume) x respiratory rate
what is pulmonary ventilation less than alveolar ventilation?
due to the presence of anatomical dead space
what 2 things would you need to increase to increase pulmonary ventilation?
1) depth of breathing (tidal volume)
2) rate of breathing (respiratory rate)
what is ventilation
RATE at which GAS passes through the lungs
what is perfusion
RATE at which BLOOD passes through the lungs
is blood flow fastest at top of bottom of lung
blood flow = fastest at BOTTOM
is ventilation fastest at top of bottom of lung
ventilation = fastest at TOP of lung
what effect does differences in blood flow and ventilation have on average arterial and alveolar partial pressure.
the average arteriole and alveolar partial pressure of O2 is not exactly the same
describe alveolar dead space
= ventilated alveoli which are not adequately perfused with blood
when the match between air in the alveoli and blood in pulmonary capillaries is not perfect
describer the process that occurs when the perfusion is greater than ventilation
1) accumulation of CO2 in alveoli
2) decreased airway resistance
3) increased airflow
describe the process that occurs when the ventilation is greater than perfusion
1) accumulation of O2 concentration
2) causes pulmonary vasodilatation
3) increases blood flow tot match large airflow
describer what happens to the; - gas levels - smooth muscles - airflow/bloodflow when perfusion is greater than ventilation
- CO2 increases
- O2 decreases
- dilation of local airways
- constriction of local blood vessel
- increased airflow
- decreased blood flow
describer what happens to the; - gas levels - smooth muscles - airflow/bloodflow when ventilation is greater than perfusion
- O2 increases
- CO2 decreases
- constriction of local airways
- dilation of local blood vessels
- increased blood flow
- decreased airflow
4 factors that influence the rate of gas exchange across alveolar membranes
1) partial pressure of O2 & CO2
2) diffusion co-efficient for O2 and CO2
3) surface area of alveolar membrane
4) thickness of alveolar membrane
Dalton’s law of partial pressure states that;
the total pressure exerted by a gaseous mixture
= the sum of the partial pressures of each individual components in the gas mixture
what determines the pressure gradient for a gas
the partial pressure
what is the partial pressure of a gas
the pressure that gas would exert if it occupied the total volume for the mixture in the absence of other components
e.g. if total pressure = 100kPa
partial pressure = 50kPa
how would you write the formula for the partial pressure of oxygen in alveolar air
PAO2
BIG ‘A’
what is the equation for alveolar gas
PAO2 = PiO2 - [PaCO2/0.8]
what does PiO2 stand for
partial pressure of inspired oxygen
what does PaCO2 stand for
partial pressure of CO2 in ARTERIAL blood
a = arterial
what is 0.8 represent
respiratory exchange rate, amount of CO2 excited fo amount of O2 used
how do you calculate the PiO2
- air in respiratory tract is saturated with water
- water vapour contributes 47mmHg to total pressure in the lungs
- therefore, the pressure of inspired air;
= atmospheric pressure - water vapour pressure
= 760 - 47
= 713mmHg - since O2 is 21% of air;
PiO2 = 713 x 0.21
= 150mmHg
why is the partial pressure gradient for CO2 much smaller than that of O2
- because CO2 is far more soluble than O2
what is the diffusion co-efficient
the solubility of a gas in membranes
what is the diffusion co-efficient of CO2 compared to O2
CO2’s diffusion co-efficient is 20X oft that of O2
what if Fick’s Law of diffusion
the amount of gas that moves across a sheet of tissue in unit time is PROPORTIONAL to the AREA OF THE SHEET but INVERSELY PROPORTIONAL to its THICKNESS
what role do alveoli have?
- involve in gas exchange
- they are thin walled inflatable sacs in which there walls consists of a single layer of flattened type 1 alveolar cells
where are pulmonary capillaries found?
Encircling each alveolus
name non-respiratory functions of the respiratory system
1) route for water loss & heat elimination
2) enhances venous returns
3) helps maintain normal acid-base balance
4) enables speech, singing & other vocalisation
5) defends against inhaled foreign matter r
6) removes, modifies, activates or inactivates materials passing though the pulmonary
7) nose serves as organ of smell
