week 6: respiratory physiology: pulmonary ventilation and gas exchange Flashcards
what does pulmonary ventilation refer to
mechanical process that allows the flow of air between atmosphere and lungs occurs due to differences in pressure
atmospheri pressure
pressure in air at sea level
approx 760mm Hg
intra-alveolar pressure
pressure of air within alveolar
at rest is equal to atmospheric pressure 0mm Hg relative
varies during phases of ventilation
what drives ventilation
differences in atmospheric pressure and intra-alveolar pressure
when atmospheric pressure exceeds intra-alveolar pressure
inspiration occurs
when intra-alveolar pressure exceeds atmospheric pressure
expiration occurs
intrapleural pressure
pressure inside pleural space
at rest: -4 mmHg
varies with phases of ventilation
always less than intra-alveolar pressure
why is intrapleural pressure always negative during normal breathing
because opposing forces exerted by chest walls and lungs pull parietal and visceral pleura apart
chest wall pulls outwards, lungs pull inwards
transpulmonary pressure
difference between intra-alveolar pressure and intrapleural pressure
measure of distending force across the lung
increase in transpulmonary pressure creates
larger distending pressure across the lung
alveoli therefore expand
why do chest wall and lungs not separate when forces move them apart
surface tensions of intra-pleural fluid
keep parietal and visceral pleura from pulling apart
why is breathing a mechanical process
muscular force required
(diaphragm contracting)
(breathing mechanics) rib cage and diaphragm at rest,
pressure inside and outside lungs equal
no movement of air
(breathing mechanics) inhalation
intercoastal muscles contact, rib cage expands
diaphragm contracts,
increase vol of chest
pressure of chest lowered
air moves down pressure gradient into lungs
(breathing mechanics) exhalation
intercostal muscles relax, rib cage drops inwards and downwards
diaphragm relaxes
pressure of chest deceases
air forced out
inhalation Boyles law
increase in alveolar volume and decrease in alveolar pressure
inflow of air
exhalation Boyles law
decrease alveolar volume
increase alveolar pressure
outflow of air
two factors affecting pulmonary ventilation
pressure gradients
airway resistance
lung compliance
measure of how easily lungs can be stretched
= change in volume/ change in transpulmonary pressure
larger lung compliance
advantageous
smaller change in pressure required to inspire air, less work at breathing, less work for muscles
compliance dependent on :
elasticity of lung tissue
surface tension of fluid lining alveoli
pulmonary surfactant
substance produced by type 2 alveoli cells
decrease surface tension
increase compliance
decrease work of breathing
compliance decreased if
scarring occurs (e.g pulmonary fibrosis)
production of surfactant reduced
lung compliance too high,
negatively impacts lung function
increase in resistance
seen in obstructive airway diseases
requires significantly greater pressure gradients to be produced
increases work of breathing
minute ventilation
VE
total amount of air that flows in or out of lungs per min
tidal vol x breaths per minute
average : 500ml x 12= 600ml/min
alveolar ventilation
only a proportion of air breathed in participates in gas exchange
30% of tidal vol fills trachea, bronchi and bronchioles (dead space volume)
exchange of O2 and CO2 occurs due to
diffusion across respiratory membrane
atmospheric air vs alveolar air
atmospheric air
PO2: 160
PCO2: 0.3
alveolar air
PO2: 100
PCO2: 40
residual vol, gas moved from atmosphere to lung mixes with residual volume
increased PCO2 in red blood cell causes
most of molecules to be converted to bicarbonate, some bind to hemoglobin, small proportion dissolved in blood
bicarbonate transported out of rbc into plasma
H+ ions buffered by binding to hemoglobin
decrease PCO2 by
CO2 diffuses from blood to alveolar air
bicarbonate enters rbc, H+ released from hemoglobin
bicarbonate and H+ converted to CO2
diffuses into alveoli
