physiology Flashcards
What are the 4 steps of external respiration
- Ventilation
- Gas exchange- alveoli & blood
- Gas transport in blood
- Gas exchange at tissue level
What 3 forces keep alveoli open
- Transmural pressure gradient
- Pulmonary surfactant
- Alveolar interdependence
What is pulmonary surfactant
Reduces surface tension
What 2 elastic forces promote alveolar collapse
- Elastic recoil of lungs & chest wall
- Alveolar surface tension
What 2 factors make lungs adhere to chest wall
- Transmural pressure gradient
- Intrapleural fluid cohesiveness
how is transmural pressure gradient made across lung & chest wall
sub-atomic atmospheric pressure
How is the intrapleural fluid cohesive (what does this do to pleural membranes)
Water molecules in the fluid resist being pulled apart so
-pleural membranes stick together
What 3 pressures are important in ventilation
Atmospheric (760mmHg at sea level)
Intra-alveolar (760mmHg)
Intrapleural (756mmHg)
What pressures push outwards & inwards on the lung wall
Intra-alveolar pushes outwards
Intrapleural pushes inwards
What does the 4mmHg difference in intra-alveolar & intrapleural result in
Constitutes transmural pressure gradient pushing OUT on the lungs
-Stretches them to fill thoracic cavity
What pressure gradient is essential for expansion of the lungs
Transmural
-Relationship between differences in intra-alveolar & intrapleural pressures
What condition abolishes transmural pressure gradient
Pneumothorax
-By raising intrathoracic pressure when air enters pleural space
What is boyle’s law
Pressure exerted by a gas varies INVERSELY with volume of the gas
e.g. As volume of gas increases pressure exerted by the gas decreases
which alveoli have higher tendency to collapse: small or big alveoli?
Small more likely to collapse
-Surfactant prevents this (reduces surface tension more in smaller ones)
What happens if an alveolus starts to collapse
surrounding alveoli stretch & recoil exerting expanding forces onto collapsing alveolus to OPEN IT
-Alveolar interdependence
What causes respiratory distress in premature newborns
Not having enough pulmonary surfactant as not synthesised until late in pregnancy
What are the major inspiratory muscles
Diaphragm & external intercostal muscles
What are the accessory inspiratory muscles
Sternocleidomastoid
Scalenus
Pectoral
What are the active muscles of respiration
Abdominal muscles
Internal intercostal muscles
What is tidal volume - TV
volume of air entering or leaving the lungs in a single breath
Average = 0.5 L
What is inspiratory reserve volume - IRV
Extra volume of air that can be maximally inspired above resting TV
Average = 3L
What is expiratory reserve volume (ERV)
Extra volume of air that can be actively expired by maximal contraction after resting TV
Average = 1L
What is residual volume (RV)
Minimum volume of air remaining in lungs after maximal expiration
Average = 1.2L
What is inspiratory capacity (IC)
Maximum volume of air inspired at end of normal quiet expiration
IC = IRV + TV
Average = 3.5 L
What is functional residual capacity (FRC)
Volume of air in lungs at end of normal passive expiration
FRC = ERV + RV
Average = 2.2L
What is vital capacity -VC
Maximum volume of air moved out during a single breath after maximum inspiration
VC = IRV + TV + ERV
Average = 4.5L
What is total lung capacity - TLC
Total volume of air lungs can hold
TLC = VC + RV
What volume increases when elastic recoil of lung is lost e.g. in emphysema
Residual volume
What is forced vital capacity FVC
maximum volume that can be forcibly expelled from the lungs following a maximum inspiration
What is forced expiratory volume in 1 second FEV1
volume of air that can be expired during the first second of expiration in an FVC
What is the FEV1/FVC ratio
proportion of the Forced Vital Capacity that can be expired in the first second
= (FEV1/FVC) X 100% - Normally more than 75%
What do parasympathetic + sympathetic stimulation do to airways
Parasympathetic = bronchoconstriction
Sympathetic = Bronchodilation
What factors decrease pulmonary compliance
Pulmonary fibrosis
Pulmonary oedema
Lung collapse
Pneumonia
Absent surfactant
What is pulmonary compliance
Measures the effort that goes into stretching & distending the lungs
what does decreased pulmonary compliance cause
SOB especially on exertion
greater pressure change required to give change in volume
(basically STIFF LUNGS)
What happens if pulmonary compliance increases
Emphysema
Elastic recoil of lungs is lost so having to work harder to get air OUT OF lungs
What causes increased work of breathing
Decreased pulmonary compliance
Airway resistance increases
Elastic recoil decreases
Increased ventilation (gas moving in and out of lungs)
What is anatomical dead space
where some air remains in airways, not available for gas exchange
