Relating structures to function (physiology) Flashcards
Define tidal volume (TV)
The volume of air breathed in and out of the lungs at each breath (av. 500ml at rest)
Define expiratory reserve volume (ERV)
The max volume of air which can be expelled from the lungs at the end of a normal expiration
Define inspiratory reserve volume (IRV)
The maximum volume of air which can be drawn into the lungs at the end of a normal inspiration (3L)
Define residual volume (RV)
The volume of gas in the lungs at the end of a maximal expiration
(Is always there and stops alveoli collapsing at end of expiration)
Define vital capacity (VC)
Tidal volume + inspiratory reserve volume + expiratory reserve volume
(max air you can voluntarily shift in one breath)
Define total lung capacity (TLC)
Vital capacity + residual volume
Define inspiratory capacity (IC)
Tidal volume + inspiratory reserve volume
Define functional residual capacity
Expiratory reserve volume + residual volume
(air left in lungs after end of normal expiration)
Define FEV1/FVC
Fraction of forced vital capacity expired in one second
Define anatomical dead space
Air sat in upper airways not participating in gas exchange (about 150ml)
Describe the anatomy of the pleural cavity
Made up of pleural membrane - wraps around the lungs and doubles back on itself at the hilum. Outer membrane attaches to inner surface of rib cage and diaphragm.
Pleural cavity filled with pleural fluid = lubricant
-3 mmHg pressure in cavity (0=atmos), two forces trying to pull apart the mem but unable to do so due to cohesive force.
Define visceral pleura and parietal pleura and their relationship
Visceral = lines outer surface of the lungs
Parietal = lines inner surface of ribs and diaphragm
Relationship = membranes form pleural cavity filled with pleural fluid which allows friction free gliding of membranes during breathing.
Cohesive force stops the two membranes from separating which allow your lungs to expand/contract as your chest wall expands/contracts.
Explain how the muscles of respiration increase thoracic volume
Increase volume = inspiration
Intercostal muscles
Diaphragm.
- Contracts = inc thoracic volume and dec in pressure (so air flows into the lungs down its partial pressure gradient)
Muscles used:
- sternocleidomastoids
- scalenes
- external intercostals
- diaphragm
Explain how the muscles of respiration decrease thoracic volume
Decrease = expiration = passive
Decreased via elastic recoil of lungs
Aided by intercostal and abdominal muscles when respiratory load increases.
What happens with the the ribs and sternum during breathing
Ribs = bucket handle movement
- increases lateral dimension of rib cage
Sternum = pump handle movement
- increases anterior/posterior dimension of the rib cage
Define Boyle’s law
The pressure exerted by a gas is inversely proportional to its volume
(Note: gases move from areas of high pressure to areas of low pressure)
Relate Boyle’s law to the mechanics of breathing, inspiration and expiration
As you inspire, lung/thoracic volume increases and so pressure decreases. Gases move down their partial pressure gradient and this forces air into the lungs
As you expire, lung/thoracic volume decreased and so pressure increases. This forces gases to out of the lungs, hence you exhale.
Explain why intrapleural pressure is always less than alveolar pressure
Intrapleural pressure = always negative
Alveolar pressure always less than atmospheric pressure during inspiration, during expiration pressure is always positive
(from google)
Due to the adhesive force of the pleural fluid, the expansion of the thoracic cavity forces the lungs to stretch and expand as well. This increase in volume leads to a decrease in intra-alveolar pressure, creating a pressure lower than atmospheric pressure.
What is the role of surfactant?
Reduces surface tension on alveolar surface membrane therefore reducing tendency for alveoli to collapse.
Increases the ease of breathing (it requires more effort to inflate alveoli from collapse).
Reduces lung tendency to recoil.
Increases lung compliance.
Where is surfactant produced
Type 2 alveoli cells
What is the law of Laplace?
P = 2T/r
P= pressure needed to keep alveoli open
T = surface tension
r = radius of alveoli
What is IRDS and what causes it?
IRDS = Infantry Respiratory Distress Syndrome
Caused by a lack of surfactant.
Affects baby premature 36 weeks or less as they have not developed enough surfactant by this point.
Means more energy is needed to inflate alveoli as they have collapsed due to surface tension.
Can be treated by an aerosol spray.
Define compliance
Change in volume of lung relative to the change in pressure (represents stretchability)
- High compliance = big increase in lung volume for a small decrease in interpleural pressure (good thing if matched by good elastic function).
- Low compliance = small increase in lung volume for a large decrease in interpleural pressure (lungs have to work harder to expand).
What factors affect compliance?
Decreased with age (as does elasticity)
Determined by:
- elastic forces
- surface tension at alveolar air-liquid interface
- airway resistance
