module 3: respiratory physiology Flashcards
o2 is necessary for production of cellular energy which takes the form of…
ATP, which creates Co2 that must be expelled from the cells
(this is known as internal respiration)
external respiration 4 steps
- ventilation: air is moved in and out of the lungs
- exchange of o2 and co2 between air and blood
- transport of o2 and co2
- exchange of o2 and co2 between blood and tissues
what does the upper airway include
nose, nasal cavities, pharynx, larynx
the larynx is the location of the
vocal cords
what does the lower airway include
trachea, left and right bronchi, bronchioles, alveoli
what is convective flow
requires energy in the form of muscle contraction to maintain air flow
what is diffusive flow
occurs passively to allow air to flow into the alveoli
where does the diffusive zone begin?
level of the respiratory bronchioles
what are the main inspiratory muscles
the diaphragm, and the external intercostal muscles
during inspiration diaphragm descends to enlarge the thoracic cavity. contraction of the external intercostal muscles elevates the ribs to further enlarge the thoracic cavity.
what are the main expiratory muscles
internal intercostal muscles, and the abdominal muscles (generally inactive, but get recruited in ventilator demand)
what is the pleural space (pleura)
covers the lung, and the inside wall of the thorax is lined by the parietal pleura
between these 2 membranes is the pleural space, which is relatively small and filled w fluid, the pleural fluid. this fluid allows the membranes to rub against each other during breathing w reduced friction.
2 processes for external respiration (the 4 steps broken down even further)
- ability of the resp muscles to generate the necessary pressure gradient to move air through the airways (overcoming the resistance to flow) and to inflate the lungs
- the ability of oxygen and carbon dioxide to diffuse across the alveolar-capillary barrier
what is the eqtn for external respiration
change in pressure / resistance = flow (or diffusion)
why is the pressure gradient important in respiratory mechanics
pressure gradient is drives the force of air flow
if this pressure gradient is used to overcome the elastance, or stiffness, of the respiratory system, the resistance to flow, and the inertia of the system
for air to flow out of the alveoli, the pressure in the alveoli must be _______ than the pressure in the nose
greater
what is atmospheric pressure (Pa)
- aka barometric pressure
- pressure exerted by the weight of the air in the atmosphere on the Earth’s surface
- @ sea level it is 760 mmHg and this value decreases as you gain altitude
what alveolar pressure (PA)
pressure in the alveoli, aka intrapulmonary pressure
at the end of inspiration, alveolar pressure is the same as atmospheric pressure at 0 cmH2O
what is pleural pressure (PPL)
- pressure in the pleural space aka intrapleural pressure and closely approximates the intrathoracic pressure
- pleural pressure is negative to atmospheric pressure and is normally around -5cmH2O. It is negative bc the lungs want to collapse yet the chest wall wants to expand
transpulmonary pressure (PTP)
pressure is the difference between the alveolar pressure and the pleural pressure. also referred to as lung recoil pressure, or transmural pressure
what does mmHg describe
for the partial pressures of gases when discussing diffusion
what does cmH2O describe
when discussing bulk flow (convection)
what is an important property of the lungs to remember
elastic recoil/intrinsic tendency to deflate following inflation
what are elastin fibres
connective tissues within the lung contain lots of elastin fibres that are arranged in a meshwork that enhances their elastic behaviour. when lung is stretched, this elastic recoil causes the lung to deflate
describe surface tension of the lung
the force exerted by the liquid lining the inside of the alveoli and accounts for 70% of elastic recoil properties of the lung
surface tension has a 2-fold effect on elastic recoil what are they
- the liquid layer resists any forces that try to increase its surface area. this is due to the water molecules resisting being pulled apart
- the surface area of the liquid shrinks as much as it possibly can. this is due to the water molecules being so strongly attracted to each other.
what is pulmonary surfactant
a complex mixture of lipids and proteins secreted by type 2 alveolar cells. these secretions help disperse H2O on surface of the alveoli. by dispersing H2O, the water-water attractions are decreased, which causes alveolar surface tension to be decreased. this reduced surface tension is very important for respiratory mechanics as it decreases the effort needed for inflation and it reduces the surface tension of smaller alveoli more so than it does larger alveoli.
what is alveolar interdependence
- when an alveolus in a group of interconnected alveoli starts to collapse, the surrounding alveoli are stretched by the collapsing alveolus
- as the neighbouring alveoli recoil, they pull outward on the collapsing alveolus. this helps prevent the alveolus from collapsing.
what is the law of LaPlace
states that the magnitude of this collapsing pressure is directly proportional to the surface tension and inversely proportional to the radius of the alveoli
eqtn: 2T (surface tension) / r (alveolar radius) = P (collapsing pressure)
in order to prevent alveolar collapse…
small alveoli secrete more surfactant!
what is pulmonary surfactant
a compound composed of a mixture of lipids and proteins, and is produced and secreted by alveolar cells onto the surface of the alveoli. the hydrophobicity of surfactant enables it to interfere with the attractive intermolecular forces between the water molecules found lining the alveoli, thus reducing surface tension.
what is the equation for alveolar pressure
alveolar pressure (PA) - pleural pressure (PPI) = lung recoil pressure (PI)
describe the onset of inhalation
immediately b4 inhalation, alveolar pressure equals atmospheric pressure. Air flows neither in or out. Contraction of the inspiratory muscles causes the pleural pressure to decrease and the thoracic cavity enlarges. this decreases alveolar pressure and air flows down its pressure gradient into the lungs and inflates the alveoli. This continues until the increasing alveolar pressure again equals that of atmospheric pressure. changes in alveolar pressure is relatively small.
describe the onset of exhalation
at the end of inspiration, inspiratory muscles relax. this increases pleural pressure and therefore increases alveolar pressure. air flows from lungs until alveolar pressure = atmospheric pressure. activation of expiratory muscles is not necessary for normal expiration due to the strong recoil forces
describe active exhalation
in healthy people at rest, expiration is passive. activation of expiratory muscles reduces the end-expiratory lung volume which increases the tidal volume independent of the inspiratory muscles.
during routine exercise: to breath out alveolar pressure must be increased more than is accomplished by decreased excitation of inspiratory muscles and elastic recoil.
forced expiration: activates the expiratory muscles to generate a high pleural pressure for forced expiration. as expiratory flow continues, the pressure decreases because of energy lost due to resistance. at some point along the airways the equal pressure point will be reach.
describe active expiration
pleural pressure becomes +’ve due to the increased abdominal pressure, but the lungs do not collapse. this occurs bc the alveolar pressure increases correspondingly. also, any pressure increase in the pleural pressure is offset by a proportionate increase in airway resistance due to the compression of the airways. this blocks further outflow and, as such, active expiration never results in a person exhaling past their psychological residual volume (which would collapse the bronchioles).
as lung volume increased its PI increased from _____ cmH2O to residual volume to about ______ cmH2O at total lung capacity
0, 30
in opposition the pressure of the chest wall (PW) functions more like a spring about ______ of _________, the compressed spring exerts negative pressure yet ______ total vital capacity, the chest wall now a stretched spring wants to collapse
65%, total vital capacity, 100%
Pw
if we combine ____ and ____ we get ______ which rep the pressure-volume relationship of the resp sys
PI and PW we get Prs
describe compliance
the pressure-volume curve can derive compliance, which is the slope of the curve. is the greatest at functional residual capacity, which means the amount of work, or pressure needed, to either inhale or exhale is at its minimum
describe low compliance
means more pressure is required to move air in or out. compliance is affected by lung diseases, like emphysema.
Poiseuille’s Law eqtn
flow rate (Q) = pi(triangle)Pr4/8nL
what is the primary determinant of resistance
the radius of the airway
bronchoconstriction
occurs under the influence of local chemical control. specificantly, decreased CO2 causes constriction to decrease ventilation and maintain a psychological level of CO2
pathological factors of bronchoconstriction
- histamine release
- excess mucus
- airway collapse
- oedema of the airway walls
- allergy-induced spasm of the airways caused by slow-reactive substance of anaphylaxis
what is bronchodilation
when not at rest, or during periods of sympathetic domination when body O2 demands are increased, sympathetic activity causes bronchodilation to allow max flow rates with minimum resistance
what is sympathetic activity mediated by
both direct and indirect innervation
what is direct innervation
nerve terminals release NE, which activates B2 receptors on the bronchial smooth muscle cells
what is indirect innervation
E released from the adrenal medulla circulates through the pulmonary circulation to the airway smooth muscle
true/false
there are no pathological conditions that cause bronchodilation
true/false oedema of the airway walls leads to bronchodilation of airways
false
true/false NE release activates B2 receptors on bronchial smooth muscle cells
true
true/false bronchodilation primarily occurs under the influence of local chemical control
false
true/false when body O2 demands are increased, sympathetic activity causes bronchodilation
true
what is asthma
chronic inflammatory disease of the airways that causes difficulty breathing.
sympt: SOB, chest tightness, coughing, wheezing
caused from:
1. airway walls are thickened due to histamine-induced oedema
2. thick mucus secretion physically blocks the airways
3. airway hyper-responsiveness causes spasms of smooth muscles in smaller airways, resulting in their constriction
triggers can be allergens, irritants, or infection
what is COPD
term used to cover emphysema and chronic bronchitis and is usually caused by long-term smoking
chronic bronchitis: longterm inflammatory condition of lower airways. caused by chronic exposure to smoking, allergens, or air pollution. airways become narrowed due to oedema of the airway walls and secretion of a thick mucus
emphysema: irreversible condition is characterized by the collapse of the smaller airways and breakdown of alveolar tissues. in response to chronic exposure to smoke, alveolar macrophages release substances like trypsin as a defensive mechanism. excess trypsin and other destructive enzymes destroy the lung tissue