Pulmonary Ventilation Flashcards
Why do we need a respiratory system?
→Our bodies are too large to rely on simple diffusion of gases from the atmosphere to the tissues.
What are the three functions the respiratory system has within the body?
→Provides (and ventilates) a specialised surface where gas exchange can take place between the atmosphere and blood.
→Contributes to acid-base balance (e.g. pH of the blood).
→Communication and metabolism.
How does oxygen get from the atmosphere into cells?
→O2 inhaled from atmosphere into alveoli within lungs
→O2 diffuses from alveoli into blood within pulmonary capillaries.
→O2 transported in blood, predominantly bound to haemoglobin.
→O2 diffuses into cells/tissues for use in aerobic respiration.
→CO2 diffuses from respiring tissues to blood – exchanged at lungs.
Why is ventilation of gas exchange structures necessary?
→Tissues continually demand O2 & produce CO2.
→An adequate concentration gradient between alveolar air and blood is required for efficient gas exchange (diffusion).
Why is fresh air required from the atmosphere?
→fresh air required from atmosphere to ensure alveolar oxygen pressure (PAlvO2) = high
→alveolar CO2 pressure (PAlvCO2) = low, relative to the blood.
Where do gases naturally move?
Gases naturally move from (connected) areas of higher pressure to lower pressure, until an equilibrium is re-established.
What is the ideal gas law?
→PV=nRT
→P = pressure →V = volume → n = number of moles →R = gas constant →T = temperature
What does Boyle’s law state?
pressure of a gas is proportional to the number of has molecules within a given volume.
P ∝ n/v
What happens if the n remains constant in Boyle’s law and you increase the volume?
→If the n remains constant
→increasing the volume will decrease the pressure.
How can we calculate partial pressure?
→Partial pressure can be calculated by multiplying the total pressure by the mole fraction.
What is the equation for P gas?
P gas = (P barometric - P H2O) x n gas
P gas = partial pressure of the individual constituent gas
P barometric = atmospheric pressure
P H2O = water vapour pressure and n gas is the mole fraction.
What do cells require to function?
→Cells require energy to function, and we need O2 to make that energy
What does aerobic respiration require?
→ Aerobic respiration requires O2 and produces CO2.
→The atmosphere provides a source of O2, and CO2 can be expelled.
What are the typical partial pressures in arterial, and venous pressure?
→Arterial: PaO2 = 13 kPa PaCO2 = 5 kPa → Venous: PvO2 = 5 kPa PvCO2 = 6 kPa Alveoli: → PAO2 ≈ 14 kPa PACO2 ≈ 5 kPa
What happens to partial pressure of O2 as ventilation increases?
→ As ventilation increases, the level of oxygen increases but then plateaus because contents of alveoli become the same
What happens to partial pressure of CO2 as ventilation increases?
→The partial pressure of CO2 within alveoli decreases as ventilation increases
What does ventilation depend on?
→volume (depth) and rate of breathing
Equation for ventilation…
𝑉̇=V(t)×𝑓
tidal volume x frequency
→𝑉̇ = minute volume (mL), the total volume of air inhaled in all breaths over one minute. →𝑉_𝑇 = tidal volume (mL), the volume of air inhaled in each breath. →𝑓= frequency (min-1), the number of breaths per minute
Where does gas exchange occur?
Only in alveoli
What is dead space?
air occupying airways
→150ml first bit of air breathed out
→that the final ≈150mL (dead space volume) of each inspiration never reaches the alveoli or takes place in gas exchange
What is the difference between fresh and stale air?
Fresh air- not taken part in gas exchange
→Stale air- taken part in gas exchange
Equation for ventilation with dead space taken to account…
𝑉̇_𝐴=(𝑉_𝑇−𝑉_𝐷 ) ×𝑓
→𝑉̇_𝐴= alveolar minute volume (mL), the total volume of fresh air entering the alveoli across all breaths over one minute.
→𝑓= frequency (min-1)
→𝑉_𝑇 = tidal volume (mL)
→𝑉_𝐷 = Dead space volume (mL), the volume of air remaining in the respiratory system at the end of expiration.
→𝑉_𝑇−𝑉_𝐷 = the volume of fresh air entering the alveoli in each breath.
How does the respiratory system achieve movement of air?
Gases naturally move from (connected) areas of higher pressure to lower pressure, until an equilibrium is re-established.
→If the pressure in alveoli is high than atmosphere, air will move from alveoli to atmosphere
What happens to diaphragm and thoracic cavity during inspiration and expiration?
INSPIRATION:
Diaphragm contracts →thoracic cavity expands.
→Alveolar pressure decreases
EXPIRATION:
→Diaphragm relaxes (and lung recoils). →Thoracic cavity volume decreases →alveolar pressure increases.
What happens to pressures during inspiration and expiration?
Inspiration:
The outer surfaces of the lung are pulled outwards (expansion).
↑volume = ↓alveolar pressure.
Palveoli < Patmosphere
Air flows from high (atmosphere) to low (alveoli) pressure.
Expiration: Air within the lung is compressed. ↓volume = ↑alveolar pressure. Palveoli > Patmosphere Air flows from high (alveoli) to low (atmosphere) pressure.
At the end of expiration, Palveoli = Patmosphere, therefore there is no movement of air
What is pleural cavity?
fluid filled space between the membranes (pleura) that line the chest wall and each lung - helps to reduce friction between lungs and chest.
→Respiratory muscles are not attached to or pull on the lungs directly. Instead, the lungs and chest wall are separated by a pair a serous membranes know as pleurae
What are the properties of the pleural cavity?
→sealed and fluid filled.
What can the properties of the pleural cavity achieve?
it resists changes in volume.
→Thus, changes in the volume of the thoracic cavity (due to resp. muscle activity) result in changes in lung volume.
What is the difference between visceral and parietal pleura?
The (inner) visceral pleura lines each lung,
→whereas the (outer) parietal pleura lines the thoracic cavity, surrounding the chest, diaphragm and mediastinum (which contains the heart).
How does the lung and chest recoil?
the lungs recoil inwards, the chest wall recoils outwards
How is pressure reduced in the pleural space?
→The tissues attached to each pleura recoil in opposite directions due to their elastic properties
→stretching the sealed pleural cavity between them.
→decrease the pressure within the pleural space as it now occupies a greater volume but with the same number of molecules within it
Why does the pleural cavity resist changes in volume?
→filled with liquid, meaning that it resists changes in volume more than if it were filled with gas,
What is negative pleura city pressure?
lower number of molecules per volume (relative to surroundings) → generates collapsing force (pulls surfaces of contained space together).
→acts to pull the two pleura (and as a result, the lungs and chest wall) together
→the greater the level of negative intrapleural pressure, the greater the level of force acting to pull the pleura together
What is positive pressure?
→the lungs and chest will be pushed apart.
→increased number of molecules per volume (relative to surroundings) → generates expanding force (pushes surfaces of contained space apart). Expiration
What is the role of elastic recoil?
acts to pull the visceral pleural inwards and compress the lung volume.
What happens during forced expiration?
→muscle contraction generates inward force on the parietal pleura, compressing the pleural cavity (further increasing PIP) lungs, and
→results in more pronounced decline in lung volume, in terms of both speed and magnitude.
→. In quiet breathing, elastic recoil is sufficient to decrease lung volume.
Overall movements of inspiration…
Respiratory muscles (e.g. diaphragm) contract
↓
Volume of thoracic cavity increases
↓
Intrapleural pressure becomes more negative
↓
Lungs expand, increasing volume
↓
PAlv (alveolar pressure) decreases below PAtm (atmospheric pressure)
↓
Air moves down pressure gradient, through airways into alveoli, expanding the lungs
Overall movements of expiration…
Respiratory muscles (e.g. diaphragm) relax, lungs recoil due to elastic fibres ↓ Volume of thoracic cavity decreases ↓ Intrapleural pressure increases ↓ Lungs compressed*, volume decreases ↓ PAlv increases above PAtm ↓ Air moves down pressure gradient, into atmosphere, deflating lungs
What happens if either of the pleural is ruptured?
the pressure gradient between the pleural cavity and the atmosphere will cause air to enter the pleural space (‘pneumothorax’)
→Entry of air into the pleural cavity results in its volume increasing, at the expense of the lung
→recoil of the lungs and expansion of the chest wall during breathing will potentially draw additional air into the cavity, further decreasing lung volume
Why is loss of negative intrapleural space bad?
elastic recoil of the chest wall and lungs is no longer resisted.
→the chest wall and lung are no longer indirectly attached, they will recoil in opposite directions
→This will cause affected regions of the lungs to collapse,
→overall effect depending on the site and extent of the injury.
What is pneumothorax?
intrapleural pressure = atmospheric pressure.
