Pulmonary Ventilation Flashcards
(41 cards)
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.
