Pulmonary Ventilation

Question 1

Why do we need a respiratory system?

Answer 1

→Our bodies are too large to rely on simple diffusion of gases from the atmosphere to the tissues.

Question 2

What are the three functions the respiratory system has within the body?

Answer 2

→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.

Question 3

How does oxygen get from the atmosphere into cells?

Answer 3

→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.

Question 4

Why is ventilation of gas exchange structures necessary?

Answer 4

→Tissues continually demand O2 & produce CO2.

→An adequate concentration gradient between alveolar air and blood is required for efficient gas exchange (diffusion).

Question 5

Why is fresh air required from the atmosphere?

Answer 5

→fresh air required from atmosphere to ensure alveolar oxygen pressure (PAlvO2) = high
→alveolar CO2 pressure (PAlvCO2) = low, relative to the blood.

Question 6

Where do gases naturally move?

Answer 6

Gases naturally move from (connected) areas of higher pressure to lower pressure, until an equilibrium is re-established.

Question 7

What is the ideal gas law?

Answer 7

→PV=nRT

→P = pressure
→V = volume
→ n = number of moles
→R = gas constant
→T = temperature

Question 8

What does Boyle’s law state?

Answer 8

pressure of a gas is proportional to the number of has molecules within a given volume.

P ∝ n/v

Question 9

What happens if the n remains constant in Boyle’s law and you increase the volume?

Answer 9

→If the n remains constant

→increasing the volume will decrease the pressure.

Question 10

How can we calculate partial pressure?

Answer 10

→Partial pressure can be calculated by multiplying the total pressure by the mole fraction.

Question 11

What is the equation for P gas?

Answer 11

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.

Question 12

What do cells require to function?

Answer 12

→Cells require energy to function, and we need O2 to make that energy

Question 13

What does aerobic respiration require?

Answer 13

→ Aerobic respiration requires O2 and produces CO2.

→The atmosphere provides a source of O2, and CO2 can be expelled.

Question 14

What are the typical partial pressures in arterial, and venous pressure?

Answer 14

→Arterial: 
PaO2 = 13 kPa
PaCO2 = 5 kPa
→ Venous:
PvO2 = 5 kPa
PvCO2 = 6 kPa
Alveoli:
→ PAO2 ≈ 14 kPa
PACO2 ≈ 5 kPa

Question 15

What happens to partial pressure of O2 as ventilation increases?

Answer 15

→ As ventilation increases, the level of oxygen increases but then plateaus because contents of alveoli become the same

Question 16

What happens to partial pressure of CO2 as ventilation increases?

Answer 16

→The partial pressure of CO2 within alveoli decreases as ventilation increases

Question 17

What does ventilation depend on?

Answer 17

→volume (depth) and rate of breathing

Question 18

Equation for ventilation…

Answer 18

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

Question 19

Where does gas exchange occur?

Answer 19

Only in alveoli

Question 20

What is dead space?

Answer 20

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

Question 21

What is the difference between fresh and stale air?

Answer 21

Fresh air- not taken part in gas exchange

→Stale air- taken part in gas exchange

Question 22

Equation for ventilation with dead space taken to account…

Answer 22

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.

Question 23

How does the respiratory system achieve movement of air?

Answer 23

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

Question 24

What happens to diaphragm and thoracic cavity during inspiration and expiration?

Answer 24

INSPIRATION:
Diaphragm contracts →thoracic cavity expands.
→Alveolar pressure decreases

EXPIRATION:
→Diaphragm relaxes (and lung recoils). →Thoracic cavity volume decreases →alveolar pressure increases.

Question 25

What happens to pressures during inspiration and expiration?

Answer 25

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

Question 26

What is pleural cavity?

Answer 26

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

Question 27

What are the properties of the pleural cavity?

Answer 27

→sealed and fluid filled.

Question 28

What can the properties of the pleural cavity achieve?

Answer 28

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.

Question 29

What is the difference between visceral and parietal pleura?

Answer 29

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).

Question 30

How does the lung and chest recoil?

Answer 30

the lungs recoil inwards, the chest wall recoils outwards

Question 31

How is pressure reduced in the pleural space?

Answer 31

→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

Question 32

Why does the pleural cavity resist changes in volume?

Answer 32

→filled with liquid, meaning that it resists changes in volume more than if it were filled with gas,

Question 33

What is negative pleura city pressure?

Answer 33

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

Question 34

What is positive pressure?

Answer 34

→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

Question 35

What is the role of elastic recoil?

Answer 35

acts to pull the visceral pleural inwards and compress the lung volume.

Question 36

What happens during forced expiration?

Answer 36

→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.

Question 37

Overall movements of inspiration…

Answer 37

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

Question 38

Overall movements of expiration…

Answer 38

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

Question 39

What happens if either of the pleural is ruptured?

Answer 39

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

Question 40

Why is loss of negative intrapleural space bad?

Answer 40

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.

Question 41

What is pneumothorax?

Answer 41

intrapleural pressure = atmospheric pressure.