Pulmonary ventilation

Question 1

What is the primary function of the respiratory system?

Answer 1

To supply respiring tissues with oxygen and remove excess carbon dioxide by ensuring sufficient levels of gas exchange take place within the lungs.

Question 2

What does gas exchange rely on?

Answer 2

On the partial pressure gradients (the gas equivalent of concentration gradients) between alveolar air and blood, the respiratory system functions to maintain gradients of oxygen and carbon dioxide by ventilating gas exchange surfaces.

Question 3

Where does air move to?

Answer 3

This involves moving air from the atmosphere to the alveoli and then out again, ensuring that fresh oxygen is supplied to alveoli and carbon dioxide does not accumulate.

Question 4

What are the partial pressures inside the alveoli and capillaries?

Answer 4

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Question 5

What is Hypoventilation and hyperventilation?

Answer 5

Hypoventilation and hyperventilation are defined as insufficient/excessive levels of breathing relative to that required to meet the metabolic demands of the body, and can be identified by the level of CO2 present within the blood .

Hypoventilation results in excessive levels of CO2 within arterial blood (PaCO2 > 6.0 kPa)

Hypoventilation reduces alveolar oxygen pressure and increases carbon dioxide pressure. 

Hyperventilation results in reduced levels of CO2 within arterial blood (PaCO2 < 4.9 kPa).

Hyperventilation increases alveolar oxygen pressure and reduces carbon dioxide pressure.

Question 6

What does increasing and decreasing the rate of ventilation do?

Answer 6

Increasing the rate of ventilation increases alveolar oxygen partial pressure (PAO2), and decreases alveolar carbon dioxide partial pressure (PACO2). Decreasing the rate of ventilation has the opposite effects.

Question 7

What does lung volume depend on?

Answer 7

Height, sex, age and extent of respiratory diseases

Question 8

What is the total lung capacity?

Answer 8

The maximum volume of air that can fill the lungs

Question 9

What is vital capacity?

Answer 9

The total volume of air an individual is able to breath in, going from a max forced expiration to a max forced inspiration

Question 10

What is residual volume?

Answer 10

The volume of air remaining in the lungs after a maximum forced expiration

Question 11

What is expiratory reserve volume?

Answer 11

he additional volume of air that can be expired at the end of a resting/quiet expiration

Question 12

What is functional residual capacity?

Answer 12

The volume of air within the lungs at the end of a resting/quiet expiration

Question 13

What is inspiratory reserve volume?

Answer 13

The inspiratory reserve volume (IRV) is the additional amount of air that can be inhaled after a normal inspiration (tidal volume).

Question 14

What is the equation for the total volume of air inhaled in all breathes over a minute (minute volume)

Answer 14

V = Vt x f

Vt = = tidal volume (mL), the volume of air in each breathe

f = frequency min^-1, the number of breaths per minute

Question 15

What is the term for the air that resides in the lungs even after forced expiration

Answer 15

dead space that does not contribute towards gas exchange

Question 16

What is the purpose of residual air?

Answer 16

Ensure the lungs do not collapse

Question 17

How do we calculate the volume of air reaching respiratory surfaces (alveolar ventilation)

Answer 17

We need to account for the volume of air that does not reach the alveoli

Va = (Vt - Vd) x f

Va = Alveolar minute volume (mL), the total volume of fresh air entering the alveoli across all breaths over a minute

Vt = tidal volume

Vd = Dead space volume (mL), then the volume of air remaining in the respiratory system at the end of expiration

f = frequency (min^-1)

Vt - Vd = the volume of fresh air entering the alveoli in each breath

Question 18

What does Boyles Law state?

Answer 18

This describes the relationship between pressure, volume and molar quantity

Question 19

What is required to move air into the lungs

Answer 19

Alveolar pressure must fall below must fall below atmospheric pressure, so air moves down pressure gradient

Question 20

What is required to move air out of the lungs?

Answer 20

Alveolar pressure must rise above atmospheric pressure

Question 21

How are changes in pressure achieved?

Answer 21

These pressure changes are achieved by contraction/relaxation of respiratory muscles. This alters the volume of the thoracic cavity (with the opposite effect on alveolar pressure).

Question 22

Describe the changes in pressure and volume during inspiration and expiration

Answer 22

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Question 23

What are the lungs and the chest cavity separated by?

Answer 23

Membranes known as pleurae

Question 24

Where does the (inner) visceral pleura line?

Answer 24

Each lung

Question 25

Where does the (outer) parietal pleura line?

Answer 25

Thoracic cavity, surrounding the chest, diaphragmatic and mediastinum (contains the heart)

Question 26

What is between the pleurae?

Answer 26

Fluid-filled cavity

Question 27

What causes the pressure between the pleura to become sub-atmospheric?

Answer 27

The tissues attached to each pleura recoil in opposite directions due to their elastic properties (i.e. the lungs recoil inwards, the chest wall recoils outwards), stretching the sealed pleural cavity between them very slightly and resulting in the pressure within the cavity being naturally sub-atmospheric (approximately -0.5kPa at the beginning of inspiration).

Question 28

Describe the steps in inspiration?

Answer 28

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Question 29

Describe the steps in expiration?

Answer 29

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Question 30

how are lung volume, intrapleural pressure, alveolar pressure and airflow all related?

Answer 30

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Question 31

What is Pneumothorax?

What are the 2 effects of this?

Answer 31

If either of the either of the pleural membranes is ruptured (e.g. due to trauma, bleb formation, or disease), the pressure gradient between the pleural cavity and the atmosphere (or lungs, depending on the particular injury) 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. Furthermore, 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 32

Describe the the effects of rupturing the pleural membrane and entry of air into the pleural cavity (pneumothorax) on intrapleural pressure and lung volume.

Answer 32

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