Ventilation

Question 1

What happens during inspiration

Answer 1

Pressure difference is produced by increasing lung volume

Thoracic cage expands & lung volume increases

Expansion is brought about by inspiratory muscles

Diaphragm contracts – dome flattens & moves caudally

Ribs pulled cranially & outwards by contraction of external intercostal muscles

Question 2

What happens during expiration

Answer 2

Caused by relaxation of inspiratory muscles

Ribs recoil back to original position

Question 3

Fill in the table of airflow during inspiration

Answer 3

Question 4

Fill in table of airflow during expiration

Answer 4

Question 4

What is compliance in lungs

Answer 4

Ability of lungs chest wall to expand & stretch in response to changes in pressure during breathing

Reduced lung compliance causes scar tissue in lungs or pleura

Increased lung compliance can aid inspiration but if prolonged (due to excessive coughing) can reduce elasticity in lungs

Question 5

What is alveolar surface tension

Answer 5

Occurs at interface between water & air

Inner surface of alveoli lined with fluid

Surface tension reduced with production of surfactant

Pressure higher in smaller spaces

Question 6

How is ventilation regulated

Answer 6

Medulla is respiratory centre in brain

Generates action potentials, modulated by feedback from
Chemoreceptors
Mechanoreceptors

Question 7

What mechanisms limit ventilation regionally & globally

Answer 7

Globally:
Resistance to flow in airways
Lung compliance
Alveolar surface tension

Regionally:
Lower portions of lung ventilated more than upper zones
Intra-pleural pressure higher at base of lung than apex due to weight of fluid
Lung easier to inflate at low volumes than high volumes

Question 8

How do lung diseases & cardiac function affect perfusion

Answer 8

Lung diseases:
Asthma
Pneumonia
Mountain sickness

Cardiac function:
Congenital heart defects
Hypovolemia
Pulmonary oedema

Question 9

What is ventilation/perfusion mismatch

Answer 9

Optimal gas exchange in lungs requires appropriate ratio between ventilation & blood flow in each alveolus

V/Q ratio should ideally be 1

Ventilation/perfusion mismatch = disturbance in O2 supply & blood supply to alveoli

Question 10

What are the effects of V/Q mismatch on animals

Answer 10

Impaired oxygenation
In areas of lungs were ventilation is less than perfusion (V/Q < 1 ) oxygen uptake is reduced
Results in hypoxemia – decreased oxygen in arterial blood

Shunting
Blood bypasses poorly ventilated alveoli & directly moves from right side of heart to left without being oxygenated
Leads to decrease in arterial oxygen saturation

Alveolar dead space
In areas of lungs where ventilation higher than perfusion (V/Q > 1)
Resulting in decreased CO2 elimination leading to increased arterial CO2 levels (hypercapnia)

Question 11

Fill in the graph

Answer 11

Question 12

Define tidal volume

Answer 12

volume of air flowing through airways during each inspiration & expiration
(increases with exercise)

Question 13

Define minute ventilation

Answer 13

volume of air inspired or expired per minute

Tidal volume X frequency of breathing

Question 14

Define dead space ventilation

Answer 14

portion of minute ventilation that isn’t available for gas exchange

Dead space volume X frequency of breathing

Question 15

What is the pathway of oxygen from outside in

Answer 15

1. Atmosphere
2. Into lungs by ventilation
3. Into blood by diffusion
4. Heart
5. Circulated to tissues in blood
6. Into tissues by diffusion
7. Into mitochondria

CO2 is reverse

PO2 reduces as it travels through system

PCO2 increases as it travels through system

Question 16

How is oxygen transported in blood

Answer 16

Dissolved in plasma (1.5%)

Bound to haemoglobin in erythrocytes (98.5%)

Question 17

How do temperature and pH affect oxygen-haemoglobin curve

Answer 17

Both tend to be increased in respiring tissues

Tissues/cells doing metabolic work = right-ward shift in curve = unloading of O2

Question 18

How is carbon dioxide transported

Answer 18

Dissolved in blood (10%)

Carboxyhaemoglobin on proteins (20%)

Bicarbonate ions in plasma (70%)
CO2 enters RBC where it reacts with water to form carbonic acid
Carbonic acid dissociates to:
Bicarbonate ions (transported to plasma)
Hydrogen ions (buffered by Hb)

Question 19

What is Fick’s law of diffusion

Answer 19

Links together nature of membrane, surface area, partial pressure gradient, membrane thickness

Rate of diffusion is inversely proportional to distance over which diffusion occurs

Question 20

What factors affect diffusion

Answer 20

Concentration gradient
Surface area
Membrane thickness
Diffusion distance
Solubility of gases
Blood flow
Metabolic rate

Question 21

What does hyperventilation cause

Answer 21

Getting rid of too much CO2 = increased alveolar ventilation that leads to reduced arterial pCO2
Causes respiratory alkalosis
(Increased pH, decreased pCO2)

Question 22

What does hypoventilation cause

Answer 22

Hypoventilation (not blowing off enough CO2) = reduced alveolar ventilation that leads to increased arterial pCO2
Causes respiratory acidosis
(decreased pH, increased pCO2)

Question 23

Define inspiratory reserve volume

Answer 23

Amount of air a person can inhale forcefully after normal tidal volume inspiration
(decreases with exercise)

Question 24

Define residual volume

Answer 24

Volume of air remaining in lungs after maximum forceful expiration

Question 25

Define inspiratory capacity

Answer 25

Maximum volume of air that can be inspired after reaching end of normal, quiet expiration

Question 26

Define vital capacity

Answer 26

Total amount of air exhaled after maximal inhalation

Question 27

Define functional residual capacity

Answer 27

Volume remaining in lungs after normal passive exhalation

Question 28

Define conditions under which ventilation perfusion mismatch would occur

Answer 28

Asthma, COPD, bronchiectasis, cystic fibrosis, interstitial lung diseases, pulmonary hypertension