Ventilation

Question 1

describe airflow in the lungs

Answer 1

air flows from areas of high pressure to areas of low pressure
- the rate is proportional to the pressure difference where F = change in pressure/Resistance to flow)

inspiration
- change in pressure is produced by increasing lung volume (the thoracic cage expands and lung volume increases)
- this expansion is brought about by inspiratory muslces
- atmospheric pressure is then higher than alveolar pressure, causing air to move into the lungs

expiration
- volume of lungs decreases, pressure in lungs increases, forcing air out of the lungs

Question 2

describe the diaphragm

Answer 2

• dome shaped musculotendinous sheet separating the thoracic from the abdominal cavity
• the muscular part is peripheral and tendinous part is central
• the muscle is attahced to the xiphoid process ventrally, to the inside of the lower costal cartilages and ribs by digitations laterally and to the vertebral column dorsally by crura
• innervated by the phrenic nerve

Question 3

describe the intracostal muscles

Answer 3

external and internal muscles occupy the intercostal spaces
exterior: runs caudoventrally
interior: cranioventrally

Question 4

describe how the inspiratory muscles function for inspiration

Answer 4

• diaphragm contracts (dome flattens and moves caudally)
• ribs are pulled cranially and outwards by contraction of the external intercostal muscles
• together these increase the volume of the thoracic cavity

Question 5

describe how the inspiratory muscles function for expiration

Answer 5

• inspiratory muscles relax
• ribs recoil back to original position

Question 6

describe the pleural cavity

Answer 6

the pleural cavity is the space between the visceral pleural (facing inside of body) and the parietal pleural (facing outside of body).
- fluid filled
- sub-atmospheric pressure (less than atmosphere)
- if pierced, air rushes in = pneumothorax = collapses lung

Question 7

describe how the pressure within different compartments of the lungs aids respiration

Answer 7

alveolar pressure fluctuates between -1 mmHg (during inspiration) and 1 mmHg (during expiration)
intrapleural pressure normally negative
transpulmonary pressure: difference between alveolar pressure and intrapleural pressure

Question 8

describe the sequence of events that happen during inspiration

Answer 8

1. inspiratory muscles contract
2. thoracic cavity expands
3. intrapleural pressure becomes more negative
4. transpulmonary pressure increases
5. lungs distend
6. alveolar pressure falls below atmospheric pressure
7. air flows into the lungs until the alveolar pressure becomes equal to atmospheric pressure

Question 9

describe the sequence of events that occur duing expiration

Answer 9

1. relaxation of inspiratory muscles, ribs recoil back to original position
2. thoracic cavity contracts
3. pressure within intrapleural cavity becomes less negative
4. transpulmonary pressure decreases
5. lungs contract
6. alveolar pressure increases above atmospheric pressure
7. air flows out until alveolar pressure becomes equal to atmospheric pressure

Question 10

describe how locomotion can assist ventilation

Answer 10

the breathing cycle of galloping animals is synchronised to the stride cycle

Question 11

what 3 factors influence ventilation

Answer 11

1. resistance to flow in the airways
2. lung compliance
3. alveolar surface tension

Question 11

how does compliance influence ventilation

Answer 11

compliance is essentially how stretchy the lungs are
- depends of elasticity of the tissue and surface tension in the alveoli
- calculated by compliance=volume increase/transpu,monary pressure
- structures that contribute to compliace = coiled collagen fibres, lung elastic fibres, intercostal muscles, joints and pleura of the thoracic cage

Question 12

how does resistance to flow influence ventilation

Answer 12

calibre of airways
- same factors as resistance to flow in blood vessels
- resistance to flow is inversely proportional to the 4th power of the tube radius (as radius of tube decreases, resistance increases)
- mouth breathing halves airway resistance
- to overcome: each bifurcation increases number of parallel branches, as lung colume increases, elastic fibres in lung pull to expand tube diameter. relaxation of smooth muscles can also increase airway diameter (tubes get smaller as you go deeping into lung, but number of tubes increases)
turbulence
- airflow pattern is turblunet (in trachea and large bronchi) and laminar (in small bronchi and bronchioles

Question 13

how does alveolar surface tension influence ventilation

Answer 13

• surface tension occurs at the interface berween water and air
• inner surface of alveoli lined with fluid
• surface tension can restrict alveoli so they cant expand as easily
• reduced with production of surfactant (makes it easier for alveoli to expand by disrupting surface tension)
• pressure increases inside smaller alveoli (law of LaPlace => pressure inside alveolus = (2)surface tension of lining fluid/radius) therefore, to encourage equal airflow in different sized alveolus, the concentration of surfactant is higher in smaller alveoli (this prevents smaller alveoli from being disuesed)