Breathing Flashcards
What is the volume of air inhaled/exhaled per minute?
5 litres
Define transpulmonary pressure.
Difference in pressure between the inside and outside of the lung
How do you calculate transpulmonary pressure?
Alveolar pressure - intrapleural pressure
Define intrapleural pressure.
The pressure in the pleural space
Define alveolar pressure.
Air pressure in the alveoli
Describe the steps of inspiration.
- Diaphragm contracts, moves down and causes thorax volume to increase
- External intercostal muscles contract, causing the ribs to move upward and outward. This further increases thoracic volume
- As the thorax expands, the intrapleural pressure is lowered and transpulmonary pressure increases - causing lung expansion
- Lung expansion causes alveolar pressure to become negative. This results in inward airflow.
Describe the steps of passive expiration.
- Motor neurones to diaphragm and external intercostal muscles reduce their firing so the muscles relax. Diaphragm ascends, decreasing thoracic volume.
- Lungs and chest walls passively collapse due to elastic recoil. Transpulmonary pressure decreases due to increased intrapleural pressure
- As the lungs become smaller, the alveolar pressure exceeds atmospheric pressure. This results in the outflow of air
Describe the steps of forced expiration.
- Internal intercostal muscles contract
- Causes ribs to move downwards and inwards. This actively decreases thoracic volume
- Abdominal muscles contract, forcing the diaphragm up further and decreasing thoracic volume even more
- Results in more air being expired
When does forced expiration occur?
During exercise
Which airway provides the greatest resistance to air being breathed in or out?
Trachea. Although bronchioles are the smallest, there are many of them and they provide a much larger surface area so have less resistance.
What is dead space?
The volume of air not contributing to ventilation.
How much total dead space is there?
175ml
Which part of the brain controls breathing?
Respiratory centre in the medulla
Name the two groups of neurones in the respiratory centre.
Dorsal respiratory group
Ventral respiratory group
Describe the role of neurones in the dorsal respiratory group.
- Primarily fire during inspiration.
- Fire impulses to spinal motor neurones that activate cause contraction of diaphragm and external intercostal muscles
Describe the role of neurones in the ventral respiratory group.
- Neurones fire during active expiration and quiet inspiration
- Send impulses to cause contraction of expiratory muscles
- Houses respiratory rhythm generator in pre-Botzinger complex
- Respiratory rhythm generator is composed of pacemaker cells that set the basal respiratory rate
Where do medullary inspiratory neurones receive synaptic input from?
Pons
Which area of the pons fine tunes the output of inspiratory neurones in the medulla?
Apneustic centre
Which area can override the apneustic centre?
Pneumotaxic centre
Which area acts to smooth the transition between inspiration and expiration? It also switches off inspiratory neurones to prevent hyperinflation.
Pneumotaxic centre. Also known as pontine respiratory group.
Name the pulmonary stretch receptors.
- Slowly adapting stretch receptors
- Rapidly adapting stretch receptors
- C fibre J receptors
Describe the role of slowly adapting stretch receptors.
- activated by lung distension
- high activity inhibits further inspiration, begins expiration
- if inflation is maintained, they slowly adapt to low frequency firing
Where are slowly adapting stretch receptors found?
Smooth muscle of airway
Describe the role of rapidly adapting stretch receptors.
- activated by lung distension and irritants
- produce brief burst of activity
- high activity causes bronchoconstriction
- respond at the onset of stimulus but very quickly cease responding
