Breathing and Airways
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What are the three types of respiration?
- External - breathing and exchange of gases with atmosphere
- Internal - distribution/carriage of gases in the body
- Cellular - oxidative metabolism
What two areas can the airways be divided into?
The conducting zone and respiratory zone
What structures start to appear in the respiratory zone?
How does movement of gases occur in the respiratory zone?
By diffusion only - there is no forward bulk flow of air into this area
What pathway is prominent in the respiratory zone to prevent particles sticking to the walls of the vessels?
The mucociliary pathway which carries mucus and particles up away from the lungs
What is the term for each breath you take?
- A tidal breath/Volume expired (VE)
What is VE further subdivided into?
- Alveolar ventilation (VA) and dead space volume (VD)
- VE = VA + VD
True or false: dead space volume takes part in gaseous exchange?
Which volume is constant: dead space volume or alveolar ventilation?
Dead space volume
What effect does taking a deep/shallow breath have on alveolar ventilation?
Taking a deep breath increases alveolar ventilation, whereas taking a shallow breath decreases alveolar ventilation.
Describe how respiration is affected in panting animals
- In animals that pant they are trying to lose heat but don't want to upset VA (and consequently respiration). During panting VA is reduced and VD is constant so VE must be reduced. During panting air moves up and down the conducting zone with very little air going to the respiratory zone. The dog forces air over wet areas of mucus membranes in the airways and evaporates water from here to cool the blood.
The volume of gas transferred across a barrier is proportional to ...?
the surface area of the barrier divided by the thickness of the barrier
Which side of the heart provides the blood supply for the left and right pulmonary arteries?
The right side of the heart
The conducting airways are supplied by the ... derived from the aorta?
What is the difference between the visceral and parietal pleura of the lungs?
- Visceral - covers lungs
- Parietal - lines thoracic cavity
What is between the visceral and parietal pleura?
The pleural space (2-3mm)
Is there positive/negative intra-pleural pressure in the pleural space?
Describe the process of inspiration
Inspiration involves the movement of the diaphragm caudally and the ribcage outwards (contraction of external intercostal muscles). Due to adhesion of the pleural membranes when the chest wall moves out it pulls the visceral pleural and when the diaphragm moves down it pulls the parietal pleura. The intra-alveolar pressure within the lungs drops and airflow is induced into the airway.
Describe the process of expiration
The muscles involved in respiration relax during expiration - the lungs pull the chest wall and diaphragm back. This passive process is aided by the intercostal muscles and muscles of the chest wall. Movement of the abdominal contents against the diaphragm during expiration is important in quadrupeds, especially when running. The net effect of expiration is that the chest wall is returned down onto the lungs and air is expelled.
Which area of the brain controls rhythmic discharge of the nerves controlling respiration?
The respiratory centre in the medulla
Which nerves stimulate a) contraction of the diaphragm b) contraction of the intercostals?
- a) phrenic nerve
- b) intercostal somatic nerves
Define pneumothorax. Why does it cause breathing difficulties?
- Pneumothorax is when the seal between the visceral and parietal pleura is broken, usually due to trauma to the thoracic cavity
- This renders the breathing apparatus ineffective as you cannot expand the lungs
What force causes alveoli to collapse and increases inspiratory effort?
What do alveoli produce to combat surface tension?
What does lung compliance mean?
The volume change per change in pressure of the lung
Does surfactant increase or decrease lung compliance?
Increase lung compliance
Why will premature animals have breathing difficulties?
As surfactant is produced in the 'term' foetus so premature animals will not have made surfactant yet
Where are irritant receptors found in the airways?
In the respiratory zone
What is the function of irritant receptors?
They cause reflex coughing and bronchoconstriction to cause an explosive release of air to try and expel the irritant/gases in the airways
Give an example of an inflammatory mediator that smooth muscle in the airways is susceptible to
What effect can engorgement of the oesophagus have on the airways?
It can restrict air flow by putting pressure on the airway and occluding it. This reduces alveolar ventilation.
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