Breathing and Airways

• External - breathing and exchange of gases with atmosphere
• Internal - distribution/carriage of gases in the body
• Cellular - oxidative metabolism

The conducting zone and respiratory zone

Air sacs

By diffusion only - there is no forward bulk flow of air into this area

The mucociliary pathway which carries mucus and particles up away from the lungs

• A tidal breath/Volume expired (V_E)

• Alveolar ventilation (V_A) and dead space volume (V_D)
• V_E = V_A + V_D

False

Dead space volume

Taking a deep breath increases alveolar ventilation, whereas taking a shallow breath decreases alveolar ventilation.

• In animals that pant they are trying to lose heat but don't want to upset V_A (and consequently respiration).  During panting V_A is reduced and V_D is constant so V_E 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 surface area of the barrier divided by the thickness of the barrier

The right side of the heart

bronchial circulation

• Visceral - covers lungs
• Parietal - lines thoracic cavity

The pleural space (2-3mm)

Negative

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.

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.

The respiratory centre in the medulla

• a) phrenic nerve
• b) intercostal somatic nerves

• 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

Surface tension

Surfactant

The volume change per change in pressure of the lung

Increase lung compliance

As surfactant is produced in the 'term' foetus so premature animals will not have made surfactant yet

In the respiratory zone

They cause reflex coughing and bronchoconstriction to cause an explosive release of air to try and expel the irritant/gases in the airways

Histamine

It can restrict air flow by putting pressure on the airway and occluding it.  This reduces alveolar ventilation.