The ins and outs of respiratory
physiology
Reverend Dr David Taylor
dcmt@liv.ac.uk
http://www.liv.ac.uk/~dcmt
Before the lecture
 What do you know about breathing?
 We all do it
 It involves the cardiovascular system as well…
 It is a process of allowing gasses (which?) to exchange
between blood and air
 It has active and passive phases (which are which?)
 it is hard to stop doing it (why?)
 In this lecture we will look at the relationship
between the cardiovascular and respiratory systems
and the control of breathing.
Learning outcomes
 By the end of this lecture you should be able to
discuss:




The importance of matching ventilation and perfusion
The (local) ways in which perfusion is controlled
The inputs to the pathways which control breathing
The physiological control of breathing
I used the following texts
 Naish’s Medical Sciences (2009 edition)
 Silverthorn’s Human Physiology (2010 edition)
 Ganong’s Review of Medical Physiology (2010 edition)
 But the subject is covered reasonably well in most
basic texts
The case....
 (Alice Springer) becomes wheezy and short of breath,
despite using her blue inhaler. Her neck and chest
muscles are working hard, but she cannot get control
of her breathing.
highlighting
 (Alice Springer) becomes wheezy and short of breath,
despite using her blue inhaler. Her neck and chest
muscles are working hard, but she cannot get control
of her breathing.
Some words
 Ventilation (alveolar ventilation)
 The volume of air (L/min) entering and leaving an
alveolus (4L/min)
 Perfusion
 In this case, pulmonary blood flow (5L/min)
 Both change with position in the lung
 (range 3.3-0.8L/min)
Ventilation/perfusion ratio (V/Q)
Distance above bottom of lung
30
No blood flow
V/Q=3.3
20
Flow is
regulated by
alveolar
pressure
10
V/Q=0.8
0
Relative blood flow
Pulmonary venous
pressure above
atmospheric
pressure
Top
Left atrium
The importance of matching ventilation
and perfusion
 Take the obvious extremes
 Lung is well ventilated but there is no perfusion
 Lung is well perfused, but there is no ventilation
 Both would be fatal.
The (local) ways in which perfusion is
controlled
 If ventilation is poor
 Local hypoxia (low O2)
 Leads to vasoconstriction
 So blood is diverted to other (better perfused regions of
the lung)
The inputs to the pathways which
control breathing
 Receptors:
 Central chemoreceptors (ventral surface of medulla) –
increase rate and depth with ↑ CO2
 Peripheral chemoreceptors (carotid bodies, aortic arch)
– increase rate and depth with ↓O2 or pH
 Stretch receptors (bronchi) - inhibit rate
 There are several others, but these are the most
important for now.
The physiological control of breathing
Emotions etc.,
CO2
Higher centres
Central
chemoreceptors
Limbic system
O2 and pH
Peripheral
chemoreceptors
Afferent sensory
neurones
Medulla oblongata
and pons
Expiratory
motor neurones
Inspiratory
motor neurones
Scalene and
sternomastoid
External
intercostals
Diaphragm
Internal
intercostals
Abdominal