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Respiratory anatomy and
Physiology
Caia Francis
Chair RCN Respiratory Forum
Senior Lecturer- Respiratory Specialist
0117 32 88631
[email protected]
Outline of session
 Review and orientation to respiratory
anatomy and physiology.
 Learning outcomes:
– Understand fundamental law of diffusion and
apply it to gas exchange.
– Understand the mechanics of breathing and
how this is influenced to maintain ‘normal’
respiratory functioning.
Respiratory Physiology.
 Lung is for gas exchange.
 Prime function is to allow oxygen to move
from the air into the venous blood and
carbon dioxide to move out.
 Metabolizes some compounds, filters toxic
materials from the circulation and acts as a
reservoir for blood.
 Oxygen and carbon dioxide move between
air and blood by simple diffusion, i.e. from
an area of high to low partial pressure.
(Fick’s law of diffusion). Blood- gas barrier
is exceedingly thin and has an area of
between 50- 100 m2.
 Large surface area is obtained by wrapping
capillaries around air sacs (form alveoli).
300 million alveoli in human lungs.
 Airways consist of a
series of branching
tubes, becoming
narrower, shorter and
more numerous as
they penetrate deeper
into the lung.
 Trachea divides into
right and left main
bronchi, divide into
lobar, then segmental
bronchi. This process
continues down to
terminal bronchioles,
smallest airways
outside the alveoli.
 These make up the
conducting airways.
Function is to lead
inspired air into gas
exchanging regions of
the lung.
 Terminal bronchioles divide into respiratory
bronchioles, finally arriving at the alveolar
ducts, which are completely lined with
alveoli.
 This region is known as the respiratory
zone.
 Portion of lung distal to a terminal
bronchiole forms an anatomical unit called
acinus or lobule.
Ventilation
 Static volumes of the lung can be measured
mainly by spirometry.
 Tidal volume
 Vital capacity.
 Minute volume.
 But some gas remains in the lungs, residual
volume and functional residual volume.
Measured by body plesthysmography.
Ventilation -part 2
 Volume exhaled with each breath is 500ml,
15 breaths per minute; total volume leaving
the lung each minute is?
 500*15 = 7500ml/min.
 =Total ventilation or minute volume.
 But not all air that passes lips reaches the
aleovlar gas compartment where gas
exchange occurs.
Anatomic dead space.
 Volume of the conducting airways.
 Normal value is circa 150ml, but depends
upon the size of inspiration and posture of
subject.
Physiologic dead space.
 Volume of the lung which does not
eliminate CO2.
 In normal subjects this is nearly the same as
anatomic dead space.
 However in patients with lung disease the
physiologic dead space may be considerably
larger because of inequality of blood flow
and ventilation within the lung.
Regional differences in
ventilation (V) (upright person)
 Upper zone lowest
ventilation
 Lower zone greatest
ventilation.
Blood flow (Q) through the lungs
 Regional variations in
blood flow through the
lungs.
 Lowest blood flow
 Highest blood flow.
In ‘well’ human
 O2 will have fully diffused across alveolar
membrane to bind with Hb within 0.25s.
 C02 will have diffused across the alveolar
membrane within 0.25s to be expired.
 Blood will take 0.5s to traverse pulmonary
capillary in association with alveolar sac.
Respiratory disease.
 Asthma… mucus, airway thickening
(hypertrophy) will increase ‘width’ of
alveolar membrane and thus delay diffusion
across membrane of both CO2 and O2.
 COPD as above plus pulmonary and cardiac
circulation problems will delay the above.
 Genetic conditions eg cystic fibrosis will
compromise blood flow through alveolar.
What happens once oxygen is
delivered to the alveoli?
 Oxygen dissociation curve.
 Dissolved oxygen in blood, in some cases
of significance in respiratory disease.
Oxygen dissociation curve.
 Haemoglobin (Hb)
 02 forms easily
reversible combination
with Hb to give
oxyhaemoglobin.
 02 + Hb
HbO2
 Consider this in more
detail.
Oxygen dissociation curve.
 Consider:
 anaemia Hb 10gdl-1
 Altitude.
 Paediatrics.
 Temperature.
 pH.
Why do you need to know this?
 Understand normal respiration and its
measurement, function.
 Establish a common frame of reference.
 Revise known anatomy and physiology.
 Introduce some issues of importance in
respiratory disesase.
Mechanics of breathing.
 Inspiration: lower intra-thoracic pressure to
allow air to pass by diffusion into lungs.
Usually only 1cmH20 lower but in
respiratory disease can be many times
greater.
 Diaphragm moving down in quiet
breathing.
 Expansion of rib cage in rapid deep
breathing and using accessory muscles.
 Expiration. Diaphragm returning to rest.
 Ribs returning to status quo.
 Increases slightly intra- thoracic pressure
higher than the atmosphere and allows
expiration. Usually only 1cmH20 higher but
in respiratory disease can be many times
greater.
 Positive end
expiratory pressure
(PEEP) aides in
complete expiration.
 Occurs in ‘well
individuals’ easily and
automatically.
References.
 Francis C., (2006) “Respiratory care” Blackwell




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Publishing Oxford
Jevon P., Ewens B., (Eds) (2002) “Monitoring the
critically ill patient” Blackwell Science Oxford.
Levitzky M. (2002) 7th Edition “Pulmonary Physiology”
McGraw Hill New York.
West J., (2010) 8th Edition. “Pulmonary Pathophysiology”
Lippincott Williams & Wilkins London.
West J., (2009) 10th Edition. “Respiratory Physiology the
essesentials” Lippincott Williams & Wilkins London.
Woodcock A., Partridge M., (1995) “Respiratory
Handbook” Boehringer Ingelheim.