Dr' Johnny Tang

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Dr. Johnny Tang BSc (Hons), MPhil, PhD (HK) ,
CBiol, MIBiol Department of Applied Biology and
Chemical Technology Room Y 851 Office Tel 3400
8727 E-mail bccotang_at_polyu.edu.hk
Johnnys Teaching and Learning Homepage http//my
web.polyu.edu.hk/bccotang/index2.htm (or via
WebCT)
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Respiratory System

• Objectives
• To understand the mechanisms of moving air to and
  from the exchange surfaces of the lungs.
• To learn the basic principles of pulmonary
  function test.
• To learn how O2 and CO2 are transported in human
  body.
• To get the overview about the mechanisms and
  significance of regulating breathing.

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Respiratory System

• Expected Learning Outcomes
• After learning this topic, students
• are able to describe the processes of how the air
  can reach and leave the site of gases exchange
• can explain how O2 and CO2 are transported in
  human body
• understand the basic mechanisms of regulation of
  breathing.

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Respiratory System 2 zones respiratory zone,
conducting zone Respiration (1)
Ventilation -- mechanical process moves
air (2) Gases exchange -- O2, CO2 air ? blood
down the conc. gradient high surface area
short diffusion distance) (3) Oxygen
utilization -- energy cell respiration
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The conducting and respiratory zones
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The conducting zone
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Respiratory System (contd)
External Respiration -- ventilation gases
exchange (air ? blood) Internal
Respiration -- gases exchange (blood ? tissues)
O2 utilization
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Structure of the Respiratory System Alveoli
sites for gases exchange 300 million gt high
surface area (60-80 m2) One-cell thick
characteristic 2 cell layers Mouth / nose gt
pharynx gt larynx gt trachea gt 1º bronchi gt
branching of bronchioles gt terminal bronchioles
gt respiratory bronchioles gt alveolar sacs
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The alveoli and pulmonary capillaries
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The alveoli and pulmonary capillaries (contd)
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Functions of different components of respiratory
system
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A. Physical Aspects of Ventilation Flow of air in
the conducting zones a pressure difference
between the 2 ends a 1 / resistance
 Intrapulmonary and Intrapleural Pressures 2
membranes (visceral and parietal pleurae) lungs
are stuck to the chest wall  
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A cross section of thoracic cavity
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• Intrapulmonary and Intrapleural Pressures
  (contd)
• Thin layer of fluid between the membranes
• Pleural cavity is just a potential cavity
• Inspiration atm. presssure gt intrapulmonary
  pressure ( 3 mmHg for quiet inspiration)
• lack of air in the intrapleural space gt
  intrapleural pressure lt intrapulmonary pressure
  gt transpulmonary pressure is created gt
  expansion of the lungs
• Expiration intrapulmonary pressure gt atm.
  pressure
• Boyles Law (P a 1/V)

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Mechanisms of pulmonary ventilation
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Physical Properties of the Lungs Inspiration
high compliance (ability to be expanded when
stretched) Expiration good elasticity (get
smaller when the stretching force is
released) Compliance measured as the change in
lung vol. per change in transpulmonary pressure
reduced by resistance of distension, e.g.
pulmonary fibrosis Elasticity tendency of a
structure to return to its initial size after
being distended (elastic recoil) presence of
elastic proteins
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Surface Tension Fluid in the alveoli attractive
forces from underneath surface molecules are
pulled tightly together Directed inward creates
pressure within the alveoli Law of LaPlace (P
2T / r) (pressure in smaller alveolus gt that of
the larger one) Normally, smaller ones will
not collapse themselves !! surface tension is
also reduced when radius gets smaller
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Surface Tension (contd) Alveolar fluid contains
a kind of phospholipid (dipalmitoyl lecithin) --
lung surfactant Smaller alveoli gt surfactant is
more concentrated gt ability of lowering surface
tension is improved gt prevent collapsing (remain
open even after forceful expiration) Less surface
tension has to be overcome at the next
inspiration Type II alveolar cells
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Surface Tension (contd) Respiratory distress
syndrome before 8 months old, little
surfactant alveoli are collapsed pulmonary
edema 15-20 times more difficult to start the
1st breath saved by mechanical ventilators,
exogenous surfactant
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Mechanics of Breathing Inspiration muscle
contraction Expiration muscle relaxation and
elastic recoil Thorax flexible bony surfaces
for muscle attachment rib cage is
pliable (the presence cartilages) elastic
tension
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Mechanics of Breathing (contd) Quiet
inspiration contraction of diaphragm, external
intercostals (pull the ribs upward and forward)
abdominal muscles relaxed (allows movement of
abdominal organs) decrease in pressure by 3
mmHg Posture lying abdominal organs push
against the diaphragm difficult to contract
Quiet expiration passive elastic recoil of
the lungs, costal cartilages relaxation of
inspiratory muscles intra-alveolar pressure gt
atm. pressure gt air moves out
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The muscles involved in breathing
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Mechanics of inspiration and expiration
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Mechanics of Breathing (contd) Forced
inspiration aided by the contraction of
accessory muscles -20 mmHg Forced
expiration forceful contraction of abdominal
muscles, internal intercostals, latissimus dorsi,
quadratus lumborum further depress the rib cage
30 mmHg
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The muscles involved in breathing
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The muscles involved in breathing (contd)
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The muscles involved in breathing (contd)
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Pulmonary Function Tests Spirometry spirometer
shows various lung volumes and capacities
A spirogram
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Pulmonary Function Tests (contd) Diagnosis of
lung diseases restrictive or obstructive
disorders Restrictive disorder e.g. pulmonary
fibrosis normal rate reduced VC Obstructive
disorder e.g. asthma normal VC reduced
rate FEV1 and FVC
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A recording chart of pulmonary function test
Volume (L)
FVC
FEV1
Time (s)
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A recording chart of pulmonary function test
(contd)
Volume (L)
FVC
FEV1
FVC
FEV1
Time (s)
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B. Oxygen Transport Simple Calculation Daltons
Law Ptotal PA PB PC product of (the
total pressure times the fraction of that gas in
the mixture) Total pressure is reduced in high
altitude Consideration of moisture dilution
effect Ptotal PO2 PN2 PCO2 Pwater  
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Partial pressures of gases in inspired air and
alveolar air
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Partial Pressures of Gases in Blood Large surface
area short diffusion distance gases
equilibrium between blood and alveolar air
aided by capillaries Henrys Law Amount of
gas dissolved into fluid depends
on I) solubility of the gas II) Tº of the
fluid III) partial pressure of the gas Human
body constant body Tº partial pressure is
critical
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The alveoli and pulmonary capillaries
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Partial pressure pf gases in blood
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Hemoglobin (Hb) and O2 Transport O2 is chemically
bound to Hb Globin parts Heme groups 1 Heme
group, 1 Fe 1 Hb gt 4 O2 In one RBC, a
billion of O2 Oxyhemoglobin
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The structure of hemoglobin
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Loading and Unloading Reactions Loading deoxy-Hb
O2 ? oxy-Hb ------ (a) Unloading oxy-Hb ?
deoxy-Hb O2 ------ (b) 2 factors PO2
affinity between O2 and Hb High PO2, favours (a)
low PO2, favours (b) Hb-O2 binding should be
strong weak enough  
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Oxyhemoglobin Dissociation Curve Predict the of
unloading at a particular PO2 value S-shaped
(sigmoidal) Flat and steep parts
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Effect of pH and Temperature on O2
Transport Affect the affinity between Hb and
O2 Bohr effect low pH gt increases
unloading increased metabolism CO2 more
O2 to tissues Shift the sigmoidal curve High
Tº gt increased unloading (weakens the Hb-O2
bonds) More O2 to muscles exercise
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The effects of pH on oxyhemoglobin dissociation
curve
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The effects of temperature on oxyhemoglobin
dissociation curve
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Effects of 2,3-DPG on O2 Transport Anaerobic
respiration of glucose in RBC 2,3-diphosphoglyceri
c acid (2,3-DPG) as a side product Oxy-Hb
inhibits the enzyme for producing 2,3-DPG ? O2 gt
? 2,3-DPG ? O2 gt ? 2,3-DPG (e.g. in anemia
high altitude) 2,3-DPG can stabilize deoxy-Hb gt
more O2 are unloaded oxy-Hb ? deoxy-Hb O2
Shift to right
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A summary of factors that affect the affinity of
hemoglobin for oxygen
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C. Carbon Dioxide Transport and Acid-Base
Balance 3 forms I) dissolved CO2 II) carbamin
ohemoglobin III) bicarbonate ions (HCO3-)
Within RBC, carbonic anhydrase speeds up this
reaction CO2 H2O ? H2CO3 Exchange of
anions (-) as blood travels through the tissue
capillaries gt Chloride Shift
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Transport of CO2 in blood
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Transport of Oxygen and Carbon Dioxide in Blood
In the tissue side. Transport of O2 and CO2
interact with each other H (from carbonic
acids) binds to oxy-Hb gt more unloading of O2
to tissues (Bohr effect) gt more deoxy-Hb are
formed gt higher buffering ability (H binds
better to deoxy-Hb) gt more CO2 will be
removed (shift of the equilibrium CO2
H2O ? H2CO3 ? H HCO3- )
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Transport of Oxygen and Carbon Dioxide in Blood
(contd)
In the pulmonary side more oxy-Hb will be
formed gt lower affinity to H H released
from oxy-Hb gt HCO3- will be attracted to RBC
H2CO3 formed gt reverse of chloride
shift gt H2CO3 ? CO2 H2O low PCO2 and actions
of carbonic anhydrase Haldane effects near
the tissues, ? PO2 gt ? CO2 transportation near
the lungs, ? PO2 gt ? CO2 transportation
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Transport of CO2 in blood
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Ventilation and Acid-Base Balance Acidicity
metabolic acids H ions Buffers in blood Hb,
plasma proteins, HCO3- ions (major) Still can be
saturated removal of acids (CO2 from lungs, H
in urine) 
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D. Regulation of Breathing 2 descending
pathways I) from cerebral cortex (voluntary
breathing) II) from medulla oblongata
(involuntary breathing) Contraction and
relaxation of respiratory muscles PO2 is
relatively less effective than pH and PCO2
large reservoir of O2 in Hb 97 saturated
normally
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Brain Stem Respiratory Centres Rhythmicity area
neurons in the pons autonomic breathing I
neurons (inspiration) stimulate spinal
motoneurons E neurons (expiration) inhibit I
neurons Reciprocal way rhythmic pattern Dorsal
group neurons gt phrenic nerve gt
diaphragm Ventral group neurons gt motor neurons
to intercostal muscles Apneustic centre
(stimulates I neurons) pneumotaxic centre
(antagonizes the apneustic centre) cyclic
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The brain stem respiratory centers
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Chemoreceptors Central and peripheral Central
chemoreceptors (in medulla oblongata) slower
response arterial PCO2 cerebrospinal fluid
stimulates respiratory centres Peripheral
chemoreceptors (aortic bodies and carotid
bodies) faster response H in arterial blood
sensory nerve fibers to the respiratory centre
in M.O. aortic bodies gt vagus nerve (X)
carotid bodies gt glossopharyngeal nerve (IX)
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Aortic and carotid bodies
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Sensitivity of chemoreceptors
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Chemoreceptor control of breathing
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The regulation of ventilation by the CNS
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End