Download L8 Respiratory PPt - Moodle

Responding to ill Health
Life Science
The Respiratory System
Anatomography (2012)
https://commons.wikimedia.org/wiki/File:Internal_intercostal_muscles_frontal2.png
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Learning Outcomes
• Discuss the structure and function of the respiratory
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•
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system.
Explain the principles of gas exchange and diffusion of O2
and CO2.
Explain the principles involved in the process of
respiration and the common lung volumes.
Describe factors affecting the efficiency of ventilation (i.e.
compliance, airway resistance and surfactant).
Explain the significance of pCO2 and pO2 as a stimulus for
breathing and the underlying principles behind chemical
nervous control of this process.
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Ventilation - movement of air in and out of lungs
Respiration - exchange of gases
external respiration
 exchange of gases by diffusion between alveoli
in lungs and blood in pulmonary capillaries
internal respiration
 exchange of gases by diffusion between blood
in systemic capillaries and body cells
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The Respiratory System
Main function ??
transfer of:
 oxygen (air  blood)
 carbon dioxide (blood  air)
Other functions ??
 some metabolism
 filtration of toxins from blood
 blood reservoir
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Structure & Function
Divided into:
Upper tract
 nose
 mouth
 pharynx
head /
neck
Lower tract
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•
•
•
larynx
trachea
bronchi
lungs
neck /
chest
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Function of Upper Respiratory Tract
Nasal
Pharyngeal
cavities
Laryngeal
All :
filter, heat &
moisten air
– have rich blood supply
– produce copious mucus
Epiglottis:
– at entrance to trachea (& oesophagus)
– small flap of cartilage
– blocks trachea during swallowing
BruceBlaus (2013)
https://commons.wikimedia.org/wiki/File:Blausen_0872_UpperRespiratorySystem.png
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Structure of Lung and Pleura
each lung divided into lobes
lobes divided into segments
segments subdivided into lobules
CRUK (2014)
https://commons.wikimedia.org/wiki/File:Diagram_showing_the_removal_of_one_lobe_of_the_lung_(lobectomy)_CRUK_366.svg
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Structure of Lung and Pleura
each lung covered by thin epithelial layer
i.e. pleura – has 2 layers:
visceral pleura
outer surface of lung
parietal pleura
inner chest wall
pleural space contains
watery pleural fluid = lubricant
• pleura / lung  pericardium / heart
• allows virtually frictionless movement
OpenStax College (2013) 2313 The Lung Pleurea
https://commons.wikimedia.org/wiki/File:2313_The_Lung_Pleurea.jpg
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AIRWAYS & AIR FLOWS
 air conducted in/out of lungs
via branching respiratory tree
 held open by C-shaped rings of
cartilage
 lined by ciliated epithelium
 sweeps carpet of mucus
(traps particles) out of
lung
•BruceBlaus (2013
•https://commons.wikimedia.org/wiki/File:Blausen_0865_TracheaAnatomy.png
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BruceBlaus (2013)
https://commons.wikimedia.org/wiki/File:Blausen_0766_RespiratoryEpithelium.png
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Lower respiratory tract
trachea divides progressively into:
 main bronchi
 secondary bronchi
 tertiary bronchi
 terminal bronchioles (smallest airways
without alveoli)
all have no part in gas exchange
 anatomical dead space
total volume approx 150ml of air
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Lower Respiratory Tract
terminal bronchioles divide sequentially into:
respiratory bronchioles (a few alveoli)
alveolar ducts (completely lined with alveoli)
gas exchange occurs here (respiratory zone)
volume 2.5 to 3 litres in each lung
NB. as airways get narrower, become more
numerous
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Cycle of respiration
12 to 15 times / minute:
 inspiration
 expiration
 pause
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VENTILATION
air moves from high pressure to low pressure
Inspiration (lung air intake)
 volume of chest
 intrathoracic pressure
air sucked into lungs
• achieved by:
– diaphragm contracting (pulling down)
– external intercostal muscles (pull ribs up & out)
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INSPIRATION
air sucked in to the level of terminal bronchioles
terminal bronchiole  alveoli
air transport via DIFFUSION:
• large Cross Sectional Area
• slow airspeed - can lead to dust
settling in terminal bronchioles
LadyofHats (2008)
http://commons.wikimedia.org/wiki/File:Inhalation_diagram.svg
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Expiration
• elastic lungs recoil when inspiratory muscles rest
(i.e. passive)
 intrathoracic
air ‘forced’ out
pressure
lungs
LadyofHats (2008)
https://commons.wikimedia.org/wiki/File:Expiration_diagram.svg
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Expiration (cont.d)
during EXERCISE:
• expiration becomes ‘active’
• abdominal muscles contract, forcing diaphragm upward
• internal intercostal muscles contract, pulling ribs down
and inward
 thoracic
these actions:
volume
 thoracic
pressure
assists
expiration
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Factors Affecting Ventilation
Compliance
 measure of ‘stretchability’
 effort required to inflate lungs
 lungs normally very compliant
Airway Resistance (resistance to airflow)
 normally very low
 thus pressure needed to move air is small ( work)
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Factors Affecting Ventilation
Compliance
Airway Resistance (resistance to airflow)
Surface Tension
 surface of alveoli moist to promote gas exchange
 this moisture leads to  surface tension, tending to
collapse alveoli
 problem averted by surfactant:



secreted by alveolar cells
acts like detergent
 surface tension dramatically
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Factors Affecting Ventilation
Normally
- high compliance
 lungs have
- low airway R
 low energy cost to breathing
However, if
•  compliance (scarring)
•  resistance (inflammation)
•  surfactant
  ‘work’ of breathing
also, alveoli collapse
e.g. respiratory distress syndrome
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Lung volumes
total capacity approx 6 litres
tidal volume
volume moved in & out at each inspiration/expiration
(0.5 L at rest)
inspiratory & expiratory reserve volumes
 volumes of air that can be inspired & expired, over &
above tidal volume
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Lung volumes
vital capacity
maximal volume that can be exhaled (typically
approx 4.8L)
( inspiratory reserve volume + tidal volume +
expiratory reserve volume)
residual volume (typically approx 1.2L)
gas remaining in lungs after maximal expiration
in anatomical dead space & in alveoli to keep
them open
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M•Komorniczak (2009)
https://commons.wikimedia.org/wiki/File:Lung_Volumes_And_Capacities_en.svg
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Lung Volumes
.
Minute Volume (V)
total volume of air breathed in/out each minute
.
V = tidal volume x respiratory rate
(L/min)
(L/breath)
(breaths/min)
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Lung Volumes
.
Minute Volume (V )
At rest:
tidal volume 0.5L, 12 breaths/min
minute volume = 0.5 x 12 = 6L /min
taking into account dead space (150mL)
(500 – 150) x 12 = 4.2 L/min fresh air available for gas
exchange (known as alveolar ventilation)
If body’s demand for oxygen increases, tidal & minute
volumes increase markedly
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Blood-Air Interface
 Concentration of a gas is related to its pressure (P)
 oxygen & carbon dioxide move between air and blood by diffusing
down their pressure gradients
 diffusion rate increases with:
  surface area
  pressure gradient
  thickness of surface
 blood-air barrier in lung ideal
for gas exchange:
 very thin
 very large surface area (50-100 m2)
LadyOfHats (2007) Alveolus diagram
https://commons.wikimedia.org/wiki/File:Alveolus_diagram.svg
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Partial Pressures
concentration of gas in mixture referred to as
partial pressure (P)
The atmosphere consist of approximately:
 20 % oxygen
 0.05 % carbon dioxide
 80 % nitrogen
Air pressure is ~760 mmHg therefore:

pO2 + pCO2 + pN2 = 760mmHg

pO2 = 20% of 760
= 160 mmHg

pCO2 = 0.05% of 760
= 0.4 mmHg
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alveolus
Which way will
oxygen flow ??
capillary
pO2
100 mmHg
pO2
40 mmHg
0.3 m
Impairment of Diffusion
e.g. high altitude -  press. gradient between air
& blood
e.g. fibrosis
- thickening of exchange barrier
e.g. emphysema - lung surface area 
UWS Staff (2015)
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Gas Exchange
pressure of CO2 in :
blood entering pulmonary capillary 44mmHg
alveolar air 40mmHg
Which way
does carbon
dioxide
flow?
alveolus
capillary
pCO2
40 mmHg
pCO2
44 mmHg
0.3 m
UWS Staff (2015)
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Control Mechanisms & Regulation
breathing
 usually automatic
can be consciously controlled
negative feedback - basic principle of control of
breathing (whether conscious or not)
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Control mechanisms
negative feedback
sensors gather information
control unit (in brain) analyses information &
initiates response
effectors produce required change
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Respiratory Control
sensors:
 many different sensors involved in control of
normal respiration
 most important - chemoreceptors
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Levels of pO2 and pCO2 determine
manner in which we breathe
Medullary
Respiratory
Centre
sympathetic +
parasymp. NS
Respiratory
muscles
Sensor
blood
gases
chemoreceptors
UWS Staff (2015)
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Sensors in Automatic Respiratory
Control
chemoreceptors
respond to changed blood levels of:
 O2
CO2
H +
normal partial pressures in arterial blood are
O2 100mmHg
CO2 40mmHg
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Sensors in Automatic Respiratory
Control
chemoreceptors :
in brain:
• sense changes in pCO2 & H + concentration in CSF
surrounding brain
in some major arteries:
• sense changes in arterial pO2, pCO2 & H +
concentration
increased pCO2 & H + or decreased pO2 bring about
increased respiratory effort (& vice versa)
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Respiratory Control
other sensors include stretch receptors in the lung
 these modify respiration to degree of lung stretch:
  stretch   respiratory rate ( expiration time)
  stretch   respiratory rate (stimulates inspiratory muscles)
lung has receptors in airways, nose, trachea etc. –
stimulation  reflex constriction (e.g. asthma)
all control mechanisms involve ANS
voluntary control initiated in cerebral cortex
can over-ride automatic control – but only briefly
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SUMMARY
Respiratory system comprises upper & lower parts
Lungs:
 have a branching respiratory tree
 are surrounded by the pleura
Ventilation is affected by:
 compliance
 resistance
 surface tension
Blood-air interface
 gas exchange via diffusion
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