Respiratory System

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Respiratory System Breath in Breath Out
Contact Details Dr Hora Ejtehadi, Ext. 5489,
Baker B704, Perry Barr Campus
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Respiratory System
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Respiratory System
Exchange of O2 and CO2 between the environment
and the cells of the body
Structure Function Relationships
1 Conducting pathways
2 Lungs
3 Thorax (chest)
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Nasal Passages
Lined by nasal mucus
Blood vessels line mucosa ? work as radiators ?
cool warm air and warm cool air
Mucus adds moisture to dry air traps fine dust
particles
Celia move dust-containing mucus into the throat
Pharynx
Air leaves nose and enters pharynx
From pharynx, air enters larynx
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Larynx
Cartilagenous structure
Projection of thyroid cartilage of larynx (Adams
apple)
Cavity of larynx lined by vocal cords (production
of sound)
Preventing food from entering the lower airways
is a cartilagenous flap Epiglottis
Trachea
Long rigid tube (12 cm)
Supported by C-shaped cartilage, opening at the
back
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Bronchi And Bronchioles
Trachea branches out into two primary bronchi
The primary bronchi branch into smaller bronchi
(less cartilage more smooth muscle)
Bronchi become completely smooth muscle narrow
to 1 mm diameter bronchioles
Final branch is terminal bronchioles (smallest
air passage ways)
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Smoking !!!!!
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Alveoli
Thin-walled inflatable grape-like sacs
Walls consist of single layer of type I cells
Single layer of pulmonary capillaries encircle
each alveolus
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Alveoli. Continued.
Space between air in alveolus and blood in
capillaries in very little
Alveolar air-blood interface large surface area

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Alveoli. Continued.
Therefore 1 Short distance 2 Large surface
area
Result high rate of diffusion
Alveolar epithelium contains Type II alveolar
cells (secrete surfactant)
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Pulmonary Surfactant
Complex mixture of lipid and protein
Prevent alveolar collapse
Pre-mature infants do not produce enough
surfactant New born respiratory distress
syndrome
Collateral ventilation
Small pores between alveoli pores of Kohn
Allow airflow between adjacent alveoli
Important especially when disease blocks terminal
conducting airways getting air to certain alveoli
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Lungs
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Diaphragm
Dome-shaped skeletal muscle that forms the floor
of the thoracic cavity
Respiratory Mechanics
Rule 1
Air moves down a pressure gradient from a region
of high pressure to a region of low pressure
Rule 2
The larger the volume of the chamber, the lower
the pressure
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Atmospheric Pressure
760 mmHg
Intraalveolar Pressure
Pressure within alveoli
760 mmHg
Intrapleural Pressure
Pressure within pleural sac
756 mmHg
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Because of this, the pressure gradient tends to
keep lungs open and stretched TRANSMURAL
PRESSURE GRADIENT
If air enters pleural cavity PNEUMOTHORAX,
pressure become 760 mmHg not 756 mmHg resulting
in collapsed lung ATELACTASIS
Inspiration And Expiration
Muscles involves in inspiration or expiration act
on the thoracic cavity not the lungs
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Inspiration
Aim Reduce intraalveolar pressure to allow air
to enter alveoli from atmosphere
i.e. You must increase size of alveoli by
increasing size of thorax
Muscle involved are
a) Diaphragm
b) External intercostal muscle
When diaphragm contracts, it moves downward
(increases chest size)
When external intercostal muscles contract, ribs
move upward and outward (increase chest size)
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This allows lungs to enlarge and expand ? drop in
pressure ? air enters from atmosphere
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Passive Expiration
Results from relaxation of inspiratory muscles
Active Expiration
Internal intercostal muscles move ribs inward and
downwards
Abdominal muscles play a role
Chest size decreases ? lungs compressed ?
intraalveolar pressure increases ? air leaves
lungs to atmosphere
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Chronic Obstructive Pulmonary Disease
Increased airway resistance due to narrowing
lumen of airway
Larger pressure gradient must be established ?
muscles must work harder
Asthma, chronic bronchitis and emphysema
Expiration is more difficult than inspiration
This is because during inspiration, as thorax
expands it indirectly dilates conducting airways
? lower airway resistance in inspiration compared
to expiration
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Emphysema
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Pulmonary Elasticity
Elastic recoil Lungs rebound after stretch
Compliance Effort required to stretch the lungs

The above two factors upon elasticity of the lung
tissue and alveolar surface tension
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Alveolar Independence
Contributes to alveolar stability
Alveoli are interconnected
If one collapses, its walls stretch the other
alveoli
When the walls of the other alveoli recoil, they
stretch the collapsed alveoli
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Lung Volumes
Measured using a spirometer
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Spirogram
Adult male lung holds 5700 ml of air
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Spirogram
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Spirogram
TV Volume of air moved in or out in each breath

IRV Extra volume of air that can be maximally
inspired over and above the tidal volume (3000
ml)
ERV Extra volume of air that can be maximally
expired over and above the tidal volume (1000
ml)
IC Maximum volume of air inspired at the end of
quiet expiration (3500 ml)
RV Minimum volume of air remaining in the lungs
after maximal expiration (1200 ml)
VC Maximum volume of air expired following
maximum inspiration (4500 ml)
Spirometry is not the only test. Other tests
include X-ray examination and blood gas analysis
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Respiratory Rate
Number of breaths per minute
Average value 12 breaths per minute
Pulmonary Ventilation
Pulmonary ventilation TV x Respiratory rate
Pulmonary ventilation 500 x 12 6000 ml/min
Except, not all the 500 ml of tidal volume are
exchanges
Approximately, 150 ml remain in the conducting
airways Dead Space
So, pulmonary ventilation (500-150) x 12 4200
ml/min
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Gas Exchange
PO2 Partial pressure of oxygen
PCO2 Partial pressure of carbon dioxide
PO2 is higher in alveoli than in the blood
Therefore, oxygen enters from alveoli to blood by
diffusion
The opposite occurs for carbon dioxide
The ventilation and gaseous exchange is
compromised in emphysema patients
Similar situation atelectic regions of the lung
or when lung tissue is surgically removed
(following lung cancer treatment)
Inadequate gaseous exchange could occur due to
increased thickness of air-blood barrier
(pulmonary oedema, pulmonary fibrosis and
pneumonia)
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Gas Transport
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Oxygen-Haemoglobin Dissociation Curve
Relationship between blood PO2 and percentage Hb
saturation is not linear
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Oxygen-Haemoglobin Dissociation Curve
Between 10-60 mmHg, the slope is steep, while
from 70-100 mmHg it starts to plateau (becomes
flat)
So at 60 mmHg, 90 of the Hb is saturated and
after that an increase of 40 mmHg only causes a
10 increase in the Hb saturation
So at high altitudes or in pulmonary diseases. If
PO2 fall from 100-60 mmHg, the total quantity of
O2 carried by the Hb in the blood decreases only
by 10
Also, if PO2 were to increase through
hyperventilation, or breathing 100 O2, little
effect would that have on addition of O2 to the
blood.
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Abnormal Blood Gas Levels
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Abnormal Blood Gas Levels
Hypocapnia Below normal arterial PCO2
Hypocapnia due to hyperventilation
This results in increased arterial PO2
Increased PO2 and reduced PCO2 may reflect body
requirement for increased O2 delivery and CO2
elimination during exercise for example
Hyperpnea
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Control Of Respiration
Dorsal Respiratory Group (DRG) Mainly
inspiratory neurons terminate in motor neurons
that supply inspiratory muscles
When DRG neurons fire, inspiration takes place,
when they cease firing expiration occurs
Ventral Respiratory Group (VRG) Inspiratory and
expiratory neurons
VRG called upon when demands for ventilation are
increased
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Control Of Respiration
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Pneumotaxic more dominant
Apneustic prolonged inspiratory gasps abruptly
interrupted
Respiratory Receptors
Changes in PO2 and PCO2 are detected by different
receptors
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Monitor arterial PO2
Only detect changes in PO2 below 60 mmHg (Hb
saturation fall dramatically at this stage. Refer
to page 37 in this handout)
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Central Chemoreceptors
Arterial PCO2 is important for control of
magnitude of respiration at resting conditions

Central chemoreceptors located in the medulla

Do not detect CO2 directly, but the H generated
from CO2 (refer to page 40 in this handout)
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Reading
Human Physiology From cells to systems. LauraLee
Sherwood. West Publishing company. Chapter 13.
Respiratory System