Respiration
Learning objectives
• To outline the respiratory system
• To define lung volumes and capacities.
• To describe the mechanisms of respiration.
• To describe the mechanisms of oxygen and
carbon dioxide transport.
• To describe the control of respiration.
The air passage
Nasal cavity
Pharynx
Larynx Trachea
Bronchi
Lungs
Nasal cavity
• Air enter the nasal cavity through the two
nostrils;
• On route, the air is
~ warmed
~ moistened
~ filtered by the hairs lining the cavity
Pharynx
• It leads to two passages:
~ trachea
~ oesophagus
• Epiglottis closes the trachea to prevent
food from entering the air-way during
swallowing.
Larynx
• It is at the upper end of the trachea.
• It is composed of 5 pieces of cartilage: the
vocal cords.
• The vocal cords vibrate to produce sound
whenever air tension passes over them.
Trachea
• A flexible pipe-like structure supporting by
C-shaped ring of cartilage.
• Mucosa secreting mucus is lining in the
inner wall of trachea.
• Cilia are found on the mucosa.
• Movement of cilia remove any foreign
object or mucus from the trachea.
Bronchi
• The trachea divides to form two bronchi:
~ right bronchus right lungs
~ left bronchus left lungs
• The bronchus divides repeatedly into
bronchioles inside each lungs.
• The bronchioles lead into air sacs
eventually.
Lungs
• It is the place for gaseous exchange:
exchange of carbon dioxide and oxygen
between environment and organism.
• Within each lung:
Bronchus smaller bronchioles
air sacs & alveolus
Features of alveoli
• Large surface area
• Thin wall
• Moist surface
• Rich supplied with blood capillaries
Pleural membrane
• It is a sheet of smooth membrane.
• It covers the outside surface of the lungs and the
inside surface of the thorax.
• It consists of two layers:
~ inner pleura
~ outer pleura
• Pleural cavity is present between the pleurae.
• Pleural fluid fills the pleural cavity.
• Pleural fluid reduce friction between pleurae
during breathing.
Ventilation
• It is the passage of air
into and out of the
respiratory tract.
• Breathing is the act.
• It consists of
~ inspiration( breathe
in)
~ expiration(breathe
out)
Accessories for ventilation
• Diaphragm
~ fibrous sheet of tissue
~ dome shape when it relaxes (expiration)
~ flatten when it contracts(inspiration)
• Intercostal muscle
~ muscle between ribs
• Anterior abdominal wall
Inspiration
• Diaphragm: contracts and flattens
• Anterior abdominal wall: relaxes
• Thoracic volume:
• Pressure in pleural cavity:
• Movement of air: into the lungs
• Shape of the lungs : inflated
Expiration
• Diaphragm: relaxes and becomes dome
shape
• Anterior abdominal wall: contracts
• Thoracic volume:
• Pressure in pleural cavity:
• Movement of air: forced out of the lungs
• Shape of lungs: deflated
Lung volume and capacitites
• Tidal volume
• Inspiratory reserve volume
• Expiratory reserve volume
• Vital capacity
• Residual volume
• Dead space
• Total lung capacity
Tidal volume
• The amount of air
moves in or out of the
lungs with a single
breath at rest.
• It is about 0.5 L.
Inspiratory reserve volume
• The amount of air that
can be taken into the
lungs over and above
the tidal volume.
• It is about 1.5 L.
Expiratory reserve volume
• The extra amount of
air that can be forced
out after a normal
expiration.
• It is about 1.5 L.
Vital capacity
• The greatest volume
of air that can be
expired after a
maximum inspiratory
effort.
• It is about 3.5L.
Residual volume
• The amount of air
remain in the lung
even after forced
expiration.
• It is about 1.5L.
Dead space
• The volume of
inspired air which
cannot reach lungs for
gaseous exchange and
remains in the
respiratory tract.
• It is about 0.15L.
Total lung capacity
• Vital capacity +
residual volume.
• It is about 5 L.
Transport of gases
• Haemoglobin is the most common example
of respiratory pigment.
• Haemoglobin is an iron-containing
pigment (haem group).
• Haemoglobin is confined to red blood cells
Transport of oxygen
Low O2
tension
Hb + O2 HbO2 + O2 HbO4 + O2 HbO6 + O2
High O2
tension
Transport of oxygen
• At the lungs:
~ amount of oxygen (PO2) is huge
~ oxygen binds to haemoglobin(Hb) to form
oxyhaemoglobin
~ nearly 95% of Hb is saturated with
oxygen
~ 100% saturation of haemoglobin is rarely
achieved
Transport of oxygen
• At tissue:
~ amount of oxygen(PO2) is limited
~ haemoglobin cannot binds with the
oxygen
~ oxyhaemoglobin dissociates and release
oxygen to the tissue cells
S-shaped curve
• The oxygen dissociation curve is S-shaped
(sigmoid).
• The shape of haem group distorts as O2
combines with the Hb.
• The distortion enhances further attachment
of O2 to Hb.
• The more the O2 that have been loaded,
the faster further attachment.
S-shaped curve
• The first O2 is released to the tissues very
rapidly.
• But the second, third and fourth O2 are
given up much less readily.
The S-shaped oxygen dissociation curve
provides the mechanism for fast loading
and unloading of oxygen.
Factors affecting the oxygen
dissociation curve I
• Acidity (Carbon dioxide concentration)
~ PCO2, efficiency at taking up O2 by
Hb, but efficiency at releasing it.
e.g. At muscle and liver
~ high respiration rate of the cells
~ rapid release of O2 from the blood
supplying them
Factors affecting the oxygen
dissociation curve II
• Temperature
~ blood temperature, affinity of Hb for
O2 unloading of O2 from the Hb
e.g. oxygen dissociate from Hb efficiently
and rapidly in endotherms(warm blooded
animal) than in ectotherms(cold blooded
animal).
Factors affecting the oxygen
dissociation curve III
• Altitude
~ altitude, volume of O2 in the
atmosphere, affinity of Hb for O2
• Size of animal
~ size, affinity of affinity for O2
unloads it more readily
Factors affecting the oxygen
dissociation curve IV
• Fetal haemoglobin
~ the fetal haemoglobin has a higher
affinity for O2 than maternal haemoglobin;
~ the fetal blood pick up O2 from maternal
blood across the placenta readily.
Factors affecting the oxygen
dissociation curve V
• Carbon monoxide
~ the affinity of Hb for carbon monoside is
several hundred times as great as it is for
O2;
~ Hb will combines with any carbon
monoxide available in preference to O2
As little as 0.1% carbon monoxide is
dangerous, it causes asphyxiation.
Factors affecting the oxygen
dissociation curve VI
• Myoglobin
~ It release O2 only when the O2
concentration falls very low;
~ myoglobin stores O2 in the muscle and
releases in an emergency case.
Transport of carbon dioxide
• In plasma (5%)
~ carbonic acid forms in this process
~ the acid influences the plasma pH greatly
• Enter red blood cells(95%)
Control of ventilation
• Breathing centre
• Chemoreceptors
• Baroreceptors
• Stretch receptors
• Voluntary control
• Effect of carbon dioxide on breathing rate
• Effect of oxygen
Breathing centre
• It is in the medulla oblongata of the brain.
• It sends impulses to the intercostal muscle
and diaphragm.
• The muscle respond by bringing thorcic
movements.
• It consists of inspiratory centre and
expiratory centre.
Chemoreceptors
• They are located in the carotid and aortic
bodies of the blood system.
• When concentration of carbon dioxide ,
they discharge impulses to the respiratory
centre.
Baroreceptors
• They are located at the carotid artery and
aorta.
• They detect the change of blood pressure.
• Blood pressure, the baroreceptor
discharge impulse to respiratory centre,
rate and depth of breathing.
Stretch receptors
• They are located in the wall of alveoli.
• Lung expand stimulates the stretch
receptors impulses to the respiratory
centre switches off the inspiratory
centre.
Voluntary control
• The rate and depth of breathing can be
controlled by our mind.
• Cerebrum sends impulses to the breathing
centre.
Effect of carbon dioxide
acidity ( carbon dioxide concentration)
Respiratory centre send impulses
Diaphragm & intercostal muscle
in general, PCO2, fast & large
ventilation
Effect of oxygen
• The respiratory centre is insensitive to
oxygen concentration in blood.
• The chemoreceptors only respond to
serious decrease in oxygen concentration.
• The regulation of breathing depends
primarily on accumulation of carbon
dioxide and not only lack of oxygen.