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STRUCTURE OF
HUMAN LUNG1. Respiratory system of man:
- consists of trachea, lungs, bronchus,
bronchioleand air sacs ( or alveolus )
- structure of trachea is supported by
cartilage tissue( ring shaped ,
preventing it from collapse when there
is a change in air pressure inside I
- bronchioles end up at numerous tiny air
sacs, the alveoli. Alveolus has a wet
and thin / single layer of squamousepithelial cellsthrough which gaseous
exchange takes place.
- alveolus is well provided with a network
of blood capillaries. Oxygen diffuses
out of alveolar air into blood capillaries,
combines with haemoglobin in the red
blood cells to form oxyhaemoglobin .
Oxygen is transported to body tisues in
the form of oxyhaemoglobin.
2. Both lungs ( and the heart ) are situated
and enclosed in the thoracic cavityby
ribs, intercostal muscles and the
diaphragm.
3. The contraction of external and internal
intercostal muscles bring about the
inhalation and exhalationof air during
breathing.
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RESPIRATION Dur ing inhalat ion:
-External intercostal muscle
contracts, internal intercostal
muscle relaxes ( both are
antagonistic muscles) results
in the raising up of the ribs
-Diaphragm also contractscuausing it to move
downward and becomes less
curved
-The capacity ( volume ) of
thoracic cavity increases and
the air pressure iside it is
lower than in the atmosphere.
-Air from outside is pushed
into the lungs.
-The revers process occures
during exhalation.
Haemoglobin molecule is
made up of 2 alpha- and
two beta- polypeptides. It
is nearly spherical. Thehydrophobic R-groupsare
pointing towards the
centreand the hydriphilic
ones are pointing
outwards. Each heme
group contains Fe+ion.
Each haemoglobin
molecule can combine
with 4 oxygen moleculesto form oxyhaemoglobin.
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OXYGEN DISSOCIATION CURVE
The rate at which haemoglobin in saturated withoxygen depends on the partial pressure oxygen
in the al veolar air, blood and insterstitial fluid in
body tissue. Haemoglobin takes up more
oxygen molecules and becomes saturated with
oxygen faster in the region where partial
pressure of oxygen is higher. Oxyhaemoglobin
dissociatesto release oxygen and haemoglobin
when partial pressure of oxygen is low(and
higher partial pressure of CO2 )
An increase in partial pressure of carbon dioxidewilltend to reduce the the rate of oxyhaemoglobin formation,
and hence the saturation of oxyhaemoglobin with
oxygen. Therefore the dissociation curveof oxygen will
move to the rightas more carbon dioxide enters / added
to the blood. This phenomenon is called the Bohr Effect
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Oxygen Dissociation Curve and
Transport of CO2in Blood
5% CO2 dissolves in blood plasma / part of it forms
carbonic acid and carried to the lungs. 10
20% is carriedas carbamino-haemoglobin in the red corpuscles. Carbon
dioxide combines with the amino group at one end of the
haemoglobin polypeptide to form carbaminohaemoglobin.
HHbNH2 + CO2 HHbNHCOOHHaemoglobin Carbaminohaemoglobin
In the cytoplasm of red blood cell, CO2is converted into
H2CO3, catalysed by the enzyme carbonic anhydrase.
H2CO3 dissociates into H+ and HCO3-. HCO3 diffuses outinto blood plasma and carried to the lungs ( about 80%)
Chlor ide shi f t
diffusion of Cl-
(chloride) ions into
red blood cell to
balance the
elecktric charges inthe cell.
+
Oxygen dissociation curves for adult
and foetal haemoglobin.
Oxygen dissociation curves for mioglobin and adult andfoetal haemoglobin compared.
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CONTROLL OF BREATHING
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Oxygen and Carbon Dioxide Transport
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Transport of CO2and O2 In Blood
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CONTROLL OF BREATHING
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Controll of Breathing
H++ HCO3-
H2O
Chemoreceptors
peripheral and
central (brain )Inspiratory
centre , ventral
part of medulla
oblongata
Expiratory c entre-
dors al and lateral part
of m edul la oblongata
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Controll of Breathing
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MEASURING LUNG CAPACITY
Kymograph
counterpoise
Carbon dioxide
absorber
Water level
The capacity of human lungs measured by spiromter.
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Lung Capacity During Breathing
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Lung Capacity
1. Tidal volume (0.45 lit.)
volume of air breathed in and
out at rest.
2. Inspiratory reserve volume
(1.5 lit. )- extra volume of air
taken in after normal
inhalation
3. Expiratory reserve volume
(1.5 lit.)- volume of air that
can be further breathed out
after normal exhalation.
4. Vital capacity (4.5 lit.)-
volume of air breathed out
after a forced inspiration, and
then followed by forced
expiration. Athlete has higher
vital capacity.
5. Residual volume(1.5 lit.)-
volume of air still left in thelung after a maximal forced
expiration, including air left in
the trachea, bronchi and
bronchioles.
6. Total lung capacity (5 lit.)-
maximum volume of air in the
lung after a forced inhalation
which is equal to vital
capacity + residual volume.
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OPENING AND CLOSING OF STOMATA
New hypothesis based on accumulation of K+:
Blue light stimulates the proton pump in the
membrane of the guard cells, causing fast
accumulation of H+in the cell.
This causes an active uptake of K+ ions and thus
lowering water potential in the guard cells. Water
diffuses in by osmosis from the surrounding
epidermal cells. Guard cells become turgid and stoma
opens.
The accumulation of positive charges in the cells is
balanced by Cl-ions or the formation of malate.
At night , the reverse takes place, K+ ions diffuses
out, causing water potential in the cell to increase.
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STOMATA OPENING MECHANISM
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STOMATA
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STOMATA OPENING
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REFLECTION
1. What is the significance of the following structures in respiration?
(a) alveolus
(b) intercostal muscles and diaphragm network of blood capillaries in alveolus
2. Describe the molecular structure of haemoglobin and how such structure is
adapted for its function in the transport of oxygen and carbon dioxide in
blood.
3. What is Bohr effect ? Describe the importance of the phenomenon in the
dissociation of oxyhaemoglobin.
4. Describe briefly , using suitable diagram if necessary, the transport of
carbon dioxide from tissues to the lungs.
5. Explain how breathing is regulated during a breathing cycle.
6. How is the opening and closing of stomata in a leaf influenced by light and
accumulation of K+ions in guard cells?