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RESPIRATORY SYSTEMS
Skin- unicellular and small animals
Trachea- in arthropoda
Gills- Fish
Parabronchus-Birds
Lung-many vertebrates except fish
The respiratory gases that animals must
exchange are oxygen (O2) and carbon
dioxide (CO2).
Diffusion is the only means by which
respiratory gases are exchanged between
the internal body fluids of an animal and
the outside medium (air or water).
Many anatomical adaptations maximize
the specialized body surface area (A) over
which respiratory gases can diffuse.
Invertebrate respiratory system
Respiratory gases can diffuse through air most of the way to and from every cell of
an insect’s body. This diffusion is achieved through a system of air tubes, or
tracheae, that communicate with the outside environment through gated openings
called spiracles. Insect body fluid never carries respiratory gases.
Crustaceans have internal gills. Arachnids have specialized folded tracheae
Fish Gills
The internal gills of fish are supported by gill arches that
lie between the mouth cavity and the protective
opercular flaps. Water flows unidirectionally into the
fish’s mouth, over the gills, and out.
The gills have an enormous surface area for gas
exchange because they are so highly divided. Each gill
consists of hundreds of leaf-shaped gill filaments.
Blood flows
through the
lamellae in the
direction opposite
to the flow of water
over the lamellae.
This
countercurrent
flow optimizes the
gas exchange.
Vertebrate respiratory system
Amphibia Reptiles, mammal
The surface area(alveoli) of the respiratory organs
increases from amphibia to mammals. Birds don’t
have alveoli instead they have parabronchus.They
don’t have a diaphragm.
Bird lung
The structure of bird lungs allows air to
flow unidirectionally through the lungs,
rather than having to flow in and out.
Thus there is little dead space in bird
lungs, and the fresh incoming air is not
mixed with stale air. In this way, a high
PO2 gradient is maintained.
In addition to lungs, birds have air sacs
at several locations in their bodies. The
air sacs are interconnected with the
lungs and with air spaces in some of
the bones. The air sacs receive inhaled
air, but they are not gas exchange
surfaces.
In bird lungs, the bronchi divide into
tubelike parabronchi that run parallel
to one another through the lungs
The air sacs keep fresh air flowing
unidirectionally and continuously over
the gas exchange surfaces. Thus, the
bird can supply its gas exchange
surfaces with a continuous flow of fresh
air
HUMAN RESPIRATORY SYSTEM
Air enters the lungs through the oral
cavity or nasal passage, which join
together in the pharynx. a single
trachea leads to the lungs. At the
beginning of this airway is the larynx,
or voice box, which houses the vocal
cords.
The trachea is about 2 cm in
diameter. Its thin walls are prevented
from collapsing by Cshaped bands of
cartilage that support them as air
pressure changes during the
breathing cycle.
The alveoli are the sites of gas
exchange. The total number of
alveoli in human lungs is about 300
million. Even though each alveolus is
very small, their combined surface
area for diffusion of respiratory gases
is about 70 m2
Inhalation is initiated by contraction of the muscular
diaphragm. As the diaphragm contracts, it expands the
thoracic cavity, pulls on the pleural membranes, and
increases the negative pressure in the pleural cavity.
Exhalation begins when the contraction of the diaphragm
ceases. The diaphragm relaxes and moves up, and the
elastic recoil of the lung tissues pushes air out through
the airways. When a person is at rest, inhalation is an
active process and exhalation is a passive process
When we are at rest, the amount of air that moves in and out per breath is
called the tidal volume (about 500 ml for an average human adult).
The combined tidal volume, inspiratory reserve volume, and expiratory
reserve volume is the vital capacity.
The lungs and airways cannot be collapsed completely; they always contain
a residual volume. The total lung capacity is the sum of the residual volume
and the vital capacity.
Blood Transport of
Respiratory Gases
The liquid part of the blood, the blood plasma, carries some O2 in
solution, but its ability to transport O2 is quite limited. To increase its O2
transport capacity, the blood of most animals, vertebrate and
invertebrate, also contains molecules that can bind reversibly to O2
depending on its partial pressure. Hemoglobin increases the capacity of
blood to transport O2 by about 60-fold. Each molecule of hemoglobin can
bind to four molecules of O2.
Muscle cells have their own oxygen-binding molecule, myoglobin.
External respiration: between alveoli and
blood.
Internal respiration: between blood and
tissue cells.
Cellular respiration: breakdown of glucose
..
Oxygen transport
Oxygen exchange depends
on the partial pressure of the
oxygen. The partial pressure
in alveoli is 104 . But it is 40
mmHg at pulmonary artery.
Thus oxygen passes to blood.
And is carried as
oxyhemoglobin.
Hb + O2
HbO2
(in alveoli)
HbO2
Hb+O2
(in tissues)
The oxygen partial pressure in
aorta decreases to 40 in
tissues. And oxygen passes
from blood to tissues.
Carbondioxide transport
Carbondioxide passes to
blood according to the partial
pressure.
– CO2 is carried as a soluble gas
in plasma
– Some is carried as
carboxyhemoglobin.
– Some is carried in the carbonic
acid form
When CO2 diffuses from tissues to the
blood, with the help of the carbonic
anhydrase enzyme water reacts with CO2
and forms carbonic acid. Then carbonic acid
ionizes and form H and bicarbonate ions
HCO3. H ions bind with Hb . HCO3 ions
diffuses from erythrocytes to plasma and
transported to lungs.
In tissues:
H
CO2 + H2O
H2CO3
HCO3
HCO3, binds with Na, to form
NaHCO3.
In lungs NaHCO3 ions ionizes to
HCO3 and diffuses to
erythrocytes. Then HCO3 binds
with H and form carbonic acid.
Carbonic acid ionizes to CO2 and
water with the help of enzyme.
CO2 is thrown out to alveoli.
In alveoli:
HCO3
H2CO3
CO2 + H2O
H
Control of respiration
Breathing is an autonomic function of the nervous system. The
autonomic nervous system maintains breathing and modifies its
depth and frequency to meet the demands of the body for O2 supply
and CO2 elimination. The breathing rhythm is an autonomic function
generated by neurons in the medulla(brain stem) and modulated by
higher brain centers.
The most important feedback stimulus for breathing is the level of
CO2 in the blood(decrease in pH). The breathing rhythm is sensitive
to feedback from chemoreceptors on the ventral surface of the
medulla and in the carotid and aortic bodies on the large vessels
leaving the heart
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