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AP Biology
March 2008
Respiration
Chapter 42
Gas exchange occurs across specialized respiratory surfaces.
1) Gas exchange:
a) Relies on the diffusion of gases down pressure
gradients.
i) At sea level, atmosphere exerts a total pressure of
760 mm Hg.
ii) This is the downward force equal to that exerted by
a column of mercury 750 mm high.
iii) Since the atmosphere is 21% O2 (by volume)
Then the partial pressure of oxygen is
b) Gases will diffuse down a pressure gradient across a
respiratory surface if it is:
i) permeable
ii) moist
2)
Factors Influencing Gas Exchange
1) Surface-to-volume ratio:
2) Ventilation
a)
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3) Transportation pigments
a) Aids in the movement of gases throughout the body,
increasing the quantity of molecules the blood can
carry.
b)
c)
i) It consists of four subunits, each of which is a heme
group with an embedded iron atom.
ii) The iron atom binds O2, thus one hemoglobin can
carry 4 oxygen molecules.
i) Contains copper, the oxygen-binding component.
ii) Common in arthropods and many mollusks.
iii) Dissolved in hemolymph rather than being confined
to cells.
Invertebrate Respiration
1) Respiratory medium: the source off the oxygen.
a)
b)
2) Respiratory surface: the part of an animal where oxygen
from the environment diffuses into living cells and carbon
dioxide diffuses out.
a) Always moist
b)
3)
a) Used by small invertebrates, such as flatworms and
earthworms.
b)
c) Earthworms have a mucus coating on their surface that
helps keep the surface moist to allow the O2 to diffuse
inward through the epidermis.
4) Gills
a) Used by invertebrates in aquatic environments.
b) A gill has a thin, moist, vascularized epidermis.
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c) Gill walls are highly folded to increase surface area.
5) Tracheal respiration
a)
b) Consists of internal tubes that branch repeatedly and
deliver air directly to body cells.
c) Air enters the tracheae through openings called
spiracles on the body surface and passes into smaller
tubes called tracheoles.
i)
d) In most cases no participation by the circulatory system
is needed, neither is any respiratory pigments needed.
Vertebrate Exchange
1) Gills of Fishes and Amphibians
a) Gills: variously shaped outfoldings of the body surface
specialized for gas exchange.
i) The total surface are of the gills is often much
greater than that of the rest of the body.
b)
c) Water flows over the gills and blood circulates through
them in OPPOSITE DIRECTIONS.
i) Countercurrent Exchange:
d) This mechanism is highly efficient in extracting O2 from
water whose oxygen content is lower than air.
2) Lungs
a)
b) Lungs provide a membrane for gaseous exchange with
blood.
i)
ii) Gases diffuse across the inner respiratory surfaces of
the lungs.
iii)
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iv) In body tissues,
O2 diffuses from
CO2 travels the route in reverse.
c) Lungs also participate in sound production by forcing
air to pass through the glottis opening causing the
vocal cords on either side to vibrate.
d) Amphibians have small lungs or no lungs, and they rely
heavily on the diffusion of gases across other body
surfaces.
i) Frogs: the skin supplements gas exchange.
e) Turtles are another vertebrate exception.
i) Rigid shell restricts breathing movements.
ii) Supplement with gas exchange across moist
epithelial surfaces in their mouth and anus.
Human Respiratory System
1) Anatomy of respiratory system
a) Located in the thoracic (chest) cavity.
b)
c) Then filtered by hairs, warmed, humidified, and
sampled for odors as it flows through a maze of spaces
in the nasal cavity.
d) Nasal cavity leads to the pharynx.
i)
ii) When food is swallowed, the larynx (the upper part
of the respiratory tract) moves upward and tips the
epiglottis over the glottis (the opening of the wind
pipe).
iii) This allows food to go down the esophagus to the
stomach.
iv) The rest of the time the glottis is open and we can
breath.
e) From the larynx, air passes into the trachea, or
windpipe.
f)
i) One leading to each lung.
g) Within the lung, the bronchus branches repeatedly into
finer and finer tubes called bronchioles.
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h)
i) The thin epithelium of the millions of alveoli in the lung
serves as the respiratory surface.
i) O2 in the air conveyed to he alveoli dissolves in the
moist film and diffuses across the epithelium and into
a web of capillaries that surrounds the alveolus.
ii)
Breathing – Cyclic Reversals in Air Pressure Gradients
1) The Respiratory Cycle
a)
i) Negative pressure breathing: works like a suction
pump, pulling air, instead of pushing it, down into
the lungs.
ii) Results from changes in the volume of the lungs.
iii) Diaphragm:
b) In exhalation, the actions listed above are reversed; the
elastic lung tissue recoils passively.
i)
ii)
iii)
2) Lung Volumes
a) Vital capacity: the maximum volume that can be
moved in or out.
b) Lungs cannot be completely emptied.
c) Tidal volume: the amount of air that enters and leaves
with each breath -- about 500 ml.
Gas Exchange and Transport
1) Gas Exchange
a)
b) The partial pressure gradients are sufficient to move O2
in and CO2 out of the blood passively.
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2) Oxygen transport
a)
b) Hemoglobin is a protein with four heme groups that
bind oxygen.
c) O2 diffuses down a pressure gradient into the blood
plasma, then into the red blood cells, where it binds
reversibly to hemoglobin
i) Each hemoglobin molecule can bind 4 O2
molecules.
ii)
iii) Consists of four subunits, each with a cofactor called
a heme group that has an iron atom at its center.
iv) Iron actually binds the oxygen.
d) Hemoglobin gives up its O2 in tissues where:
i)
ii)
iii)
iv)
3) Carbon Dioxide Transport
a) Because the concentration of CO2 is higher in body
tissues, it diffuses into the blood.
b)
c)
d)
4) Matching Air Flow with Blood Flow
a) Gas exchange in the alveoli is most efficient when
airflow equals the rate of blood flow.
b)
c) The brain monitors input from CO2 sensors in the
bloodstream and from receptors sensitive to decreases
in O2 partial pressures (carotid bodies and aortic
bodies)
i)
ii)
iii)
iv)