Transcript Gas Exchange

GAS EXCHANGE
Chapter 22
GAS EXCHANGE
Respiration or the interchange of O2 and CO2
 3 phases which use digested food to produce work

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Breathing exposes large, moist internal surface to air
O2 diffuses from lungs into blood vessels and CO2 in reverse
 Exhalation removes CO2 from body
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Transport of gases by circulatory system
O2 attaches to hemoglobin in RBC’s
 Red vessels = O2 from lungs, blue vessels = CO2 from tissues
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Body cells take up O2 from blood and release CO2 into it
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Important for cellular respiration
Continuous supply of O2 and removal of CO2
RESPIRATORY SURFACES
Part of an animal where gases are exchanged
 Made of living cells that must be moist to function
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Single layer to allow rapid diffusion of gases
Surface area must be large enough to take up
sufficient O2 for every body cell and dispose of CO2
 4 types which vary between species (pictures)
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Skin, gills, tracheal systems, and lungs
‘SKIN BREATHERS’

Outer skin is gas
exchange organ

No specialized organs
O2 diffuses in
capillaries just below
outer surface
 Must live in damp
places
 Generally small and
long, thin, or flattened
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High ratio of SA to
body volume
GILL SYSTEMS
Extensions of the body
surface, specialized for
gas exchange
 O2 across gills to
capillaries and CO2 in
opposite direction
-countercurrent
 Found in most aquatic
animals
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Not a problem staying
moist
TRACHEAL SYSTEMS

Branching internal
tube system in insects
Surface at tips
 Direct exchange with
body cells
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Open to external
environment via
narrow tubes
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No circulatory system
Helps retain moisture
Most terrestrial
animals
LUNGS
Internal sacs with
moist epithelium
 Inner surfaces branch
extensively to increase
SA
 Circulatory system
carries gases between
lungs and body cells
 Most terrestrial
vertebrates
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AQUATIC ENVIRONMENTS
O2 as dissolved gas in bodies of water
 Trade off: no limit to moisture, but decreased O2
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Warmer and saltier = less O2
Structure of gills
Less O2 available so gill SA larger then rest of the body
 Respiratory surfaces are so tiny that RBC’s flow
singularly in close contact with O2 in water
 Positioned so water can enter mouth, flow over gills, and
exit
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Gills remove 80% of O2, lungs only 25%
Gills outside body so H2O loss terrestrially would be
large
 Terrestrial animals house respiratory organs inside body
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GILL SYSTEMS
Countercurrent
exchange:
transfer of a
substance from a
fluid flowing in 1
direction to a fluid
flowing in the
opposite direction
Sets up a
concentration
gradient to favor
O2 diffusion from
H20
TERRESTRIAL ORGANISMS
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Air has higher [O2] and easier to move than H2O

Less energy to ventilate, move O2 containing
substances across respiratory organs
Higher probability of H2O loss from evaporation
 Tracheal system allows exposure to all body parts
and gas exchange independent of a circulatory
system
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Flight in insects can increase exchange rate to
sustain high energy needs for flight
TRACHEAL SYSTEMS
Tracheae open
to external
environment
Smaller
branches are
tracheoles that
participate
directly in gas
exchange
O2 directly to
body cells
EVOLUTION OF TETRAPODS

Fossil evidence of skeletal tetrapod changes
Current hypothesis that pectoral girdle changes to
enable pushing up out of water to gulp air
 Had lungs and gills
 Stronger & elongated snout and neck to lift head out of
water
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Diverged into amphibians, reptiles, and mammals
Amphibians with small lungs and heavy reliance on
gas exchange across body surfaces
 Reptiles and mammals have lungs whose size and
complexity correlate with metabolic rate or O2 needed
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RESPIRATORY PATHWAY
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Air into our nostrils to be filtered and warmed
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Mouth breathing skips processing by the nose
Flows into pharynx where food and air paths cross before
entering the trachea
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Passes through the larynx or voicebox
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Rings of cartilage in the trachea prevent collapse
Rest of the path lined with moist, ciliated epithelium and
mucus
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When exhaling the vocal cords are tensed to produce sounds by
changing the vibrations made
High pitch when stretched tight and vibrate fast
Moves contaminates trapped in mucus to the pharynx
Trachea branches into 2 bronchi, 1 to each lung
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Branching continues into bronchioles and dead end at alveoli,
or dead end grape-like sacs
Increases SA to 50X’s greater than skin
Diffusion across epithelium cells into and out of capillaries
around each
HUMAN LUNGS
RESPIRATORY PROBLEMS
Bronchitis from inflammation of bronchioles which
impede breathing
 Premature babies have difficulty keeping alveoli open
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Surfactants are secreted to combat surface tension,
resulting from moisture surrounding the tiny sacs, which
causes the alveoli to stick together
 Don’t appear until about 33 weeks after conception
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Alveoli highly susceptible to contaminants
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Macrophages patrol, but extensive damage can decrease
gas exchange
Pollutants from air and tobacco can inflame the lungs
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Can lead to COPD
SMOKING RISKS
1 drag exposes lungs
to 4,000+ chemicals
 Can irritate ciliated
cells and inhibit
flagellum movement
 Kills macrophages in
lungs
 Can lead to
emphysema, lung
cancer, ‘smoker’s
cough’, heart attacks,
and stroke
 15 years of quitting
can reverse effects
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VENTILATING OUR LUNGS
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Breathing is the alternation of inhalation and
exhalation
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Inhalation rib cage expands as rib muscles and
diaphragm contract to enlarge chest cavity
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Increases lung volume, pressure in alveoli less than
atmosphere, are diffuses from nostrils to alveoli =
negative breathing
Exhalation reverses muscle movements
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Maintains high O2 and low CO2
Decreases lung volume, pressure is more so air
pushed out, aided by upward movement of diaphragm
Vital capacity is max amount of air inhaled and
exhaled
BREATHING TECHNIQUES
AUTOMATIC CONTROL
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Breathing control centers in the brain include the
pons and medulla
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Voluntarily hold our breathe and change rate, but
most breathing is involuntary
Nerves from brain signal contraction of rib
muscles and diaphragm
 Regulated in response to CO2 levels in blood
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Exercise speeds up metabolism so more CO2 created
 Forms carbonic acid, sensed by medulla which
increases breathing rate
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Aorta and carotid arteries also have CO2 sensors
and O22 ones
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Signals control centers accordingly
RESPIRATORY CONTROL SYSTEM
RESPIRATORY GAS TRANSPORT
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Blue colored side is O2 poor
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Red side is O2 rich
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Blood from capillaries to heart
which transports to alveoli for
exchange
Blood from alveoli return to
heart which transports to
tissues
Gas exchange via diffusion
across a pressure gradient
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Air is a mix of gases with
pressure
Each type of gas contributes a
partial pressure
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Each gas type moves down
individual gradients
HEMOGLOBIN
O2 is not soluble in H2O so must be transported
by proteins called respiratory pigments, or
colored molecules
 Iron containing pigment that turns red with O2
 4 polypeptide units of 2 types, each with an
attached heme group and Fe atom in the center
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1 Fe to 1 O2 molecule
Helps transport CO2 and buffer blood
Upon entering RBC’s, hemoglobin binds some CO2,
rest dissociates into H+ and HCO3 Hemoglobin binds H + to minimize blood pH change
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Remember pH drop increases breathing rate
O2 AND CO2 EXCHANGE
CO2 + H2O
Carbon
dioxide
Water
H2CO3
Carbonic
acid
H+
+
Hydrogen
ion
HCO3-
Bicarbonate
Reaction reverses as blood flows through the capillaries
in the lungs
HUMAN FETUS
Within the uterus the fetus survives in the
amniotic fluid, a watery environment
characteristic of most terrestrial animals
 Lungs are nonfunctional and fluid filled
 Gas exchange occurs through the placenta
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A vascularized organ of maternal and fetal tissue
Capillaries branch to exchange gas within the
maternal circulatory system
Fetal hemoglobin has a higher affinity than adult for
O2
Upon birth placental gas exchange stops
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CO2 in fetal blood increases, pH drops, and breathing
centers are stimulated = first breath