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Gas Exchange
Chapter 22
The Air Up There
• Air is a fixed ratio of partial
pressures (Px)
• Air thins with increasing
altitude
– Gas in same ratio, but less of
– 3000 m 1/3 less O2
• Sherpas, athletic training, and
blood doping
• Mountain sickness
Revisiting Respiration
Gas Exchange
Breathing
• Organismal level
• O2 in CO2 out via
diffusion
Cellular Respiration
• Cellular level
• Use O2 to produce
CO2 and ATP
Exchange
Application
Respiratory Surfaces
• Thin
– Diffusion distance
– Speed
• Moist
– Gases dissolved in
solution
• Large
– SA to volume ratio
– Energy demands
Respiratory Mediums
Water
• Pro
Air
• Pro
– Direct contact of respiratory
surface to medium
• Con
– Less O2
• warm and salty even less
– O2 diffusion slower
– More energy to ventilate
• Larger structures
• Water supports weight
– High concentration of O2
– Less dense
– O2 diffusion faster
• Con
– Desiccation of respiratory
surface
• Small openings externally
• Indirect contact of
respiratory surface to
medium
Gill Systems
• Aquatic organisms
• Convoluted extensions of body
surface (pink)
• Ventilation varies between
organisms
– Move respiratory medium
across respiratory surfaces
• Inefficient on land
– Desiccation
– Tissue Mass
• Mollusks, annelids, arthropods,
echinoderms, fish, and
amphibians
Countercurrent Exchange
• Exchange between 2 oppositely flowing
currents
• Maximizes O2 diffusion out of H2O
– Concentration gradient maintained entire length
– Compare to concurrent
‘Skin Breathers’
• Earthworms and
some amphibians
• Skin is respiratory
surface
– Circulatory system to
distribute
(hemoglobin assists)
– Lower invertebrates
without
• Moist environments
Tracheal System
• Insects
• Internal branched tube system
– Connect all cells to environment
– Prevents desiccation
• Direct exchange
– Open circulatory system
• Hemolymph = nutrients only
• Body movements assist
Lungs
• Branched internal sacs
– Moist epithelium
• Pigmented, closed circulatory system
– Nutrient and gas transport
• Most terrestrial vertebrates
– Elaboration with movement to land
– Variations between classes
Lung Adaptation
• Amphibians
– O2 via positive pressure into small
sacs
– Skin also for exchange
• Birds
– 1 way flow increases efficiency
– 2 cycles to complete
• Mammals
– Negative pressure
– Incomplete removal
– Myoglobin content varies
Mammalian Respiratory System
• Upper respiratory system
– Nasal cavity
• Warms air
• Smells
– Pharynx
– Larynx
• Vocal cords tensed to create sound
• Lower respiratory system
– Trachea
• Cartilage rings
– Bronchi (2)
– Bronchioles
– Alveoli
• Diffusion with capillaries through interstial
fluid
Respiratory Cycle
Inhale
• Rib muscles (up) and
diaphragm (down) contract
• Chest cavity increases
• Lowers air pressure in alveoli
Exhale
• Rib muscles (down) and
diaphragm (up) relax
• Chest cavity decreases
• Increases air pressure in alveoli
Respiratory Disruptions
• Smoking
– Inhibit cilia movement causes ‘smoker’s cough’
• Thicken bronchioles and reduce elasticity
• Alveoli rupture
– Stopping allows cilia and alveoli damage to reverse
• Premature birth (37 weeks or less)
– Surfactant production incomplete
• Keeps alveoli from collapsing
– Each breath requires large effort
• Emphysema
– Bronchi swell, tearing alveoli
– Reduced SA for gas exchange
• Pneumonia
– Fluid in alveoli
• Bronchitis inflames of bronchioles
Respiratory Gas Transport
• Blood circulates to all cells
– Hemoglobin binds/carries
• Protein bound to a metal
• Carry 4 O2 molecules, some CO2 too
• PO2 and PCO2 vary within the circulatory
system
– Blue and red vessels
– Lungs: high O2, low CO2
– Body tissues: low O2, high CO2
• Pressure gradient facilitates gas
exchange in tissue capillaries (purple)
Control of Human Breathing
• Most is involuntary
– Control centers in brain
• Medulla: inhalation signaling
• Pons: smoothes out rhythm and depth
• Driven by [CO2] in blood
– Reactions
• CO2 + H2O
• H2CO3
H2CO3 (carbonic acid)
H+ + HCO3
– CO2 levels increase
• pH in blood/CSF lowered
• Respiratory centers signaled
• Carotid arteries and aorta monitor
O2 also
– Severe deficit, i.e high altitude
– Increase rate and depth
Human Fetus
• Amniotic sac in uterus
– Lungs are fluid filled
• Placental role
– Blood exchange with mother
– Fetal hemoglobin
• Birth stops gas exchange
– pH drop, why?
– First breath