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Respiratory system
Function:
• Gas exchange with environment
• Exchange CO2 for O2 depends on:
Diffusion ~ SA x gradient
distance
Encouraging diffusion
• surface area - gill lamellae, infolding
lamprey X-section
Encouraging diffusion
• gradient - counter-current exchange of gills, tetrapod ventilation
Encouraging diffusion
• distance across - thin walls of capillaries, thin skin for cutaneous respiration.
Cell thickness at aveoli
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Fish respiratory systems Development of internal gills
• Ectoderm meets endoderm
Fish respiratory anatomy
• Lamprey, Chondrichthyes, Osteoichthyes
Countercurrent exchange
80-95 of O2 taken up
Osmotic issues may cause fish to not ventilate or exchange
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Ventilation mechanics –Water flows over gills via suction and
force pump, using branchial muscles
Fig. 18-6
Fish respiratory systems
• Low oxygen-content environments
–Solubility of O2 is better in cold water
(at OoC ~10 ml O2 at 30oC ~5 ml O2)
Accessory respiratory surfaces: cloaca, mouth, esophagus, intestine, skin, lungs
Modified gill arches poke into air chamber in mouth
Dissolved O2 in water is only 3% of O2 in the same volume of air
Lungs evolved early in Gnathostomata from an outpocketing of the gut
Fish lungs
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During the “age of fishes”
• Early freshwater bony fish would have low O2 environments
Lungs and swim bladders
• Even in fish, there is surfactant, glottis
• Pulse pump of most fish w/lungs, amphibians • Lungs later
developed a hydrostatic fxn
• (swim bladder)
• Swim bladders became dorsally located
Lungs vs. swim bladders
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Physostomous vs. Physoclistous Physoclistous swim bladder
• Gas still secreted against strong gradient
• Countercurrent multiplier w/rete mirabile
• Incoming O2
• Gas gland
Result of exchange
Tetrapod respiration • Need moist surfaces, but little water loss
when ventilating
• Septas provide SA
– Frog lung 1 cm3, 20 cm2 surface area
– Mouse lung 1 cm3, 800 cm2 surface area
Amphibian respiration, vocalization
• Cutaneous respiration usually dominates
Vibrations here get resonated here
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Reptile respiration • Because of longer neck, larynx and
trachea are found in reptiles
• Lungs primary gas exchange site
• Aspiration pump in amniotes
Crocodilian ventilation
• Muscle extends from liver to pelvis, liver movement is similar to mammal diaphragm
p.593
Evolutionary constraint: running and breathing
• Tetrapods w/ sprawled limbs depend on lateral bending in locomotion.
– Flexion of trunk interferes with lung expansion on that side
Solutions to the constraint
• Erect stance – movement in vertical plane
• Bounding encourages breathing w/each gait
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Solutions to the constraint
• Aquatic air breathers:
– Use dorsal ventral flexion
– Use limbs simultaneously
Bird respiration • Most efficient respiration bc of flying and
endothermy constraints
• Lungs small, non expanding
• Air sacs hold great volumes, allow for unidirectional flow
• Inhalation
• Exhalation
• Lungs - parabronchi – exchange at air capillaries
Air through parabronchi
Bird respiration
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Bird ventilation • Uncinate processes
increase lever arm for rib cage ventral expansion
Bird syrinx
• Syrinx - similar to larynx, but after split into bronchi.
Mammal respiration
• Larynx has vocal cords, epiglottis
Breathing Talking
Nasal and oral cavities
• In mammals, the soft palate touches the epiglottis, allowing constant separation of food and air
epiglottis
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Humans are an exception
• Humans - Epiglottis does not contact soft palate. Modification for speech
– Young babies have
contact
soft palate
epiglottis
Mammal respiration • Bidirectional ventilation – dead air (20%)
• Greatest SA of tetrapods
• Pleural cavity, diaphragm
Costal ventilation
External
Intercostal
Internal
Intercostal
