Respiratory system
Function:
• Gas exchange with environment
Encouraging diffusion
surface area - gill lamellae, infolding
•
• Exchange CO2 for O2 depends on:
Diffusion ~ SA x gradient
distance
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
1
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
2
Ventilation mechanics
– Water flows over gills via suction and
force pump, using branchial muscles
Fish respiratory systems
Fig. 18-6
• 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
Fish lungs
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
3
During the “age of fishes”
• Early freshwater bony fish would have low
O2 environments
• Pulse pump of most fish w/lungs,
amphibians
Lungs and swim bladders
• Even in fish, there is surfactant, glottis
Lungs vs. swim bladders
• Lungs later
developed a
hydrostatic fxn
• (swim bladder)
• Swim bladders
became dorsally
located
4
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
5
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.
Solutions to the constraint
• Erect stance – movement in vertical plane
– Flexion of trunk interferes with lung expansion
on that side
• Bounding encourages breathing w/each
gait
6
Solutions to the constraint
• Aquatic air breathers:
– Use dorsal ventral flexion
Bird respiration
• Most efficient respiration bc of flying and
endothermy constraints
• Lungs small, non expanding
– Use limbs simultaneously
• Air sacs hold great volumes, allow for
unidirectional flow
Bird respiration
• Inhalation
• Lungs - parabronchi – exchange at air
capillaries
• Exhalation
Air through parabronchi
7
Bird ventilation
• Uncinate processes
increase lever arm for
rib cage ventral
expansion
Mammal respiration
• Larynx has vocal
cords, epiglottis
Breathing
Bird syrinx
• Syrinx - similar to larynx, but after split
into bronchi.
Nasal and oral cavities
• In mammals, the soft palate touches the
epiglottis, allowing constant separation of
food and air
Talking
epiglottis
8
Humans are an exception
• Humans - Epiglottis does not contact
soft palate. Modification for speech
– Young babies have
contact
Mammal respiration
• Bidirectional ventilation – dead air (20%)
• Greatest SA of tetrapods
• Pleural cavity, diaphragm
soft palate
epiglottis
Costal ventilation
External
Intercostal
Internal
Intercostal
9