Respiratory System
Updated 4 November 2004
Body cavities (coelom
partitioning; slide
1)
A. Transverse septum
(fish, amphibians, most reptiles)
1. Pericardial
cavity, peritoneal (=abdominal) cavity (or pleuroperitoneal
cavity, if lungs present)
B. Pleuroperitoneal septum (crocodilians, some squamates, mammals)
1. Pericardial
cavity, pleural cavity, peritoneal cavity
C. Mammals –
complicated by ventral growth of [originally dorsal] lungs
1. Male mammals -
descend testes into scrotal cavity (may be seasonal)
D. Birds - air sacs
(outgrowths of lungs - permeate all major body parts, including long bones);
results in complex subdivision of coelom
E. Abdominal pores -
external openings (only in agnathans and some other
primitive fish)
1. Exit for gametes,
fluid balance
A. Function:
exchange of gases (O2, CO2) by passive diffusion -
necessity of respiratory system (maximum diameter for spherical aquatic organism
= 0.5 mm)
B. Requirements:
thin (diffusion), moist (maintain integrity; gases absorbed in solution),
highly vascularized, large surface area, exposed to
oxygen
1. Many mucous
membranes fulfill requirements (accessory respiratory systems); e.g., mouth,
pharynx, gut, cloaca (proctobranch);
skin (slide
2); amphibians, plethodontids (lungless); epidermal outgrowths (hairy frog, hellbender)
Primary respiratory systems (gills, lungs)
A. Functional (i.e.,
exchange at required rate), both gills and lungs require
1. Respiratory
system with pump (respiratory medium - air or water)
2. Circulatory
system with pump (blood)
1. Unidirectional vs.
tidal flow of respiratory medium
2. Exchange
efficiency (e.g., concurrent vs. countercurrent)
3. Physical support
of respiratory organ: water support (collapse in air) or structural support
4. Ventilation
1. Locomotion (=ram)
pump (sharks)
2. Dual pump (most
fish) slide
3
3. Buccal cavity (pharyngeal muscles)
D. Air
1. Pulse (=force)
pump (fish, amphibians) slide
4
2. Buccal cavity (pharyngeal muscles)
3. Aspiration
(=suction) pump (amniotes) slide
5 (ribs, intercostals)
4. Birds (sternal pump)
5. Crocodilians
(liver "piston" moved by diaphragmatic muscles)
6. Mammals (ribs +
diaphragm)
7. Most vertebrates
- ventilatory movements correlated with locomotory movements
E. Environmental
considerations
1. Water: low and
highly variable oxygen concentration; high cost of moving water
2. Air: high and
relatively invariable oxygen concentration, low cost of moving air
A. External - no
pharyngeal skeleton; e.g., larval fish and amphibians, also some adult
amphibians [=perennibranchs]
B. Internal -
supported by pharyngeal skeleton; e.g., fish
1. Structure slide
6
a. gill filament
(primary lamellae)
b. gill lamellae
(secondary lamellae)
2. slide
7; septal gills (sharks); opercular
gills (teleosts)
3. Unidirectional
flow (except lamprey); slide
8
A. Structure –
homologous, evagination of gut, gas-filled
B. Functions –
hydrostatic organ, air-breathing
1. Lung primitive;
air breathing in fish (survive in warm and/or low O2 water); slide
9, slide
10, subdivided into faveoli in some
2. Physostomous, physoclistous (swim bladder -
hydrostatic organ); advanced (slide
11)
C. Evolutionary
reversals between respiration and buoyancy control are common
1. At least >23
genera actinoptergians rely on air breathing to such
an extent that gill area is reduced
D. Tetrapods (lungs retain connection to gut; differentiated along
length)
1. Glottis®larynx®trachea®bronchi®bronchioles®lungs
2. Lung structure
(trend increased surface area)
a. sac-like, no
subdivisions (e.g., salamanders)
b. variously
subdivided (especially anteriorly)
c. simple (septal): frogs, some reptiles (faveoli
- each opens into common central chamber)
d. more complex
(spongy)
1) turtles,
crocodilians, some squamates (faveoli);
snakes (right lung only; anterior®respiratory-posterior®saccular)
2) mammals
(alveoli); bronchioles terminate in separate chambers (surface area 10x frog)
E. Other functions
of gas bladder
1. Sound production
– fish
2. Muscles vibrate
on bladder (drum)
3. Shunt air back
& forth to gut (rapid burping)
4. Rub bones/teeth
(pharyngeal) together
5. Sound production
– tetrapods
a. larynx - frogs (vocal
sac resonator), few lizards, mammals
b. syrinx - birds
6. Sound reception
(compressible - transmit to inner ear)
a. bladder
extensions in fish (slide
12); snake lungs
b. Weberian ossicles (slide
12)
1. Paradox - high
metabolic rate but small lungs (high efficiency)
2. Structure
a. nonvascular air
sacs (lung outgrowths); slide
13);
1) functions:
temperature regulation, respiration (facilitate 1-way flow)
b. lungs have little
expansion
c. air flow complex
(slide
13); inspired air®through lungs (no
exchange)®posterior air
sacs®parabronchi (crosscurrent exchange)®anterior air sacs®expiration
3. Air sacs also
present in some reptiles (how evolve - function?)
G. READ
1. Form and function
2. Evolution of respiratory
organs