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gas exchange

passive diffusion. due to partial pressure across an exchange surface.

passive diffusion

limited by 1. surface area - thin, multi-branching gills, lungs, from sacs to aveoli 2. must work with circulatory system (a second pump) 3. resistance by the tissue barrier - a thin moist membrane

cellular and chemical respiration

deriving energy from aerobic breakdown of fuels. delivery of O2 to the tissues and removal of CO2

external respiration

exchange between environment and blood

internal respiration

exchange between tissues and the blood


active movement of the respiratory medium (air or water) across the exchange surface (barrier between the blood and the environment


ventilation in water. unsuitable for breathing in air (collapse without water). one way flow of water.

internal gills

associated with the pharyngeal arches, slits, and pouches. covered with interbranchial septa (elasmobranchs). osteichthyans: opercula

external gills

larvae, some adult amphibians (neotony)


adaptation for breathing air. all internal. true one is ventral to digestive tract, arise as outpocketings of the gut (endoderm), glottis, trachea, tronchi, bronchioles

tidal breathing

two-way breathing

freash air for exchange

tidal volume - dead space

total volume

tidal volume + residual volume

gas bladder

usually a single sac. dorsal to the digestive system. same embryonic origins as lungs. dual functions, not mutually exclusive, unclear origins, buoyancy and gas exchange. "lungs" found in one placoderm species. no lungs or gas bladders in agnathans or elasmobranchs

cutaneous respiration

different contributions in different organisms. amphibians - plenthodontidae, no lungs or gills. humans - mostly CO2 loss upto 5%. bats - eliminate upto 12% of CO2 through wing membranes. reptiles - very little (scales)

the chorioallantoic membrane

amniotic (bird and reptile) eggs. highly vascularized, adjacent to the porous shell.


ventilatory mechanisms for prochordates and larval agnathans

relatively passive ventilation

external gills, ram ventilation (as swimming opens mouth, goes through and come out of gills)

muscular pumps

active movement. dual pump - buccal and opercular: work in series, suction phase - force phase, water ventilation

buccal pump

pulse pump. forces air into lungs of gas bladders (2 or 4 stroke)

aspiration pump

amniotes. lungs filled by negative pressure, muscular pump consists of abdominal muscles, intercostals, diaphragm. buccal cavity is no longer a ventilatory organ - feeding and respiration "decoupled"

agnathan ventilation

cilia in larvae, gills are medial to branchial arches instead of lateral (larvae), velar pump and muscular pharyngeal pouches in adults. parasitic adult lamprey: 2 way pump when attached to host.

elasmobranch ventilation

gill lamellae are lateral to branchial arch: holobranch, hemibranch, respiratory unit. 2 stage buccal/parabranchial pump provides constant flow from pharynx, over gills, through gill slits. intake through spiracle allows for breathing when sub-terminal mouth is on substrate.


arch and lamellae


half of holobranch

respiratory unit

2 facing hemibranchs

osteichthyan ventilation

lateral gills are V shaped, lamellae are subdivided. bony or cartilaginous operculum covering the branchial arches - allows for a dual (buccal and opercular) pump. swim bladders and gas bladders. air bladders

air bladders

for air-breathing, sound amplification (hearing), sound production (communication)

lung fish ventilation

sarcopterygians. faveoli


small interconnected compartments

amphibian ventilation

ventilations depends on buccal and pharyngeal pumping - no diaphragm or ribs. gills - some not all adults, most larva, not all, internal or external. lungs - most, not all adults. septal: increased surface area, faveoli, more gas exchange in anterior, less in posterior. adaptations in larvae to increase efficiency of buccal pumping and to attach to surfaces.

reptile ventilation

highly keratinized epidermis make cutaneous respiration impractical, well-developed lungs with numerous faveoli, muscular pumping (aspiration) from intercostal and other somatic muscles, occasionally, passive expiration. posterior portion of lungs often less divided and less vascularized, greater contribution from anterior

crocodilian ventilation

intercostals contract to expand ribs. diaphragmatic muscles (connected to posthepatic septum) move the liver like a pison. gastralia.

snake ventilation

left lung is reduced or lost. elongated opening to trachea ("trenchlike")

turtle ventilation

ribcage cannot expand due to the rigid shell. internal sheets of muscles contract and expand to aspirate the lungs (diaphragmaticus, others in tortoises attach to limiting membrane, move it to change internal pressure). cutaneous exchange during hibernation.

mammal ventilation

well-developed lungs with bronchioles terminating in alveoli, muscular diaphragm as muscular pump - passive exhalation due to elatic recoil. tidal (2 way) breathing with residual volume.

bird ventilation

no cutaneous respiration. trachea, paired lungs, muscular aspiration pump. air sacs (non-respiratory tissue) attached to respiratory system. increased surface area not due to alveoli or faveoli but rather a series of fine tubular passages called parabronchii with tiny tubes called air capillaries. one- way system.


dead-end sacs, very thin, for gas exchange. very extensive increase in surface area (10x reptiles)

air capillaries

tiny tubes that are the site of gas exchange

fish gas transfer

countercurrent. most efficient transfer of gases.

bird gas transfer

cross current. very efficient transfer of gases. no residual volume.

lung gas transfer

faviform or alveolar. uniform pool. stable gas concentrations

ventilation: perfusion ratio

amount of O2 available: amount taken in. rate of ventilation needs to match the rate of gas exchange and circulation to be efficient. diffusion slower in water, water harder to move than air. V:P lower in air. Fish 35:1. Reptiles 5:1. mammals 1:1

ventilation in water

highly efficient countercurrent flow. high (>80%) extraction of oxygen. high metabolic cost. CO2 highly soluble in water.

ventilation in air

tidal breathing less efficient. lower (25%) efficiency oxygen extraction. lower cost metabolically.

acid base regulation

elimination of CO2 is another huge hurdle to overcome in order to breathe air. need to eliminate H+ to maintain pH balance and oxygen-carrying capacity of hemoglobin

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