Transcript Gas Exchange

Gas Exchange
Metabolic Pathways: Glycolysis
Glucose
2ATP (without O2 )
( Lactate
) Pyruvate
TCA
TCA
36ATP (with O2)
Metabolic Pathways: anaerobic
•
Lactate pathway – rapid but inefficient conversion of pyruvate to lactate –
used for burst work (muscle tissue temporarily. out of O2)
3ATP/pyruvate
•
Opine pathway – rapid but inefficient – used for burst work
3ATP/glucose (Opine is a class of amino acid derivitives, slightly different
ones in different organisms e.g. Octopine in Octopoids, Strombine in some
bivalves)
•
Succinate pathway – slower but more efficient than above – used in animals
living in anoxic environments (e.g. bivalves in anoxic mud flats,
endoparasites in anoxic parts of hosts) 4-6 ATP/glucose
•
Phosphogens – not a pathway but a class of phosphoamino acids that can
store energy from ATP during periods of relaxation and deliver it under
conditions of anoxia or exhaustion (phosphoarginine in invertes.
phosphocreatine in verts. , echinoderms have both, annelids have 4 others)
Gas exchange
In order for
gas to
diffuse
across a
membrane
it must be
in solution.
Therefore
gas
exchange
surfaces
must
remain
moist.
Oxygen Diffusion
• Organisms that live in aquatic, marine, or even moist terrestrial
environments and which have all tissues within 1 mm of the
moist integument, do not have specialized gas exchange
structures nor do they require a circulatory system to transport
oxygen. In some, such as nemertean worms a circulatory
system exists that functions to carry nutrients from the gut to
other tissues.
• Larger organisms and organisms living in low oxygen
environments have evolved such structures and circulatory
systems. The diffusion of O2 across such surfaces is most
efficient where the medium is in motion and the underlying
circulatory fluid is also in motion especially if it is moving in the
opposite direction
Oxygen Transport
• Water is not an efficient O2 carrier – compounds have evolved that
bind O but will give it up easily - Respiratory Pigments:
•
Haemoglobins - iron containing – in solution or in cells –
common among invertebrates.
•
Haemocyanins – copper containing – in solution only –
molluscs and some arthropods.
•
Haemerythrins – iron containing – in cells – more storage
than transport – some polychaetes, sipunculans, brachiopods
•
Chlorocruorins – iron containing – in solution – some
polychaetes
Mollusca: Bivalve Ctenidium
Mollusca: Generalized Circulatory System
Mollusca
Annelida: Polychaetes
• Parapodia as
multipurpose
structures
Adaptations: Snorkel Worm
Annelida: Oligochaetes, the Earthworm
Echinoderms: Echinoids
• Note the currents
in sea water,
water vascular
system and the
haemal system
containing
coelomic fluid
moved by ciliary
action allow gas
exchange across
podia and
ampullae.
Crustacea
Hexapoda – Tracheal System
Myriapoda
Cheliceriformes
Horseshoe
crab
Spider
Dealing with Change in O2 Availability
oxyregulator
high
Pc
O
O2
oxyconformer
uptak
e
low
low
high
Ambient O2 Tension (pressure of O2)
Dealing with Changes in O2 Availability
• Oxyconformer – reduces or increase uptake to match availability
can chnage metabolic activity and/or switch to succinate
pathway – usually found in organisms living in environments that
seldom fall very low in O2 tension or do so in a regular predictable
way.
• Oxyregulators – maintain uptake despite changes in availability
may change ventilation of gas exchange structures, change
blood flow and volume, change synthesis of respiratory pigments –
usually found in organisms living in environments which experience
occasional and unpredictable changes in O2 tension.
• Organisms vary in their ability to conform or regulate – thus react
differently to human induced changes in O2 tension. E.g. Tubifex sp.
and Asellus sp increase ventillation and respiratory pigment and
survive in polluted freshwaters where Hydra, and some crustaceans
can’t survive.
SOD
• Too much O in tissues can be harmful by forming superoxide
radicals that denature macromolecules. This a potentially serious
problem for organisms that harbor symbiotic algae in their cells.
• Many cnidarians and giant clams have evolved a system whereby
they synthesize superoxide dismutase (SOD) an enzyme that
eliminates superoxide radicals