Respiration

Invertebrate Zoology
Week 4
Chris Foster
Respiration


- Involves gas diffusion across a membrane, O2 moves from high to low conc
- Rate of diffusion dependent on pressure gradient and properties of tissues [diffusion
coefficients]
- Distance between metabolizing tissues and a respiratory surface can be <1mm
[constraints on body with aerobic metabolism]
- Jellyfish and Anemones are large and solid, but outer and inner tissue is thin or in
contact with water / largely devoid of cells which lowers O2 demand.
Circulation Systems;
1. Open System;
o With large haemocoel [persistent blastocoel or expanded blood vessels
containing circulatory fluid]
o Arthropods and Mollusks
2. Closed System;
o Arteries and veins
o Found in annelids.
- Both require muscular pumps “hearts” / pairs of valved ostia [arthropod] / pulsating
blood vessels [annelids]
- Echinoderms and Hemichordates; intermediate system with small vessels connected
to large sinuses.
- Holothurian echinoderms; well developed closed system
- Isopod Crustaceans; larger muscular hearts and vessel like lacunae [closed system]
- Insects; open system, evolved trachea and tracheoles
o Air enters through spiracles [with valves]
o Trachea  tracheoles
o Tracheoles contain fluid
 Active metabolism, osmotic pressure of surrounding tissue increases
[flid withdrawn]
 Air in via tracheoles, air passed by diffusion through walls to the
tissues.
o System limits the size of the insect [more O2 available = larger the insect]


Blood; Respiratory Pigments;
- All urochordate, some mollusks/echinoderms and cephalochordate = blood is
colorless.
- All O2 contained in physical solution, more O2 carries by give volume = evolve
respiratory pigments [specialized proteins capable of binding reversibly to O2]
- Found in 1/3 of inverts, some occur in blood;
o Packaged into cells;
 Hemoglobin of some annelids/mollusks/echinoderms
 Haemerythrin of brachiopods and polychaetas.

, Invertebrate Zoology
Week 4
Chris Foster
o Dissolved in blood;
 Arthropods and mollusks = haemocyanins
 Annelids = chlorocruorin
o Protein found in body wall of nematodes, muscles of annelids, pharynx of
platyhelminths [lack of pattern suggestion gin dependent evolution]
Name Location Group Color
Haemoglobin In solution Widely Red with O2
In cells Distributed Blue without O2
Haemocyanin In solution Arthropod Blue with O2
Mollusk Colorless without O2
Chlorocruorin In solution Polychaeta Green = dilute
Worm Red = concentrated
Haemerythrin In cells Widely Violet with O2
Distributed Colorless without O2


- Common function; cooperatively O2 binding [O2 binding makes successfully easier
to bind more] Illustrated with a sigmoid curve:
o Fully saturated; adding O2 concentration will not change it
o ½ saturation pressure p50 [measure for affinity of O2 pigment
o Curve shifts RHS when increase in respiratory pigments // lower pH // higher
CO2 tension [Bohr Effect] to aid unloading of O2 at respiring tissues
o High energy demand [CO2 higher in metabolic tissues]
o Patterns;
1. Inverts that live in low O” environments have a higher affinity for O2
pigments
2. Lowest p50 values are hemoglobin’s of parasitic animals [inhabit
chronically low O2 environments]
3. Daphnia; exposure to low O2 induces a change in molecular structure of
respiratory pigment [low  high O2 affinity] to increase amount of
pigment [individual turns bright red]
4. Some species in O2 rich environments still have a high affinity for
pigments = considerable barriers of diffusion [usually a high O2
environment = low affinity for O2 pigments]
Gas Exchange Organs;
- Limit = S.A of organs [unspecialized in flatworms/long, thin nemertines and annelids]
- Increase in size, activity, protected impermeable coverings = evolution of
vascularized respiratory surface.
1. Gill like – Evaginated Surfaces;
o Ctenidia in mollusks // gill books in limulus // podia of echinoderms
o Blood pumped through heart opposite to direction of water flow [by lateral
cilia] typical of gills to maximize absorption [counter current flow]
2. External Organs;
o Freshwater forms
3. Invagination;