Gas Exchange structures - Insects and Fish

Gills

The respiratory organs of fish specialized for extracting dissolved oxygen from water.

Operculum

A bony flap that covers and protects the gills in bony fish and aids in pumping water over them.

Gill Arch

A curved bony support structure that holds the gill filaments and gill rakers in place.

Gill Filaments

Long thin projections extending from the gill arch that increase the surface area for gas exchange.

Lamellae

Microscopic highly vascularised folds on the surface of gill filaments where gas exchange takes place.

Counter-current Exchange

The mechanism where fish blood flows in the opposite direction to the water flowing over the gills maximising oxygen absorption.

Concentration Gradient

The difference in oxygen concentration between water and blood maintained across the entire lamellae by counter-current flow.

Spiracles

Small pores or openings on the exoskeleton of an insect that allow air to enter and leave the respiratory system.

Tracheae

An internal network of large air-filled tubes in insects that carry oxygen throughout the body.

Taenidia

Spiral bands of chitin that line the tracheae to keep them open and prevent them from collapsing.

Tracheoles

Tiny highly branched fluid-filled tubes at the ends of tracheae that deliver oxygen directly to body cells.

Tracheal Fluid

Fluid at the tips of tracheoles that retreats into muscle tissues during activity to increase the surface area for gas exchange.

Surface Area to Volume Ratio

A structural adaptation maximised by both lamellae (fish) and tracheoles (insects) to optimize the rate of diffusion.