A large surface 

A thin cuticle 

One can increase the surface area,partial pressure gradient between body and environment. 

Thick ness of diffusion barrier must be minimized. 

Blood with higher oxygen content meets water with the highest oxygen 

content so that oxygen diffuses into the blood. HIGH EFFICIENCY OF EXTRACTION !

Deoxygenated blood reaches the gills by way of afferent branchial arteries.  

The blood passes through the gill lamellae where it is oxygenated.

It then passes to efferent branchial arteries and on to the body.

Directed away from a central organ or section 

An element vessel 

Afferent Definition, give an example 

Carrying inward to a central organ, 

Gill Arch 

Fish open their mouth while swimming foward. They alter gape to change flow over the gill. 

if a fish swims forward with its mouth open, water will flow across the gills without active pumping by the muscles surrounding the buccal and opercular cavities. 

The fish does not need to use the muscles around its buccal and opercular cavities to move water through the gills. However the fish is swimming which the opened mouth may increase drag and increase the cost of locomotion.

The Electric Eel. 

Mouth lined with papillae.

-Unidirectional pumping of water over respiratory epithelium (tissues), 

-Tissues folded into filaments and folded again in secondary lamaelle

-Countercurrent blood flow

-Filaments stacked very close together forming a mesh. 

Few fish, some reptiles, mammals and birds. 

Change volume and pressure of thoracic cavity, to draw air in , elastic recoil pushes air out. 

-Air flows directly into posterior sacs and dorsobronchii

-Air from posterior sacs flow into lung

-Air from lung flows into anterior sacs

-Air from anterior sacs flows to outside 

-Increse Surfarce Area

-Air: large lung 

-Water: large gill, primary secondary lamallae

-

Blood flow relative to air/water flow 

-air to blood: High, little selective pressure 

-water to blood: Low, great selective pressure to maximize

expansion of ribcage by sucking in air

-expiration is partly passive

-bi directional and moves air tidally 

-feeding and ventilation decoupled 

-ventilate lungs more frequently. 

Cells of respiratory system : 

Type I

-most abundant 

-major part of lung epithelium 

-squamous, epithelial cells with platelike structure

Cells of respiratory system : 

Type II

-Have surface villi

-produce surfactant 

Cells of respiratory system : 

Type III

-Mitochondria rich, with brush border

-rare cells involved in NaCl uptake from lung fluid 

maintain internal conditions at relative constant state despite changes in external conditions 

-They can live in a wide variety of habitats

Closely related species are adapted to different environments. 

-Lack of phylogenetic affinity of phenotype. 

Fish- selective pressure to improve gas exchange 

ventilation- unidirectional water flow over gills. 

- perfusion- opposite direction of water flow. (countercurrent,maximal extraction of O2)

-during excersice

-oxygen limitation 

-oxygen 

-branchial cavity

internal chemoreceptors

oxygen 

-Extracellular 

-54%

Right Shift Curve

-increased blood PCO2 

-Decreased pH

-Higher P50 

Haemocoel -Open space

Haemolymph- fluid

-blood flows in a continuous circuit 

-rapid delivery of O2 to tissues. 

-venolymphatic

-pretetrapod stage

-early tetrapod stage 

-higher ectotherm stage 

-avian stage

-mammalian stage