Circulation in non avian reptiles and amphibians

Circulatory plan of most fish

Gills are in series with the systemic tissues and there is single circulation so the pressure produced by the heart must be sufficient enough to drive blood through the resistances of both the gills and systemic vasculature

What do fish hearts consist of?

Four chambers arranged in series with the ventricle providing the majority of the pressure to the blood

Most fish have at least some myocardium. what is the distribution of myocardium different for fishes

More active fish like tuna have more compact myocardium while less active fish have less compact myocardium

Fish with air-breathing organ have what?

The oxygen source in parallel with the systemic tissues

What is the advantages and disadvantages of air-breathing organ fish to have that oxygen source in parallel with the systemic tissues?

It is a disadvantage as the blood returning to the gills is more oxygenated as the oxygen rich blood from the air-breathing organ mixes with the oxygen poor blood of the tissues making oxygen transport less efficient as the gradient is smaller. It is an advantage because it provides an increase in oxygen availability for the spongy myocardium

How is an incompletely divided central circulation an advantage for intermittent air breathers

Since they do not breathe constantly, the air in their lungs loses oxygen over time. By using ventilation-perfusion matching, they can match the air in the lungs to the blood entering the lungs and bypass the lungs and send blood directly to the body if the lungs are not-ventilated. If the air in the lungs is deoxygenated, they bypass them so save energy from pumping to the lungs

Can oxygenated and deoxygenated blood be selectively distributed in amphibians?

Their ventricles lack a septum but spongy myocardium of the ventricle and spiral fold of conus arteriosus can produce selective distribution of oxygenated and deoxygenated blood but less effective. Oxygenated pulmonary venous blood is directed to the systemic arteries and deoxygenated systemic venous blood is directed towards the pulmonary arteries

Can amphibians maintain different blood pressures in the systemic and pulmonary circuits?

No, this is only possible with complete separation of the ventricles and amphibians have partial separation

Can cardiac output be redistributed between the two circuits in amphibians?

Yes as regulation of relative vascular resistances within the pulmonary and systemic circuits can cause redistribution of cardiac output

Skin in amphibians

It is an important site of oxygen uptake in amphibians. Deoxygenated blood is preferentially pumped to the skin via the pulmocutaneous arteries and veins from the skin connect to the veins from the systemic system before entering the heart again. This could be an advantage as it increases oxygen availability to spongy myocardium

Can non-avian reptiles selectively distribute oxygenated and deoxygenated blood?

Even though their ventricle is incompletely separated, they can do this by regulating relative vascular resistances within the pulmonary and systemic circuits. Pythons and varanid lizards can temporarily achieve complete separation during systole.

Can different blood pressure be maintained in the two circuits for non-avian reptiles

Not for most although it can be for pythons and varanid lizards when they achieve temporary complete separation