What is the complication of the structure of the circulatory system in amphibians compared to fish?
Fish and amphibians are cold-blooded animals, that is, their body temperature depends on the ambient temperature, since venous and arterial blood mix in the heart.
Fish have one circle of blood circulation, a two-chambered heart, consisting of 1 atrium and 1 ventricle. The heart contains venous blood, which enters the gills through the abdominal aorta. There, the blood gives off carbon dioxide, turns into arterial and enters the spinal aorta through the branchial arteries. Arterial blood in organs and tissues gives off oxygen, turns into venous blood and returns to the heart.
Amphibians have a second circle of blood circulation, as lungs appear. The blood goes from the heart to the lungs, takes oxygen, returns to the heart. This circle is called pulmonary or small.
The second circle of blood circulation – large – supplies blood to all organs and tissues.
The heart of a frog, unlike fish, is three-chambered: 2 atria (left and right), 1 ventricle. A septum appears in the ventricle, but it is incomplete, so the blood (venous and arterial) mix, and the organs receive mixed blood.
