11 Biology By BISM Academy
18 – Evolution of heart in fishes and amphibians
HEART OF FISHES
Parts of heart. The heart of fishes has sinus venosus, an atrium, a ventricle, and bulbus arteriosus or conus arteriosus. Blood Flow Direction. Sinus venosus receives deoxygenated blood from the body, and then blood is passed to atrium, which on contraction passes it to ventricle. Ventricle has thick muscular wall. When the muscles of ventricle contract, they push the blood via conus arteriosus or bulbous arteriosus (proximal swollen portion of ventral aorta). Thus the heart of fishes works as a single circuit heart. The blood flows in one direction only, from sinus venosus to atrium then to ventricle and to ventral aorta via bulbus arteriosus or conus arteriosus to the gills and then to the body. The blood returns to the heart in the sinus venosus Coronary arteries. The oxygenated blood is supplied from dorsal aorta through coronary arteries, to the heart and is carried back by coronary veins from the heart).