![]() Though the circulatory system of fish is simple when compared to that of humans and other mammals, it serves an important purpose by illustrating the different stages of evolution of the circulatory system in animals. The oxygenated blood is supplied to the cells in the body, and the cycle continues. The venous blood is carried to the heart, which pumps it to the gills, where the carbon dioxide gets replaced with oxygen. Arteries carry the oxygenated blood (from the gills) throughout the body.Īrteries branch into arterioles, which drain into capillaries, where the arterial blood becomes venous blood, as it supplies oxygen and other nutrients to the cells and absorbs carbon dioxide and waste materials. absorption of oxygen from water and elimination of carbon dioxide. Gills are the primary respiratory organs of fish. The main function of this structure is to reduce the pulse pressure generated by the ventricle, in order to avoid damage to the thin-walled gills. Conus arteriosus has many valves and muscles, whereas bulbus arteriosus has no valves. While bulbus arteriosus is the name of the chamber in teleosts (rayfinned, bony fish), the structure is known as conus arteriosus in elasmobranchs (fish with cartilaginous skeleton and placoid scales). ![]() ![]() The ventricle pumps blood inside it into bulbus arteriosus, a small chamber with elastic components. It generates enough pressure to pump the blood throughout the body. The ventricle is a thick-walled structure with lots of cardiac muscles. The atrium generates weak contractions so as to push blood into the ventricle. The sinus venosus has pacemaker cells that are responsible for initiating contractions, so that the blood is moved into the thin-walled atrium, which has very few muscles. The veins carry the deoxygenated blood into the sinus venosus, which is like a small collection chamber. Capillaries are minute blood vessels located within body tissues, and they form the link between arteries and veins.Ĭapillaries with deoxygenated blood (contains carbon dioxide) drain into small veins called venules, which in turn drain into larger veins. Arterioles are small, thin-walled arteries that end in capillaries, while venules are tiny veins that are continuous with capillaries. While arteries carry oxygenated blood from the gills to the rest of the body, veins return deoxygenated blood from different parts of the body to the heart. they help in blood clotting.īlood vessels carry the blood throughout the body. The thrombocytes perform functions that are equivalent to the role of platelets in the human body, i.e. The white blood cells comprise an indispensable part of the immune system. The red blood cells or the erythrocytes contain hemoglobin, a protein that carries oxygen throughout the body. The blood contains plasma (the fluid portion) and blood cells. Usually, they are found one behind another. Unlike humans, the four parts of a fish heart do not form a single organ. Though it has four parts, the heart of a fish is considered two-chambered. The heart consists of an atrium, a ventricle, a thin-walled structure known as sinus venosus, and a tube called bulbus arteriosus.
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