The term circulation means movement to and from something. Similarly, the circulation of blood means that the blood is being moved around the body, typically in a closed system. It is the flow of blood from one organ of the body to another.

The circulatory system is also used to transport gases, nutrients, and wastes around the body organs. The waste or harmful substances produced in the body of an organism constantly need to be removed to keep the organism healthy and functioning. Different types of animals have developed different types of transport systems through their bodies for the exchange of these substances.

The Circulatory System

The circulatory system consists of organs that comprise the heart, blood vessels, and blood which is circulated throughout the body, be it a human or any other vertebrates, all part of the Kingdom Animalia. The circulatory system consists of two divisions, i.e., systemic circulation and pulmonary circulation.

The pulmonary circulation may be defined as a circular loop circuiting the right part of the heart, which carries de-oxygenated blood to the lungs. This de-oxygenated blood supplies oxygen to the lungs and then returns to the left part of the heart.

On the other hand, systemic circulation is a circular loop. It delivers the blood which is oxygenated beforehand, from the left part of the heart to the rest of the parts of the body, and restores the deoxygenated blood to the right heart through large veins known as the venae cavae.

Types of Circulation

Open Circulation

In animals, there are two types of circulatory systems: open and closed. Here, the blood rather than travelling in a closed vessel travels openly passing through every organ. Instead of the heart, there are blood vessels that are like pumps. They push the blood along. Instead of capillaries, blood vessels join right with the open sinuses.

Closed Circulation

The closed circulatory system of a few molluscs and all different kinds of vertebrates, higher invertebrates is generally much more structured and well-organised. There is a closed system that consists of arteries, veins, and capillaries. The cells are surrounded by the capillaries, thus they have an equal chance of getting food and nutrition and elimination of their waste products.

The Heart

The heart is a major organ of the body of humans/animals which pumps blood to each part of the body or body organs. It nourishes them with nutrients and oxygen to every cell. It also removes waste products. The oxygenated blood is then supplied through the left side of the heart (left ventricle), to the rest of the part of the body in the systemic circulation. Whereas the deoxygenated blood is supplied through the right side of the heart, to the lungs, so that the blood gets oxygenated in the pulmonary circulation.

Circulation in Various Animals

• Most animals only have only one heart. But some marine animals like octopuses and squids have three hearts. Two of three hearts help in pumping blood to the gills to take up oxygen, and the last one sends blood throughout the body.
• Worms are also unlike a typical animal, with five divided structures called aortic arches acting in the place of basic hearts. The hagfish which is sometimes also referred to as the slime eel has only one true heart and three accessory pumps helping the blood to locomote.
• Some animals are even heartless. For example, the Jellyfish, starfish, and corals can make do without the presence of hearts. Starfish do not have blood, which explains the reason why no heart is required. Instead of a heart, they use their small hair-like projections called cilia to plunge the seawater with the help of their bodies and extract oxygen from the water.
• For the flow of blood, fish have a single loop and a two-chambered heart with just an atrium and a ventricle.
• Amphibians possess a 3-chambered heart with two atria and one ventricle.
• The majority of the reptiles have a three-chambered heart that is fairly identical to the amphibian heart. However, the ventricle is separated more constructively by a preliminary septum that results in a not so sizeable amount of mixing of oxygenated and deoxygenated blood.
• In mammals and birds, the heart is divided into four chambers: two atria (left and right) and two ventricles (left and right). Oxygenated blood is completely separated from deoxygenated blood, which improves the effectiveness of double circulation.

Conclusion

Circulation is important for the well-being of physiological needs and the proper functioning of the body parts of an animal. It helps to maintain the continuous flow of blood and oxygen throughout the body. The main organ responsible for it is the heart, which is present in most animals but depending on the type of animal, the number of hearts varies from one, two, three, etc., and even the absence of the heart in some cases.