Different Types of Circulatory Systems
A large number of invertebrates do not possess a circulatory system. The cells within their bodies are close to the environment for gases, nutrients and wastes to move in and out of the cells by diffusion. Land animals have multiple layers of cells and possess a different circulatory system from invertebrates. Essentially, there are two types of circulatory systems in higher animals. They are the open circulatory system and the closed circulatory system. We will look at each one briefly.
1. Open Circulatory System: The heart and capillaries are lacking in this type of system. Blood vessels, which are joined to open sinuses, exist that push the blood along like pumps. Blood is forced from the vessels into the sinuses, where it bathes the organs. At the same time, various other vessels receive blood from the sinuses and send it back again to the vessels for pumping. This type of system is found in arthropods such as insects and spiders, as well as some mollusks. The system is not very efficient and there are many limitations to it when compared to the closed circulatory system.
2. Closed Circulatory System: In this type of system, blood flows through a closed system of blood vessels. The blood vessels include arteries, veins and capillaries. Diffusion takes place between the capillaries and the tissues and organs of the animal of the various nutrients, gases and wastes. Closed circulatory systems in humans have a functioning heart that acts as the primary pump for the blood. There are different types of closed circulatory systems found even in vertebrates. For example, fishes possess a system where the heart is two-chambered, frogs have a closed circulatory system with a three-chambered heart and humans have a four-chambered heart.
The circulatory system in humans has three main components to it. These are the pulmonary circulation, systemic circulation and coronary circulation. We will first discuss the anatomy and functioning of the heart, and then we will examine the various aspects of the circulatory system.