The human circulatory system, in its most basic form, is actually a simple loop which starts and ends in the same place – the heart. It is believed to be a closed system because the blood neither enters nor leaves the system during its journey from the heart to different parts of the body, and back to the heart again. In this particular system, the continuous flow of the blood is the main component, as it is the one that is pumped through the loop over and over again.
The circulatory system is actually made up of five main parts:
The heart is a hollow muscular sac which is divided into four separate chambers. These chambers are separated by thin and muscular walls. These chambers would be the right atrium, right ventricle, left atrium, and the left ventricle. The function of the heart is to drive the circulation by contracting ad squeezing blood and making it circulate to the body.
The arteries are blood vessels which function by carrying blood from one place to another. It is a large type of smooth muscle that is controlled by hormones and other special signals from the nervous systems. Arteries function by carrying the blood away from the heart and sending it to other places in the body. They are also responsible for carrying the oxygen and other nutrients through the organs in the body. They are also necessary for the protection of the heart, as they are able to resist the high pressures that exist near it.
Arteries, in general, get smaller as they get further away from the heart. They will now be called arterioles, which are strong and have relatively think walls that defied their sizes. They also contain a high percentage of smooth muscle. Like the arteries, arterioles work by carrying the blood away from the heart and out into the different tissues in the body. Arterioles are very important because they are capable of regulating all the blood flow and blood pressure from the body.
The capillaries are the smallest blood vessels in the body and are mainly responsible for the deliverance of the oxygen and other nutrients to the tissues in the body. They are so small that you wouldn’t be able to see them without using a microscope. The walls of capillaries are generally one or two cells thicker. The process of the distribution of the oxygen to several tissues in the body is called diffusion, and it is the process that allows for the cells to receive food. Every organ in the body has specific capillaries, and their functions vary from one organ to the other
Unlike the arteries that are thick and very muscular, veins are very thin and are almost muscle-less. The walls of the veins are very thin such that you will be able to see the blood inside them. The main function of the veins is to carry the blood back to the heart. This blood is now devoid of oxygen and nutrients and is consequently loaded with waste products.