The blood is the liquid part that is constantly flowing throughout the body, composed of a liquid part called plasma and the solid parts of formed components which are the red blood cells, white blood cells, and platelets.
The last formed components of blood are the platelets or thrombocytes, which are the smallest of formed components of blood that help in blood clotting.
The blood vessels are the vast networks of small tubes that carry blood throughout the body, with arteries carrying oxygen-rich blood away from the heart, veins carrying deoxygenated blood back to the heart, and capillaries serving as a connection between arteries and veins.
The circulatory system has two types of circulation: the pulmonary circulation, which is the movement of deoxygenated blood from the heart and into the lungs, and the systemic circulation, which is the movement of oxygenated blood from the heart to the different parts of the body.
The heart, known as the pumping organ of the body, keeps the blood moving throughout the body and has four chambers: the left and right atrium which are responsible for receiving used blood coming from all parts of the body, and the left and right ventricles which are the pumping chambers.
Oxygen-poor blood enters the heart through two large veins, the inferior and superior vena cava, emptying blood from the body into the right atrium of the heart.
As the ventricle contracts, oxygen-rich blood leaves the heart through the pulmonic valve into the pulmonary artery into the lungs where it is oxygenated.
As the ventricle contracts, oxygen-rich blood leaves the heart through the aortic valve into the aorta to the arteries and eventually into the veins to complete the blood circulation in the body.
The circulatory system is a good example of how body systems interact with each other to keep the body alive, with each organ of the system working together to circulate blood throughout the body.