Mohammad Amin Fallah
The cardiovascular system consists of heart, blood vessels, and blood. One of the main functions of the system is to transport oxygen from long to the tissues and transporting the nutrients and hormones to various organs, in addition to bringing the waste products to the kidneys for filtration. Blood also contains cells of the immune system and transports them to sites of infection, and produces clots by supplying thrombocytes and coagulation factors following injury to blood vessels. Transporting fluids over distances no matter how long needs pumps. The heart is a four chambered pump consisting of muscle tissue that transports blood. It is divided into left and right sides. The right side of the heart receives blood from venous system and pumps it to lungs. Blood then passes into the left side of the heart, where it is pumped to the body. Oxygenated blood leaves the heart through arteries and returns to heart with low oxygen concentration via veins. Hence, the system of blood vessels can be described as being consisted of three sub-systems based on the vessel categories. The arterial system and the venous system as described above, and microcirculation system that is consisted of small blood vessels in which solutes and solvents are exchanged with tissue. The structure of vascular system is adapted to its function. The arterial system is a high pressure and high-flow-rate system. The system is highly adaptable duo to the complex structure of vessel. Blood vessels consist of endothelium, smooth muscle cells, and extracellular matrix. Arteries are consisted of three layers: the intima, the media, and the adventitia. The intima is composed of the endothelium and a layer of extracellular matrix consisting of proteoglycans and collagen. The media consists of extracellular matrix and smooth muscle cells beneath an internal elastic lamina, providing structure and elasticity to the vessel. Contraction and relaxation of the smooth muscle cells regulate the blood vessel's diameter. The adventitia is a layer of loose connective tissue, smooth muscle cells, and fibroblast. Capillaries and lymphatic vessels outer portion of the arterial wall are located within the adventitia. Capillaries are the sites of fluid and mass transfer between the blood and the tissue.