blood_vesselsThe vascular system is composed of arteries, veins, between which are found the capillaries. The three types of blood vessels have different structures. They all have an inner cell layer in common which is suitable for blocking blood coagulation.

Arteries are blood vessels with thick, muscular walls that carry blood away from the heart to the periphery. By leaving the heart together with the aorta and after branching out successively, they lead into the capillary system.

They are also called pulses as the contractions of the heart produces a pulse within the artery. Their walls are thicker than those of the veins. They are less in number than the veins of the body.

Veins: carry blood towards the heart from the periphery so they are also called varicose veins. In contrast to arteries they begin to run with tiny branches then continue to merge into successively larger branches. Their walls are thinner and their cavities are wider than those of the arteries. They contain valves that prevent blood from flowing back. The tubes are filled with the returned blood so that they block the lumens of veins, so the blood can only flow towards the heart and not back in a healthy vascular system and with healthy valves. The heart, the chest and the muscular pump help the circulation within them.

Capillaries: are small blood vessels found between the arteries and veins. They are typically able to widen and to become narrow to a great extent. Their walls are very thin which can only be seen with a microscope. Consequently, they give place to the transmission of nutrients and oxygen from blood, as well as to the absorption of carbon dioxide and waste substances from tissues. The capillaries occur in various tissues in different density and most of them are confined and at rest. Their total cross section is the widest part of the vascular system. When they are at rest about 10% of them carry blood, the others are in a confined state.