CVS Lec. 1

Introduction

The cardiovascular system is considered as the transport system of the body. This system has three main components: the heart, the blood vessels and the blood itself. The heart is the system’s pump and the blood vessels are the ways of delivery. Blood can be thought of as a fluid which contains the oxygen and nutrients the body needs and carries the wastes which need to be removed.
Blood vessels
Blood vessels are part of the circulatory system. Blood vessels play an important role in the transportation of blood around the body. There are three main types of blood vessels: arteries, veins and capillaries.

Arteries
Arteries are the blood vessels that carry blood from the heart to the body. It has a thicker, more muscular wall with extensive development of elastic tissue when compared with a vein, to cope with the extra pressure from the force of the heart’s pumping. They are stretched during systole and recoil during diastole, to prevent excessive rise (during systole) and excessive fall (during diastole) of blood pressure. The volume of blood in the arteries is called the stressed volume.
Arterioles
They are the smallest branches of the arteries. Their walls have less elastic tissue than arteries. They are the site of the highest resistance to the blood flow.

Venules and veins
The venules collect blood from the capillaries and coalesce to larger veins. Veins are the blood vessels that drain blood back from the body to the heart. It has thin, flexible walls when compared to an artery. Some veins, especially large ones, have valves in them to prevent blood from running away from the heart again, such as in the legs. The veins are called capacitance vessels because they contain the largest percentage of blood in CVS, which is about 65-75% of the circulating blood volume. The volume of blood contained in them is called the unstressed volume.
Capillaries
Capillaries are the smallest of blood vessels. They serve to distribute oxygenated blood from arteries to the tissues of the body and to feed deoxygenated blood from the tissues back into the veins. They are the site where nutrients, gases, water and solutes exchange between the blood and tissues. Their diameter is just sufficient to permit RBC in single file. The total area of all capillary walls in the body exceeds 6300 m2 in an adult.