Circulation is the movement of blood around the body. There are a number of different systems of circulation including pulmonary, systemic and cardiac.

In pulmonary circulation the right side of the heart receives deoxygenated blood and pumps it to the lungs for oxygenation.

The left side of the heart receives oxygenated blood from the lungs and pumps it to the rest of the body; this is known as systemic circulation.

The heart requires its own blood supply in which oxygenated blood flows from the left ventricle to the ascending aorta. This splits between the right and left coronary aorta, which in turn feed into the heart tissue. Deoxygenated blood is directed from the heart to the coronary sinus before entering the right atrium. This is known as coronary circulation.

The contracting rhythm of the cardiac cells needs to be controlled so that the heart functions in a co-ordinated manner. This control comes from the autorhythmic cells and the sinoatrial node, the heart’s pacemaker. The rate of the heartbeat is also controlled by the autonomic nervous system and some hormones.

The heart rate is the number of beats per minute. The average resting male rate is 70 beats per minute (bpm), whilst the average resting female rate is 75bpm.

Blood pressure is the force exerted by the blood on the walls of a vessel. It is this which keeps the blood moving, and comes about from the contractions of the left ventricle. As the blood moves further away from the left ventricle, the pressure falls.

The beating of the heart and the circulation can be measured by the pulse, which is a pressure wave felt in the arteries. This wave corresponds to the beating of the heart, and can be felt at any point where an artery lies near the surface.

A variety of vessels pump blood from the heart around the body, and they form a closed system of tubes. These either carry blood away from the heart and take the form of arteries and arterioles and branch through tissues as capillaries, or carry blood towards the heart as veins and venules.

Arteries are large triple-walled vessels with a hollow centre through which blood flows. The artery walls consist of an outer layer of fibrous tissue called the tunica adventitia, a middle layer of smooth muscle and elastic tissue called tunica media and an inner layer of squamous epithelium known as the tunica intima. They carry blood away from the heart to provide tissues and organs with oxygen and nutrients.

Elastic arteries such as the aorta have thin walls, and their tunica media has more elastic fibres than muscle fibres, so that they can stretch and recoil as the blood flows from the heart to smaller arteries.

Another type of artery is the muscular artery; the brachial artery is an example of a muscular artery. Muscular arteries are medium sized and their tunica media has more smooth muscle fibres making the walls thick and capable of greater vasodilation and vasoconstriction, or expansion and contraction.

Once the blood has flowed from the arteries into the arterioles it moves into the capillaries. These are the smallest of the blood vessels and the only ones to have semi-permeable walls, meaning they have gaps in them. It is here where oxygen and nutrients can pass into the tissues surrounding them in exchange for carbon dioxide and waste. Interstitial fluid is the intermediary that allows this exchange to take place.

The capillaries are microscopic vessels that pass through tissues and connect the arterioles and venules. This is known as microcirculation. Vasoconstriction and vasodilation enable the capillaries to help adjust body temperature as these processes alter blood flow.

The walls of the capillaries are made up of a single layer of endothelium and a basement membrane which allows nutrients, oxygen and waste to pass between the interstitial fluid.

Veins have a similar structure to the arteries; however they have thinner walls due to lower levels of muscle and elastic tissue. Some veins also have valves similar to those in the heart which prevent backflow.

Blood Circulation And The Arteries Of The Thorax

The thoracic aorta has branches of arteries that supply the thorax and are divided into two groups. The visceral branches are arteries that feed the viscera, the internal organs of the body.These include the pericardial arteries which supply the pericardium, the bronchial arteries which supply the lungs, the oesophageal arteries which supply the oesophagus and the mediastinal arteries which supply the mediastinum.

The mediastinum is a group of structures in the thorax surrounded by loose connective tissue. It is the central compartment of the thoracic cavity. It contains the heart, the great vessels of the heart, oesophagus, trachea, phrenic nerve, cardiac nerve, thoracic duct, thymus, and lymph nodes of the central chest.

The parietal branches feed the wall structures and consist of the posterior intercostal and subcostal arteries; they supply muscles and the skin of the thorax, vertebral canal and mammary glands. The superior phrenic arteries supply the diaphragm.

The thorax is drained by a network of veins including the azygos, hemiazygos and accessory hemiazygos collectively called the azygos system. This system receives blood from the parietal and visceral branches of the thoracic aorta. The azygos feeds the superior vena cava or brachiocephalic veins.

The abdominal aorta has paired and unpaired branches that supply the abdominopelvic region and are divided into two groups. The visceral branches that serve the internal organs of the body are:

• The coelic artery which divides into three branches:

1. Common hepatic artery which supplies the liver, gall bladder, sections of the stomach, pancreas and duodenum
2. Left gastric artery which supplies the stomach
3. Splenic artery which supplies the spleen, pancreas and

• The superior and inferior mesenteric arteries supply the small and large intestines. Suprarenal arteries supply the adrenal glands, renal arteries supply the kidneys and gonadal arteries supply the gonads.
• The parietal branches that supply the structures of the body walls include the inferior phrenic arteries which supply the diaphragm, lumbar arteries which supply the spinal cord and muscles of the lumbar region and median sacral arteries which supply the coccyx, sacrum and rectum.

The blood from the abdomen returns to the heart through the inferior vena cava, which receives blood from smaller veins carrying blood from the branches of the abdominal aorta. Blood from the digestive organs passes through the liver before draining into the hepatic veins and into the inferior vena cava. The right and left common iliac veins drain blood from the lower limbs and unite to form the inferior vena cava.

Massage movements are performed with pressure being directed toward the heart following venous flow. This helps improve blood circulation and the components of blood reach their destinations more quickly with waste being removed more efficiently.