Blood vessels

There are three main types of blood vessel: arteries, veins and capillaries.

Arteries transport oxygenated blood from the heart around the body to all tissues and organs. The main artery, the large aorta, leaves the left ventricle of the heart and divides to form other arteries, which further subdivide forming a network of arteries all over the body. Arteries finally divide into small thinly-walled vessels called arterioles, which enter the capillary networks among the tissues. Arteries transport blood carrying oxygen, nutrients, hormones etc around the body. Artery walls have three layers of tissues: a fibrous outer layer, a muscular middle layer and an inner lining of smooth epithelium. The middle muscular layer of arteries is thicker than the muscular layer of veins and their lumen is smaller. Blood is pumped through the

Node Pathway
Exchange of substances between tissue cells and blood takes place

Artery to

Arterioles to

Capillaries to

Venules to

Vein

Figure 2.12a Blood flow from artery to vein. Figure 2.12b

Artery to

Arterioles to

Tissue fluid

Cells

Capillaries to

Venules to

Vein

Waste products pass out of the cells into the blood via tissue fluid

Cells

Waste products pass out of the cells into the blood via tissue fluid

ARTERIOLE END OF CAPILLARY

Nutrients and oxygen pass out of the blood into the cells via the tissue fluids

VENULE END OF CAPILLARY

ARTERIOLE END OF CAPILLARY

Nutrients and oxygen pass out of the blood into the cells via the tissue fluids

VENULE END OF CAPILLARY

Figure 2.12a Blood flow from artery to vein. Figure 2.12b

Cells Blood

Transfer of substances between the blood and cells.

arteries, around the body, by the contraction of the heart; with each contraction the blood is forced along. The rate at which the heart is beating can be felt as a pulse at arteries that lie near the surface, such as the radial artery at the wrist.

Veins transport deoxygenated blood back to the heart. The walls are similar in structure to those of arteries but the middle muscular layer is thinner. The inner layer of epithelial cells is folded to form valves. These valves prevent the backward flow of blood. The lumen of veins is larger than that of arteries.

Blood is pumped along the veins by the contraction and relaxation of muscles and by the expansion and contraction of the thorax and diaphragm during breathing. If muscles are not contracting, e.g. during long periods of standing and inactivity, gravity exerts a downward force. If the valves are weak, blood 'pools' in the veins. This pressure overloads the veins and the wall bulges outwards, causing the condition known as varicose veins. Regular leg massage speeds up the flow of blood through the veins. This prevents overloading of the veins, which helps prevent varicose veins.

During periods of prolonged inactivity such as bed rest or sitting in cramped conditions for a long time, the flow of blood through the veins slows down and there is a risk of blood clots forming in the veins. A clot may attach to the vessel wall where it is called a thrombus or it may become detached and be carried in the bloodstream, where it is known as an embolus. The clot may end up blocking the blood supply to the lung with potentially fatal consequences. This is one of the greatest dangers of massage, making thrombosis an absolute contra-indication to massage (see page 116).

Capillaries are thin-walled, tiny vessels that form networks among the tissue spaces. Arterioles enter capillary networks and venules leave. The primary function of capillaries is to allow the exchange of gases, nutrients and metabolic waste between the cells and the blood. Arterioles bring oxygen and nutrients to the capillaries. These pass through the thin vessel walls into the tissue fluid and then through the cell wall into the cell. Carbon dioxide and metabolites pass out of the cell and into the blood in the same way.

Venules leave the capillary networks and join to form larger veins that transport the deoxygenated blood and the waste products of metabolism (metabolites) back to the heart via the largest veins, namely the inferior vena cava and the superior vena cava. These two large veins empty into the right atrium of the heart.

When the metabolic needs of the tissues are low, parts of the capillary network can shut off, limiting blood flow. More blood is then available for those tissues with greater metabolic needs. Thus blood flow can be shunted in this way to areas that require a greater supply of oxygen and nutrients, e.g. exercising muscles.

Massage aids the dilation of these surface capillaries by reflex action, promoting blood flow. An accumulation of waste products in the tissues, or tension in muscle fibres, exerts pressure on the capillaries and restricts blood flow. Massage helps to relieve this pressure, as it speeds up the removal of waste products and promotes muscle relaxation. Thus the pressure is reduced and normal blood flow through the capillaries is restored. This helps the recovery of the muscles and restores normal function.

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  • proserpio lucciano
    How Can One Massaging The Weak Vain In The Body?
    1 year ago
  • Taija
    How to massage vessels?
    1 year ago

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