Circulatory system

How it works and why its important

The function

The circulatory system is the network of veins, arteries and blood vessels that transports blood from heart, services the body's cells and then re-enters the heart.

The relationship between the structure and function of arteries,capillaries and veins.

Arteries have a thick outer layer of longitudinal collagen and elastic fibers to prevent leaks and bulges. They have a thick wall which is essential to withstand the high pressures. They also have thick layers of circular elastic fibres and muscle fibres to help pump the blood through after each contraction of the heart. In addition the narrow lumen maintains the high pressure inside the arteries.

Veins are made up of thin layers with a few circular elastic fibres and muscle fibres. This is because blood does not flow in pulses and so the vein walls cannot help pump the blood on. Veins also have thin walls which allows the near by muscles to press against them so that they become flat. This helps the blood to be pushed forwards towards the heart. There is only a thin outer layer of longitudinal collagen and elastic fibres as there is low pressure inside the vein and so little chance of bursting. Finally, a wide lumen is needed to accommodate the slow flowing blood due to the low pressure.

Capillaries are made up of a wall that is only one cell layer thick and results in the distance for diffusion in and out of the capillary being very small so that diffusion can occur rapidly. They also contain pores within the their wall which allow some plasma to leak out and form tissue fluid. Phagocytes can also pass through these pores to help fight infections. In addition, the lumen of the capillaries is very narrow. This means that many capillaries can fit in a small space, increasing the surface area for diffusion.

How the blood travels through the heart.

2 major disorders that occur within this system

1 of the major disorder is

Polyarteritis Nodosa

Ployarteritis nodosa -- PAN -- is a serious inflammatory disease of the small to medium sized arteries. Many body systems are involved, including the skin, central nervous system, heart, kidneys and intestinal tract. PAN is commonly associated with hepatitis B infection, but in most cases the cause for the illness is unknown. Symptoms of PAN are quite variable, although fever, night sweats, weight loss, fatigue, and muscle and joint aches are typical. Treatment of the disease depends on the extent of the illness, and which parts of the body are involved. Corticosteroids and other immunosuppressive drugs are often used.

The 2nd one is

Arteriovenous Malformations

Arteriovenous malformations -- AVMs -- are abnormal tangles of blood vessels within an area of the circulatory system. They typically develop before or right after birth. AVMs that form in the brain or spinal cord can result in particularly severe problems and even death. Most people with AVMs in the brain or spinal cord experience few, if any symptoms. If they do occur, it is due to a decrease in oxygen to the area, bleeding, or pressing on a vital structure. Headaches, seizures and paralysis are some possible side effects.