Circulatory system
How it works and why its important
The function
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.
Right side of the heart
- Blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium of the heart.
- As the atrium contracts, blood flows from your right atrium into your right ventricle through the open tricuspid valve.
- When the ventricle is full, the tricuspid valve shuts. This prevents blood from flowing backward into the atria while the ventricle contracts.
- As the ventricle contracts, blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs where it is oxygenated.
Left side of the heart
- The pulmonary vein empties oxygen-rich blood from the lungs into the left atrium of the heart.
- As the atrium contracts, blood flows from your left atrium into your left ventricle through the open mitral valve.
- When the ventricle is full, the mitral valve shuts. This prevents blood from flowing backward into the atrium while the ventricle contracts.
- As the ventricle contracts, blood leaves the heart through the aortic valve, into the aorta and to the body.
The composition of blood, including plasma, erythrocytes, leukocytes and platelets .
Blood is a specialized body fluid. It has four main components: plasma, red blood cells, white blood cells, and platelets. Blood has many different functions, including:
- transporting oxygen and nutrients to the lungs and tissues
- forming blood clots to prevent excess blood loss
- carrying cells and antibodies that fight infection
- bringing waste products to the kidneys and liver, which filter and clean the blood
- regulating body temperature
The blood that runs through the veins, arteries, and capillaries is known as whole blood, a mixture of about 55 percent plasma and 45 percent blood cells. About 7 to 8 percent of your total body weight is blood. An average-sized man has about 12 pints of blood in his body, and an average-sized woman has about 9 pints.
Plasma
The liquid component of blood is called plasma, a mixture of water, sugar, fat, protein, and salts. The main job of the plasma is to transport blood cells throughout your body along with nutrients, waste products, antibodies, clotting proteins, chemical messengers such as hormones, and proteins that help maintain the body's fluid balance.
White Blood Cells (also called leukocytes)
White blood cells protect the body from infection. They are much fewer in number than red blood cells, accounting for about 1 percent of your blood.
The most common type of white blood cell is the neutrophil, which is the "immediate response" cell and accounts for 55 to 70 percent of the total white blood cell count. Each neutrophil lives less than a day, so your bone marrow must constantly make new neutrophils to maintain protection against infection. Transfusion of neutrophils is generally not effective since they do not remain in the body for very long.
The other major type of white blood cell is a lymphocyte. There are two main populations of these cells. T lymphocytes help regulate the function of other immune cells and directly attack various infected cells and tumors. B lymphocytes make antibodies, which are proteins that specifically target bacteria, viruses, and other foreign materials.
Platelets (also called thrombocytes)
Unlike red and white blood cells, platelets are not actually cells but rather small fragments of cells. Platelets help the blood clotting process (or coagulation) by gathering at the site of an injury, sticking to the lining of the injured blood vessel, and forming a platform on which blood coagulation can occur. This results in the formation of a fibrin clot, which covers the wound and prevents blood from leaking out. Fibrin also forms the initial scaffolding upon which new tissue forms, thus promoting healing.
A higher than normal number of platelets can cause unnecessary clotting, which can lead to strokes and heart attacks; however, thanks to advances made in antiplatlets therapies, there are treatments available to help prevent these potentially fatal events. Conversely, lower than normal counts can lead to extensive bleeding.
2 major disorders that occur within this system
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.