The lymphatic system

This body system consists of lymph vessels that carry lymph from the tissue spaces between cells all over the body to lymph glands, or nodes. Lymph is a clear fluid that derives from plasma in blood from which proteins and other nutrients have been removed. Lymph drains from the bloodstream into capillaries and then into the lymph vessels. The flow of lymph is controlled by muscle contractions and valves. Invading organisms are trapped in lymph glands dotted throughout the lymphatic system. Here they are attacked by scavenging white blood cells called macrophages. Lymph glands also produce lymphocytes, another form of white blood cell. Some lymphocytes (B-cells) produce antibodies that attack antigens on the surface of an invading organism (see page 206); other lymphocytes (T-cells) destroy invading organisms directly.

Lymphocytes have the ability to remember invaders that they have come across before, and so respond quickly if the body is invaded again. On the other hand, the immune system can fail to spot invaders, or it can overreact— by developing allergies—or react abnormally to the body's own tissues, as in autoimmune diseases such as rheumatoid arthritis (see page 197). Alternatively, it may fail to recognize that its own cells have begun to function abnormally, hence the development of cancer.

Lymph drains from body into right and left subclavian vein

White blood cells migrate from bone marrow to thymus gland, where they develop into T-cells

Adenoids are glandular swellings that protect against respiratory infections

Tonsils are lymphoid tissues that guard against inhaled or ingested organisms

Enzymes secreted in stomach destroy ingested organisms

Peyer's patches are clusters of lymph tissue in lower small intestine

Lymph capillaries are smallest vessels in lymphatic system

Lymph vessels lie just beneath skin and roughly follow venous system

IMMUNE SYSTEM The immune system is a complex network of glands, vessels, tissues, and organs that attempt to eliminate harmful organisms that might cause infection or disease in the body. Lymph vessels cover the whole body and are studded with lymph glands, masses of lymph tissue in which invading organisms are attacked. Lymph from all over the body is filtered by flowing through lymph glands before draining back into the bloodstream.

Lymph drains from body into right and left subclavian vein

White blood cells migrate from bone marrow to thymus gland, where they develop into T-cells

Lymph capillaries are smallest vessels in lymphatic system

Lymph vessels lie just beneath skin and roughly follow venous system

Adenoids are glandular swellings that protect against respiratory infections

Tonsils are lymphoid tissues that guard against inhaled or ingested organisms

Enzymes secreted in stomach destroy ingested organisms

Peyer's patches are clusters of lymph tissue in lower small intestine

White blood cells are generated in bone marrow

Skin is first defensive barrier against invading organisms

White blood cells are generated in bone marrow

\ Lymph gland is enclosed mass of lymph tissue that acts as filter

Skin is first defensive barrier against invading organisms

CHRONIC FATIGUE SYNDROME (CFS)

Also known as myalgic encephalomyelitis (ME) and postviral syndrome, CFS was first recognized as a condition in conventional medical circles in the 1990s. Its symptoms mimic many other illnesses. It has been described as a physical illness brought on by stress. Three times more women than men are affected in the developed world.

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