Most vertebrate animals have a thymus gland. Until the early 1960s, its function was a mystery. Around that time, the thymus gland was determined to be prominent in the body’s immune system development.
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Human thymus glands are situated under the breastbone in the top portion of the chest. The gland is pinkish gray, spongy and flat. In other animals, the gland is located in the neck or chest regions.
Size & Growth
A newborn baby’s thymus gland is typically the size of an infant fist, which is large in relation to the rest of the baby’s body. It normally weighs about 1.2 ounces and grows as the child grows into puberty, when it ceases to enlarge. At this point, the gland starts to shrink and incorporates itself into the tissue around it.
As soon as a fetus starts to develop, the thymus gland sends lymphocytes into the bloodstream to create T cells. T cells develop the body’s immune system. Several months after the child is born, a properly functioning thymus gland has provided it with an immune system that lasts a lifetime. Although the lymphoid tissues continue to develop, the precise substance that causes this had not been determined as of 2010.