The First Lymphoid Organ to Develop Thymus

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nhia moua F4cJtI7HCMw unsplash 1

The first lymphoid organ to develop is the thymus. It begins as a small, red organ that can be found under either of the two lobes of your sternum. The thymus comes into play when our immune system is first established. This is where T and B cells mature from single cells into elite fighting forces known as macrophages, capable of rejecting self-antigens and ferreting out foreign invaders like bacteria and viruses.”

In this blog post, you will find out the anatomy and function of the thymus, including how it helps immune development in children. You’ll also learn about what happens when this tissue does not form properly or cannot function properly.

The thymus forms early in the developmental process — at two to four weeks after conception. By 11–14 days after conception, you can see its beginnings in the embryo. It is not until 18–31 days later that thymic development makes the transition from primitive to mature tissue. It takes another month or so for it to “come of age” and produce T-cells.

Which lymphoid organ is primarily active during the early years of life?

The thymus is the only lymphoid organ that actively matures during the early years of life. It is also the only lymphoid organ that can be felt in the human body. After puberty, it becomes little more than a clump of fatty tissue and shrinks in size to five or six grams, which is smaller than an average-size egg.

1. There are two types of cells in the human body:

 The immune system and the nervous system. The thymus is a part of the immune system. Different types of T cells are found in different parts of the body. Those in the thymus come from the bone marrow, while those in the peripheral blood come from the blood. The thymus produces a significant number of foreign T-cells. These cells circulate in the blood and can help to defend against diseases like measles, chickenpox, and cancer.

2. The thymus is located under the chest between the two lungs.

The thymus is located in the center of your chest directly under the lungs. It has a covering of connective tissue and is about a quarter-inch wide and about an inch long. It takes up most of the space between your breastbone (sternum) and the bottom of your neck, underneath the armpits. The top part of it — called your neck — can be felt when you touch it with your fingers. This part does not move or grow, but simply sits there like a kidney bean, hanging from one side to the other.

3. This gland produces T cells, which are part of your immune system.

The thymus is the part of the lymphatic system that matures T-cells into “fighting cells.” In adults, the thymus is responsible for maintaining these cells and ensuring that their numbers remain adequate. It does so by producing new ones every time its owner comes into contact with something foreign as well as when a particular area of the thymus deteriorates. Until puberty hits and production ceases, there are always some T-cells present in our bodies.

4. This gland is only active in early infancy, when a child’s immune system matures.

The thymus does not begin to operate until two or three months after conception. At six weeks, you can see the beginnings of it under the breastbone (sternum) at the top of your chest between the two lungs. The thymus does not develop very much after that. At eight weeks, it is still too early for it to operate and produce T cells, so there aren’t any T-cells in your blood when you are born. The thymus grows some more as your immune system matures between five and ten months old.

5. The thymus is where T and B cells mature into “fighting cells.”

In a baby, the thymus produces the T-cells that form the antibodies that can prevent a number of diseases like measles, chickenpox, and cancer. But there are also B-cells in the thymus and these are responsible for producing antibodies against parasitic worms. In order to work properly, we need to have both T and B cells present at the same time. These two classes of cells are known as “T helper” or “natural killer” T-cells and “B helper” or “cytotoxic” T-cells (or killer) .

6. The thymus requires a double dose of exposure to foreign antigens to produce the necessary T-cells.

The thymus needs to be exposed to foreign antigens in two doses in order to produce enough T-cells. These two doses are required for children under one year old and adults, respectively. For example, exposure to HIV in the mother during pregnancy has a dramatic effect on how much T-cells can be produced by the thymus; she must have been exposed in both her first and second trimesters or it wouldn’t work. For mice, researchers exposed one group of them during their first six weeks of life, while another group was not exposed at all during this period.


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