An adaptation is __________.
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Explanation:
What are the organs of the immune system?
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Our immune system is made up of both individual cells and proteins as well as entire organs and organ systems. The organs of the immune system include skin and mucous membranes, and the organs of the lymphatic system too.
Organs that function as barriers
Your skin and mucous membranes are the first line of defense against germs entering from outside the body. They act as a physical barrier with support from the following:
Antibacterial substances can kill germs right from the start. A certain enzyme found in saliva, the airways and tear fluid destroys the cell walls of bacteria.
Mucus in the bronchi helps trap many of the germs we breathe in so they can be moved out of the airways by hair-like structures called cilia.
Stomach acid stops most of the germs that enter the body in the food we eat.
Harmless bacteria on our skin and many of the mucous membranes in our body also act as part of the immune system.
In addition, the reflexes that cause us to cough and sneeze help to free our airways of germs.
Illustration: The parts of the immune system
The parts of the immune system
Lymphoid organs
The lymphatic system is composed of:
Primary lymphoid organs: These organs include the bone marrow and the thymus. They create special immune system cells called lymphocytes.
Secondary lymphoid organs: These organs include the lymph nodes, the spleen, the tonsils and certain tissue in various mucous membrane layers in the body (for instance in the bowel). It is in these organs where the cells of the immune system do their actual job of fighting off germs and foreign substances.
Bone marrow
Bone marrow is a sponge-like tissue found inside the bones. That is where most immune system cells are produced and then also multiply. These cells move to other organs and tissues through the blood. At birth, many bones contain red bone marrow, which actively creates immune system cells. Over the course of our life, more and more red bone marrow turns into fatty tissue. In adulthood, only a few of our bones still contain red bone marrow, including the ribs, breastbone and the pelvis.
Thymus
The thymus is located behind the breastbone above the heart. This gland-like organ reaches full maturity only in children, and is then slowly transformed to fatty tissue. Special types of immune system cells called thymus cell lymphocytes (T cells) mature in the thymus. Among other tasks, these cells coordinate the processes of the innate and adaptive immune systems. T cells move through the body and constantly monitor the surfaces of all cells for changes.
Lymph nodes
Lymph nodes are small bean-shaped tissues found along the lymphatic vessels. The lymph nodes act as filters. Various immune system cells trap germs in the lymph nodes and activate the creation of special antibodies in the blood. Swollen or painful lymph nodes are a sign that the immune system is active, for example to fight an infection.
Spleen
The spleen is located in the left upper abdomen, beneath the diaphragm, and is responsible for different kinds of jobs:
It stores various immune system cells. When needed, they move through the blood to other organs. Scavenger cells (phagocytes) in the spleen act as a filter for germs that get into the bloodstream.
It breaks down red blood cells (erythrocytes).
It stores and breaks down platelets (thrombocytes), which are responsible for the clotting of blood, among other things.
There is always a lot of blood flowing through the spleen tissue. At the same time this tissue is very soft. In the event of severe injury, for example in an accident, the spleen may rupture easily. Surgery is then usually necessary because otherwise there is a danger of bleeding to death. If the spleen needs to be removed completely, other immune system organs can carry out its roles.
