Introduction
Lymph nodes are found throughout the body. They are part of the lymphatic system, consisting of the lymph vessels and the lymphatic organs. They are responsible for the immune defense.
The lymphatic organs can be divided into primary and secondary organs. The lymphocytes are formed in the primary lymphatic organs – the bone marrow and the thymus. They belong to the white blood cells and arise from stem cells from the bone marrow.
Their maturation into finished immune cells, which can recognize foreign substances and dangerous antigens, takes place in the secondary lymphatic organs. In addition to the lymph nodes, these include the spleen, lymphatic tissue in the mucous membranes (for example the tonsils) and the appendix in the intestine (often incorrectly called the appendix). Antigens, i.e. potentially dangerous foreign substances circulating in the body, are checked here.
The spleen is responsible for antigens that circulate in the blood. The lymphatic tissue in the mucous membranes checks the antigens that have entered the mucous membranes superficially via the mouth. Lymph nodes, on the other hand, react to substances that have already penetrated the tissue and spread via the lymph vessels.
This is because the lymph vessels form a drainage system that takes up tissue fluid and returns it to the bloodstream. It consists of tiny, blind ending vessels that are found in almost all organs (the central nervous system, for example, is an exception). They take up free fluid, channel it through ever-increasing lymph vessels to the center and finally into the venous angle (this is where the veins from the neck and arm unite). Most of it reaches the left venous angle, from where it flows with the venous blood through the upper vena cava towards the heart. The lymph nodes are interposed between the lymph vessels and serve as filter stations.
Anatomy
The lymph nodes are usually round or bean-shaped, between 2 and 20 mm in size, and filter the lymph before it is returned to the bloodstream. Lymph refers to the fluid in the lymph vessels, i.e. the intermediate step between tissue fluid and blood plasma. It is slightly yellowish, consists mainly of water, contains lymphocytes and also some electrolytes and proteins.
After meals it can also be cloudy and milky white, as fats are also absorbed via the lymph. There are about 600 to 700 lymph nodes in the whole body, with each organ and body part having its own so-called regional lymph node, which is the first filter station for this area. The area for which this lymph node is responsible is called the tributary area. The incoming lymph vessels enter the lymph node from all directions, then the lymph flows through certain pathways, the so-called sinuses, through the lymph node to a pole (the hilum), where it is discharged via an exiting lymph vessel. In the tissue of the lymph nodes there are lymphocytes that have reached this pole via an afferent artery and which can come into direct contact with antigens from the lymph here.
All articles in this series:
