Monophageal system / endothelial retina system
The complete combination of monocytes, mobile macrophages, fixed tissue macrophages, and a few specialized endothelial cells in the bone marrow, spleen, and lymph nodes is called the endothelial retinal system
Macrophages are mainly mobile cells that have the ability to enter tissues. However, after entering tissue into macrophages, most monocytes become attached to the tissues and remain attached for months or even years, until they are mobilized to function. local protection. They have the same ability as mobile macrophages to phagocytic large amounts of bacteria, viruses, necrotic tissue, or other foreign objects in the tissue. In addition, when properly stimulated, they can leave the binding site and revert back to a mobile macrophage in response to the chemotaxis and other stimuli of the inflammatory process. As a result, the body has a "mono-macrophage system" that spreads in nearly all tissue areas.
The complete combination of monocytes, mobile macrophages, fixed tissue macrophages, and a few specialized endothelial cells in the bone marrow, spleen, and lymph nodes is called the endothelial retinal system. However, all or most of these cells are derived from monoclonal stem cells; therefore, the endothelial retina system is almost synonymous with the mono-macrophage system. Because the term endothelial retinal system in the literature is much better than the term mono-macrophage system, it should be remembered as a phagocytic system that says they are in all tissues, especially in regions. tissue with a large amount of foreign matter, toxins and excess substances must be destroyed.
Tissue macrophages in the skin and subcutaneous tissue (tissue)
Although the skin is largely impregnable to an infectious agent, this is no longer true when the skin is damaged. When an infection begins in the subcutaneous tissue and local inflammation follows, the local tissue macrophages can divide in place and remain shaped like most macrophages. They then perform the normal function of attacking and killing the infectious agent, as described above.
Macrophages in the lymph nodes
Basically, no foreign matter that penetrates tissues, such as bacteria, can be absorbed directly through the capillary membrane into the bloodstream. Instead, if the foreign bodies are not destroyed locally in the tissue, they enter the lymphatic vessels and reach the lymph nodes that are localized along the path of the lymphatic vessels. Foreign bodies are captured in these nodes in a network of sinuses lined with tissue macrophages.
Figure. Functional map of a lymph node.
The lymphatic vessels enter through the shell of the lymph nodes by the arrival of the lymph nodes, then flow through the medullary sinus nodes, and eventually out of the umbilical lymph nodes into the vessels and then into the blood vessels.
There are a large number of macrophages lining the lymphoid sinuses, and if a few foreign bodies enter the sinuses with the lymphatic vessels, they will be destroyed by the macrophages and prevent their spread throughout the body.
Alveolar macrophages in the lungs
One way organisms frequently enter the body is through the lungs. A large number of tissue macrophages are present as an integral component of the alveolar wall. They can phagocytic foreign bodies that have been trapped in the alveoli. If the foreign bodies are digested, the macrophages can also digest them and secrete digestive products and white blood vessels. If the foreign body cannot be digested, the macrophage usually turns into a "giant cell" surrounding the foreign object until the foreign body gradually disintegrates. Such envelopes are usually formed around tuberculosis bacteria, silicate dust particles and even coal particles.
Macrophages in the liver sinuses (Kupffer Cells)
Foreign organisms can also enter the body through the digestive tract. Large amounts of bacteria from food always pass through the gastrointestinal mucosa to enter the portal system. Before pouring into the general circulation, portal venous blood passes through the hepatic sinuses, which are lined by tissue macrophages called kuffer cells, as shown in the figure. These cells form an efficient filtration system that barely allows bacteria from the digestive tract to pass through the portal system to enter the general circulation. Indeed, the kuffer cell phagocytic activity demonstrated the phagocytosis of a single bacterium in less than 0.01 s.
Figure. Kupffer cells line the hepatic sinuses, showing phagocytosis of Indian squid particles into the cytoplasm of Kupffer cells.
Macrophages in the spleen and bone marrow
If a foreign organism successfully enters the general circulation, there are other protective mechanisms of the tissue macrophage system, especially the macrophages of the spleen and bone marrow. In both of these tissues, the macrophage is retained by the retinal system of these two organs and when the foreign body comes into contact with the macrophage, they are phagocytosed.
The spleen is like the lymph nodes, instead of blood, lymph flows through the tissue areas of the spleen. Figure 34-5 shows a peripheral segment of the spleen. Note that a small vascular segment penetrates from the sheath into the spleen and ends in the small capillaries. The capillaries are highly porous, allowing whole blood to flow out of the capillaries into the red marrow. The blood is then gradually squeezed through the network of the medulla and eventually returned to circulating blood through the endothelial walls of the venous sinuses. The red marrow and the venous sinuses are lined with a large number of macrophages. This special segment of blood through the red medulla provides a special means of phagocytosis of unwanted debris in the blood, especially senile erythrocytes and abnormal erythrocytes.
Figure. Functional structure of the spleen.