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Leukocyte extravasation describes monocyte entry into damaged tissue through the endothelium of blood vessels as they become macrophages. Monocytes are attracted to a damaged site by chemical substances through chemotaxis, triggered by a range of stimuli including damaged cells, pathogens and cytokines released
The monocyte is formed in the bone marrow and transported by the blood; it migrates into the tissues, where it transforms into a histiocyte or a macrophage. Macrophages are diffusely scattered in the connective tissue and in liver (Kupffer cells), spleen and lymph nodes (sinus histiocytes), lungs (alveolar macrophages), and central nervous ...
Monocytes can migrate into tissues and replenish resident macrophage populations. Macrophages have a high antimicrobial and phagocytic activity and thereby protect tissues from foreign substances. They are cells that possess a large smooth nucleus, a large area of cytoplasm, and many internal vesicles for processing foreign material.
Monocytes will then develop into macrophages or dendritic cells upon tissue damage and recruitment of monocytes into the infected area. [1] During recruitment monocytes are distinct from macrophages and dendritic cells, but upon entering the infected area, monocytes will acquire inflammatory effector functions and then differentiate into ...
Since all previous researchers have indicated that epithelioid cells are formed from monocytes, and monocytes and macrophages were combined into a single mononuclear phagocyte system, Van Furth et al. (1972), referring to the work of Sutton J. and Weiss L. (1966), [6] formally attributed epithelioid cells to the mononuclear phagocyte system. [2]
An electron micrograph of a macrophage. This is the general morphology of macrophages. The anatomy of human skin. Dermal macrophages are usually present in the dermis and around hair follicles. Dermal macrophages are macrophages in the skin that facilitate skin homeostasis by mediating wound repair, hair growth, and salt balance. [1]
Monocytes form two groups: a circulating group and a marginal group that remain in other tissues (approximately 70% are in the marginal group). Most monocytes leave the blood stream after 20–40 hours to travel to tissues and organs and in doing so transform into macrophages [70] or dendritic cells depending on the signals they receive. [71]
They circulate through the body and enter various organs, where they undergo differentiation into histiocytes, which are part of the mononuclear phagocytic system (MPS). However, the term histiocyte has been used for multiple purposes in the past, and some cells called "histocytes" do not appear to derive from monocytic-macrophage lines. [3]