The mesenchyme envelops the fetus as embryonic connective tissue with a protective envelope and is relevant for morphogenesis. Multipotent mesenchymal cells differentiate into connective tissue, muscle, blood, and fat cells, among others, during embryogenesis. Because of its high division rate, mesenchyme is susceptible to tumors.
What is the mesenchyme?
During the embryonic period, the supporting and filling tissue of the human develops. This tissue is also known as embryonic connective tissue. It develops from polipotent cells. Polipotency allows the cells to differentiate into almost all cell types of the three germ layers. In addition to the gelatinous connective tissue, this gives rise to the so-called mesenchyme. This is connective tissue from the mesoderm, which later forms the loose, tight and reticular connective tissue. In addition to the connective tissue types, bones and cartilage develop from the mesenchyme. Smooth muscle and heart muscle also depend on mesenchyme. The tissue also forms the basis for the development of the kidneys and adrenal cortex. In addition, the cells of the mesenchyme are involved in the formation of the hematopoietic system and the development of the blood and lymph vessels. The developmental processes take place through differentiation and determination. Determination specifies the developmental program that all daughter cells of a poli- or omnipotent cell must later undergo. Cell development from the mesenchyme is thus a specialization.
Anatomy and structure
Mesenchyme is histologically a distinct type of tissue that arose from the stem cell cluster of the mesoderm or cotyledon. Mesenchyme contains star-shaped branched cells. These cells are also called mesenchymal stem cells, mesenchymal stromal cells, or mesenchymal cells. The individual cells of the mesenchyme are mechanically and interactionally connected to each other by cytoplasmic extensions. Mesenchymal stem cells have a relatively high division rate or mitotic rate. They are multipotent cells. This means that they are not yet determinate and can still differentiate into relatively many tissue types. The intercellular substance is a viscous fluid containing hyaluronic acid. From the eighth week of development, it contains collagen fibrils. However, it does not contain fibers. The lack of fibers distinguishes the mesenchyme from the fully differentiated connective tissue. In this tissue, a fibrous intercellular substance is what makes up the properties of the tissue in the first place. In addition, unlike epithelium, the cells of mesenchyme exhibit little or no cell polarity-
Function and tasks
The mesenchyme plays a critical role in embryonic cell differentiation and determination. Even in adulthood, mesenchymal cells are still relevant for tissue formation. This is true, for example, in the context of ossification, in which bone tissue and cartilage are formed from reticular connective tissue. Determination is a differentiation step. Both processes give the organism its shape during embryogenesis. All shaping processes on the multicellular organism are included under the term morphogenesis. Besides differentiation, cell division is crucial for this morphogenesis. Mesenchymal cells have a high division rate and are multipotent. Thus, they can develop into different tissues. They end up forming the tissue type of connective tissue as well as that of muscle tissue, bone tissue, blood and adipose tissue. The path of differentiation depends on external and internal factors. In addition to neighboring cells and cell contacts, for example, the origin of the cell from its precursors has an influence on the path of development. Growth factors and hormones also exert an influence. In embryology, the term intraembryonic mesenchyme refers to the mesenchymal cells that serve as the origin of other tissue types. To be distinguished from this is the extraembryonic mesenchyme. The cells of this tissue support and envelop the fetus. Consequently, they are created as a kind of protective cover around the embryo. The mesenchyme performs its various tasks on the embryo from the third week of development. It forms shortly beforehand from cotyledons such as the mesoderm and, in small proportions, from the ectoderm and entoderm.
Diseases
Because of its high division rate, the mesenchyme plays a role in the context of tumor diseases. Tumors are ultimately growths of tissue that result from increased cell division.Embryonic mesenchyme can accordingly be rapidly affected by mesenchymoma or malignant sarcoma. Malignant mesenchymoma is a malignancy of the soft tissues. Benign mesenchymoma, on the other hand, is a benign growth of soft tissue or bone. The prognosis is more favorable the earlier the tumor is detected. However, these tumors hardly ever occur in adults because their mesenchyme has a much lower division rate than that of the embryonic stage. In addition to tumors, inflammation and degenerative phenomena can also be present in the mesenchyme. Inflammation in the mesenchyme may be described as a systemic disease. Especially in embryonic mesenchyme an inflammatory process with the determination of the cells is possibly included in the program of all daughter cells. Primary metabolic disorders of the kidney are also often related to a degenerative disease of the mesenchyme. In this context, amyloid degeneration should be mentioned above all. The degeneration of the mesenchyme leads to glomerulide bleeding disorders. Under certain circumstances, this can promote the demise of the secretory renal elements. During embryogenesis, errors in the determination of the mesenchyme may also occur. Such errors may be recovered by transdeterminations. If this is not done, serious consequences may occur.
