mesenchyme

Mesenchyme is a loose, primitive connective tissue present in the embryos of vertebrates. It consists of sparsely distributed mesenchymal cells embedded in a gelatinous extracellular matrix rich in hyaluronic acid and proteoglycans. The cells are typically spindle-shaped or star-shaped and are highly migratory, allowing the developing embryonic tissues to form.

In development, mesenchyme is primarily derived from the mesoderm, although craniofacial mesenchyme is largely neural crest derived. The tissue provides a cellular and extracellular scaffold for the formation of the body's connective tissues. Through differentiation, mesenchymal cells give rise to fibroblasts, chondroblasts, osteoblasts, adipocytes, and other lineages; they also contribute to the formation of blood vessels and muscles in the developing embryo.

Mature or specialized connective tissues originate from mesenchyme. The differentiation of mesenchymal cells leads to cartilage, bone, connective tissue proper (loose and dense), and adipose tissue, among others. In regions where its derivatives organize, mesenchymal cells form the stroma of organs and participate in wound healing and tissue regeneration.

In post-embryonic life, residual mesenchymal cells persist as mesenchymal stem cells (MSCs) in bone marrow, adipose tissue, and other sites. These multipotent cells are capable of differentiating into several connective tissue lineages and are studied for regenerative medicine and immunomodulatory therapies.