Mesenchymal

Mesenchymal refers to mesenchyme, the embryonic connective tissue from which much of the body's connective tissues develop. In humans, mesenchyme is primarily mesodermal in origin, though neural crest–derived mesenchyme contributes to certain head and neck structures. It consists of loosely organized, spindle-shaped cells embedded in a gel-like extracellular matrix rich in proteoglycans and collagen, with relatively few mature epithelia.

In post-embryonic contexts, the term describes cells and tissues that originate from mesenchyme, including fibroblasts, adipocytes, chondrocytes, osteoblasts and osteocytes, and smooth muscle cells. These cells organize into connective tissues such as fascia, ligaments, tendons, cartilage, bone, and adipose tissue, providing structural support, elasticity, and metabolic functions.

Mesenchymal stem cells (MSCs) are a prominent type of mesenchymal cell. Found in bone marrow, adipose tissue, the umbilical cord, and other sites, MSCs are multipotent, capable of self-renewal and differentiation into osteogenic, chondrogenic, and adipogenic lineages, among others. They also exhibit immunomodulatory properties and are explored for regenerative medicine, with several clinical applications and ongoing research into broader uses.

In pathology, mesenchymal describes tissues and tumors arising from mesenchymal origin, known as sarcomas, as opposed to epithelial tumors. The concept also relates to epithelial-to-mesenchymal transition (EMT), a developmental and cancer-related process in which epithelial cells acquire mesenchymal characteristics, enhancing migratory and invasive abilities.