Mesangial

Mesangial refers to the mesangium, the central supporting tissue of the renal glomerulus. The mesangium lies among the glomerular capillary loops and is located between the capillary basement membranes and Bowman's capsule. It is composed of mesangial cells and an extracellular mesangial matrix, together providing structural support and a regulatory environment within the glomerulus.

Mesangial cells are specialized pericyte-like cells embedded in the mesangial matrix. They have contractile properties due to actin-containing filaments, allowing modulation of capillary surface area and glomerular filtration. They also perform phagocytosis of immune complexes and debris and secrete cytokines and growth factors. The mesangial matrix is produced by mesangial cells and consists of a network of proteins, including collagens, laminin, and proteoglycans, which provide structural support and a scaffold for the capillary loops.

Functions of the mesangium include structural support for glomerular capillaries, regulation of filtration by contraction and relaxation of mesangial cells, clearance of immune complexes, and participation in inflammatory and remodeling processes through cytokine signaling. The mesangium thus acts as both a mechanical and immunologic component of the glomerulus.

Pathology involving the mesangium is seen in many glomerular diseases. Mesangial expansion (increased matrix) or mesangial hypercellularity can occur in conditions such as IgA nephropathy and diabetic nephropathy, the latter often showing nodular mesangial sclerosis (Kimmelstiel-Wilson nodules). Immunofluorescence may reveal mesangial deposits of immunoglobulins or complement, and electron microscopy can show mesangial electron-dense deposits in various diseases.