Ultrastructure of the synovial membrane.

This research focuses on the microscopic structure of a normal synovial membrane, revealing different layers of lining cells with varied functionalities, components of the synovial matrix, and the presence of various other structures within the synovium.

Microscopic Structure of Synovial Membrane

• The normal synovial membrane, when observed using an electron microscope, is found to have one to three layers of lining cells.
• Among these lining cells, some possess phagocytic function – allowing them to absorb and eliminate harmful particles or bacteria.
• Other cells in the lining are noted to be rich in endoplasmic reticulum, an organelle crucial for protein production.
• Lining cells displaying a pronounced Golgi apparatus, an organelle responsible for processing and packaging materials within the cell, are most likely involved in the production of synovial hyaluronic acid.

Synovial Matrix and Other Identifiable Structures

• The synovial matrix, the non-cellular component present within all connective tissue, is made up of collagen and mucopolysaccharides.
• This matrix doesn’t present any significant barrier to the diffusion of most materials.
• Superficial capillaries and venules within the synovial membrane are fenestrated (possess small openings), allowing quick exchange of fluids and electrolytes.
• The deeper venules feature thick endothelium (inner lining of blood vessels) which can open up at intracellular junctions and potentially consume circulating particles, a process known as phagocytosis.
• Other recognized structures in the synovial membrane are fibrocytes (cells responsible for producing and maintaining connective tissues), macrophages (specialized cells involved in the detection, phagocytosis, and destruction of bacteria and any cellular debris), lymphatics (involved in the body’s immune response), mast cells (cells that play a crucial role in allergic reactions), non-myelinated nerves, and fat cells.