Connective tissue develops from the mesoderm of a developing embryo and consists of cells, fibers, and ground substance: a gel-like material containing large complexes of carbohydrates and proteins. Connective tissue was first identified as a separate tissue family in the 18th century, and Johannes Peter Muller coined the term connective tissue.

Fat cells (adipocytes), smooth muscle cells (myoblasts), and bone cells (osteoblasts) are some connective tissue cell types. Some immune system cells are part of the connective tissue family, including macrophages, mast cells, and plasma cells. Macrophages are white blood cells that engulf bacteria or any pathogenic organisms attacking the host cells. Mast cells modulate the immune response, including allergic reactions, by releasing chemicals such as histamine and inflammatory cytokines.

Connective tissue is prone to diseases, often due to hereditary or nutritional factors. Systemic lupus erythematosus (SLE) is an autoimmune disease where the entire connective tissue of the body is inflamed. The inflammation affects many organs and organ systems, including the skin, lungs, and inner lining of the blood vessels. Symptoms include skin rashes, muscle and joint pain, and weakness, among many others.

Environmental factors, including vitamin deficiency, may lead to connective tissue disorders. Vitamin C (ascorbic acid) is an essential cofactor in collagen biosynthesis. Vitamin C deficiency results in defective collagen synthesis, causing internal bleeding, loose teeth, and fragile bones. Similarly, vitamin D regulates the immune system and supports calcium homeostasis and bone development. Low vitamin D increases the risk of connective tissue diseases such as SLE and inflammatory bowel disease.