Fibroblasts are long, flat, spindle-shaped cells that produce tropocollagen, the precursor of collagen, and ground substance, an amorphous gel-like material that fills the intracellular spaces in connective tissue. Inactive fibroblasts, embedded in ground substance, are known as fibrocytes and are smaller than their active counterparts. If an organ becomes injured, however, fibrocytes are induced to propagate and migrate to the wound. There they aid in the deposition of fresh collagen, resulting in a scar upon the organ’s surface.