Light micrograph of human fibroblasts. Fibroblasts are flat, elongated, undifferentiated cells in connective tissue that give rise to various precursor cells that form the fibrous, binding, and supporting tissue of the body. Fibroblasts can become chondroblasts, collagenoblasts, or osteoblasts. Fibroblasts may be cultured in the laboratory and are often used to study how genes regulate growth and multiplication.