Basic Anatomy Study Guide - Biology is the natural science that studies life and living organisms, including their physical structure, chemical processes, molecular interactions, physiological mechanisms, development and evolution. Despite the complexity of the science, there are certain unifying concepts that consolidate it into a single, coherent field. Biology recognizes the cell as the basic unit of life, genes as. Fibroblasts are the most common resident cells in ordinary connective tissue.Fibroblasts are responsible for secreting collagen and other elements of the extracellular matrix of connective tissue. In microscopic appearance, fibroblasts lack obvious specialized features. And fibroblasts throughout the body all appear similar to one another, wherever they occur in ordinary connective tissues.. The histology of the entire gastrointestinal tract is largely the histology of epithelial tissues. Click here for a basic introduction to epithelial tissue..