Stromal Nutrition

The fibroblasts and other cells of the stroma are surrounded by a dense layer of secreted materials through which nutrients must reach the cells and waste must be excreted. The arteriolar ends of blood capillaries have tiny junctions between the endothelial cells so that small molecules leak out under hydrostatic pressure. This fluid, interstitial fluid, feeds the stroma and then drains back into the venous end of capillaries under the influence of increased capillary osmotic pressure and reduced hydrostatic pressure. It contains glucose, amino acids, some metabolites such as citrate, pyrophosphate, and extracellular ATP (Sect. 9.1.4) as well as vitamins and inorganic ions. It is free of the proteins and other large molecules present in blood plasma, but it receives soluble proteins that are secreted into it by matrix cells such as fibroblasts. 

The basal cells of a layered epithelium such as skin or gingiva (Sect. 5.2.1), or the periosteal cells covering bone, have such high nutrient demands that they need to be close to a rich capillary bed. Thus, although capillaries permeate the stroma, they are especially dense beneath the basal lamina of a layered epithelium (Sect. 13.3.1) or within a periosteum (Sect. 9.2.1). The gingival-tooth interface is especially susceptible to bacterial agents that 

3 The Connective Tissue Extracellular Matrixand Its Major Components 

---