Connective Tissue Proper
Mesenchyme -- embryonic c.t. with multipotential cells. The stellate cells are beginning to form fibers. Sometimes cells are more spindle shaped. Ground substance material is watery and invisible.
Reticular tissue (silvered, black). A network of very fine reticular fibers can be seen here, forming the stroma (framework) of a lymph node. These fibers are produced by reticular cells. The pale cells seen in the meshes of the reticular fibers are lymphocytes.
Stellate reticular cells - forming a meshwork of their own cytoplasmic processes. These are in addition to the reticular fiber network which these cells produce -- and which we would see if this tissue were silvered. Notice particularly clear cells in upper left quadrant of field. This slide is from lymph node.
Detail of lymph node, showing stellate reticular cell in middle of field.
Loose (areolar) connective tissue - (in blue) - surrounding the epithelium of tubules. In areas like this, the finest collagen fibers lying closest to the tubules would be reticular fibers; the only way to distinguish them here from heavier collagen fibers would be to silver them. (The blue here simply stains collagen in general.) REMEMBER: in an area like this, reticular fibers (like all other fibers) are produced by fibroblasts. Only in the primitive reticular tissue of bone marrow, lymph node, and spleen are reticular fibers produced by reticular cells.
Loose irregular connective tissue (also called areolar tissue) as seen underlying and supporting epithelium in an ordinary section. It is rather cellular and supports many small blood vessels which travel through it.
Areolar c.t. immediately underlying simple columnar epithelium. This is a very cellular variety of areolar c.t., with a high population of lymphocytes.
A stretched preparation of areolar connective tissue. The pink fibers of different thicknesses are collagenous (or white) fibers. The dark, thin, more tortuous fibers are elastic (or yellow) fibers. Most of the nuclei belong to fibroblasts.
Dense irregular c. t., with fibers running in all directions. The fibers are mainly collagenous, but keep in mind that some would be elastic and can be seen only if specifically stained. This kind of c.t. is found where firmer packing and binding is needed. The two arrows at top of picture are pointing to elongate, dark, fibroblast nuclei.
Dense irregular c.t. (blue) packing around a nerve bundle. The coat immediately surrounding the whole nerve bundle is particularly dense and consists mainly of collagen fibers. In between the individual pale, round nerve fibers is a very fine areolar c.t. packing, with mainly reticular fibers.
Fat cells -- note nucleus and rim of cytoplasm pushed to one side by the accumulation of fat. The lipid itself has been dissolved out in fixation. In the center of the picture, in the space bounded by the four large fat cells, there is a small, round cross-cut of a capillary with a dark, shrunken red blood cell inside.
Fat cells developing in areolar connective tissue.
Adipose tissue aggregate of fat cells.
Adipose tissue as seen in a regular histological section. The pale pink tissue mixed in with it is skeletal muscle. The dark purple = serous glands. There is a small muscular artery in the middle, with a branch going off it to the left.
Tendon (dense, regular c.t.), cut longitudinally. The thick collagen fibers (pink) are lined up parallel to each other, in response to the stress placed on them by muscle and joint action. Fibroblasts are squeezed between the fibers and therefore also line up in parallel rows. We often refer to this as a "railroad train" appearance.
Tendon, cut in cross-section. The pale pink background represents the cut ends of bundles of thick collagen fibers, very closely packed together. The wispy lines you see throughout are the "cracks" between fiber bundles. In the cracks lie fibroblasts which often look triangular or stellate because of being squeezed between the fibers.
