Types[ edit ] Connective tissue can be broadly subdivided into connective tissue proper, and special connective tissue. Loose connective tissue has much more ground substance and a relative lack of fibrous tissue, while the reverse is true of dense connective tissue. Dense regular connective tissue, found in structures such as tendons and ligamentsis characterized by collagen fibers arranged in an orderly parallel fashion, giving it tensile strength in one direction.
Characteristic connective tissue cell types include both resident cells and immigrant or wandering cells. Fibroblasts which secrete the fibers and ground substance of the extracellular matrix.
Adipocytes which store fat. Macrophages which ingest and remove foreign material or damaged cells. 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. There is thus little about fibroblasts to attract the attention of an observer.
However, fibroblasts are essential for normal development and repairand recent research PLoS Genetics has shown that fibroblasts from different regions display extensively differentiated patterns of gene expression Protein and dense connective tissue may guide differentiated patterns of tissue organization, such as different types of skin and hair in different areas.
Indeed, the single cell type called "fibroblast" may properly represent many distinctly but invisibly different cell types, including "mesenchymal stem cells" which retain capacity to differentiate into other cell types see Science The name "fibroblast" is something of a misnomer, since most cells with "blast" in their name are embryonic precursor cells which subsequently differentiate into specialized cell types.
Fibroblasts are already a mature, differentiated cell type although some may have the capacity to differentiate into other mesenchymal cell types as well.
Resting fibroblasts typically have so little cytoplasm that the cells commonly appear, by light microscopy, as "naked" nuclei. Fibroblast nuclei appear dense heterochromatic and are usually flattened or spindle-shaped. The pink material in this thumbnail image is extracellular collagen.
Fibroblasts are active during growth but are normally quiescent in the adult. When active, fibroblasts are actively secretory, manufacturing the collagen and other components of the extracellular matrix of connective tissue.
Active fibroblasts appear larger than resting ones, with more cytoplasm and with nuclei that are more euchromatic less densely stained.
Resting fibroblasts retain the ability to become active and to multiply when necessary, as during healing after injury. Scars are formed by fibroblast activity during tissue repair. The substance of the scar is collagen deposited by fibroblasts to replace damaged tissue.
For an image of scar formation, see WebPath. For recent research on fibroblast involvement in scar formation, see Science Closely related to fibroblasts are the chondroblasts which produce the matrix of cartilage and the osteoblasts which produce the matrix of bone.
The appearance of "blast" in a cell name normally indicates an embryonic cell that transforms into a mature cell type e. However, in the case of "fibroblast", "chondroblast" and "osteoblast", this designation indicates a cell which secretes fibers, cartilage or bone.
Adipocytes are large connective tissue cells which contain a substantial amount of lipid stored in the form of conspicuous round droplets.
Adipocytes function primarily as warehouses for reserve energy. En masse, they also assist in thermoregulation maintaining body temperature and in a few sites offer some cushioning capacity e. Since most loose connective tissue contains scattered clusters of adipocytes, the term adipose tissue is usually reserved for large masses grossly visible of these cells.
The most common type of adipocyte is called the unilocular adipocyte or white fat. Each cell contains one single fat droplet hence, unilocular surrounded by a thin rim of cytoplasm.
Under the light microscope, the appearance of an adipocyte is that of a conspicuous clear space with a very thin border. The lipid droplet which comprises the bulk of each adipocytes is not stained by ordinary aqueous stains, and may even be removed by solvents during specimen preparation.
Furthermore, adipocyte cytoplasm itself is inconspicuously thin, and the nucleus of any particular adipocyte is unlikely to be included in any given section see Viewing Tissues. On microscope slides, clusters of adipocytes present an appearance somewhat like a "foam".
The individual "bubbles", each representing a lipid droplet within a single cell, are fairly consistent in the size. Typically diameter is about 50 micrometers, comparable to a skeletal muscle fiber or a small terminal arteriole. The shape of the droplet, in a tissue section on a slide, depends on how carefully the specimen was prepared.
Ideally the droplets are smooth and round as in the image abovebut they may also be distorted, shaped more like jigsaw-puzzle pieces as in the image at right. Adipocytes may occur in almost any sample of ordinary connective tissue, where they may be found as individual cells or in clumps.
Even when clustered together and apparently touching, adipocytes remain separated by a thin layer of matrix ground substance and collagen which includes numerous capillaries.Dense connective tissue contains more collagen fibers than does loose connective tissue.
As a consequence, it displays greater resistance to stretching. There are three major categories of dense connective tissue: regular, irregular, and elastic. Scientists discovered the new organ, which consists of fluid-filled spaces, in the body's connective tissue, including in the skin's dermis, which is shown above as the light pink layer at the.
Connective tissue disease refers to a group of disorders involving the protein-rich tissue that supports organs and other parts of the body. Examples of . Additional Resources. These links will open a new browser window. Large Images Search the Large Images page with these keywords: dense irregular connective tissue, dense regular connective tissue, reticular connective tissue, mesenchymal connective tissue, white adipose tissue, brown adipose tissue, macrophage, adipocyte, mast cell or elastic fibres.
Connective tissue is a term used to describe the tissue of mesodermal origin that that forms a matrix beneath the epithelial layer and is a connecting or supporting framework for most of .
Dense connective tissue can be categorized into dense regular, dense irregular, and elastic connective tissues. Dense regular: Tendons and ligaments are examples of dense regular connective tissue.
Dense irregular: Much of the dermis layer of the skin is composed of dense irregular connective tissue.