What Are the Different Types of Fibrous Tissue?

Fibrocytes are inactive fibroblasts. The cell body is spindle-shaped, with less cytoplasm, weak eosinophilia, small nucleus, and deep staining. Under electron microscope, the rough endoplasmic reticulum and Golgi apparatus were not well developed. When tissue is damaged, fibroblasts can be transformed into fibroblasts to participate in the repair process. ^[1]

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Fibroblasts have a variety of morphologies, such as fusiform, mostly angular, and flat star. The morphology of fibroblasts can be changed according to the changes in the function of the cells and the physical properties of the cells. Fibroblasts

Fibrocyte wound repair

Trauma can cause different degrees of cell degeneration, necrosis and tissue defect, and tissue repair must be performed through cell proliferation and formation of intercellular matrix. Fibroblasts play a very important role in this repair process. Taking the wound healing process as an example, fibroblasts proliferate in large numbers through mitosis, and begin to synthesize and secrete a large amount of collagen fibers and matrix components from 4 to 5 or 6 days. Together with new capillaries, granulation tissue is formed to fill the wound tissue defect. To create conditions for epidermal cell coverage. In wound healing, fibroblasts are mainly derived from local fibroblasts and undifferentiated mesenchymal cells in the dermal papilla, and fibroblasts and pericytes around the blood vessels are damaged during the visceral injury. Connective tissue from the stroma and capsule, as well as the submucosa or subserosal layer. Some people think that the large number of fibroblasts gathered in the wound during the wound healing process is, on the one hand, derived from fibroblasts through proliferation and division, and on the other hand, it is more composed of adjacent mesenchymal cells, fibroblasts and pericytes. Wait for the evolution or swim to the wound. In the later stage of wound repair, fibroblasts participate in tissue reconstruction after repair by secreting collagenase. Under certain pathological conditions, granulation tissue or proliferative tissue mass with fibroblasts as the main cell component can also calcify in non-bone tissue, causing ectopicossification. However, it is not very clear about the participating cells of ectopic ossification and its mechanism. Undifferentiated mesenchymal cells, fibroblasts, endothelial cells and pericyte cells can be classified as induced bone progenitor cells. Participate in this process. ^[2]

Fibroblastic bone trauma repair

The simplest and most common bone trauma is a fracture, and the healing process must go through 4 stages of inflammatory response, dissection, fibrous epiphysis and osteophysis. The cell bodies involved in different stages are different. Fibroblasts have appeared in the localized hematoma of the fracture since the third day of the fracture. A large number of fibroblasts are present in the space around the mechanized hematoma and the fracture stump at 5 days after the fracture. At this stage, fibroblasts divide and proliferate on the one hand, and synthesize and secrete a large amount of type I collagen on the other hand, so that the granulation tissue gradually becomes loose connective tissue, surrounding the stump of the bone, forming a huge joint that joins the two stumps Fibrous epiphysis However, this kind of fibrous connective tissue composed of numerous fibroblasts and abundant granulation tissues will not evolve into purulent tissues that are common in wound healing in other tissues, but will be crystallized inside by calcium salts. Continuous deposition, gradually evolved into osseous callus, so that the local repair of the fracture to achieve bone healing, restore the structure of bone tissue. At this time, the bone healing was the only part of the fracture healing area, and no fibroblasts were present. ^[2]

Fibroblast osteogenesis

Electron microscopic observation of the bone formation area of the fracture shows that in addition to the osteoblasts playing osteogenic effects here, fibroblasts do have similar osteogenesis. For example, calcium salt particles can be clearly seen in its mitochondria, mature collagen fibers can be seen in some endoplasmic reticulum cavities, and high-density calcium salt crystal deposits can be seen in the collagen fibers secreted to the surroundings. Not only that, fibroblasts can also generate stromal vesicles like osteoblasts and cause calcium salt deposition in the vesicles. The calcified stromal vesicles form tufted globular calcium spheres, which subsequently merge and fuse into bone tissue. The above phenomena show that fibroblasts, like osteoblasts, have the necessary conditions to provide calcium salt deposition and bone formation. During the evolution from fibrous epiphysis to osteophysi, fibroblasts also evolved into osteocytes, consistent with the fate of osteoblasts. However, the performance of the two in the evolution process is different, and the following points can be identified:

(1) Fibroblasts and their nuclei are irregularly oval or rectangular, while osteoblasts and their nuclei are oval with relatively smooth edges;

(2) Fibroblasts exist alone, there are many collagen fibers separated between cells, and osteoblasts appear in a continuous arrangement;

(3) Lysosomes are rare in the cytoplasm of fibroblasts, and lysosomes are often visible in the cytoplasm of osteoblasts;

(4) Bone tissue around fibroblasts is composed of plexus spherical calcium spheres or needle-shaped calcium salt crystals, while osteoblasts all have a mature and dense bone tissue on one side.

(5) Osteoblasts are surrounded by bone tissue (osteoid) one by one to become bone cells, while fibroblasts can be two or more simultaneously surrounded by bone tissue in a pit, and then With the calcification of the matrix between the cells, they are separated into a bone pit each.

For the osteogenesis of fibroblasts, some scholars believe that this is the result of the inherent characteristics of fibroblasts being expressed in the specific case of fracture. Live and inactivated bone and cartilage tissues at the fracture site, as well as certain macromolecules in the bone matrix, may induce fibroblasts to express their osteogenesis and evolve into osteocytes. Bone morphogenetic protein (BMP), which was found earlier in the bone matrix, has a certain induction effect on fibroblasts and studies on the role of BMP in fracture healing. Release and induce mesenchymal cells or fibroblasts in the surrounding soft tissue to transform into osteogenesis. Using the PAP method, it was found that the fibroblast-like mesenchymal cells in the local fibrous granulation tissue on the 35th day after the fracture and the fibroblast-like mesenchymal cells in the fibrous tissue between the new bone trabecula on the 14th day were all related to The presence of BMP in osteoblasts, chondrocytes and bone matrix indicates that these fibroblast-like mesenchymal cells have been induced to synthesize and secrete BMP and have osteogenic cells. And the osteoinductive ability of Sampath isolated and purified from bovine bone matrix to fibroblasts was more than that of BMP and other bone growth factors known at the time.

After fibroblasts express their osteogenesis, they may be osteogenic in two ways: (1) intra-membrane osteogenesis; (2) osteogenesis in the fibrous layer surrounding cartilage. After starting to secrete collagen fibers, the fibroblasts involved in osteogenesis have only two destinations: (1) degeneration, death, fragmentation until disappearance. This evolution occurs early and has a wide range. Therefore, from the beginning of the formation of fibrous epiphysis, gradually There are matrix components that calcify and then transform into bone matrix; (2) evolve into bone cells, this process appears later and intersperses with the previous process, so while forming the cellular components of bone tissue, it also enriches The fibrous epiphysis evolved into bony epiphysis forming bone tissue. However, it is still unclear how the biological characteristics of such bone cells evolved from fibroblasts are the same as those derived from osteoblasts. For example, after detachment of bone cells from bone pits, they can return to active osteoblasts. Once again, they participate in the formation of bone tissue and the bone cells evolved from fibroblasts become osteoblasts or cells after they leave the bone pits. A series of questions such as the restoration of fibroblasts and whether they still have osteogenesis at this time have not been studied. ^[2]