Fibroblasts are anabolic cells. They produce all the fibers and molecular components of connective tissue, giving it its structure and strength.
What are fibroblasts?
Fibroblasts are connective tissue cells in the strict sense. They are motile and divisible and produce all the important components of intercellular substance. This is the basic structure in tissue into which the cells are incorporated. It determines the properties of the tissue. Its components are the so-called amorphous matrix (shapeless, gel-like fluid) and fibers. If the synthesis capacity of fibroblasts is low, they become inactive and immobile. In this state they are called fibrocytes. However, the transitions from one form to the other are fluid, so that a precise demarcation is not possible. In the literature, the terms are sometimes used synonymously. This opinion is also supported by the fact that a reversion from the inactive to the active state is possible at any time. A special form are the myofibroblasts, which are a mixture of cells of the connective tissue and the smooth musculature. They have the ability to contract like muscle fibers. The contraction is transmitted to the neighboring structures via the surrounding elastic connective tissue fibers. This process plays an important role in wound healing, for example.
Anatomy and structure
Active fibroblasts have high synthesis activity. They have a round to oval nucleus with a distinct nucleolus and contain many cell organelles that are responsible for the formation of matrix components. The Golgi apparatus is very large, there is abundant rough endoplasmic reticulum, and many vesicles and mitochondria. In this state, the cell has many irregularly shaped projections through which contact with each other occurs. Active fibroblasts rarely form a cell association, usually they lie scattered in the ground substance. In the inactive state, the shape of the cell and nucleus and the composition inside the cell change. The shape as a whole and of the nucleus is more like a spindle. The synthesis-active cell organelles are more weakly developed. All of the above features result in the fibrocyte being smaller than the active form. In the inactive state, the arrangement in the cell cluster is more often observed. Myofibroblasts are distinctly spindle-shaped and bear long projections. They contain actin-myosin complexes capable of contraction. Their shape resembles that of smooth muscle cells.
Function and tasks
Active fibroblasts produce all the components of the matrix, i.e., fibers, glucosamine glycans, and proteoglycans. All these constituents determine the property of connective tissue in tendons, ligaments, cartilage, capsules, fascia, and subcutaneous tissue. The precursor of collagen, procollagen, is produced in the rough endoplasmic reticulum. It is transported to the cell membrane via the membrane system of the Golgi apparatus and released to the outside. Collagen consists of very resistant fibers that align along the direction of traction and give the matrix its tensile stability. In the event of tissue damage, the production of collagen is strongly stimulated in order to form a network of fibers at an early stage, which is then laid over a defect for protection. This is a very important step in wound healing. Elastic fibers contain a lot of elastin and are needed where stretching stresses occur frequently, for example in the aorta and lungs. Reticular fibers form a loose network and are used to embed cells or organs such as the spleen. Glucosamine glycans are linearly arranged multiple sugars, while proteoglycans are large molecules made up of sugar residues and a small protein component. Both groups have an enormously high ability to bind water, which determines the volume and tightness of the matrix. In addition to their restorative function, fibroblasts also prepare the degradation of damaged or dead connective tissue. They produce collagenase, a degradative enzyme that is stored in vesicles. When needed, it is secreted and made available for the breakdown process. Myofibroblasts play an important role in the initial phase of wound healing. They possess an actin-myosin complex that enables them to contract. With this process, they tighten and stabilize the newly formed tissue after an injury and pull the wound edges together.
Diseases
Fibroblast activity decreases with age, changing the shape and properties of connective tissue. It becomes flabbier, and its support and stability functions diminish. The same applies to connective tissue weakness. It is constitutional, there is a congenital weakness of fibroblast activity. They do not produce enough substances for the matrix and as a result it is less firm and taut than in other people. This process can be supported by external conditions, especially by being overweight. The consequences are visible on the skin (orange peel skin) and veins (varicose veins), but affect the entire connective tissue. Dysfunctions can also occur in internal organs or the ligaments of the joints. A typical disease in which increased fibroblast activity occurs is fibrosis. It is usually triggered by toxins that are ingested over a long period of time, such as coal dust, flour or asbestos. The increased production of collagen leads to a decreased ability of the connective tissue to expand. Depending on which organ is affected, its ability to function is severely impaired. In the case of vital organs, death may be the result. A typical site of manifestation is the lung. Another significant group of diseases in which there is increased fibroblast activity are the collagenoses. These are autoimmune diseases that belong to the inflammatory rheumatic group. The immune system forms antibodies against the body’s own connective tissue, which lead to the inflammatory process. In the course of the disease, the connective tissue solidifies, which can lead to calcification. The joints (rheumatoid arthritis), the skin or the connective tissue of the internal organs (scleroderma) are frequently affected. The reaction affects not only the fibroblasts, but also the cells that become active during an inflammatory response.
Typical and common connective tissue diseases.
- Stretch marks
- Progressive systemic scleroderma
- Stretch marks
- Cellulite (orange peel skin)
