Extracellular Matrix: Structure, Function, and Components
TISSUE: Introduction: ECM is a complex network of macromolecules that acts as “cement” between the universal biological cells, as part of highly specialized structures: cartilage, tendons, bones, etc. This function supports the ECM’s role in regulating the behavior of cells that contact it, influencing their differentiation, development, migration, and shape. The ECM is produced by ECM-producing cells called connective tissue, connective, or supportive cells.
Supporting tissues: broadly refer to the ECM and the cells embedded within it, regardless of their occurrence. ECM-producing cells: are mainly derived from the mesoderm, although some originate from the ectoderm. They share structural features and have cell adhesion mechanisms that interact with ECM materials instead of other cells. They represent fixed cell populations in the supporting tissues, where the ECM is the predominant component.
1. Mesenchymal cells: morphologically, these are stellate cells with long, thin extensions that make contacts with one another, forming a mesh-like network. They are located in the embryonic mesenchyme. In adults, some multipotent mesenchymal cells remain, mainly situated in the vicinity of blood vessels, which are called adventitial cells. Due to their function, it is more appropriate to refer to them as stem cells. Functionally, they have a high mitotic index, and their most prominent property is their multipotency for differentiation.
2. Fibroblasts: Concept and location: These are common, tissue-specific cells responsible for the synthesis of the ECM. They are known as fibroblasts when fully differentiated and stop producing ECM. Structurally: they exhibit a stellate morphology in culture and a fusiform shape in tissues. The nucleus is large and central, and the cytoplasm is PAS-positive for secretion. Functionally: they synthesize ECM, resist aggression, are able to divide actively, participate in tissue repair, and can be transformed into histiocytes, fat cells, smooth muscle cells, etc. Types:
- Myofibroblasts: share typical features with fibroblasts and smooth muscle cells. They are located at the level of the adrenal glands, testes, seminiferous tubules, etc.
- Pericytes: located in the walls of some venules and capillaries, they are involved in the elaboration of the basal lamina of the capillary or venule.
3. Chondroblasts/cytes: Concept and location: These are cells of chordoid tissue that produce specific ECM. When they stop actively synthesizing ECM, they are called chondrocytes. Their origin is ectodermal. Structurally: they resemble epithelial cells, with little intercellular substance mediating between them.
4. Chondroblasts/cytes: Concept and location: These are the cells of cartilage that produce the specific ECM, which is solid and non-mineralized. When they stop synthesizing ECM, they are called chondrocytes. Structurally: chondroblasts have a round or oval morphology, with a central nucleus and loose chromatin. Chondrocytes show variable appearances and are housed in condroplasmas carved for themselves in the ECM. All cells of an isogenic group come from the division of a single chondroblast, and their disposition depends on the planes of division.
5. Osteoblasts/cytes: Concept and location: These are the ECM-secreting cells in bone tissue. The newly formed material, the osteoid matrix, is quickly transformed into bone by the deposition of calcium phosphate salts. Structurally: osteoblasts have an epithelial appearance and signs of high metabolic activity, being located on the bone-forming surfaces. Osteocytes are cells endowed with fine processes and long extensions, with an oval nucleus and dense cytoplasm poor in organelles. Lysosomes highlight the enzymes that are discharged into the bone matrix to carry out the process of osteolysis. Osteocytes are important in regulating phospho-calcium balance.
6. Cells producing ECM in dental tissues:
- Ameloblasts: enamel
- Odontoblasts: dentin
- Cementoblasts: cement
Except for ameloblasts, which are derived from ectoderm, all other cells are derived from mesoderm.
Macromolecules of the extracellular matrix:
A) fibrillar proteins: 1. Collagenase: (* concept and general) its amino acid composition is unique in the body, stressing the glycine, proline and hydroxyproline. Collagen molecules biochemically consist of tropocollagen subunits: ?-helical structure with three chains coiled polipetidicas. (* Types): Type 1: two chains ? 1 subtype and a string 2. It is located in deep dermis tendons and bones, set high strength fibers. Type 2: three chains ? 1,. It is found in cartilage. Just as fiber. Type | | |: three chains ?1, | | |. Aperece in fetal skin. Collagen fibers and reticular form. Type | V: three chains ? 1, | V It is found in basal lamina. Form meshes. Type V: two chains ? 1, ? V and chain 2. Appears in small numbers and diffuse distribution in the tissues. Form thin fibers. Type V |: three chains ? 1, V |. Form thin fibrils. Type V | |: a short and striated fibrils which are anchored in the basal lamina of the skin. (* synthesis): The colagenogenesis starts in mec-producing cells, the polymerization of protein subunits to form fibrils and fibers, occurs in the extracellular medium. The subunits of tropocollagen, to polymerize, cause collagen fibrils, when added set thicker fibers. The formation of collagen fibers depends on the amino acids located in lso tropocollagen ends of the molecule. (* collagen fibers) appear white and beam forming undulating course. Very high tensile strength, flexible and slightly elastic. They are in the supporting tissues of organisms that must withstand large tensile stresses. At the mo are seen scattered swirling in fascicles … I checked with a fiber resulting from the aggregation of microfibrils with a cross-striations. (* reticular fibers) collagen protein microfibrils coated with carbohydrates and lipids that prevent them from aggregated to form fibers of larger caliber. Tendency to form networks. They are located in liver, bone marrow and lymphoid organs. 2. Fibrillin: fibril forming glycoprotein which is the PRINCIPAL component of extracellular microfibrils. Associated with elastin is secreted, which organizes to form elastic fibers. Is detected in the mesangium of renal glomeruli and spleen. 3. Elastin: (* concept and general) insoluble fibrous protein whose structural unit is the tropoelastin. Composition, cysteine, proline and glycine. The elastogenesis happens after the establishment of cross-bridges between tropoelastin molecules, giving rise to the formation of desmosine, and lysine-Norleucine isodesmosine.(* elastic fibers): the formation occurs by interaction between elastin and fibrillin so that fibrillin microfibrils secreted elastin organized, which is deposited among those to be individualistic forming fibers. Most prominent physical property, elasticity. They may be doing and networks, parallel sheets or bundles. cn mo stains are required, cn me appear little more or less homogeneously electron dense and consisting of microfilaments tropoelastin. 4. Fibronectin: fiber-forming glycoprotein consisting of two chains linked by disulfide bonds. Appears in the mec form aggregates. Spoke on mechanisms of cell adhesion and cell migration during embryonic development. Ability to meet various components of tissues such as collagen, heparin … in cell membranes there are receptors belonging to the generic group of integrins to fibronectin. It participates in the orientation of collagen fibrils and the arrangement of macromolecular proteoglycan ref.