connective tissue

• Connective tissue consists of cells and extracellular matrix (ECM) which is produced by the cells of the connective tissue.
• Connective tissue cells are not connected to each other, they are separated by an intercellular space.
• Majority of connective tissue contain blood and lymph vessels, and nerves.
• Mucopolysaccharidoses are inherited malfunctions in degradation of glycosaminoglycans (GAGs) due to mutations in lysosomal enzymes.
• Intracellular accumulation of GAGs leads to disturbed embryonic development.
• During locomotion of cells, dynamic reconstruction and degredation of cell-matrix connection occurs.
• The function of connective tissue depends on the cells and fibers present within the tissue and the composition of the ground substance in the ECM.
• Loose connective tissue is composed of fibroblasts that produce the extracellular fibers and the ground substance, and many other cells.
• Bone tissue is composed of one cell type – osteocyte, which produce the fibers that make up the bulk of the bone tissue.
• Undifferentiated connective tissue is classified into cell-rich connective tissue and embryonic connective tissue.
• Mesenchyme, primarily found in the embryo, has small spindle shaped cells with processes and gap junctions, is undifferentiated, pluripotent, and collagen (reticular) fibers are present, and the extracellular space is with viscous ground substance.
• There are 28 kinds of collagen, named collagen I to collagen XXVIII, each with different a chain combinations (homo/heterometric).
• En dotendineum is a CT extension of the epitendineum which subdivides the tendon to fascicles.
• Cells of connective tissue proper include resident cells (mesenchymal cells, fibroblasts, fibrocytes, myofibroblasts), transient cells (white blood cells, lymphocytes, granulocytes, monocytes), and connective tissue fibers.
• Ligaments are fibers that are less regularly arranged than in tendons, are more elastic, and some need extra elasticity.
• Collagen is a right-handed triple helix (~300 nm) of three intertwined polypeptide (a) chains stabilized by hydrogen bonds between OH groups.
• In H&E - longitudinal section, Tendinocytes appear as rows of flattened basophilic nuclei.
• Dense irregular CT contains mostly collagen fibers, and few cells (typically fibroblasts), is strong, has little ground substance, and its fibers are arranged in bundles in various directions.
• Collagen is a glycoprotein, with sugar groups associating with the helix post-translationally.
• Aponeuroses resemble broad, flat tendons.
• Epitendineum is a thin CT capsule around the tendon, with less orderly fibers.
• In H&E - cross section, Tendinocytes appear as stellate cells.
• Each fiber is produced by fibroblasts and is composed of proteins with long peptide chains.
• Reticular/deep layer of the dermis is a relatively thick layer of dense irregular CT in the skin that provides resistance to tearing.
• Type I collagen is heterometric - 2* a1 and 1* a2, so: [a1(I)] 2 a2(I).
• Collagen molecules align head to tail in overlapping rows, giving strength to the collagen fiber.
• Three types of fibers are collagen, reticular, and elastic.
• Mucous connective tissue is found in the umbilical cord, it is widely separated spindle-shaped cells, has a gelatin-like ECM with “wharton’s jelly” ground substance which is found between thin collagen fibers.
• Mesenchymal cells produce hyaluronic acid rich ECM.
• Mesenchyme develops from mesoderm of the embryo via epithelo-mesenchymal transformation of cells and ECM production.
• Connective tissue proper consists of cells and ECM (intercellular material), ECM= connective tissue fibers + ground substance (glycosaminoglycans, proteoglycans, glycoproteins).
• There are two general subtypes of connective tissue: Loose connective tissue (areolar) and dense connective tissue (regular).
• Loose connective tissue (areolar) is composed of small amount of collagen fibers, lots of ground substance, primarily located beneath epithelia that cover the body surfaces and line its internal surfaces, associated with epithelium of glands and surrounds smallest blood vessels, pathogens that passed the epithelium are destroyed by the immune system here, and lamina propria is the loose connective tissue of the mucous membrane and contains large numbers of immune cells.
• Hyaluronan immobilizes certain molecules in desired locations of the ECM.
• Fibronectin is the most common multi-adhesive glycoprotein in connective tissue.
• If a large foreign body is found, the macrophages may fuse to form a large, 100 nucleus-wide cell called foreign body giant cells (Langhans cells).
• Macrophages are phagocytotic cells, derived from monocytes, members of mononuclear phagocytotic system (MPS), and have important role in immune responses as APCs that have MHC II on their surface for displaying proteins (antigens) that CD4 T lymphocytes interact with and may trigger a response.
• Hyaluronan is produced by hyaluronan synthases and degraded by hyaluronidases.
• Proteoglycans are fibrillary core proteins with GAG side chains accounting for the physicochemical properties of the molecules.
• Syndecans are integrant plasma membrane proteoglycans with receptor functions.