China
Africa
Explore chapters and articles related to this topic
Neck and chest
Published in Jani van Loghem, Calcium Hydroxylapatite Soft Tissue Fillers, 2020
Yana A. Yutskovskaya, Anna Daniilovna Sergeeva
Aging of the skin occurs mainly due to atrophic changes in the dermis and hypodermis. The main substance is the redistribution of glycosaminoglycans, which undergo qualitative changes. The content of glycoproteins, in particular fibronectin, plays a role in the interaction of fibroblasts with collagen fibers. The fibers themselves atrophy and become looser. Collagen fibrils can lose periodic striation, and there is a delay in their maturation. Elastin fibers become coarse and partially fragmented. There are areas where they thicken, especially under the epidermis (senile elastosis). In this case, the hypodermis plays a major role, since it participates in the formation of granulation tissue—an important morphofunctional element of the regenerative process; there is a pool of undifferentiated, young and mature fibroblasts. The hypodermis also contains collagen, elastin, and reticular fibers [1].
Pathological Processes of Skin Damage Related to Toxicant Exposure
Published in David W. Hobson, Dermal and Ocular Toxicology, 2020
Collagen Degeneration — Replacement of normal collagen fibrils with eosinophilic, glassy to granular substance which may be disorganized and fragmented (collagenolysis). Most collagen changes are not consistent with specific toxicant exposure.
Introduction and Review of Biological Background
Published in Luke R. Bucci, Nutrition Applied to Injury Rehabilitation and Sports Medicine, 2020
Collagen structure begins with synthesis of procollagen chains. Procollagen chains are unique to each type of collagen, but are approximately 1055 amino acids in length. Three procollagen chains form a triple helix, which is the basic unit of collagen. Because of the amino acid sequence of collagen, which is mostly a trimer of glycine, a variable amino acid (usually lysine) and proline, each polypeptide chain forms a left-handed helix which can be intertwined with two other chains to form a right-handed triple superhelix (tropocollagen). Tropocollagen is 300 nm in length and around 285,000 Da. Extensive posttranslational modifications ensue, which are dependent on adequate nutrient status, as will be detailed in subsequent chapters. Collagen is glycosylated, and modified proline and lysine residues provide stabilization of the triple helix structure. Cross-linking with other collagen molecules forms collagen microfibrils. Collagen fibrils are formed from further cross-linking of large numbers of microfibrils. Finally, collagen fibers are formed by aggregation of collagen fibrils, which by now are macroscopic in size. Thus, simple chains of amino acids can be amplified into large physical structures.
A Review of Lens Biomechanical Contributions to Presbyopia
Published in Current Eye Research, 2023
The lens capsule plays a critical role in the development of the ocular lens as well as influencing how lens properties change throughout life. Changes to the lens capsule structure can heavily influence lens behavior, especially with regard to accommodation since the lens capsule is the densest and most stiff structure in the ocular lens. It is also the thickest basement membrane in the body.3 Electron microscope analysis revealed that the lens capsule is composed of parallel lamellae which are more tightly packed near the outer surface of the lens. The lamellar structure of the lens capsule appears to disappear with age and the capsule becomes more homogeneous.3 The capsule consists mostly of collagen types I, III, and IV, with collagen IV forming the majority of the basement membrane. Type IV collagen forms a mesh network loosely resembling chicken wire, with crosslinking between the triple helical collagen strands. These cross links are thought to consist largely of 7S domain disulfide cross-link bonds. Collagen IV may also be more flexible than other collagen types like collagen I and II due to having more interruptions between its triple helical segments where crosslinking and molecular binding occurs. Collagen molecules typically interlink through bonding of triple helical domains to form thicker collagen fibrils, and these fibrils can then continue to lace together into thicker rope like fibers or intertwine into a mesh.3
Tensile Viscoelastic Properties of the Sclera after Glycosaminoglycan Depletion
Published in Current Eye Research, 2021
Hamed Hatami-Marbini, Mohammad Pachenari
The scleral viscoelastic properties are important to keep the overall shape of eyeballs resilient against loads resulting from variations in the intraocular pressure (IOP) and eye movement.1,2 The mechanical behavior of the sclera depends on the assembly and mechanical properties of its extracellular matrix (ECM).3 Microscopically, the sclera is a dense collagenous tissue consisting of collagen fibrils of various diameters.4 Scleral collagen fibrils are primarily made of type I (~90%) and type III (~5%).5 The proteoglycans (PGs), composed of a core protein to which glycosaminoglycan (GAG) side chains are covalently attached, occupy the interfibrillar compartment.6 GAGs are inherently hydrophilic and absorb water molecules into the ECM; thus, they affect the hydration and solute diffusion inside the sclera.7 Among various types of PGs, decorin and biglycan, containing dermatan and chondroitin sulfate GAG side chains, are plentiful in the sclera.8 PGs have a dominant role in the scleral development and repair; they are involved in the regulation of collagen fibrillogenesis and cell adhesion.2,9,10
Glimpses into the molecular pathogenesis of Peyronie’s disease
Published in The Aging Male, 2020
Evert-Jan P. M. ten Dam, Mels F. van Driel, Igle Jan de Jong, Paul M. N. Werker, Ruud A. Bank
Collagen types I, III, and V are fibrillar collagens and can form heterotypic fibrils, i.e. molecules of all three collagen types are found to be associated in a single fibril [44]. An inverse relationship has been found between fibril diameter and the amount of collagen type III or V towards collagen type I [45]. Thus, an increased amount of collagen type III or V at the expense of collagen type I results in thinner collagen fibrils. Keeping in mind that we observed an increased COL3A1 and COL5A1 mRNA ratio towards COL1A1 in affected plaques, compared to healthy tunica albuginea, one would expect thinner collagen fibrils in plaques. We have not investigated this, but thinner collagen fibrils have indeed been observed in PD [46]. The same applied for an increased amount of collagen type V protein, which is in agreement with our mRNA data.