The ground substance is an aqueous gel of glycoproteins and proteoglycans that occupies the space between cellular and fibrillar elements of the connective tissue. It is characterized by a gel-like viscous consistency and is polyanionic.
Elastin and Elastic Tissue | SpringerLink
The characteristics of the ground substance determine the permeability of the connective tissue layer to solutes and proteins. Collagenous connective tissue is divided into two types, based upon the ratio of collagen fibers to ground substance:. Reticular fibers are composed of type III collagen.
Unlike the thick and coarse collagenous fibers, reticular fibers form a thin reticular network. Such networks are widespread among different tissues and form supporting frameworks in the liver, lymphoid organs, capillary endothelia, and muscle fibers. Elastic fibers contain the protein elastin, which co-polymerizes with the protein fibrillin.
These fibers are often organized into lamellar sheets, as in the walls of arteries. Dense, regular, elastic tissue characterizes ligaments. Elastic fibers are stretchable because they are normally disorganized — stretching these fibers makes them take on an organized structure. Although the connective tissue has a lower density of cells than the other tissues you will study this year, the cells of these tissues are extremely important. Fibroblasts are by far the most common native cell type of connective tissue.
The fibroblast synthesizes the collagen and ground substance of the extracellular matrix. These cells make a large amount of protein that they secrete to build the connective tissue layer. Some fibroblasts have a contractile function; these are called myofibroblasts. Chondrocytes and osteocytes form the extracellular matrix of cartilage and bone. More details and chondrocytes can be found later in this laboratory; osteocytes will be covered in the Laboratory on Bone.
The macrophage is the connective tissue representative of the reticuloendothelial, or mononuclear phagocyte, system. This system consists of a number of tissue-specific, mobile, phagocytic cells that descend from monocytes - these include the Kupffer cells of the liver, the alveolar macrophages of the lung, the microglia of the central nervous system, and the reticular cells of the spleen. You will encounter each of these later in the course; for now, make sure you recognize that they all descend from monocytes, and that the macrophage is the connective tissue version.
Macrophages are indistinguishable from fibroblasts, but can be recognized when they internalize large amounts of visible tracer substances like dyes or carbon particles. Macrophages phagocytose foreign material in the connective tissue layer and also play an important role as antigen presenting cells, a function that you will learn more about in Immunobiology. Mast cells are granulated cells typically found in connective tissue. These cells mediate immune responses to foreign particles.
In particular, they release large amounts of histamine and enzymes in response to antigen recognition. This degranulation process is protective when foreign organisms invade the body, but is also the cause of many allergic reactions. White fat cells are specialized for the storage of triglyceride, and occur singly or in small groups scattered throughout the loose connective tissue.
They are especially common along smaller blood vessels. When fat cells have accumulated in such abundance that they crowd out or replace cellular and fibrous elements, the accumulation is termed adipose tissue. These cells can grow up to microns and usually contain once centrally located vacuole of lipid - the cytoplasm forms a circular ring around this vacuole, and the nucleus is compressed and displaced to the side.
The function of white fat is to serve as an energy source and thermal insulator.
Brown fat cells are highly specialized for temperature regulation. For example, a project entitled Nasaltis is testing 3D-printed polymers that imitate the cartilage of the nose. The goal is to improve the elasticity of the prostheses used in rhinoplasty, since the printable biomaterials in biomedicine are currently too rigid. Cardiovascular diseases are another key target for this research. Blood vessels have a natural capacity to dilate and contract in order to facilitate blood circulation, powered by the heartbeat.
We also have to consider their biocompatibility with the organism and with blood, their mechanical resistance, etc. As a result, this bioglue can be used to close a wound on an organ in a few seconds, providing high-quality healing. The bioglue developed by D. Letourneur and L. Leibler can close a wound in a matter of seconds.
After three days, this nanoparticle bandage produces esthetically superior results compared with conventional sutures or cyanoacrylate adhesives see bottom right, click to zoom. Under the effect of air pushed up from the lungs through the trachea, the vocal folds change shape and produce periodic vibrations that modulate the frequencies of the voice.
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A 3D visualization of a network of collagen, elastic and muscle fibers in a human vocal fold vocal chord obtained by high-resolution X-ray microtomography. They have developed a proof-of-concept showing the impressive regenerating capacities of the periosteum, even in critical situations like the regeneration of large masses of bone tissue. A study now in progress, based on elastin hydrogels that were originally developed for artificial skin, is testing the effectiveness of this type of substitute on femur fractures in rats, with a view to potential applications in humans.
This cross-section shows the different layers of the periosteum, a vascularized soft membrane that covers certain bones. Until relatively recently, there was no effective method for measuring the elasticity of organs and tissues. French research, at the cutting edge of ultrasound technology, helped resolve this problem with the development of new ultrafast imaging techniques in the early s. Just as ultrafast cameras can reveal astonishing details invisible to the naked eye, the new ultrafast ultrasound techniques now make it possible to record an acoustic image of shear wave propagation and thus determine the elastic properties of tissues.
Since modifications in the elasticity of biological tissues are often linked to pathologies, the ability to measure this property provides valuable diagnostic information. In this example, 2D ultrasound elastography is used to screen for breast cancer. Bauraln, M. Guay, J. Factors Affecting the Proteolytic Degradation of Elastin. Kagan, R. Jordan, R. Lerch, D. Mukherjee, P. Stone, C. Proteolysis of Tropoelastin. Robert Mecham, Judith A. Foster, Carl Franzblau. Elastin Degradation in Human and Experimental Emphysema. Ines Mandl, T. Darnule, J. Fierer, S. Keller, Gerard M. Stone, V. Pereira, D.
Biles, G. Snider, H. Kagan, C.
Robert M. Senior, David R. Bielefeld, Barry C. General Discussion on Turnover and Elastolysis. Torres, V. Alvarez, L.
Special Stains – Which One, How and Why? Part II: Connective Tissue
Sandberg, W. Primary Structure of Porcine Tropoelastin. Gray, J.