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Lecture 20

DEV2011: Lecture 20 summary

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Department
Medicine
Course
DEV2011
Professor
Various
Semester
Spring

Description
LECTURE 20 Connective Tissue Composition: Connective tissue (CT) is a kind of biological tissue that supports, connects, or separates different types of tissues and organs of the body. It is one of the four general classes of biological tissues—the others of which are epithelial, muscular, and nervous tissues. All CT has three main components: cells, fibers, and extracellular matrices, all immersed in the body fluids. Fibroblasts: A fibroblast is a type of cell that synthesizes the extracellular matrix and collagen, the structural framework (stroma) for animal tissues, and plays a critical role in wound healing. Fibroblasts are the most common cells of connective tissue in animals. Fibroblasts and fibrocytes are two states of the same cells, the former being the activated state, the latter the less active state, concerned with maintenance and tissue metabolism. Chondocytes: CHondocytes are the only cells found in healthy cartilage. They produce and maintain the cartilaginous matrix, which consists mainly of collagen and proteoglycans. The organization of chondrocytes within cartilage differs depending upon the type of cartilage and where in the tissue they are found. Osteoblasts: Osteoblasts are mononucleate cells that are responsible for bone formation; in essence, osteoblasts are specialized fibroblasts that in addition to fibroblastic products, express bone sialoprotein and osteocalcin. Osteoblasts produce a matrix of osteoid, which is composed mainly of Type I collagen. Osteoblasts are also responsible for mineralization of this matrix. Bone is a dynamic tissue that is constantly being reshaped by osteoblasts, which are in charge of production of matrix and mineral, and osteoclasts, which break down the tissue. The number of osteoblasts tends to decrease with age, affecting the balance of formation and resorption in the bone tissue,and potentially leading to osteoporosis. Adipocytes: Adipocytes, also known as lipocytes and fat cells, are the cells that primarily compose adipose tissue, specialized in storing energy as fat. Collagen: Collagen is a group of naturally occurring proteins found in animals, especially in the flesh and connective tissues of vertebrates. [1It is the main component of connective tissue, and is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content. Collagen, in the form of elongated fibrils, is mostly found in fibrous tissues such as tendon, ligament and skin, and is also abundant in cornea, cartilage, bone, blood vessels, the gut, and intervertebral disc. The fibroblast is the most common cell which creates collagen. Reticular Fibres: Reticular fibres is a type of fiber in connective tissuecomposed of type III collagen secreted by reticular cells. Reticular fibers crosslink to form a fine meshwork (reticulin). This network acts as a supporting mesh in soft tissues such as liver, bone marrow, and the tissues and organs of the lymphatic system. Reticular fiber is composed of one or more types of very thin and delicately woven strands of type III collagen. These strands build a highly ordered cellular network and provide a supporting network. Many of these types of collagen have been combined with carbohydrate. Elastic Fibres: Elastic fibres are bundles of proteins (elastin) found in extracellular matrixof connective tissue and produced by fibroblasts and smooth muscle cells in arteries. The elastic fiber is formed from the elastic microfibril (consisting of numerous proteins such as microfibrillar-associated glycoproteins, fibrillin, fibullin, and the elastin receptor) and amorphous elastin. Loose Connective Tissue: Loose connective tissue is a category of connective tissue which includes areolar tissue, reticular tissue, and adipose tissue. Loose connective tissue is the most common type of connective tissue in vertebrates. It holds organs in place and attaches epithelial tissue to other underlying tissues. It also surrounds the blood vessels and nerves. Cells called fibroblasts are widely dispersed in this tissue; they are irregular branching cells that secrete strong fibrous proteins and proteoglycans as an extracellular matrix. The cells of this type of tissue are generally separated by quite some distance by a gel-like gelatinous substance primarily made up of collagenous and elastic fibers. Loose connective tissue is named based on the "hair weave" and type of its constituent fibers. There are three main types: - Collagenous fibers: collagenous fibers are made of collagen and consist of bundles of fibrils that are coils of collagen molecules. - Elastic fibers: elastic fibers are made of elastin and are "stretchable." - Reticular fibers: reticular fibers consist of one or more types of very thin collagen fibers. They join connective tissues to other tissues. Dense Connective Tissue: Dense connective tissue has fibers as its main matrix element. Dense connective tissue is mainly composed of collagen type I. Crowded between the collagen fibers are rows of fibroblasts, fiber-forming cells, that manufacture the fibers. Dense connective tissue forms strong, rope-like structures such as tendons and ligaments. Tendons attach skeletal muscles to bones; ligaments connect bones to bones at joints. Ligaments are more stretchy and contain more elastic fibers than tendons. Dense connective tissue also make up the lower layers of the skin (dermis), where it is arranged in sheets. It is often divided into "Dense regular connective tissue" and "Dense irregular connective tissue". Dense Regular Connective Tissue: Dense regular connective tissue provides connection between different tissues. The collagen fibers in dense regular connective tissue are bundled in a parallel fashion. Dense Irregular Connective Tissue:
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