Unit 3

• Connective tissue originates from the embryonic mesenchyme
• The ECM of connective tissue is made up of protein fibres (collagen and elastic fibres) and ground substances (hydrophilic proteoglycans, glycosaminoglycans and glycoproteins alongside the common ECM component, water )
• The ground substances that make up the ECM of connective tissue are glycosaminoglycans, glycoproteins and hydrophilic proteoglycans
• The main functions of connective tissue is the structural support and connection of tissue and cells and offers metabolic support of cells
• The cells of connective tissue include macrophages, adipocytes, fibroblasts, mast cells, plasma cells and other leukocytes
• Fibroblasts: structurally they are long, ireegular and have oval nuclei. Their function is to synthesize and secrete the components of the ECM such as elastin, GAG and collagen
• Adipocytes: structurally they are large and mainly found in adipose tissue and functionally they store triglycerides
• Macrophages: structurally they are different to those found circulating in the blood. Functionally they aid with the turnover of the ECM, they mediate the phagocytosis of dead cells and debris and finally, they act as APCs by presenting antigens to lymphocytes
• Mast cells: They differentiate into blood cell precursors. These blood precursors are filled with secretory granules which release vasoactive components during inflammation and allergic reactions.
• Plasma cells: they result from the differentiation of B lymphocytes. Functionally they provide surveillance against antigens and stimulate tissue repair
• Fibres are a crucial component of connective tissue. Structurally they are elongated, made up of proteins that polymerise after secretion from fibroblasts. The three main types of fibres are collagen, reticular and elastic (elastin). The type of fiber is mediated by the properties and function of the connective tissue
• Collagen is a key element of all connective tissue, epithelial basement membrane and the external laminae of muscle and nerve cells. Collagen is the most abundant protein in the body.