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Transcript
Connective Tissue Characteristics of Connective Tissue Key word is variability. The distribution type changes depending on the organ. For example the skin has a lot but there is very little in the brain. This is the tissue that binds us together. 4 major classes Connective Tissue o Fat o Fibrous Cartilage Bone Blood Although the types are diverse they are classified together because they carry out the following functions: Support Protection Insulation Transport Just as their functions are diverse, their characteristics are as well: Share a common origin from the embryonic mesoderm (mesenchyme) Vasculature varies from avascular to vascular Make a nonliving extracellular matrix that can bear weight and abuse. Despite their diversity, all connective tissue is made up of the following elements. Their exact make up varies depending on the tissue’s functions. Ground substance Fibers Cells Together, the ground substance and fibers make up the matrix. This material varies from soft delicate material to tough tissue such as tendons and ligaments. The extracellular matrix (ECM) fills the voids between cells. 1 Components of the Matrix 1) Ground Substance. This is a featureless substance that is made up of water and proteins. This transparent fluid is found to one degree or another in all of the body's connective tissues. This viscous liquid, much like raw egg whites in appearance and consistency, surrounds all the cells in the body. It is made up of the following three components: Interstitial fluid Cell adhesion proteins Proteoglycans Interstitial Fluid The interstitial fluid (or tissue fluid) is a solution that bathes and surrounds the cells of multicellular animals. It is the main component of the extracellular which also includes plasma and transcellular fluid. On average, a person has about 11 liters (2.4 imperial gallons) of interstitial fluid, providing the cells of the body with nutrients and a means of waste removal. Interstitial fluid consists of a water solvent containing amino acids, sugars, fatty acids, coenzymes, hormones, neurotransmitters, salts, as well as waste products from the cells. Cell Adhesion Proteins (CAP) Cell adhesion proteins (CAP) are involved in cell-cell and cell-extracellular matrix binding. The major classes of cell adhesion molecules are the integrins, cadherins, selectins and the immunoglobulin. These are the glue that holds the cell and tissue together. They become continuous with the basement membrane and the various types of adhesion proteins such as desmosomes. Proteoglycans Are a complex group of proteins modified with sugar groups that control how viscous the ground substance is. Proteoglycans are heavily glycosylated proteins. They have a core protein with one or more attached glycosaminoglycan (GAG) chain(s). The chains are long, linear carbohydrate polymers that are negatively charged under physiological conditions, due to the occurrence of sulfate and uronic acid groups. Proteoglycans are a major component of the animal extracellular matrix, the “filler” substance existing between cells in an organism. Here they form large complexes, both to other proteoglycans and to fibrous matrix proteins (such as collagen). They are also involved in binding cations, and also regulating the movement of molecules through the 2 matrix. Evidence also shows they can affect the activity and stability of proteins and signalling molecules within the matrix. Examples of these include chondrotin sulfate and hyaluronic acid. The picture below shows how these proteins weave with each other to form a net work of anchoring structures for cells. The nature of this matrix depends on the tissue type. 2) Fibers There are three types of protein fibers which make up the matrix. These protein fibers intermingle with the proteins of the ground substance. These proteins are: Collagen fibers Elastic fibers Reticular fibers As with other components of the connective tissue network, their distribution depends on the function of the organ. Collagen This is a heavily crossed linked protein and as a result is tough and has a high tensile strength. Grossly collagen appears white. It 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. 3 Elastic Fibers Unlike collagen, elastic tissue as the name implies can stretch like a rubber band. It is made of the protein elastin which can stretch and recoil. It is found in the skin and lungs. If large amounts are present the tissue can appear yellow. Elastin tends to deplete as people age, resulting in wrinkled or stretched out skin. One might note the “pregnancy pouch” many women have many years after having a baby. In part, the leftover skin is a result of inadequate elastin, and also overstretching of the skin covering the abdomen during pregnancy. Reticular Fibers Reticular fibers or reticulin is a histological term used to describe a type of fiber in connective tissue composed of type III collagen. Reticular fibers crosslink to form a fine meshwork (reticulum). This network acts as a supporting mesh in soft tissues such as liver, bone marrow, and the tissues and organs of the lymphatic system. 3) Cell Component Within the connective tissue framework are “resident cells” These cells can become activated and form the characteristic fibers of their matrix. The suffix “blast” is used to describe these cells. Common cells include the: Fibroblast- lays down the connective tissue matrix Chondroblast- found in cartilage Osteoblasts- found in bone Blood cells 4 Other cell types found in the connective tissue are often associated with the immune system and healing these include: Fat cells White blood cells (neutrophils, eosinophils and lymphocytes) Macrophages Mast Cells 5 6