A Complete Classification of Connective Tissues There are many systems of classification of connective tissues. The main criteria used for categorization are fibers( amount and type), and ground substance ( composition and physical consistency). Time of appearance, cell types, tissue vascularity, and functions are minor characteristics applied to refine classifications. The following is a commonly used categorization: 1. Embryonic Connective Tissues 1A. Mucous connective tissue: the mucoid contents of umbilical cords 1B. Mesenchyme : the embryonic connective tissue in the fetus. All mature connective tissues derive from mesenchyme. Mesenchyme tissue is replaced by mature connective tissue as the organism passes through infancy, childhood, adolescence and into adulthood. However, traces may still be found in some young adults. 2. Mature Connective Tissues 2A. Loose connective tissues 2Ai. Areolar tissue 2Aii. Adipose tissue 2Aiii. Reticular tissue 2.B. Dense connective tissues 2Bi. Dense regular connective tissue 2Bii Dense irregular connective tissue 2Biii. Elastic connective tissue 2C. Cartilage 2Ci. Hyaline cartilage 2Cii. Fibrocartilage 2Ciii. Elastic cartilage 2D. Rigid Connective tissue: Bone 2Di. Compact bone 2Dii. Cancellous/Spongy bone 2E. Liquid Connective Tissues 2Ei. Blood 2Eii. Lymph :
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Connective Tissues Composition: Connective tissues comprise the following components :cells, fibers, ground substance and blood supply --in some cases. Cells: Some cells of found in various types of connective tissue are fibroblasts, chondroblasts, chondrocytes, osteoblasts, osteocytes, reticular cells, fat cells, mast cells, plasma cells, formed elements of and lymphocytes. Matrix. The matrix of a connective tissue is the non-living substances secreted by fibroblasts the two constituents of matrix are fibers and the ground substance.. Fibers: The fibers of connective tissues are collagen fibers, reticular fibers and elastic fibers different types and combination of fibers are found in different types of connective tissues. Ground substance: The character of ground substance varies from the solid calcified substance of bone through the firm gel of cartilage , the viscous gel of areolar cartilage to the frank fluid consistency of blood plasma and lymph . mainly, ground substance is a solution of ions,salts, proteins, mucopolysaccharides ( glycosaminoglycans) proteoglycans of varying viscosity. A. Loose connective Tissue; The subtypes in this group are areolar, adipose(fat) and reticular connective tissue.. In this type cells are few( except for the adipose type) . Loose connective tissue underlies epithelium in many body locations. It anchors and supports the epithelium ; it also supplies it with nutrients and oxygen and removes carbon-dioxide and various kinds of dissolved waste solutes. Areolar tissue is able to perform all of these functions because of its rich vascular supply and the open loose texture of its ground substance Dense Connective Tissues: The sub-types in this group are dense regular connective tissue, dense irregular connective tissue and Dense elastic connective tissue. The cells are mainly fibroblasts but the relatively few fibroblasts and the scant ground substance are of less importance than the type,amount and orientation of the fibers. Fiber type is the most important characteristic in this grouping. The fibers are Type I collagen, Type II collagen and elastic fibers. Large Type I collagen fibers are arranged in wavy parallel bundles in dense regular tissue. In dense irregular Tissue collagen fibers display a 3-D arrangement in the ground substance. Fibers of elastic connective tissue are made of elastin and fibrillin. Type I collagen have great tensile strength. Type II network resists stress from several directions and elastic fibers enable tissue to extend ( up to 150%) and recoil to original dimensions. Cartilage: The subtypes of the class are hyaline cartilage, fibrocartilage and elastic cartilage Cells : The cells are chondroblasts (modified fibroblasts) and chondrocytes( mature chondroblasts). Matrix. The ground substance is usually a firm but flexible gel in which is embedded a network of collagen and elastic fibers.. The collagen fibers confer toughness on cartilage and the elastic fibers confer flexibility. However, collagen ground substance may have over 70% water. The dissolved solutes are usually proteins and the glycosaminoglycans(GAGs) chondroitin sulfate, hyaluronic acid(HLA), keratan sulfate, and dermatan sulfate. Hyaline cartilage has a perichondrium with fibroblasts and chondroblasts. . Chondrocytes exist in spaces of matrix called lacunae. This cartilage is found at the ends of ribs and in the epiphyseal plates of long bones Fibrocartilage. there is no perichondrial layer of connective tissue around this type of cartilage Cells; Chondrocytes in lacunae fibers: Thick collagen fibers ground substance(GS) : Scant; semi-firm in consistency This is the strongest type of cartilage. it may be found in menisci(pads) of knees, and in intervertebral discs. This tissue resits compressive shocks. Elastic cartilage; Perichondrial layer layer present Cells; Chondrocytes in lacunae Fibers: Elastic fibers plus some Type II collagen fibers This tissue confers strength and elasticity but maintains shape Locations ; pinnae, epiglottis, Rigid Connective Tissue : Bone Compact bone Cells ; osteoblasts and osteocytes, osteoclasts osteoblasts produce the proteinaceous ground substance as well as the collagen fibers. The matrix is then hardened to a rigid consistency by the infiltration of salts of inorganic elements, principally, calcium and phosphorus. Organization. The matrix of compact bone is organized into cylindrical structures around a central of Haversian canal. The cylinders are called osteons. The central canal contains blood vessels and nerves. Chondrocytes live in spaces in the matrix called lacunae. Canaliculi , small passages, connect the lacunae with the central canal. This enables the osteocytes to access the blood supply of the central canal This permits them to get nourishment and get rid of wastes. Long bones which are partly compact bone in structure, have a marrow cavity in which is fatty (yellow) bone marrow with adipocytes and triglyceride stores. Cancellous or Spongy bone. Cells: osteoblasts and osteocytes No osteons exist in this type of bone Matrix: collagen fibers and calcified ground substance Structure: Three dimensional network of spikes and trabeculae(processes) Red bone marrow and blood vessels exist inspaces between the trabeculae Spongy bone exist in cranial bones, ribs and at the ends of long bones. Spongy bone houses hematopoietic tissue and protects internal organs from physical shock. Liquid Connective Tissue: Blood Cells : Leukocytes, erythrocytes and thrombocytes ( platelets). Platelets are not living cells. They are fragments of bone marrow cells known as megakaryocytes Matrix: Blood plasma-- an aqueous solution of gases, ions , salts, and proteins; The major protein solutes are hormones, enzymes, albumin, globulins, and fibrinogen ( precursor of fibrin fibers) Blood is in heart and blood vessels . It distributes nutrients and oxygen. It also removes wastes of all types. White blood cells protect against microbes, antigens, allergens. Platelets are essential factors that induce clotting to protect against excessive bleeding. The high water content of blood enables it to function in the distribution of body heat, and the maintenance of temperature homeostasis. Lymph Cells : mainly lymphocytes;:These cells are important in immunological antigen-antibody reactions. Lymph matrix: This is a pale proteinaceous fluid found in lymph vessels and lymphoid organs. It links the interstitial fluid with blood plasma. One of its functions is to return water and proteins to the cardiovascular system. Lymph flows in a one - -way route to the blood vessels and the heart.