HISTOLOGY CHAPTER 3

• Connective tissue are composed of cells and an extracellular matrix
• The connective tissue is classified into 2 major groups: connective tissue proper and special types
• All connective tissues are derived from mesoderm
• Some connective tissues found in the head that are derived from ectoderm
• Connective tissue proper is found all over the body
• The function of connective tissue proper is to provide support framework 'stroma" of tissues and organs
• Connective tissue proper acts as an avenue for the passage of blood vessels and nerves into and from the interior organs and other parts of the body
• CONNECTIVE TISSUE PROPER PROVIDES ARENA AS WELL AS THE CELLS THAT ARE NEEDED TO DEFEND THE BODY AGAINST INVADING ORGANISMS AND OTHER HARMFUL SUBSTANCES
• Ground substances consists mainly of water, stabilized by proteoglycans, hyaluronic acid, mineral salts, and glycoproteins
• Proteoglycans are the main constituents, responsible for the gelatinous character of the ground susbstance
• Extracellular fibers are the one that responsible for the supportive functions of connective tissue
• Three types of fibers are collagen, elastic, and reticular fiber
• The collagen fibers appears pink in h&e preparation
• Collagen fibers are made up of collagen, the most abundant protein in the body
• There are 28 types of collagen in the body
• The tendons appears white in fresh tissue
• Collagen fibers are made of collagen type 1
• COLLAGEN FIBERS HAVE A TENSILE STRENGTH GREATER THAN STEEL, SLIGHTLY FLEXIBLE BUT INELASTIC
• COLLAGEN FIBERS IS THE MAIN EXTRACELLULAR FIBERS OF THE COLLAGENOUS CONNECTIVE TISSUES
• FIBROBLAST AND MESENCHYMAL CELLS PRODUCE AND SYNTHESIZE THE MOLECULAR PRECURSOR OF COLLAGEN FIBER,
• PROCOLLAGEN OF CARTILAGEAND BONEARE PRODUCED BY CHONDROBLASTAND OSTEOBLAST
• Elastic fibers impart yellow color in fresh tissue
• Elastic fibers remains unstained in h&e preparation
• The core of elastic fibers is made up of elastin
• Elastin is a highly insoluble protein responsible for the elasticity of the elastic fibers
• Elastic fibers form the elastic sheets seen in the walls of large and medium-sized arteries
• Elastic fibers also found in the ligamenta flava of the vertebrae
• Elastic fibers have less tensile strength than collagen fibers but are very flexible. it can stretch up to twice the original length and can recoil back
• ELASTIN FORMS THE LAMELLAE OF THE ARTERIES ARE SYNTHESIZED BY SMOOTH MUSCLE CELLS.
• MEANWHILE THE SAME CELLS ALSO PRODUCE THE PRECURSOR PROTEIN OF ELASTIN CALLED TROPOELASTIN
• Reticular fibers also made up of collagen type iii
• The reticular fibers stain black in h&e preparations when impreganted with silver salts, that is why they are referred to as argyrophilic fibers
• The reticular fibers is the main extracellular fibers of reticular tissue
• RETICULAR FIBERS ARE FORMED IN A SIMILAR MANNER AS COLLAGEN FIBERS HOWEVER, THE PRECURSORS OF RETICULAR FIBERS ARE SYNTHESIZED AND EXCRETED BY SPECIALIZED FIBROBLASTS CALLED RETICULAR CELLS
• There are two types of cell of the connective tissue: Resident and vitising cells
• Resident cells are cells that stay permanently in connective tissue
• Resident cells consists of mesenchymal cells, fibroblasts and fibrocytes, reticular cells, adipose cells, mast cells, and resident macrophages
• Visiting cells refers to a cells that are transient in connective tissue
• Visiting cells consists of inflammatory macrophages, plasma cells, and leukocytes
• Mesenchymal cells refers to a multipotential stem cells that have differentiated from pluripotential cells