CONNECTIVE TISSUE First lecture By Dr. Wahda A. M. Kharofa

Objectives: To give information about: What is connective tissue? Characterized, functions, ground substance. Types of fibers. Types of cells in connective tissue.

Connective Tissue Connective tissue is a form of fibrous tissue. It is one of the four types of tissue in traditional classifications (the others being epithelial, muscle, and nervous tissue). Collagen is the main protein of connective tissue in animals and the most abundant protein in mammals, making up about 25% of the total protein content. Connective tissue are found in all organs of the body except the central nervous system, you see it underlying epithelia, between layers of smooth muscles, separating glandular tissue into lobules and lobes and every providing a framework for blood vessels.tissueepithelialmuscle nervous tissueCollagen

Connective Tissue is characterized by: Binding and supporting the organs. It is vascular except the cartilage. It is derived from mesoderm layer. It is consists of cell immersed in large amount of intercellular substance, which is formed by cells.

The major constituent of connective tissue is: Extracellular matrix: composed of fibers and ground substance. Connective tissue cells. Functions of connective tissue: Support, surround, connect other tissues Structural framework for body Protect organs Transport fluids and dissolved materials Store energy and minerals Immunity

Extracellular matrix: The extracellular matrix composed of: Ground substance: is a hydrated colorless and transparent, amorphous material, It is binding cells to the fibers of connective tissue. Ground substance is found in all cavities and clefts between the fibers and cells of connective tissues, but its main structural constituent is proteoglycans which consists of proteins (~5%) and polysaccharide chains (~95%). The polysaccharide chains belong to one of the five types of glycosaminoglycans, which form the bulk of the polysaccharides in the ground substance.

Fibers: there are three types of connective tissue fibers as shown:  Collagenous fibers (white fiber): Collagen fibers (white fiber): they are the most numerous and strongest fibers in the body derived from connective tissue cells called "fibroblasts". These fibers are straight or wavy, unbranched consist of protein called "collagen". They always run parallel to each other form  ing bundles, which branched and anastomose. Collagen is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content. Collagen found in fibrous tissues such as tendon, ligament and skin, cartilage, bone and blood vessels. So far, 28 types of collagen have been identified and described. fibrous tissues

 The five most common types are: Collagen I: skin, tendon, dentin, cementum and bone. Collagen II: cartilage (main component of cartilage). Collagen III: reticulate (main component of reticular fibers), commonly found along side type I. Collagen IV: forms bases of cell basement membrane. Collagen V: cells surfaces, hair and placenta.

◦ Elastic yellow fibers: they differ from collagen that they are thinner than fibers (the white fibers), they branched and unite with one another forming irregular network. They formed from protein called "elastin", which resist boiling, dilute acids, alkaline and gastric juice. They are generally formed by fibroblasts. They are found ligaments and vocal cords

Reticular fibers: they are very fine fibers, branched and anastomose forming a network, they are found around spleen, lymph nodes, red bone marrow, liver, endocrine glands and kidney. They are associated with special cells called reticular cells. Reticular fibers consist of collagen - although the main type of tropocollagen found in reticular fibers. Reticular fibers give support to individual cells, for example, in muscle and adipose tissue.

Connective tissue cells : There are many types of cells found in connective tissue: Fibroblast : it is the most common cell found in the connective tissue, the young fibroblast is star in shape with many processes, the nucleus is large oval & pale in color while the mature cell is called "fibrocyte", which is smaller than fibroblast, it is spindle in shape have few processes, the nucleus is smaller, darker & elongated. The function of fibroblast is the formation of fiber & matrix.

◦ Undifferentiated mesenchymal cells (cells of regeneration) : These cells have ability to give rise any kind of cells, it form the muscle cells, they are smaller than fibroblast but have the same appearance, they have an elongated nucleus.

◦ Macrophages : they are either fixed or wandering, the fixed macrophage known as histiocytes, while the wandering macrophage is called amoeboid. The fixed macrophages are spindle or star in shape have an ovoid nucleus while the wandering is irregular in shape and the nucleus is round. The functions of macrophage is engulf of the foreign bodies and accumulate it in their cytoplasm in the form of granules by their thick pseudopodia (Fig below).

Pigment cell: they are elongated cells with short irregular outgrowth, the cytoplasm contains small granules of melanin (brown or black pigment granules). it is seen in the skin and eyes.

◦ Reticular cells : they are star in shape with processes extending in several directions and often in contact with the processes of neighboring cells, they have a large pale nucleus and centric, they lie between the reticular fibers, they engulf the foreign bodies, they found in lymphatic nodes, spleen and liver.

Plasma cell: it is ovoid in shape with eccentric nucleus, the chromatin granules in the nucleus are coarse and deeply stained, they arranged at the periphery of the nucleus forming a cart- wheel or o clock face appearance.Above the nucleus there is a pale colorless area which represent the Golgi region called Golgi image, the function of plasma cell is the formation of antibodies against antigen which enter the body.

Mast cells: they are large ovoid in shape with small ovoid nuclei and coarse cytoplasmic granules.The function of mast cell is the production of heparin (anticoagulation) and also produce histamine (vasodilator) which cause dilation of capillaries, it produce third substance serotonin in some animals.

Fat cells: these cells found singly or in groups contain fat globules, are derived from undifferentiated mesenchymal cells. The function is the synthesis and storage of triglycerides. There are two types of fat cells: i. Unilocular fat cells: cells with a single, large lipid droplet form white a dispose tissue which ii. Multilocular fat cells: cells with multiple, small lipid droplets, form brown adipose tissue.

Some blood cells: some types of blood cells might be seen in the connective tissue, in special conditions such as neutrophils in the site of infection, eosinophil in the site of sensitivity and lymphocytes in the chronic infection.