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Lec-3 Histology Dr.Ahmed_2015 Connective Tissues are responsible for providing and maintaining form to the body. They function in a mechanical role, providing a matrix that connects and binds the cells and organs and ultimately gives support to the body. Connective tissue composed of:C.T. fibers; C.T. cells; and Matrix Function of C.T. The functions of the various types of C.T. are generally depending on the types of cells, fibers, and the characters of the ground substances in the matrix. The functions include the binding together, support, and physical and immunologic protection of other tissues and organs, as well as storage. 1 FIBERS OF CONNECTIVE A. Collagen fibers TISSUE PROPER They provide strength, the more cartilage the stronger the tissue is. It is demonstrated using the Masson & Gomori techniques and with the Van Gieson stain. The only monosaccharide found in the human body. B. Elastic fibers They are abundant in tissue that needs flexibility, as they allow tissue to stretch. These fibers cannot usually be seen in H&E stains. Special stains for these fibers are Verhoeff’s van Gieson, Weigerts Stain, or Gomori. C. Reticular fibers They have identified as a type of collagen. They may be demonstrated with argyrophillic reactions, as they have the ability to absorb silver from a solution. The silver may then be reduced to a metallic form. Lec-3 Histology Dr.Ahmed_2015 Types of cells in C.T. Fibroblasts – most common cells in connective tissue. *Mesenchymal – these are primitive cells that may develop into other differentiated cell types if the need arises for replacement. Adipose or Fat - these synthesize and store lipid and are more common in most loose connective tissue. Mast cells – contains abundant secretory granules. These granules contain heparin & histamine and exhibit metachromasia when stained with Toluidine Blue. Macrophages – they are known as the “big eaters” or scavenger cells that are found not only in connective tissue but in a variety of other tissue as liver, myeloid, and lymphatic tissue. Plasma cells – they derive from B lymphocytes produce immunoglobulins. Blood cells – may be found in tissue. Collagen Collagen is the main protein of connective tissue. It has great tensile strength, and is the main component of ligaments and tendons. It is responsible for skin elasticity, and its degradation leads to wrinkles that accompany aging. Collagen also fills out the cornea where it is present in crystalline form. Collagen is the most abundant protein in mammals. Collagen has an unusual amino acid composition. It contains large amounts of glycine and proline, as well as two amino acids that are not inserted directly by ribosomes – hydroxyproline and hydroxylysine Types of collagen Collagen occurs in many places throughout the body, and occurs in different forms known as types: Lec-3 Histology Dr.Ahmed_2015 • Type I collagen - This is the most abundant collagen of the human body. It is present in scar tissue, the end product when tissue heals by repair. It is found in tendons and the organic part of bone. • Type II collagen - Articular cartilage • Type III collagen - This is the collagen of granulation tissue, and is produced quickly by young fibroblasts before the tougher type I collagen is synthesized. • Type IV collagen - Basal lamina • Type V collagen - most interstitial tissue, assoc. with type I • Type VI collagen - most interstitial tissue, assoc. with type I • Type VII collagen - epithelia • Type VIII collagen - some endothelial cells • Type IX collagen - cartilage, assoc. with type II • Type X collagen - hypertrophic and mineralizing cartilage • Type XI collagen - cartilage • Type XII collagen - interacts with types I and III Elastic Elastic fibers are bundles of proteins (elastin) found in connective tissue and produced by fibroblasts and smooth muscle cells in arteries. These fibers can stretch up to 1.5 times their length, and snap back to their original length when relaxed. Bundles are formed from covalent cross-linking between two amino acids: desmosine and isodesmosine. Reticular Fibers – Reticular fibers are composed of type III collagen. - The fibrils are branched, with a narrow diameter, and do not bundle to form thick fibers. - Reticular fibers provide a supporting framework for cellular constitutes of various organs. - They are not stained by routine H&E stain, stained with Silver technique, and they are PAS positive (contain sugar group) fibers. - Reticular cells produce the collagen of reticular fibers in hemopoietic and lymphatic tissues. - Fibroblasts produced reticular fibers in other locations The ground substance contains a variety of molecules secreted by CT cells such as :- - Proteoglycans (aggrecan, syndecan) - Multiadhesive glycoproteins (fibronectin, laminin). - Glycosaminoglycans (dermatan sulfate, keratan sulfate, hyalronic acid). Lec-3 Histology Dr.Ahmed_2015 TYPES OF CONNECTIVE TISSUE Loose connective tissue - delicate, flexible, not very resistant to stress, well vascularized. All types of connective tissue cells present. Majority are fibroblasts and macropahges. Collagen, elastic, and reticular fibers present. In certain organs (intestine) and in certain disease conditions, numerous lymphocytes may be present. Loose connective tissue also called areolar tissue,suppots epithelium and organs.Its presentce in lungs,arteries,the urinary bladder allaws these organs to expand and it protective many organs ,muscles nerves ,blood vessels.The second type of loose connective tissue is adipose tissue ,is a special type of losse connective tissue in which the cells enlarge and storage fat.It has little extracellular matrix ,it stored energy,it also releases a hormone called leptin which regulates appetite-control centers in the ,around the kidney, an on the surface of heart. Dense connective tissue - Clear predominance of collagen fibers at expense of ground substance. Fewer cells than loose. Less flexible and more resistant to stress. Dense connective tissue found in tendons which connect muscles to bone and ligament which connect bone to bone. When collagen bundles are present without apparent orientation, called dense irregular connective tissue. When oriented in parallel arrays, called dense regular connective tissue. Elastic tissue - bundles of thick, parallel elastic fibers. Small amount of loose connective tissue around each bundle. Yellow color. Reticular tissue - a specialized loose connective tissue with reticular cells that form a fine matrix of reticular fibers. Provides a structural framework for hematopoietic organs such as bone marrow and spleen. Mucous tissue - a lot of amorphous ground substance composed mainly of hyaluronic acid (glycosaminoglycan). Forms a jellylike tissue. Mainly fibroblasts present. Found in umbilical cord and pulp of young teeth. Adipose tissue - fat cells are connective tissue cells that are specialized for lipid synthesis and storage. As they differentiate, these cells retract their cytoplasmic processes and become spherical. This type of connective tissue is an exception to the rule in that it does not have much “extra”cellular ground substance. Lec-3 Histology Dr.Ahmed_2015 Instead, these cells synthesize and store copious amounts of lipid. This means that the bulk of the tissue is composed of lipid rather than cells. This is probably the reason it is classed as a connective tissue. There are two types of adipose tissue, White adipose tissue - Composed of adipose cells, each with a single very large droplet (unilocular) of lipid (mostly triglyceride) tat occupies nearly all the volume of the cell. This lipid is a stored energy reserve that the body may call on in times of need. The nulclei are always at the periphery of these cells. Brown adipose tissue - each cell contains multiple droplets of lipid (multilocular). The nuclei of these cells may be central with in the cell. Also contain lipochrome pigments that cause the tissue to have a brown hue. Widespread in fetus and young child. In adult humans it occurs in localized in small areas,; however, it is abundant in animals that hibernate. Important in heat production in the fetus, young child, and in hibernating animals. Specialized connective tissue 1-Cartilage 2-Bone 3-Blood