Adobe Systems Department of Histology and Embryology 1 Tissue definition. Connective tissue classification and function. visualization of connective tissues. Concept of tissue & Connective tissue [USEMAP] Adobe Systems Department of Histology and Embryology 2 What is a tissue? quick remainder Functional three-dimensional group of morphologically similar cells and their products. [USEMAP] Adobe Systems Department of Histology and Embryology 3 What is connective tissue and what is its function? Connective tissue is made of Cells, and ECM. ECM is made of amorphous component and a fibrillar component. Function of connective tissue: Structure, defense, Environment, repair [USEMAP] Connective tissue Connective tissue is made of cells and extracellular matrix. Extracellular matrix (ECM), as general definition made of fibrous component and amorphous component (ground substance). Connective tissue is the most abundant tissue of the body. Connective tissue is unique in that it is mainly composed of matrix and to lesser extent from cell (unlike muscle, epithelium or nervous tissue). Function of connective tissue: Structural support – mechanical support and shape. Defense – mechanical protection (skin, hair, bones), immune (monocytes, macrophages, skin). Functional environment – reticular fibers in hematopoietic tissue. Repair – injury repair and scarring (fibroblasts, myofibroblasts). Adobe Systems Department of Histology and Embryology 4 Classification Proper Special Connective tissue Adipose Elastic Mesenchymal Reticular Dens Loose Regular Irregular [USEMAP] Adobe Systems Department of Histology and Embryology 5 Connective tissue proper Dense – regular Function: resistance to pull. Components: collagen I, cell Found in: tendons, ligaments Dense – irregular Function: resistance all directions Components: collagen I, cells Found in: sclera, fascia, joint capsule Loose Function: house immune cell, structural. Components: collagen I, III, elastic fiber, cells Found in: tunica submucosa, adventitia of vessels. Collagen mnemonic 1 – one – bone 2 – two – cartwolage 3 – three – three-ticular – reticular c.t. 4 – four – under the floor – basement membrane [USEMAP] Classification of connective tissue proper First, we may classify the cells of connective tissue as being resident cells (fibroblast, reticular cells, adipocytes) or wandering cells (plasma cells, mast cells, macrophages). Next, we can classify according to the response to deformation  dens, loos or elastic connective tissue. Dens Dens connective tissue is one that has high content of collagen type I. Provides mechanical protection of organs. Characterized in small amount if cells and abundant fibrillar component in ECM. Cells of the connective tissue are called fibroblast (active), fibrocytes (non-active). Regular Regular means that all fibers are oriented parallel, in the same direction. This organization provides very strong resistance to pull applied in parallel to fibers. Seen in tendons and ligaments. Irregular Here we may again see high content of fibers however, in this case the fibers are oriented in all directions. And provide mechanical resistance to pull in various directions. Can be found in the sclera, fascia, fibrous capsule of internal organs. Loose Loss collagen connective tissue consist of relatively low content of fibers, high content of cells. It has better blood supply compared to dens C.T. it also houses immune cells. Found in dermis, in lamina propria and in tunica submucosa of viscera. Fibrous component consists of collagen and elastic fibers. Adobe Systems Department of Histology and Embryology 6 Special types of connective tissues Elastic Function: elasticity Components: elastic fibers Found in: elastic vessels, lungs Reticular Function: 3D network Components: reticular fibers, cells Found in: basement membrane Mesenchymal Function: differentiation, signaling, structural. Components: mesenchymal cells, Ground substance. Found in: Wharton's jelly, chorion. Adipose Function: energy storage Components: adipocytes, collagen (few) Found in: subcutaneous, around viscera. [USEMAP] Specialized connective tissue Those connective tissue show some special features allowing the function of specific body part or organ. Elastic connective tissue High content of elastin protein (fiber). Relatively low number of cells. Characterized by the ability of the tissue to return to original shape after deformation applied (= elasticity). Typically seen in the vocal cords or in elastic membranes of the aorta. Visualization is made by special staining – orcein – stain elastic fibers in brown. Reticular connective tissue Made by reticular cells that produce reticular fibers (type III collagen). This tissue is organized in a 3D network that specialized to house blood precursor cells and lymphocytes. Therefore, this type of tissue is seen in lymphoid tissue, and in hematopoietic tissue -bone marrow (blood producing). Visualization is made by special staining – silver impregnation that stain reticular fibers in black. Adipose tissue Adipose tissue can be subdivided in to white and brown adipose tissue. White adipose tissue Adipose tissue is specialized in storing triglycerides (fat storage). This tissue is abundant with cells called adipocytes. It has also a function of producing the hormone leptin. Adipocytes are typically having large droplet of fat and their nucleus is compressed at the periphery. Brown adipose tissue This tissue is found mainly in newborns and small children up to first year of life. The cells here are multivacular, (meaning multiple droplets). Brown adipose tissue is specialized in heat production and energy production. Those cells have a lot of mitochondria which accounts for its’ brown color. Adobe Systems Department of Histology and Embryology 7 Staining of connective tissue Silver impregnation stain Used for lymphatic tissue Reticular fibers stain black to dark brown. Lymph node, spleen, tonsils Azan stain used Visualize collagen fibers blue. Nuclei stain pink-red Can be used for all tissues having collagen. Orcein staining allows to visualize the elastic fibers as brown. Typically used in large arteries, vocal cord. The nuclei stain blue-black. HE & saffron stain allows Visualization of collagen as yellow and the cells stain regularly according to hematoxylin eosin stain. Adobe Systems Department of Histology and Embryology 8 Literature -Junqueira’s Basic Histology -Atlas of Histology FM MU -Atlas of Cytology and Embryology [USEMAP] Adobe Systems Department of Histology and Embryology 9 Klára Dolinová Peter Staňo Yehonatan Solomonov Petr Vaňhara Department of Histology and Embryology (EN) - Barevné provedení 2020