CONNECTIVE TISSUE

1. CONNECTIVE TISSUE

2. It connects between the different types of tissues and organs, carrying their blood and nerve supply. • It is derived mainly from the mesoderm. • It has connective tissue proper and specialized connective tissue (blood, cartilage and bone). • It is composed of cell and extra-cellular matrix which consists of ground substance and fibers. • According to the amount and role of these three components (cells, fibers and ground substance), there are many types of connective tissue.

3. Functions of Connective Tissue • Support. • Medium for exchange. • Defense and protection. • Storage of fat.

5. Ground substance • Amorphous gel-like material composed of glycosaminoglycans, proteoglycans and glycoproteins. • Glycosaminoglycans are of two types: • Sulfated such as: keratin sulfate, heparin sulfate and chondroitin sulfate. • Non-sulfated such as: hyaluronic acid. • Proteoglycans are responsible for the gel state of the extra-cellular matrix. • Glycoproteins such as: fibronectin, chondronectin and osteonectin.

6. Connective Tissue Fibers • Collagen fibers. • Reticular fibers. • Elastic fibers.

7. Collagen Fibers • Tough, firm, inelastic fibers which resists the tensile forces upon the tissues. • Most common fibers in connective tissue. • Formed of branching bundles of strong flexible collagen fibers. • It is formed of tropocollagen units running parallel and overlapping each other. • This tropocollagen unit is formed of 3 polypeptide chains rich in proline, glycine, hydroxyproline and hydroxylysine. • Vitamin C is important in collagen synthesis.

8. Collagen Fibers • Are synthesized mainly by fibroblasts. • Chondroblasts, osteoblasts and smooth muscle fibers also synthesize collagen. • There are many types of collagen fibers (depending on their amino acid sequence): • Type I: in connective tissue, bone, dentine. • Type II: in hyaline and elastic fibers. • Type III (reticular fibers): lymphatic system, spleen, skin and vessels. • Type IV: in basal lamina. • Type V: with type I and placenta. • Type VI: in basal lamina.

9. Reticular Fibers • Thin collagen fibers arranged in framework instead of bundles. • Synthesized by the fibroblasts. • They form the reticular network of some organs such as lymph nodes and bone marrow. • They present also in basement membrane.

10. Elastic Fibers • Slender, long and branching fibers in loose connective tissue, but coarse bundles in elastic ligaments. • Formed by the fibroblasts and smooth muscle cells. • Composed of protein elsatin and can be stretched to one and half times its original length. • It is present in large arteries, larynx and trachea, ligamentum flavum and framework of the spleen.

12. Fixed Cells • Fibroblasts. • Adipose cells. • Pericytes. • Mast cells. • Fixed macrophages (histiocytes).

13. Transient Cells • Plasma cells. • Lymphocytes. • Neutrophils. • Eosinophils. • Basophils. • Monocytes. • Transient macrophages.

14. Fibroblasts • They are derived from the undifferentiated mesenchymal cells. • They synthesize the extra-cellular matrix. • They occur either in active state or inactive state (fibrocytes). • Present nearby the collagen fibers. • Elongated fusiform cells with pale staining cytoplasm and large granular, ovoid nucleus.

15. Adipose Cells • They are derived from undifferentiated mesenchymal cell. • They synthesize, store and release fat. • They are two types of adipose cells: • Unilocular fat cells: from white adipose tissue. • Multilocular fat cell: from brown adipose tissue.

16. Pericytes • They surround the endothelial cell of capillaries. • They are derived from undifferentiated mesenchymal cell. • After injury they may differentiate to form endothelial cell and smooth muscle cells.

17. Mast cells • They are derived from precursors in bone marrow. • Found near blood vessels and body surfaces (dermis of skin and digestive and respiratory tract). • They are large ovoid cell with central spherical nucleus. • Their cytoplasm have large metachromatic granules containing heparin, histamine and many other mediators.

18. Macrophages • They may be fixed or transient. • They are active phagocytes removing cell debris and protecting the body against foreign invaders. • They are derived from monocytes (transient) or from UDMC (histiocytes). • Highly motile, irregular in shape with pseudopodia. • Have dark nucleus and basophilic cytoplasm containing numerous lysosomes, vacuoles and residual bodies.

19. Plasma Cells • They are derived from B-lymphocytes. • Large ovoid cells with eccentrically placed nucleus. • Its cytoplasm is intensely basophilic (RER). • Its nucleus has the characteristic “clock-face” or “radial spoke” appearance. • They present in areas of chronic inflammation and foreign bodies, where they manufacture and secrete antibodies.

20. Embryonic C.T.: Mesenchymal Mucous (mucoid) Specialized C.T.: Cartilage. Bone. Blood. Mature C.T. proper: Loose areolar Dense Dense regular Dense irregular Collagenous Elastic Reticular Adipose Classification of C.T.

21. Mucous C.T. • Present in the umbilical cord and subdermal C.T. of the embryo. • Loose amorphous C.T. with a jelly-like matrix containing hyaluronic acid and little amounts of collagen types I and III and fibroblasts. • This type of C.T. is called Wharton’s jelly.

22. Loose areolar C.T. • Contains abundant ground substance and tissue fluid, nearly all type of C.T. cells and less amounts of fibers. • Located in subcutaneous tissue, lamina propria of gastrointestinal & respiratory tracts, around blood vessels & organs and under serous membranes. • In inflammatory condition it swells because of increased extra-cellular fluid (Edema).

23. Dense regular C.T. • Contains abundant amounts of fibers with less cells and ground substances. • Has tightly packed coarse collagen bundles arranged in parallel fashion to form cord-like cylinders (tendons & ligaments) or sheets (aponeurosis). • Fibroblasts are arranged between the collagen fibers so they appears elongated with their dash-like elongated nuclei. • It is also called white fibrous C.T.

24. Dense irregular C.T. • Contains abundant amounts of fibers with less cells and ground substances. • Has tightly packed coarse collagen bundles arranged randomly in all directions, with few elastic fibers. • Fibroblasts and other less cells are arranged between the collagen fibers. • They are found in dermis of skin, capsule of organs, sheaths around nerves and dura mater.

25. Elastic C.T. • Composed mainly of elastic fibers with little amounts of collagen fibers and few cells and ground substance. • The elastic fibers are arranged in sheaths or fenestrated lamellae. • They are present in the wall of large arteries, ligamentum flavum, trachea and larynx, and suspensory ligament of penis.

26. Reticular C.T. • Composed mainly of type III collagen fibers in a form of network or mesh, fibroblasts and macrophages. • It forms the architectural framework of liver sinusoids, bone marrow, lymph nodes, spleen, smooth muscles, islet of Langerhans and adipose tissues.

27. Adipose C.T. • Loose C.T. very rich in adipocytes. • Two types of adipose C.T. • Unilocular (white fat) C.T.: its fat cells are of unilocular type, present in subcutaneous tissue, around organs and blood vessels. • Multilocular (brown fat) C.T., present in infants and hibernating animals, cells are rich in mitochondria, supply heat.

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