1. Connective Tissues

2. Connective Tissues Responsible for providing and maintaining form in the body

3. Histogenesis Mesodermal in origin

4. General Characteristics Are made up of fewer cells that are set far apart They are supported by abundant intercellular substance They also contain connective tissue fibers The different contents of intercellular substance, CT cells and fibers account for the difference in appearance of the various connective tissues

5. General Functions Provide a matrix that serves to connect and bind the cells and organs Give mechanical support to the body Storage of fat and certain minerals like calcium in the bones Exchange of metabolites between blood and tissues Significant role in the repair and healing of wounds For protection against infection

6. Classification I. Connective Tissue Proper Loose connective Tissue Dense connective tissue – regular & irregular II. Connective Tissue with special properties Adipose CT Elastic CT Hematopoietic CT(lymphatic and myeloid) Mucous CT III. Suporting Connective Tissue Cartilage Bone

7. Composition of Connective Tissues Connective tissue cells Connective tissue fibers Intercellular or Ground substance Blood vessels – except in Mucous CT and in cartilage

8. Connective Tissue cells Fixed or permanent Wandering cells Are immigrant cells usually from blood or bone marrow. Some retain their original characteristics and may take up permanent residence there: 1. mast cells 2. plasma cells 3. pigment cells 4. blood leukocytes Are native to the tissue in which they are found: 1. undifferentiated mesenchymal cells 2. fibroblasts 3. macrophages 4. fat cells

9. Fixed Connective Tissue Cells

10. Undifferentiated Mesenchymal cells Precursor of most cells indigenous to CT including fibroblasts and adipose cells Adventitial cells remain undiifferentiated in adult CT and constitute a reserve population of stem cells Perivascular cells, often located along the walls of blood vessels Are difficult to distinguish from active fibroblasts – recognition come not with the microscope but from numerous observations of their responses to certain stimuli Pluripotential cells, capable of differentiation either into the usual cell types or into other cell types such as smooth muscle cells

11. Fibroblasts Predominant CT cells Considered to be responsible for the formation of the fibers and are also thought to elaborate most, if not all, of the amourpous ground substance Are large, flat branching cells which appear fusiform or spindle shaped in profile Classified as: lamellar or pyriform-shaped (youngest) Spindle or fusiform (intermediate in age) Stellate or star-shaped (mature)

12. Fibroblasts

13. Macrophages As numerous as fibroblasts in loose CT Often termed histiocytes, are most abundant in richly vascularized areas May either be: Fixed or resting (attached to the fibers of the matrix) Free, wandering (derived from the immigration of monocytes from the blood) Capable of ameboid movement – very irregular in outline with pseudopodia extending in numerous directions

14. Macrophages Act as scavengers, (motility and phagocytic activity) engulfing extravasated blood cells, dead cells, bacteria and foreign bodies

15. Fat cells Fully differentiated cells and are incapable of mitotic division Signet-ring appearance – cytoplasm is so thinned that it appears as a narrow rim around the edge of a single large lipid droplet with the nucleus fused to one side of the cell membrane Types: Yellow or white – found in most of the bulk of the human body Brown fat cells – concerned with heat production, particularly important in newborn and young animals

16. Fat cells

18. Wandering Connective Tissue Cells

19. Mast cells Round to oval CT cells whose cytoplasm is filled with basophilic granules The rather small and spherical nucleus is centrally situated and is frequently obscured by the cytoplasmic granules Produce an anticoagulant similar if not identical to heparin Produce histamine in allergic response to some foreign proteins

20. Mast cells Also elaborate serotonin, a vasoconstrictor Are only seen along the course of small blood vessels

21. Plasma cells Spherical cells with rounded or irregular nuclei generally eccentrically located , whose chromatin materials exhibit a characteristic “checker-board”, “clock-faced”, “cart-wheel” appearance Has an important function in resistance to disease and known as the: principal producer of antibodies

22. Plasma Cells

23. Pigment cells Resemble the fibroblast but whose cytoplasm contains pigment granules that never invade the nucleus Types: Dermal chromatophore– found in the dermis of the skin, retina, choroid and iris of eyeball Epidermal melanocytes, found in common mole and are responsible for the manufacture of melanin granules

24. Blood Leukocytes

25. Lymphocytes Smallest, with rounded nucleus which occupies most of the cytoplasm Concerned with antibody production

26. Eosinophils Have bilobed nucleus with spherical, darkly staining acidophilic granules Found abundant in lactating breasts, respiratory and alimentary tracts, and in certain allergic reactions

27. Neutrophils First line of defense, seen in regions of acute inflammation Have a segmented nucleus (3-5 lobes) having fine granules which are purple or violet in color

28. Monocytes Largest, they have a kidney-shaped nucleus and are considered as the phagocytes of the blood

29. Connective tissue cells

30. Ground Substance

31. Ground substance Colorless, transparent and homogenous Fills the space between cells and fibers of the CT It is viscous and acts as lubricant and also as a barrier to the penetration of the tissues by foreign particles Formed mainly by two classes of components: Glycosaminoglycans Structural glycoproteins

32. Connective Tissue Fibers Collagen formed by the protein collagen, Reticular most abundant protein of the body Elastic – composed mainly of the protein elastin

33. Collagen fibers Most numerous fiber in CT Fibers are colorless stands, but when present in great numbers, they cause the tissue in which it lie to be white Are inelastic and have a tensile strength greater than steel Imparts a unique combination of flexibility and strength to the tissues in which it lies

34. Collagen fibers Consists of closely packed thick fibrils with an average diameter of 75 nm In many parts of the body, are organized in parallel array forming collagen bundles In H & E sections, large or small bundles of fibrils or individual fibrils exhibit acidophilic staining properties

35. Types of Collages fibers Collagen type I Most abundant and has a widespread distribution (90% of the collagen in the body) Found in the dermis of the skin, tendons, bone, teeth and virtually all CT Collagen type II Present mainly in hyaline and elastic cartilage Only very thin fibrils are formed

36. Types of collagen fibers Collagen type III Often found in association with type I and is probably the major collagenous components of reticular fibers Can copolymerize with other types of collagen Collagen type IV Is the major collagen type in basal lamina Does not form fibrils or fibers Collagen type V Present in fetal membranes and blood vessels and in small amounts in other tissues

37. Reticular fibers Are extremely thin, with a diameter between 0.5 and 2 μm Not visible in hematoxylin and eosin stains but can be easily stained black by impregnation with silver salts Argyrophilic fibers – affinity to silver salts During embryogenesis, inflammatory processes, and wound healing, most connective tissues have an abundance of reticular fibers, but these are subsequently replaced by regular collagen fibers

38. Reticular fibers Particularly abundant in smooth muscles, endoneurium, and the framework of hematopoietic organs (e.g. spleen, lymph nodes, red bone marrow) and constitute a network around the cells of parenchymal organs (e.g. liver, kidney, endocrine glands)

39. Elastic fibers Consists of an albuminoid protein called elastin Range in diameter from 0.1 to 10 µm Histologically contains few charged amino acids so it stains poorly with standard ionic dyes Special stains such as Verhoeff’s stain and Weigert’sResorcin-fushsin stain are used in light microscope Are extremely pliable and elastic Can be stretched to 150% of their length without breaking and then return to their original length

40. Elastic fibers Found where their mechanical properties are necessary to allow tissues to stretch or expand and then return to their original shape, e.g. in arterial walls, interalveolar septa, bronchi and brionchioles of the lungs, vocal ligaments and ligamentaflava of the vertebral column