CONNECTIVE TISSUE

1. CONNECTIVE TISSUE

2. Functions of Connective Tissue Structural support (capsules, bone, cartilage) Nutrition Defense (non-specific and immune) Cell growth and differentiation Cell migration Insulation

3. Connective Tissues: Special Characteristics Common embryological origin (from mesoderm) Innervated and Vascular (direct blood supply) Cartilage is the one exception with no capillary beds Extracellular Matrix ground substance (gelatinous glycoproteins) structural fibers (fibrous proteins, e.g., collagen, elastin, reticulin)

4. Types of Connective Tissues Connective Tissue Proper areolar (loose fibrous) connective tissue adipose tissue reticular connective tissue dense (fibrous) regular connective tissue dense (fibrous) irregular connective tissue Cartilage hyaline cartilage elastic cartilage fibrocartilage Bone Blood

5. Types of Connective Tissue

6. Connective Tissue Elements Ground substance supports cells, binds them together may be solid, fluid or gel Componets: Interstitial Fluid – Cell Adhesion Proteins- Fibronectin, laminin and others Serve as connective tissue glue

7. Connective Tissue Elements Proteoglycans - large polysaccharide molecules bound to a protein core (like a bottle brush) Glycosaminoglycans (GAGs) are attached to proteoglycans They trap water. As GAGs increase, so does viscosity hyaluronic acid – gelatinous, separates cells, traps extracellular fluid; lubricates joints; gives shape to eyeballs; fills body spaces chondroitin sulfate – capable of being mineralized; cartilage, bones, skin, blood vessels dermatin sulfate – harder; skin, tendons, blood vessels, heart valves keratin sulfate - still harder; bone, cartilage, cornea of the eyes

8. Connective Tissue Elements Fibers Proteins that are embedded in the ground substance Provide structural support, adhesion, connect cells Collagen tough; provides high tensile strength Also called white fibers highly polymerized, gigantic molecules tough, moderate flexibility bone, cartilage, tendons, ligaments elastic fibers = elastin branched; smaller, thinner fibers than collagen very flexible and elastic but also strong can be stretched to 150% of its original length Also called yellow fibers

9. Connective Tissue Elements reticular fibers branched collagenous fibers that form delicate networks thin, less polymerized collagen fibers elastic & reticular fibers require special stains to be seen in the light microscope

10. Cells – fewer, rarely touching, surrounded by a matrix immature forms (-blasts) secrete the matrix and can still divide once the matrix is secreted, the cells mature into -cytes which have decreased cell divisions and secrete less matrix material chondro- cartilage, osteo- bone, fibro – connective, etc. Fibroblasts – connective tissue proper Chondroblasts – cartilage Osteoblasts – bone Hematopoietic stem cells – blood White blood cells, plasma cells, macrophages, and mast cells

11. Connective Tissue Structure

12. Connective tissue Fibers

13. Fibers Long, rope-like protein extracellular polymers Present in variable proportions in the different types of connective tissues Three types: collagen, reticular and elastic fibers. Collagen and reticular fibers are composed of various types of collagen, elastic fibers are composed mainly of elastin

14. Collagen fibers Collagens are the most abundant proteins in the body. There are many types of collagen that differ in their origin, chemical composition, functions, distribution and pathology

15. Collagen biosynthesis

16. Collagen biosynthesis

17. Collagen biosynthesis

18. Collagen fibrils

19. Collagen fibrils

20. Collagen fibrils, TEM

21. Collagen types Fibril-forming collagen: types I, II, III, V and XI Fibril-associated collagen: types IX and XII Network-forming collagen: type IV Anchoring collagen: type VII

22. Collagen types Collagen I 2 x a1 + a2 or 3 x a1 Forms fibrils, the most resistant to mechanical tension In: skin, bone, tendons, connective tissue capsules Collagen II 3 x a(II)1 Forms fibrils In hyaline and elastic cartilage Collagen IV 3 x a(IV)1 or 3 x a(IV)2 Forms a network in the basal laminae

24. Elastic fibers Isolated, thin fibers or arranged in networks Localised in lung, urinary bladder, skin, aorta and elastic cartilage Special staining : orcein

26. Elastic fibers Elastin molecules are joined by covalent bonds to generate an extensive cross-linked network. Because each elastin molecule in the network can expand and contract like a random coil, the entire network can stretch and recoil like a rubber band. )

27. Elastic fibers

28. RETICULAR FIBERS Thin fibers, forming networks Distribution : liver, spleen, lymph nodes, haematopoietic organs Special staining : silver impregnation

30. Connective tissue Elements: Ground substance Fibers Cells

31. Ground substance Composed of glycoproteins and proteoglycans Participates to binding cells to fibers Colorless and transparent in usual stains Viscous

32. Ground substance Fibronectin (homodimer) binds cells, collagen and GAG Laminin (heterotrimer) mediates attachment of epithelial cells to basal laminae Cells have membrane receptors, integrins, that bind collagen, fibrinectin, laminin and other extracellular structural components Integrins are also attached to the cytoskeleton (actin fibers)

33. Ground substance Proteoglycans (PG) = proteic core + glycosaminoglycans (GAG) GAG are linear polysaccharides composed of repetitive disaccharide units Disaccharide units =  uronic acid + hexosamine

34. Ground Substance: Proteoglycan Structure

35. Ground substance Except hyaluronic acid, GAG are part of PG PG are intensly hydrophilic polyanions They bind cations (Na+) thus attracting water – they regulate consistency of connective tissue GAG examples: dermatan sulfate, chondroitin sulfate, keratan sulfate, heparan sulfate

36. Ground substance Structural glycoproteins (GP) are glycosilated proteins – branched oligosaccharide moieties GP mediate adhesion of cells to extracellular matrix components

37. Ground substance Fibronectin (homodimer) binds cells, collagen and GAG Laminin (heterotrimer) mediates attachment of epithelial cells to basal laminae Cells have membrane receptors, integrins, that bind collagen, fibrinectin, laminin and other extracellular structural components Integrins are also attached to the cytoskeleton (actin fibers)

38. The molecular structure of proteoglycans and glycoproteins. A: Proteoglycans contain a core of protein (vertical rod in drawing) to which molecules of glycosaminoglycans (GAGs) are covalently bound. A GAG is an unbranched polysaccharide made up of repeating disaccharides; one component is an amino sugar, and the other is uronic acid. Proteoglycans contain a greater amount of carbohydrate than do glycoproteins. B: Glycoproteins are globular protein molecules to which branched chains of monosaccharides are covalently attached.

42. Connective Tissue Cells

43. Proper to CT (fixed cells) - fibroblast - fibrocyte (condro-, osteo-) - adipocyte (uni-, multilocular) - reticular cells Migrated (mobile cells) - granulocytes - B and T lymphocytes - macrophages - mastocyte - melanocyte Connective tissue cells – classification

44. Cells that produce/degrade the extracellular matrix fibroblasts, osteoblasts, condroblasts, macrophages Metabolic cells adipocytes Defense (specific/non-specific) Lymphocytes, macrophages, neutrophils Connective tissue cells – classification

45. The most frequent cell Fibers (collagen, reticulin & elastic) and ECM components synthesis Elongated cells, 20 mm, branched processes, basophilic cytoplasm, oval , euchromatic nucleus, 1 or 2 nucleoli Fibroblast

46. Fibroblasts, fibrocytes

47. Fibroblasts, fibrocytes

48. Fibroblast Produces: Elements of the extracellular matrix: procollagen, proelastin, fibrillin, GAG, PG and GP; Enzymes: matrix metalloproteinases - collagenase (degrades collagen at neutral pH), elastase; Growth factors

49. Fibroblast Properties: Ability to switch its fenotype  fibroblast ? fibrocyte Can change shape Mobile Induces differentiation of surrounding cells

50. Less active than fibroblasts: smaller, lesser cytoplasm, a few short unbranched processes Eosinophilic cytoplasm Elongated and heterochromatic nucleus Fibrocyte

51. Round (when isolated) or polygonal in groups One large lipid droplet (inclusion) A thin rim of cytoplasm at the periphery that contains a flattened, heterochromatic nucleus (“signet ring”) Unilocular (white) adipocyte

53. Smaller cells Many smaller lipid droplets in the cytoplasm – foamy look Round, central nucleus Mostly found before birth and in neonates Role in thermogenesis Multilocular (brown) adipocyte

55. Variable functions but similar morpholgy; some contribute to forming the stroma of lymphoid and hematopoietic organs Star-shaped cells with long and thin processes that establish anchoring junctions with neighboring cells; round, central, pale nucleus, larger than nuclei surrounding it Reticular cells

56. Cytoreticule Cytoreticule = Reticular cells  +Reticular fibers

57. Cell of ectodermal origin Consequently migrates to dermis, epidermis, iris, hair root Snowflake-shaped cell, with many branched processes; 30 mm Melanin granules in the cytoplasm, dark-brown; Round, central, small nucleus Melanocytes

58. Melanosomes – visible in EM: Primary melanosomes are Golgi vesicles that accumulate thyrosin (the melanin precursor) and thyrosinase, located at the base of cell processes Secondary melanosomes are heterogenous vesicles (EM) that accumulate melanin Tretiary melanosomes are found at the tips of the cell processes; they are released from melanocytes and engulfed by surrounding cells (keratinocytes) Melanocytes

60. Derived from peripheral blood monocytes, Involved in phagocytosis and inflamatory response A family of cells with various shapes, localisations and names: Histiocytes: connective tissue Kupfer cells: liver Alveolary macrophages: lung Osteoclasts: bone Microglia: central nervous system Macrophages

61. Grouped as the “mononuclear phagocytic system” Macrophages of the connective tissue: about 30 mm, “ruffled” membrane, acidophilic lysosomes in the cytoplasm, can have various heterogenous “inclusions” – ingested material Round, oval or kidney-shaped nucleus, excentrical, can have nucleoli Macrophages

62. Macrophage Main function: phagocytosis Triggered by a specific interaction between membrane receptors and ligands. Consequences: Cell movement towards target particle Pseudopodae formation – engulfment Respiratory burst Secretion: cytokines, interferons, complement & coagulation factors Production of matrix metalloproteinases

64. Macrophage, TEM

65. Localized in most of the loose connective tissue areas, along blood vessels Oval cell, 20-30 mm Cytoplasm has numerous basophilic, metachromatic granules, 0,1-1 mm. Pseudopodae in EM. Round, small and central nucleus Mast cells

66. Granules contain heparin or chondroitin sulfate, histamin, Eosinophil Chemotactic Factor, etc. The content can be released out of the cell - “degranulation”. The process is triggered by chemical, physical stimuli, or through binding of antigen-IgE complexes by specialized receeptors Degranulation is mediated by cAMP and leads also to leukotriene synthesis Mast cells

67. Mast cell degranulation

68. Mast cells, Toluidin blue stain

69. Mast cell, TEM

70. Found in lymphoid organs (lymph nodes, spleen, bine marrow) and connective tissues associated to the respiratory and digestive mucosae Originate in B lymphocytes, that are terminaly differentiated as a response to antigen challenge Secrete immunoglobulins (antibodies): IgM, IgG, IgA, IgE Plasma cells

71. Oval cell, 20 mm Basophilic cytoplasm (due to abundant RER), with a perinuclear pale area (Golgi apparatus); can contain acidophilic Russel bodies (secretory granules) Excentric nucleus, with hetero- and euchromatin in a characteristic pattern: “spokes and barrel”, “clockface”. Visible nucleolus Plasma cells

72. Plasma cell

73. Plasma cell, TEM

75. Plasma cells, TB stain

76. Lymphocytes T and B subpopulations Central role in the immune response, migrated from the blood stream Small round cells (10 mm), with a round and dark-staining nucleus and a few basophilic cytoplasm

77. Neutrophils Migrated from the blood stream, role in phagocytosis (microphage) Eosinophilic cytoplasm with small granules Characteristic nucleus: heterochromatic, 2-5 lobes