Connective Tissue Dr. Ashraf Hussain

Connective Tissue These tissues connect and support other tissues of the body

Connective Tissue Mechanical support Medium for exchange of nutrients & waste products Energy store and thermal insulation Defensive functions a) Barrier b) Engulf bacteria c) Antibodies

Connective tissue Connective tissue comprises a diverse group of cells embedded in a tissue-specific extracellular matrix Different type of connective tissue are responsible for a variety of functions Classification of connective tissue is based on the composition and organization of its cellular & extracellular components and on its functions

Structure of connective tissue Cells Intercellular substance or matrix

Matrix Amorphous ground substance Thread like formed elements called fibers (collagen fibers, reticular fibers, elastic fibers) Tissue fluid

Cellular component interspersed in intercellular substance different kinds of cells Fibers – part of the “formed substance” of C.T. embedded in ground substance Matrix = ground substance + fibers

Connective tissue cells Resident cell population Fibroblasts Macrophages Adipose cells Mast cells Undifferentiated mesenchymal cells Wondering cell population Lymphocytes Plasma cells Neutrophils Eosinophils Basophils Monocytes

Leucocytes in loose supporting tissue F-Fibroblasts, Er-Erythrocytes, N-Neurtrophils, Eo-Eosinophils, L-lymphocytes, P-Plasma cells, M-Macrophages

Connective tissue cells Fibroblasts Histiocytes (Macrophages) Plasma cells Mast cells Fat cells

ADULT CONNECTIVE TISSUE COMPONENTS Connective Tissue Cells

Connective tissue cells Fibroblasts Most abundant Appearance varies in relation to functional state Produce connective tissue fibers & secrete ground substance

Mature Fibroblasts

Active fibroblasts

Histiocytes (Macrophages) Abundant Inactive and active histiocytes Scavenger cells Foreign body giant cells Antigen presenting cells

Macrophage

Plasma cells Generally rare but numerous at certain sites e.g., intestinal mucosa, lymphoid organs Nucleus—cart wheel appearance Production of antibodies

Mast cells Mast– well fed (German) Abundant in loose connective tissue around blood vessels Secrete Heparin ( anticoagulant) & Histamine (vasodilator)

Mast Cells

Fat cells (adipocytes) Form adipose tissue when accumulate together Signet ring appearance

Blue dotted lines - Adipocytes Orange Arrows - Fat droplet "space" Green Arrow - Nuclei of Adipocyte

Connective tissue fibers Long slender protein polymers which are found in differing proportions in various types of connective tissue Predominant fiber type is responsible for conferring specific properties to the tissue

Connective tissue fibers Collagen fibers --collagen Reticular fibers --collagen Elastic fiber -------elastin

Collagen Long molecule—tropocollagen Three polypeptide chains intertwined together— triple helix By now 19 varieties of collagen have been identified Most important & best studied are I,II, III, IV &V.

Growth of molecular character of a collagen fibril

Collegen fibers are most abundant type of connective tissue fibers Collagen fiber formation involves events that occur both within and outside the fibroblast

Collagen fibers Diameter (2-10 micrometer) Run randomly in various directions In many parts, collagen fibers lie parallel to each other forming bundles of various sizes Flexible but inelastic (non-extensible) Pink colour with H&E stain

Blue arrow - Collagen Bundle Green Arrow - Fibroblast nuclei

Reticular fibers Reticular fibers provide a supporting framework for the cellular constituents of various tissues and organs Reticular fibers are named for their arrangement in a mesh-like pattern or network

Reticular fibers Very thin branching fibers (rete—net) Diameter (0.5 to 2 micrometer) Coating of proteoglycans & glycoproteins– black colour with silver staining, red with PAS Abundant in connective tissue around muscle fibers, nerve fibers, acini of glands, lymphoid organs & bone marrow

Elastic fibers Highly elastic can stretch one and half time their original length Diameter (0.2 to 1.0 mic.m) Branch & rejoin to form loose network Found in lungs, large arteries, ligamenta flava (connecting laminae of successive vertebrae)

Elastin fibres

Ground substance Ground substace occupies the space between the cells and fibers Ground substance consists largely of proteoglycans and hyaluronic acid Proteoglycans and Glycosaminoglycans (GAG) are responsible for the physical properties of ground substance

Embryonic connective tissue Develops from mesoderm & is known as Mesenchyme Composed of star-shaped cells which lie in an abundant relatively homogeneous intercellular substance Mucous tissue– Wharton’s jelly

Arrows = cells in mitosis; “C” = small blood vessels; Ground substance devoid of fibers; Cell processes extend into homogeneous ground substance

Disorders of connective tissue Marfan syndrome - a genetic disease causing abnormal fibrillin Scurvy - dietary deficiency in Vit.C leading to abnormal collagen. Ehlers-danlos syndrome - a genetic disease causing progressive deterioration of collagens affecting different sites in the body such as joints, heart valves & arterial walls

Disorders of connective tissue Osteogenesis imperfecta ( brittle bone disease) – insufficient production of good quality collagen to produce healthy, strong bones Spontaneous pneumothorax – collapsed lungs, believed to be related to subtle abnormalities in connective tissue