Connective Tissue PDF

Connective Tissue Prof. Dr. Somaya Zaghloul Dr. Alshaymaa Gamal Aboulkhair  Connective Tissue (C.T.) General Characteristics of connective tissue 1-The connective tissue is mesodermal in origin. 2- It is formed of three components (cells, fibers and ground substance)....

Connective Tissue Prof. Dr. Somaya Zaghloul Dr. Alshaymaa Gamal Aboulkhair  Connective Tissue (C.T.) General Characteristics of connective tissue 1-The connective tissue is mesodermal in origin. 2- It is formed of three components (cells, fibers and ground substance). THE CONNECTIVE TISSUE is formed of (cells + fibres + ground substance) 3- The ground substance combined with the different types of fibers forming the major component of the connective tissue (matrix). 4- The connective tissue cells are widely separated. 5- It is penetrated by blood vessels, lymphatics and nerves. Components of C.T.: 1. Cells: Fixed or Free. 2. Fibers: (Collagen, Elastic and Reticular fibers). 3. Matrix: there are four types of C.T. according to matrix consistency. a. Soft matrix in the connective tissue proper. b. Firm matrix in cartilage. c. Calcified matrix in bone. d. Fluid matrix in blood.  The cells of C.T. proper C.T. proper contains 8 types of cells, which are classified on morphological bases into two general groups 1) Irregular or branching cells: 1- Undifferentiated mesenchymal cells (UMCs) and pericytes. 2- Fibroblasts and fibrocytes. 3- Pigment cells. 4- Macrophages (histiocytes). 2) Oval or non-branched cells: 1- Mast cell. 2- Fat cell. 3- Plasma cell. 4- Blood leucocytes. The cells of C.T. proper may also be classified according to their function into two groups: 1. Undifferentiated cells: a- Undifferentiated mesenchymal cells. b- Pericytes. 2. Cells responsible for synthesis and maintenance of connective tissue intercellular substances: a- Fibroblasts. b- Fibrocytes. 4. Cells responsible for colouration: Pigment cells 5. Cells responsible for storage and metabolism of fat: Fat cells (adipocytes) 6. Cells concerned with defense mechanism of the body: a- Macrophages. b- Plasma cells. c- Mast cells. d- Blood leucocytes  Undifferentiated mesenchymal cells Sites: 1.It is present mainly in embryo as stem cells. 2. In adults some cells remain after birth in certain areas to give origin to blood elements, endothelial cells and muscle cells. The light microscope (LM): - Small branched cells. - Nucleus is large, pale and oval. - Cytoplasm is Pale basophilic. The Electron microscope (EM): Many free ribosomes and few organelles. Functions: Can differentiate to: a. Other C.T. cells. b. Blood cells. c. Smooth muscle cells. d. Endothelial cells.  2. Pericytes Origin: UMCs. Sites: Present around blood capillaries. The light microscope (LM): - Branched with long processes. - Pale basophilic cytoplasm. The electron microscope (EM): - A network of actin and myosin. - Many free ribosomes and few organelles. Functions: Pericytes = UMCs (In adults). a. During injury of C.T. and blood vessels Pericytes can differentiate into: - Fibroblasts. - Smooth muscle cells. b- Pericytes contraction leads to vaso-constriction.  The Cell Responsible for Synthesis and Maintenance of Connective Tissue Fibroblasts Origin: UMCs and Pericytes. Sites: The most common, found nearly in all types of C.T. The light microscope (LM): - Branched Flat cells (spindle- shaped in side view). - Nucleus is large pale and oval with prominent nucleolus. - Cytoplasm is scanty and deeply basophilic.  The Cell Responsible for Synthesis and Maintenance of Connective Tissue Fibroblasts The electron microscope (EM): Well developed Golgi body, rough endoplasmic reticulum, Many free ribosomes and mitochondria. (characteristics of protein secreting cells) Functions: a. Synthesis of proteins that form collagen, reticular and elastic fibres. b. Production of ground substance. c. Production of growth factors that influence cell growth and differentiation. d. Healing of the connective tissue after injury. 2. Fibrocytes (inactive fibroblasts) Compared with Fibroblasts The light microscope (LM): - Smaller with fewer processes. - The nucleus is smaller and darker. - Less basophilic cytoplasm. The electron microscope (EM): - The cytoplasm contains less rough endoplasmic reticulum. - The nucleus contains more heterochromatin. Functions: In injury they become active (Fibroblasts) for healing of wounds.  The Cells Responsible for Defense and Immune Functions 1. Fixed Macrophages (Histiocytes) Origin: Blood Monocytes. Sites: More abundant in loose connective tissue along collagen fibers. The light microscope (LM): - They have a highly variable shape due to amoeboid movements. - Nucleus is oval or kidney shaped and usually eccentric. - Cytoplasm is pale basophilic. Special stain: Stained vitally with trepan blue or India ink. The electron microscope (EM): The Cytoplasm is rich in lysosomes and phagocytosed particles. Functions: 1. Phagocytosis of antigens and destroy them by their lysosomes. 2. Act as antigen-presenting cells (to T-lymphocytes). 3. Secrete interleukin-1 which stimulates mitotic activity of T-lymphocytes. Foreign-body giant cells: are multinucleated masses of fused macrophages surrounding a foreign body. Free Macrophages: Found in lymphoid tissue, liver, lung, bone marrow and brain. They have the same structure and function as fixed Macrophages.  2. Plasma Cells Origin: Develop from activated B- lymphocytes. Sites: More abundant in lymphoid tissue. The light microscope (LM): - Oval in shape. - Nucleus is eccentric with a cart- wheel (clock-face) appearance. - Cytoplasm is basophilic with negative Golgi image near the nucleus. The electron microscope (EM): Features of protein-secreting cells. - Numerous mitochondria. - Well developed Golgi apparatus. - Rich in rough Endoplasmic Reticulum. Function: Secretion of antibodies (humoral immunity).  3. Mast Cells Origin: UMCs in bone marrow. Sites: - Abundant in loose connective tissue in groups along blood vessels. - In C.T. corium under the epithelium of respiratory and digestive system. The light microscope (LM): - Oval or rounded in shape. - Nucleus is central and rounded. - Cytoplasm is rich in basophilic granules. Specific stain: The granules could be stained (Metachromatically) with Toluidine Blue. So they stain purple or red instead of blue. The electron microscope (EM): - Cytoplasm is full of electron dense granules that mask other contents. - They have features of protein-secreting cells.  Functions a. Secretion of heparin (anticoagulant). b. Secretion of histamine which initiates allergic reactions. c. Secretion of eosinophil chemotactic factor (which attracts eosinophils). Note the similarity between mast cells and basophils.  4. Leucocytes Migrated from blood stream. (for structure and function see blood). a. Neutrophils: They migrate to sites of acute inflammation. b. Eosinophils: They migrate to sites of allergy and parasites. c. Lymphocytes: They migrate to areas of chronic inflammation. T-lymphocytes: Initiate cell-mediated immunity. B-lymphocytes: They are responsible for humoral immunity. They change to plasma cells.  The Cell Responsible for Colouration Pigment Cells Origin: Connective tissue macrophages which phagocytose melanin pigments formed by melanocytes. Sites: - Abundant in the connective tissue dermis of the skin. - Pigmented layer of the eye. The light microscope (LM): - Small branched cells. - Nucleus is small and dark. - Cytoplasm is rich in melanin pigment. The electron microscope (EM): Melanin granules appear in cytoplasm as melanosomes. Function: 1. storage of melanin which protects against ultraviolet rays of the sun. 2. Gives the skin and eyes its color. The Cell Responsible for Storage and Metabolism of Fat Fat Cells (Adipocytes) Origin: UMC which give two types of fat cells. Fat cells (Unilocular) Fat cells (Multilocular)  Unilocular Fat Cells Multilocular Fat Cells White fat cells Brown fat cells LM - Large (50 – 150 µm) oval cells. - Small rounded cells. - Nucleus: -Nucleus: Peripheral and flat. Central and rounded. -Cytoplasm: A very thin film around a single -Cytoplasm: large fat droplet. Contain many fat droplets of - In H&E stained sections fat various sizes. droplet dissolves and the cells appear as large vacuoles (signet-ring appearance). -Fat stains (Orange) with Sudan III Fat stains (Orange) with Sudan III or (Black) with Sudan black. or (Black) with Sudan black.  Unilocular Fat Cells Multilocular Fat Cells White fat cells Brown fat cells Site In white adipose C.T. In brown adipose C.T. Function 1. Storage of fat to release energy. Heat generator. 2. Heat insulator.  FIBRES OF CONNECTIVE TISSUE White Collagenous Yellow Elastic Reticular Fibres Fibres Fibres LM Wavy branching Thin branching Very thin bundles which are fibers which run network of formed of parallel singly not in fibers. non-branching bundles. fibrils.  FIBRES OF CONNECTIVE TISSUE White Collagenous Fibres Yellow Reticular Elastic Fibres Fibres Origin - Fibroblasts. Fibroblasts Fibroblasts. ‐ Chondroblasts in Cartilage. ‐ Osteoblasts in Bone. ‐ Odontoblasts in teeth.  White Collagenous Yellow Elastic Fibres Reticular Fibres Fibres Color - Colourless when Yellow on - Colourless. & present singly. They condensation. Stain are white in color when condensed. - In H&E stain they Specially stained by Specially stained by appear acidophilic. orcein (brown). silver (brown). Types Many types, the most No types No types important (I, II and III)  White Collagenous Yellow Elastic Fibres Reticular Fibres Fibres Characters - Strong rigid flexible Stretch and recoil Delicate and flexible but not elastic. (Elastic). fibers. - affected by boiling, - resist boiling, acids enzymes, acids and and alkalies. alkalies. - Digested by pancreatic elastase enzyme. Function Give the tissues Give the tissues Form the stroma of strength and rigidity. stretch and elasticity. organs. Clinical Note: Vitamin C deficiency (Scurvy) is due to defective collagen synthesis. It is characterized by bleeding gums with loss of teeth and unhealed wounds. Ground Substance It is the intercellular substance, in which cells and fibres are embedded. Chemically, it is made of hyaluronic acid, proteoglycans, fibronectin and laminin. It can be stained by periodic acid shiff (PAS) or silver nitrate.  Types of Connective Tissue Proper According to the relative abundance of the basic components of connective tissue (Cells, fibers and matrix) it is classified into two groups. A. Loose C.T. 1. Loose (Areolar) Connective Tissue. 2. Adipose Connective Tissue. 3. Mucoid Connective Tissue. 4. Reticular Connective Tissue. B. Dense C.T. 1. White Fibrous Connective Tissue. 2. Yellow elastic connective tissue.  A. Loose Types of Connective Tissue Proper 1. Loose (Areolar) Connective Tissue (The most common type) Structure: It contains potential cavities (areolae), which can accommodate large amounts of fluids or gas. It contains all the types of fibres and cells. (most common cells are fibrocytes, macrophages and mast cells). Sites: 1- Present everywhere in the body except in central nervous system (CNS). 2- Connecting all organs and tissues together. 3. Present under epithelium in submucosa and dermis of skin. Functions: 1. Binds tissues together and surrounds organs. 2. Supports epithelium and blood vessels.  2. Adipose Connective Tissue It is similar to Areolar connective tissue but fat cells predominate over other components. It consists of groups of fat cells, separated by connective tissue fibrous septa.  There are two types of adipose C.T. according to vascularity and functions. White Adipose C.T. Brown Adipose C.T. Structure - Unilocular fat cells. Multilocular fat cells. - Fat is not pigmented Fat is pigmented. Sites In Embryo & newly born: 1. Mammary gland. 1- Between the scapulae. 2. Subcutaneous tissue. 2. In the axillary region. 3. Around the kidney (Renal 3. In the mediastinal region. pad of fat). In adults: Only Around thoracic aorta.  There are two types of adipose C.T. according to vascularity and functions. White Adipose C.T. Brown Adipose C.T. Blood Poor blood supply. Rich blood supply. supply Functions 1- Storage of fat. On exposure to cold, it releases 2- Insulation of heat. heat, to warm the body (Heat 3- Support of soft organs. Generator).  3. Mucoid Connective Tissue It is an embryonic, jelly like connective tissue in which the ground substance predominates over other components. Structure: Cells: UMCs and Young fibrocytes which are branched cells communicate by their processes. Fibers: Very fine collagen fibers. Matrix: Large amount of ground substance rich in mucous. Sites: 1- Umbilical cord. 2- Vitreous humour of eye. 3- Pulp of growing teeth. Function: Protects near-by structures from pressure.  4- Reticular Connective Tissue It is a delicate type of loose connective tissue. Structure: Reticular fibers: Thin collagen fibers forming three dimensioned network Reticular cells: They are specialized fibroblasts branched cells. Staining: The reticular fibers are (argyrophilic) stained brown by silver. Sites: Reticular connective tissue forms the stroma of all organs and glands. Function: Support the cells and components of an organ or gland.  B. Dense types of Connective Tissue Proper 1. White Fibrous Connective Tissue It is a very dense type of connective tissue due to great predominance of collagen fibers and few cells. It appears white in fresh state.  There are two types according to the arrangement of collagen bundles. Regular white fibrous C.T. Irregular white fibrous C.T. Structure - Regular (Parallel) arrangement Irregular arrangement of the of collagen bundles. bundles of collagen fibers. - Fibroblasts are arranged in rows in between the collagen bundles (Tendon cells). - Very little amount of matrix.  There are two types according to the arrangement of collagen bundles. Regular white fibrous C.T. Irregular white fibrous C.T. Sites 1. Tendons of skeletal muscles. 1. Ligaments. 2. Cornea of the eye. 2. Sclera of the eye. 3. Perichondrium. 4. Periosteum. 5. Capsules of organs. Function strength in one direction. strength in different directions. Irregular white fibrous C.T. Regular white fibrous C.T. 2. Yellow Elastic Connective Tissue It is a dense type of connective tissue with great predominance of elastic fibers. It appears yellow in fresh state. Structure: Fibers: Regular parallel elastic fibers. Cells: Few fibroblasts and fibrocytes. Sites: 1- Aorta and large blood vessels. 2- Trachea and bronchi. 3. Vocal cords. Staining: Specially stained by orcein (brown). Functions: 1. It forms elastic membranes. 2. It has great elastic power (Rubber like).