Connective Tissue L6,7 PDF

1 Learning Objectives *Be able to describe the structure functions of cells commonly found in connective tissue and identify them. *Be able to recognize collagens, elastic and reticular fibers. *Be able to recognize different types of connective tissue (e.g., dense irregular, dense regular, loose,...

1 Learning Objectives *Be able to describe the structure functions of cells commonly found in connective tissue and identify them. *Be able to recognize collagens, elastic and reticular fibers. *Be able to recognize different types of connective tissue (e.g., dense irregular, dense regular, loose, adipose) and provide examples where they are found in the body. 2 What is Connective tissue? Tissue that supports, protects, and gives structure to other tissues and organs in the body. Connective tissue also stores fat, helps move nutrients and other substances between tissues and organs, and helps repair damaged tissue. 3  Connective tissue Cells Fibers Matrix  I- Connective tissue cells Fixed cells Free cells Components of CT Immune cells 1- Mesenchymal cells. 1- Plasma cells. 2- Pericytes 2- Mast cells. 3- Fibroblasts. 3- Free macrophages 4- Fat cells 4- Leucocytes. 5- Fixed macrophages. 6- Reticular cells  Fixed cells 1- Undifferentiated Mesenchymal cells (UMC) LM: Small branched cell with pale basophilic cytoplasm and oval nucleus. EM: Ribosomes and few organelles.  UMCs Function: -In embryo: stem cells -In adult can differentiate into other CT cells  2- Pericyte: -Around blood capillaries. -Branched with long processes.  3- Reticular cell: Small branched cell with long branched and anastomosing processes. Central rounded nucleus Function: Secrete reticular fibers. Supportive in stroma of organs.  4- Fibroblasts & fibrocytes: - Most common type*. LM: - Branched with deep basophilic cytoplasm, oval pale nucleus & prominent nucleolus.  Fibroblasts EM: (protein forming) Euchromatic nucleus. Well- developed rER, Golgi & mitochondria Functions: Formation of fibers & matrix. Help in growth & healing.  Fibrocyte: (older fibroblast) - Mature fibroblast. - Fusiform with pale basophilic cytoplasm & dark nucleus. Function: - Maintenance of CT - Healing  5- Fat (adipose) cells (adipocyte): a- Unilocular fat cells b- Multilocular fat cells Single large droplet of fat Multiple small droplets of fat  a. Unilocular fat cells: - Oval with flat peripheral nucleus & large single central droplet of fat → dissolved → signet ring (with H & E). -Stained with Sudan III (orange).  Unilocular fat cells EM: - ↑ sER & ↓ mitochondria. Function: Storage of fat. Heat insulation. Support some organs.  b. Multilocular fat cells: - Rounded with rounded nucleus & multiple small droplets of fat. - Pigmented (brown). EM: - ↑ mitochondria & ↓SER. Function: - Heat generation → thermogenin (in mitochondria)  Macrophages: LM: - Irregular with pale basophilic granular cytoplasm & eccentric kidney-shaped nucleus. -Vital stain → trypan blue or India ink  Macrophages: EM: - Pseudopodia - ↑ lysosomes & phagocytosed particles (phagosomes). - Well-developed Golgi & rER.  Macrophages: Function: Phagocytosis of micro-organisms. Destruction of old RBCs. Formation of giant cells. Antigen presenting.  Free cells 1- Plasma cells: - From B-lymphocytes. - Dark basophilic cytoplasm - Rounded eccentric nucleus with cart- wheel or clock-face appearance. - Negative Golgi image (H&E). EM: (Protein forming) - rER, Golgi, mitochondria. - No secretory granules *. Function:  Secrete antibodies  2- Mast cells: - Along blood vessels. - Oval with rounded pale nucleus. - Large basophilic granules. - Metachromatically stained by toluidine blue → red to purple EM: - rER, Golgi, mitochondria. - Electron-dense secretory granules. Functions: Ag binds to cell membrane → release (degranulation): 1- Histamine: Vasodilatation & bronchospasm (Bronchial Asthma) 2- Heparin: anticoagulant. 3- ECF: attract eosinophils → limit allergic reaction. 3- Free macrophage 4- Blood leucocytes:  Fibers 1-Collagen Fiber (white collagenous F White colour when fresh Do not branch,wavy present in bundle Collagen protein forms Fibres Fibres composed of fibril made of microfibrils Micro fibrils made up tropocollagen- striations Synthesized by fibroblast 2-Elastic fibre (Yellow elastic F) Yellow in color when fresh Composed of elastin protein Singly present Branched and anastomose forming a network Can be stretched (one and a half times) Synthesized by fibroblast and smooth muscle cells in blood vessels Found in ligamentum flava, ligamentum nuchae, large arteries  3-Reticular fibre (Type III collagen) Structurally similar to collagen fibres Are very thin Immature collagen fibre Actively branch to form delicate network therefore named Reticular Form supportive framework of lymphoid tissue Stained black by silver salts (argyrophillic) Composed of Collagen Type III  Ground Substance Transparent & Homogeneous Fills spaces between cells and fibres Acts as amoleculer sieve facilitating diffusion between blood and tissues. Composition: Mucopolysaccharides Structural Glycoproteins Water & Electrolytes  Connective Tissue Types A- Loose CT B- dense CT 1- Loose areolar CT 1- White fibrous CT 2- Adipose CT a) Regular 3- Reticular CT b) Irregular 4- Mucoid CT 2- Yellow elastic CT 1- Loose (areolar) CT Most common type All types of cells & fibers Everywhere except in the brain Contain cavities (areolae)  Sites - Papillary layer of dermis. - Submucosa of digestive tube. - Around blood vessels - Between organs  2- Adipose (fatty) CT ↑ fat cells, reticular and collagen fibers  a- White Adipose CT White to yellow, Unilocular fat cells, ↓ vascular Sites Subcutaneous tissue. Mammary gland. Around the kidney  b- Brown Adipose CT Multilocular fat cells, ↑ vascular, pigmented  Sites Fetus & newborn. In adult: interscapular, mediastinal regions, axilla, around aorta.  3- White fibrous CT Collagen fibers and fibroblasts Regular Irregular Regularly arranged Irregularly arranged collagen bundles collagen bundles Sites of white fibrous CT Regular Irregular - Cornea - Sclera - Tendon - capsules of organs 4- Yellow elastic CT Elastic fibers and fibroblasts Sites of yellow elastic CT - Aorta and large vessels - Ligamentum flavum & ligamentum nuchae.  5- Reticular CT Reticular fibers and Reticular cells In stroma of organs (liver-kidney)  6- Mucoid CT Mucoid connective tissue is located within the umbilical cord as Wharton's jelly and is a gelatinous tissue primarily composed of a ground substance with few collagen or reticular fibers. Fibroblast-like cells and mesenchymal-like cells can be found.  Test your knowledge 1. Compare between plasma cell & mast cell: Plasma cell Mast cell One LM feature One EM feature One function Identify the tissue depicted in the below micrograph. 1.Stratified squamous keratinized epithelium 2.Stratified squamous non- keratinized epithelium 3.Dense regular connective tissue 4.Dense irregular connective tissue 5.Loose connective tissue 46  Match column A and B: Column A Column B 1. Areolar CT a. Stroma of organs 2. Mucoid CT b. Epiphyseal plate 3. Irregular white fibrous CT c. Wall of aorta 4. Elastic CT d. Ligaments 5. White adipose CT e. Vitreous humor 6. Regular white fibrous CT f. Intervertebral discs 7. Reticular CT g. Mediastinum 8. Brown adipose CT h. Submucosa i. Mammary gland j. Cornea Test your knowledge Mention 1 histological feature & 1 function for each of the following CT cells: 1. fibroblast 2. Unilocular fat cell 3. Macrophage 4. Pericyte Give reasons for the following. 1- Unilocular adipocyte appear signet ring in paraffin technique 2- Basophilia of fibroblast cytoplasm 3- Media of the artery contain dense elastic fibers Choose only one answer A 20-year-old woman has a low-grade fever and a sore throat. Laboratory studies show antibodies to Epstein-Barr virus. Which type of cell is responsible for the production of these antibodies? A. Macrophages/histiocytes B. Neutrophils C. Platelets D. Plasma cells E. Eosinophils A lipoma is a benign tumor composed of unilocular adipose tissue. Which of the following is true of this type of adipose tissue? A. It functions as a thermogenic reservoir. B. It is less vascular. C. Each cell contains multiple fat droplets. D. It is absent in the newborn human E. It is derived from hematopoietic stem cells. References for more Readings 1. Color Textbook of Histology; 3rd ed.; Gartner LP & Hiatt JL; WB Saunders Company; 2004. 2. BRS Histology. Cell Biology and Histology. Leslie P. Gartner,James L. Hiatt, Judy M. Strum. 2011 Lippincott Williams & Wilkins. 3. diFIORE’S ATLAS OF HISTOLOGY WITH FUNCTIONAL CORRELATIONS. Victor P. Eroschenko. ELEVENTH EDI T ION. 2008 Lippincott Williams & Wilkins. 50