Lecture 11 Connective Tissue Cells PDF

General Histology Course number: 2110104 Lecture 11 Connective tissue cells Tarek Hamdy Abd-Elhamid, MBBCh. MSc. PhD. Department of Basic Medical Sciences Faculty of Medicine Aqaba Medical Sciences University Aqaba Jordan ...

General Histology Course number: 2110104 Lecture 11 Connective tissue cells Tarek Hamdy Abd-Elhamid, MBBCh. MSc. PhD. Department of Basic Medical Sciences Faculty of Medicine Aqaba Medical Sciences University Aqaba Jordan  Objectives State the general characters and functions of connective tissue. List types of connective tissue cells. Describe the structure and functions of fibroblasts, fat cells, macrophages, mast cells and plasms cells.  Connective tissue One of the basic tissues of the body (Connective, epithelial, muscular, nervous) The major constituent of connective tissue is the extracellular matrix (ECM). All connective tissues originate from embryonic mesenchyme, a tissue developing mainly from the middle layer of the embryo, the mesoderm. Functions of connective tissue: 1. Provides a matrix that supports and physically connects other tissues and cells together to form the organs of the body. 2. The interstitial fluid of connective tissue gives metabolic support to cells as the medium for diffusion of nutrients and waste products. 3. Defense & immunity  Components of connective tissue CONNECTIVE TISSUE Extracellular Connective tissue matrix (ECM) cells (Wheater ’s Functional Histology 2013) It consists of connective tissue cells and extracellular matrix (ECM) which is composed of fibers, ground substance and tissue fluid.  Connective tissue cells Fixed Cells Free (wondering) Cells -Fibroblast - Macrophage -Fat cell (adipocytes) - Mast cell -Mesenchymal cell - Plasma cell - Leukocytes  A-Fixed cells 1-Mesenchymal cells: They are spindle-shaped cells with their scant cytoplasm extended as two or more thin cytoplasmic processes. Have pale basophilic cytoplasm. Have large nuclei, with prominent nucleoli and fine chromatin. Function: Give rise to the other types of connective tissue cells.  A-Fixed cells 2-Fibroblasts Origin: from mesenchymal cells Permanent residents of connective tissue. Predominant cells in connective tissue Seldom undergo mitosis except in wound healing May differentiate into other cell types under certain conditions LM: It appears as branched cell with basophilic cytoplasm & oval pale nucleus with prominent nucleolus (Junqueira’s basic histology 2018)  A- Fixed cells 2- Fibroblasts Fibroblasts may occur in either: Active state Quiescent state. Quiescent cells are called fibrocytes; which are usually spindle-shaped. It has fewer processes; a smaller, darker, elongated nucleus; and more acidophilic cytoplasm  A- Fixed cells 2- Fibroblasts E.M.: Active fibroblast has more abundant and irregularly branched cytoplasm containing numerous RER, well developed Golgi apparatus, transfer vesicles, and a large, ovoid, euchromatic nucleus and a prominent nucleolus. Function: 1. Secretion of collagen & elastic fibers. 2. Secretion of ground substance. 3. Healing of tissue after injury.  Clinal correlations Fibroblasts undergo mitosis only during wound healing. Under certain conditions, fibroblasts may differentiate into adipose cells. During fibrocartilage formation, they may differentiate into chondrocytes. Under pathological conditions, fibroblasts may differentiate into osteoblasts.  A- Fixed cells 3- Fat cells (adipocytes) Specialized for cytoplasmic storage of lipid as neutral fats, or less commonly for the production of heat. Originate from mesenchymal cells and perhaps from fibroblasts Do not normally undergo cell division because they are fully differentiated cells Two types of adipocytes: Unilocular adipocytes Multilocular adipocytes  A- Fixed cells 3- Fat cells (adipocytes) Unilocular adipocytes L.M.: Fat dissolves in H&E preparations so fat cells appear as empty spaces with peripheral flat nucleus & thin rim of cytoplasm. This gives fat cells the signet ring appearance. Fat droplets can be stained with Sudan black stain. They are surrounded by a basal lamina called external lamina Function: 1. Synthesis, storage and release of fat  A- Fixed cells 3- Fat cells (adipocytes) Multilocular Adipocytes Also called brown adipocytes. Smaller than unilocular adipocytes Contain many small lipid droplets, therefore called multilocular Have spherical (not flatten) centrally located nucleus Function: heat production  B- Wandering cells 1- Macrophage Also called histocytes Origin: Circulating monocytes Have highly developed phagocytic activities With L.M. With H&E difficult to identify unless they display obvious evidence of phagocytic activity. Their have eccentric indented or kidney-shaped nuclei. Can be identified with vital stains such as India ink by the appearance of phagocytosed particles of the dye in their cytoplasm  B- Wandering cells 1- Macrophage With E.M. Macrophages have folds and finger-like projections, features related to their active pinocytotic and phagocytic activities. They generally have well- developed Golgi complexes and abundant lysosomes. The macrophage may also contain endocytotic vesicles and phagocytic vacuoles near the protrusions and indentations of the cell surface. (Junqueira’s basic histology 2018)  Macrophages are member of mononuclear phagocyte system BONE Peripheral TISSUES MARROW BLOOD Resident Tissue macrophages Kupffer cells (liver) Langerhans cells (skin) Bone marrow Pro- Osteoclasts (bone) precursor genitor cells Microglial cell (brain) Mon Splenic macrophages (spleen) Alveolar macrophages (lung) Macrophage in connective tissue Proper - recruited by inflammatory or Mon immunologic stimulus. pathogen clearance MΦ antigen presentation  Functions of macrophages Breaking down extracellular material and senescent or dead cells (tissue turnover & repair). Phagocytose and destroy foreign intruders. Defense Produce and release various cytokines to facilitate immune and inflammatory processes. Antigen presentation to lymphocyte.  B- Wandering cells 2- Mast Cell Originate from progenitor cells in the bone marrow L.M.: They are rounded or oval shaped cells, found in groups along blood vessels. Have central nuclei & filled with basophilic secretory granules that often obscure the central nucleus. Because of the high content of acidic radicals in their sulfated GAGs, mast cell granules display metachromasia, which means that they can change the color of some basic dyes (e.g., toluidine blue) from blue to purple or red. (Junqueira’s basic histology 2018)  B- Wandering cells 2-Mast Cell E.M.: Mast cell has an irregular outline with many small surface projections. They have membrane-bound granules vary in size, shape, and density of their internal contents. The cytoplasm contains a well- developed Golgi complex, scattered RER and mitochondria. The Golgi complex plays a role in synthesis and sulfation of glycosaminoglycans such as heparin that are packaged and stored in the granules. Granules contain inflammatory mediators including histamine & heparin. (Histology: A Text and Atlas with Correlated Cell and Molecular Biology 2015)  B- Wandering cells 2-Mast Cell Function: secrete histamine & heparin. Heparin is an anticoagulant It is sulphated acid mucopolysacharide. Therefore, granules appear metachromatic. Heparin prevents thrombosis and helps to keep the platelets from aggregation Histamine promotes increased vascular permeability and smooth muscle contraction  B- Wandering cells 3- Plasma Cell Origin: They are derived from activated B-lymphocytes and responsible for humoral immunity. L.M.: ovoid cells contain a spherical eccentrically placed nucleus with clock- face appearance, as it contains compact, peripheral regions of heterochromatin alternating with lighter areas of euchromatin. Cytoplasm is deeply basophilic because of an abundance of RER. Close to the nucleus, there is a pale area of cytoplasm called negative Golgi area. (Atlas of histology with functional and clinical correlations 2011)  B- Wandering cells 3- Plasma Cell E.M.: Plasma cells have abundant free ribosomes and an extensive RER with dilated cisterna contain flocculent, moderately electron-dense material that is probably newly synthesized immunoglobulin. The juxtanuclear Golgi complex consists of flattened sacs and a few associated vesicles. Function: Secretion of antibodies. Netter's Essential Histology, 2013  References Cui, D., 2011. “Atlas of histology with functional and clinical correlations.” Lippincott Williams & Wilkins. Mescher, A.L., 2018. Junqueira’s Basic Histology: Text and Atlas, 15th Ed. McGraw Hill. Ovalle, W.K. and P.C. Nahirney, 2013. Netter's Essential Histology: with Student Consult Access. Elsevier Health Sciences. Ross MH, Pawlina W. 2015. Histology: A Text and Atlas: with Correlated Cell and Molecular Biology: Lippincott Williams & Wilkins. Young, B., Woodford, P., & O’Dowd, G. 2013. Wheater’s functional histology (6th ed.). Churchill Livingstone. Thank you