Histology of Connective Tissue I PDF

Histology of Connective Tissue I By: Dr. Moustafa Al Sawy Dr. Shaimaa Mohamed Amer MBBCH, M.SC. M.D HISTOLOGY MBBCH, M.SC. M.D HISTOLOGY Associate Professor of Histology & Cell Bio...

Histology of Connective Tissue I By: Dr. Moustafa Al Sawy Dr. Shaimaa Mohamed Amer MBBCH, M.SC. M.D HISTOLOGY MBBCH, M.SC. M.D HISTOLOGY Associate Professor of Histology & Cell Biology Associate Professor of Histology & Cell Biology Certified Medical Educator Learning objectives Knowledge: Learning Objectives At the end of the lecture , each student will be able to: 1.Mention the general characters of the connective tissue & its composition. 2.Mention different cell types of the connective tissue. 3.Describe the histological structure of different connective tissue cells by LM & EM and mention their function.  Connective Tissue General characteristics: CON NECTIV ETIS SU E *It is mesenchymal in origin. *It consists of cells, fibers ( collagen, elastic and reticular ) and ground substance. *It contains large amount of extracellular substance (matrix), so its cells are widely separated. *Extracellular matrix is firm in cartilage, hard in bone and fluid in blood. *Some types penetrated by blood vessels , lymphatics & nerves. Composition of C.T. 1. Cells 2. Ground substance 3. C.T. fibers Extracellular Matrix (2 & 3).  Functions 1.Support & connection of cells, tissues & organs. 2. Its cells provide healing of injured tissues. 3.Resist stress as in cartilage, bone, tendons, ligaments, and capsules of organs. 4.Medium for exchange as in blood, lymph, and connective tissue proper deliver nutrients, waste products, and signaling molecules to and from cells of the body. 5.Immunity as Plasma, Mast cells and WBCs leave the bloodstream and enter connective tissue proper to protect the body from dangerous agents. 6.Lipid storage and metabolism: Adipose cells and adipose tissue. Functions  1.Connective tissue cells A- Fixed cells B- Wandering free cells *Stable and long-lived *Transient and migrating cells. from blood to the C.T. - Include: - Include:  Fibroblasts  Plasma cells Fat cells  Mast cells undifferentiated  Leukocytes mesenchymal cells (UMCs) fixed Macrophages 1.Undifferentiated mesenchymal cells (UMCs): Stem cell LM: Small irregular, branched , star shaped, pale basophilic cytoplasm. Central large oval nucleus with visible nucleoli. EM: Few organelles, many free ribosomes. Functions: It acts as a multipotent stem (mother) cell. 1. It can differentiate into other types of CT cells. 2. In bone marrow give blood cells. 2.Fibroblast Origin : UMCs, pericyte. Sites: All types of CT. LM: Flat branched, thin processes, oval nucleus prominent nucleolus. Basophilic cytoplasm. EM: Euchromatic nucleus prominent nucleolus, RER, ribosomes, Golgi, mitochondria. Function: 1-Formation CT fibers. 2-Formation ground substance. 3-Healing repair of wounds.  Fibrocytes & Myofibroblast Shape of fibrocytes (LM-EM): smaller, spindle shaped with few processes, elongated, dark nucleus. Shape of myofibroblast (LM-EM): As fibroblast & smooth muscle cells, actin & myosin inside it. It is responsible for wound closure.  Medical Application *The regenerative capacity of the connective tissue is clearly observed when tissues are destroyed by inflammation or traumatic injury. *In these cases, the spaces left after injury to tissues whose cells do not divide (eg, cardiac muscle) are filled by connective tissue, which forms a scar. *The healing of surgical incisions depends on the reparative capacity of connective tissue. The main cell type involved in repair is the fibroblast. *When it is adequately stimulated, such as during wound healing, the fibrocyte reverts to the fibroblast state, and its synthetic activities are reactivated. In such instances the cell reassumes the form and appearance of a fibroblast. *The myofibroblast, Their activity is responsible for wound closure after tissue injury, a process called wound contraction. 3.Fat cells Unilocular adipocyte(white fat) Sites: white adipose tissues. LM: Rounded, or oval large cells. Nucleus peripheral flattened. Cytoplasm is pale & reduced into thin rim around large fat drop. In H&E fat dissolves so cells appear large vacuoles (signet -ring appearance). They stains orange with Sudan III. EM: Fat drops appear as electron dense inclusion, little cell organelles around the nucleus. Functions: Storge of fat, support organs and heat insulator. 3.Fat cells Multilocular adipocyte (brown fat) Sites: Present in brown adipose CT. LM: Small rounded cell with rounded nucleus and many small fat droplets. They have many mitochondria so appear brown. Functions: Heat generation. Fat cells 4.Macrophages Origin : Blood Monocytes. Site: scattered in CT or fixed to collagen fibers. LM: Large branched cell with irregular cell boundary (pseudopodia) dark kidney shaped nucleus. Cytoplasm is pale basophilic and vacuolated. EM: Pseudopodia, lysosomes, RER, Golgi Functions: 1-Phagocytic. 2-Antigen presenting cells (APCs). Macrophages  Mononuclear phagocytic system They are present in different organs & take many names: Von -Kupffer cells in liver. Dust cells in lung. Langerhans cells in skin. Monocytes in blood, Microglia in brain. Osteoclasts in bone. Macrophages, spleen, thymus, lymph node, bone marrow & CT All have the same structure & function.  Medical Application *When adequately stimulated, macrophages may increase in size and are arranged in clusters forming epithelioid cells (named for their vague resemblance to epithelial cells), or several may fuse to form multinuclear giant cells. *Both cell types are usually found only in pathological conditions. 5.Reticular Cells Origin: UMC. Site: Reticular stroma of parenchymatous organs. (commonest cell in reticular CT). LM: Shape: Small Branched cell with many processes (The reticular fibers are attached to their processes. Stains: Hx & E → Pale basophilic. Special stain → Silver stain (brown) Nucleus: Central, oval and pale. Functions: 1.It acts as a multipotent stem (mother) cell. 2.Supportive function--APCs-----Phagocytic function).