Connective Tissue (Part 1) PDF

HISTOLOGY BMS (I) Module Connective Tissue (Part 1) Prepared by Dr. Haitham Sewilam Lecturer of Histology Faculty of Medicine - Helwan University - Egypt  Objectives List characters of connective tissue (C.T). Recognize the histologic...

HISTOLOGY BMS (I) Module Connective Tissue (Part 1) Prepared by Dr. Haitham Sewilam Lecturer of Histology Faculty of Medicine - Helwan University - Egypt  Objectives List characters of connective tissue (C.T). Recognize the histological structure of C.T. Classify types of C.T. cells. Describe the histological structure and functions of C.T cells List components of the ground substance of C.T.  Characters of the C.T 1- It originates from the mesoderm. 2- Composed of widely separated cells with large amount of extracellular matrix. 3- It is penetrated by blood vessels, nerves & lymphatic vessels. 4- It connects, supports & protects other tissues & organs.  Connective tissue structure Extracellular Cells matrix Ground Fibers substance Types of C.T. according to matrix consistency C.T. Soft proper Rubbery Cartilage Hard Bone Fluid Blood  Types of C.T. cells 1- Fixed (resident or 2-Wandering (transient or permanent cells) temporary cells) Originate locally within Originate from stem cells in the CT. bone marrow, circulate in blood then move into connective tissue where they function. Stable and long-lived Motile and short-lived cells. cells. TYPES TYPES Undifferentiated Macrophages mesenchymal cells Mast cells Pericytes Plasma cells Fibroblasts & fibrocytes Leucocytes Adipocytes  Undifferentiated mesenchymal cells (UMCs) Origin: The mother cells of all types of CT. Sites: 1. Present mainly in embryo as stem cells. 2. In adults, some cells remain after birth around blood capillaries in the form of pericytes.  Structure of UMC:  LM:  Shape: small stellate shaped cells with cytoplasmic processes (branched cell).  Nucleus: large, pale with prominent nucleolus.  Cytoplasm: basophilic.  EM:  Nucleus: euchromatic  Cytoplasm: contains many free ribosomes. Function of UMCs:  1. They can differentiate into different cells of all types of connective tissue (C.T. proper, cartilage and bone).  2. They also give the origin of blood elements.  3. Some cells remain after birth around blood capillaries (pericytes).  Pericytes Origin: UMCs. Sites: present around blood capillaries. Structure: LM:  Shape: branched cell with long cytoplasmic processes  Cytoplasm: basophilic.  Nucleus: central & oval.  EM of pericytes: Cytoplasm contains:  A network of actin and myosin.  Many free ribosomes Endothelial Functions : cells 1- In case of tissue injury, pericytes can differentiate into fibroblasts, endothelial cells & smooth muscle cells. 2- They have contractile ability so Cytoplasmic process Of pericyte they can regulate blood flow through capillaries.  Fibroblasts Origin: UMCs & pericytes Sites: The most common type of C.T cells. Structure: LM:  Shape: Flat branched cells with cytoplasmic processes.  Nucleus: large, pale with prominent nucleolus.  Cytoplasm: deep basophilic EM of Fibroblasts: (have characters of protein-secreting cells) Well developed rER. Well developed Golgi apparatus. Mitochondria. Euchromatic nucleus N.B. No secretory granules in the cytoplasm of fibroblasts.  Functions of fibroblast: 1) Synthesis of CT matrix (fibers & ground substance) Mitochondria RER Golgi 2) Synthesis of growth factors enhancing apparatus cell growth. Nucleus Collag 3) Healing of the wounds en fibers The inactive fibroblasts (fibrocytes)  Smaller, spindle shaped with fewer processes  Nucleus: smaller & darker Cytoplasm Cytoplasm Cytoplasm: pale basophilic (less rER) is deep is pale basophilic basophilic Function: maintenance of CT matrix Fibrocyte Active cells = Fibroblast fibroblasts Inactive cells = fibrocytes  Adipocytes (fat cells) Origin: UMC Types: Unilocular & multilocular fat cells Fat cells (Unilocular) Fat cells (Multilocular)  Unilocular Fat Cells Multilocular Fat Cells (White fat cells) (Brown fat cells) Site In white adipose C.T. In brown adipose C.T. Structure -Shape: Large oval cells. - Shape: small rounded -Nucleus: Peripheral & cells. flattened -Nucleus: central & -Cytoplasm: rounded A very thin rim around a -Cytoplasm: single large fat droplet. Contains many fat - by H&E, fat droplet droplets of various dissolves & the cells sizes. appear as large vacuoles -Numerous mitochondria with peripheral nucleus (signet-ring appearance). Fat cells (Multilocular)  Unilocular Fat Cells Multilocular Fat (White fat cells) Cells (Brown fat cells) Special Fat stains orange with Sudan III or stain Black with Sudan black and osmic acid Function 1. Storage of fat to Heat generation. release energy. 2. Heat insulation. 3. Support organs.  Macrophages Origin: from blood monocytes. Structure: LM: Shape: large irregular cells Nucleus: eccentric & kidney-shaped. Special stain: It can be stained trypan blue EM: Has many cell processes called pseudopodia. The cytoplasm contains many lysosomes. EM of macrophage Pseudopodia Pseudopodia Lysosomes  Functions of macrophage They play an important role in the body defense mechanism by: 1) Phagocytosis of foreign bodies, microorganism and dead cells. 2) Act as antigen presenting cells (to T-lymphocytes) 3) Secrete growth factors important for tissue repair  Plasma cells Origin: from B-lymphocytes. Site: abundant in lymphoid tissue. Structure: LM:  Shape: oval  Nucleus: Spherical & eccentric with a cart- wheel (clock-face) appearance (nucleus contains dark areas of heterochromatin alternating with lighter areas of euchromatin).  Cytoplasm: deep basophilic, with -ve Golgi image. EM: (characteristics of protein secreting cells) Well developed rER Well developed Golgi apparatus Mitochondria N.B No secretory granules in the cytoplasm of plasma cells. Function: Synthesis & secretion of antibodies (humoral immunity) EM of plasma cell  Mast cells Origin: hemopoietic stem cells Site: along the blood vessels and mucosa of the GIT & respiratory tract. LM: - Shape: oval or rounded - Nucleus: central & rounded -Cytoplasm: contains basophilic granules that obscure the nucleus. - Special stain: the granules are metachromatically stained by toluidine blue (appear purple or red instead of blue) due to their content of heparin.  EM of mast cells: (characters of protein secreting cells) RER, Golgi apparatus, mitochondria, euchromatic nucleus Electron dense secretory granules Function of mast cells:  Mast cells carry surface receptors for IgE  Binding of specific antigen to IgE antibody leads to degranulation of mast cells and release of its chemical mediators resulting in allergic reaction. Allergic Reaction Chemical mediators of mast cells released during allergy are: 1) Heparin (anticoagulant). 2) Histamine causes increased vascular permeability & smooth muscle contraction 3) Leukotrienes causes prolonged constriction of smooth muscles in bronchial tree causing bronchial asthma. 4) Eosinophil chemotactic factor, which attracts eosinophils. Release of the chemical mediators stored in mast cells promotes allergic reactions known as immediate hypersensitivity reactions Dramatic one is anaphylactic shock, a potentially fatal condition  Pigment cells -Origin: UMCs. - Have long branching processes. They are melanin storing cells Site : in dermis of skin & iris of the eye.  Ground substance of C.T. matrix  It is a highly hydrated material.  It consists of 3 macromolecules: 1. Glycosaminoglycans (GAGs): polysaccharides that may be non- sulphated (e.g. hyaluronic acid) or sulphated (e.g. chondroitin sulfate) 2. Proteoglycans (sulfated GAGs attached to a core of protein ). 3. Multiadhesive glycoproteins (large protein molecules with branched oligosaccharide chains) e.g. fibronectin 21 November 2024 Module: BMS-101 32 Water in the ground substance of connective tissue is referred to as interstitial fluid and has an ion composition similar to that of blood plasma. Edema is the excessive accumulation of interstitial fluid in connective tissue as in case of inflammation.