Connective Tissue PDF

COLLEG E OF MEDICI NE CONNECTIVE TISSUE SHIRIN N. AMIN M B C H B ; M. S C. H I S T O L O GY COLLEGE OF MEDICINE, UOS  COLLEG E OF MEDICI NE Objectives Having revised this lec...

COLLEG E OF MEDICI NE CONNECTIVE TISSUE SHIRIN N. AMIN M B C H B ; M. S C. H I S T O L O GY COLLEGE OF MEDICINE, UOS  COLLEG E OF MEDICI NE Objectives Having revised this lecture, you should be able to:  demonstrate the different structural components of the C.T.  know the embryonic origin of C.T. components.  describe the function and location of each component from cells to fibers to ground substance.  demonstrate the classification of C.T. and the basis to that. 14.Nov.2024 SHIRIN N. AMIN 2  COLLEG E OF MEDICI NE Function and structure Connective tissues provide a matrix that supports and physically connects other tissues and cells together in organs. The interstitial fluid of connective tissue gives metabolic support to cells as the medium for diffusion of nutrients and waste products. Unlike the other tissue types (epithelium, muscle, and nerve), which consist mainly of cells, the major constituent of connective tissue is the extracellular matrix (ECM). Extracellular matrix consist of different combinations of protein fibers (such as collagens and elastic fibers) and ground substance. 14.Nov.2024 SHIRIN N. AMIN 3  COLLEG E OF MEDICI NE Embryonic development of C.T. Connective tissues originate from embryonic mesenchyme , a tissue developing mainly from the middle layer of the embryo, the mesoderm. In addition to producing all types of connective tissue proper and the specialized connective tissues bone and cartilage, the embryonic mesenchyme includes stem cells for other tissues such as blood, the vascular endothelium, and muscle. This lecture focuses on “connective tissue proper”. 14.Nov.2024 SHIRIN N. AMIN 4  COLLEG E OF MEDICI NE Structural composition of C.T. proper: 14.Nov.2024 SHIRIN N. AMIN 5  COLLEG E OF MEDICI NE 14.Nov.2024 SHIRIN N. AMIN 6  COLLEG E OF MEDICI NE Connective tissue proper cells: Various types of cells are present in connective tissue. These can be classed into two distinct categories:  Intrinsic cells of C.T. (fixed): The most important cells are fibroblasts, undifferentiated mesenchymal cells, and fat cells. They synthesize the ECM.  Wandering (mobile) cells: These include macrophage cells (or histiocytes) , mast cells, lymphocytes, plasma cells , monocytes and eosinophils. 14.Nov.2024 SHIRIN N. AMIN 7  COLLEG E OF MEDICI NE 14.Nov.2024 SHIRIN N. AMIN 8  COLLEG E OF MEDICI NE 14.Nov.2024 SHIRIN N. AMIN 9  COLLEG E OF MEDICI NE 1. Fibroblasts : These are the most numerous cells of connective tissue. They are called fibroblasts because they are concerned with the production of collagen fibers. They also produce reticular and elastic fibers. Fibroblasts are fixed cells, i.e. they are not mobile. In tissue sections these cells appear to be spindle shaped, and the nucleus appears to be flattened. When seen from the surface the cells show branching processes. Two levels of fibroblast activity can be observed histologically. 14.Nov.2024 SHIRIN N. AMIN 10  COLLEG E OF MEDICI NE Some histologists reserve the term “fibroblast” to denote the active cell and “fibrocyte” to denote the quiescent cell. The active fibroblast has more abundant and irregularly branched cytoplasm. Its nucleus is large, ovoid and has a prominent nucleolus. The cytoplasm has much rough endoplasmic reticulum (RER) and a well-developed Golgi apparatus. 14.Nov.2024 SHIRIN N. AMIN 11  COLLEG E OF MEDICI NE  The fibrocyte cell is smaller than the active. the cytoplasm is scanty, organelles are few, and the nucleus may become heterochromatic.  Fibroblasts become very active when there is need to lay down collagen fibers. This occurs, for example, in wound repair. 14.Nov.2024 SHIRIN N. AMIN 12  COLLEG E OF MEDICI NE 14.Nov.2024 SHIRIN N. AMIN 13  COLLEG E OF MEDICI NE 14.Nov.2024 SHIRIN N. AMIN 14  COLLEG E OF MEDICI NE 2. Undifferentiated Mesenchymal Cells : Embryonic connective tissue is called mesenchyme. It is made up of stellate small cells with slender branching processes that join to form a fine network called as undifferentiated mesenchymal cells. 14.Nov.2024 SHIRIN N. AMIN 15  COLLEG E OF MEDICI NE 14.Nov.2024 SHIRIN N. AMIN 16  COLLEG E OF MEDICI NE 3.Fat cells (Adipocytes): Some cells store fat in large amounts and become distended with it. These are called fat cells, adipocytes, or lipocytes.  Aggregations of fat cells constitute adipose tissue. Each fat cell contains a large droplet of fat that almost fills it. The cytoplasm of the cell forms a thin layer just deep to the plasma membrane. The nucleus is pushed against the plasma membrane and is flattened resembling a signet ring. 14.Nov.2024 SHIRIN N. AMIN 17  COLLEG E OF MEDICI NE 14.Nov.2024 SHIRIN N. AMIN 18  COLLEG E OF MEDICI NE 14.Nov.2024 SHIRIN N. AMIN 19  COLLEG E OF MEDICI NE 4. Macrophages:  Macrophages are characterized by their well-developed phagocytic ability and specialize in turnover of protein fibers and removal of dead cells, tissue debris, or other particulate material.  They have a wide spectrum of morphologic features corresponding to their state of functional activity and to the tissue they inhabit. A typical macrophage measures between 10 and 30 μm in diameter and has an eccentrically located, oval or kidney-shaped nucleus. 14.Nov.2024 SHIRIN N. AMIN 20  COLLEG E OF MEDICI NE  Macrophages are usually described as ‘fixed’ when they are attached to fibers; or as motile in the circulation. Fixed macrophages resemble fibroblasts in appearance, but free macrophages are rounded. macrophages are shown to have a characteristic irregular surface with pleats, protrusions, and indentation. Macrophages derive from bone marrow precursor cells that divide, producing monocytes that circulate in the blood.  Monocytes and macrophages are the same cell at different stages of maturation. 14.Nov.2024 SHIRIN N. AMIN 21  COLLEG E OF MEDICI NE  The macrophage-like cells have been given different names in different organs, for example Kupffer cells in the liver, microglial cells in the central nervous system, Langerhans cells in the skin, and osteoclasts in bone tissue. However, all are derived from monocytes. Macrophages are present in the connective tissue of most organs and are often referred to as histiocytes.  All are long-living cells and may survive for months in the tissues. 14.Nov.2024 SHIRIN N. AMIN 22  COLLEG E OF MEDICI NE  Macrophages are distributed throughout the body and are present in most organs. Along with other monocyte-derived cells, they comprise a family of cells called the mononuclear phagocyte system. 14.Nov.2024 SHIRIN N. AMIN 23  COLLEG E OF MEDICI NE 14.Nov.2024 SHIRIN N. AMIN 24  COLLEG E OF MEDICI NE 14.Nov.2024 SHIRIN N. AMIN 25  COLLEG E OF MEDICI NE 5. Mast cell:  Are oval or irregularly shaped connective tissue cells, between 7 and 20 μm in diameter, whose cytoplasm is filled with basophilic secretory granules. The nucleus is centrally situated and often obscured by abundant secretory granules.  Mast cells originate from progenitor cells in the bone marrow. The progenitor cells circulate in the blood, cross the wall of venules and capillaries, and penetrate connective tissues, where they differentiate. 14.Nov.2024 SHIRIN N. AMIN 26  COLLEG E OF MEDICI NE  Mast cells function in the localized release of many bioactive substances with roles in the local inflammatory response, innate immunity, and tissue repair.  Important molecules released from these cells’ secretory granules includes Histamine (which promotes increased vascular permeability and smooth muscle contraction ) and Heparin (Anticoagulant) and other cytokines. 14.Nov.2024 SHIRIN N. AMIN 27  COLLEG E OF MEDICI NE 14.Nov.2024 SHIRIN N. AMIN 28  COLLEG E OF MEDICI NE 6. Plasma cells: They have a smaller, eccentrically placed nucleus. Many of these nuclei contain compact, peripheral regions of heterochromatin alternating with lighter areas of euchromatin, a configuration that can give the nucleus of a plasma cell the appearance of a clock face.  They arise from B-lymphocytes that come from the blood. They produce antibodies against antigens. 14.Nov.2024 SHIRIN N. AMIN 29  COLLEG E OF MEDICI NE They are particularly abundant in C.T. of the lamina propria of the gastrointestinal tract ,the respiratory system and the female reproductive system. 14.Nov.2024 SHIRIN N. AMIN 30  COLLEG E OF MEDICI NE 7. Leukocytes:  Besides macrophages and plasma cells, connective tissue normally contains leukocytes derived from cells circulating in the blood. Leukocytes, or white blood cells, make up a population of wandering cells in connective tissue.  They leave blood by migrating between the endothelial cells lining venules to enter connective tissue by a process called diapedesis. 14.Nov.2024 SHIRIN N. AMIN 31  COLLEG E OF MEDICI NE Eosinophils:  So called because of the presence of eosinophilic granules in the cytoplasm. Are found in the c.t of many organs. they have a characteristic bilobed nucleus. they are increased in parasitic infestation and allergy. 14.Nov.2024 SHIRIN N. AMIN 32  COLLEG E OF MEDICI NE 8. Lymphocytes:  The small lymphocytes are characterized by spherical nuclei with highly condensed chromatin and only a thin surrounding rim of scant cytoplasm. Larger lymphocytes have larger, slightly indented nuclei and more cytoplasm that is slightly basophilic. They are involved in the immune mechanism. 14.Nov.2024 SHIRIN N. AMIN 33  COLLEG E OF MEDICI NE Fibers of the connective tissue:  There are three types of connective tissue fibers: collagen, elastic, and reticular. The amount and arrangement of these fibers depend on the function of the tissues or organs in which they are found.  The fibrous components of connective tissue are formed from proteins that polymerize after secretion from fibroblasts. Collagen and reticular fibers are both formed by proteins of the collagen family , and elastic fibers are composed mainly of the protein elastin. 14.Nov.2024 SHIRIN N. AMIN 34  COLLEG E OF MEDICI NE C.T. Fibers 14.Nov.2024 SHIRIN N. AMIN 35  COLLEG E OF MEDICI NE Collagen Fibers: Collagen fibers are most abundant type of connective tissue fibers. With the light microscope collagen fibers are seen in bundles. Several types of collagen (more than 28), the most common are: Type I : are found in tendons, ligaments, fasciae, aponeuroses, dermis of the skin and in meninges. They form the fibrous basis of bone and fibrocartilage. 14.Nov.2024 SHIRIN N. AMIN 36  COLLEG E OF MEDICI NE Type I fibers are formed from group of fibrils that each have prominent cross striations. Fibers then form bundles of Collagen that are very strong and offer great resistance to tensile stresses. 14.Nov.2024 SHIRIN N. AMIN 37  COLLEG E OF MEDICI NE 14.Nov.2024 SHIRIN N. AMIN 38  COLLEG E OF MEDICI NE Collagen fiber ultrastructure 14.Nov.2024 SHIRIN N. AMIN 39  COLLEG E OF MEDICI NE Type II: These usually come in the form of fibrils (not fibers or bundles). In type II collagen striations are less prominent than in type I. Type II collagen fibers form the fibrous basis of hyaline cartilage and elastic cartilage. The fibers provide resistance to pressure. Fine type II fibers are also present in the vitreous body of eye. 14.Nov.2024 SHIRIN N. AMIN 40  COLLEG E OF MEDICI NE Type III: These are extremely thin and form network in certain organs. They form reticular fibers and found in skin, and wall of BVs. Type IV: This type of collagen consists of short filaments that form sheets. It is present in the basal laminae of basement membranes to which the basal regions of the cells attach. It is also seen in the lens capsule. Type V: This type of collagen is found in skin, bone, fetus tissues and placenta. 14.Nov.2024 SHIRIN N. AMIN 41  COLLEG E OF MEDICI NE Reticular fibers : Found in delicate connective tissue of many organs, reticular fibers consist mainly of collagen type III. This collagen forms an extensive network (reticulum) of extremely thin diameter. They differ from typical (Type I) collagen fibers:  They are much finer and have uneven thickness. They form a network (or reticulum) by branching, and by anastomosing with each other. They do not run in bundles. 14.Nov.2024 SHIRIN N. AMIN 42  COLLEG E OF MEDICI NE They can be stained specifically by silver impregnation, which renders them black. They can thus be easily distinguished from type I collagen fibers which are stained pink (acidophilic). Reticular fibers provide a supporting network in lymphoid organs like the spleen, lymph nodes and bone marrow; most glands, liver and kidneys. Reticular fibers are synthesized by fibroblasts and reticular cells (special variety of fibroblasts) 14.Nov.2024 SHIRIN N. AMIN 43  COLLEG E OF MEDICI NE 14.Nov.2024 SHIRIN N. AMIN 44  COLLEG E OF MEDICI NE 14.Nov.2024 SHIRIN N. AMIN 45  COLLEG E OF MEDICI NE Elastic fibers: Elastic fibers are thin, small, branching fibers that allow stretch. They have less tensile strength, and are much thinner than collagen fibers. They run singly (not in bundles), branch and anastomose with other fibers. Elastic fibers are composed mainly of a protein called elastin that forms their central amorphous core. The outer fibrils are made up of a glycoprotein called fibrillin. Periodic striations are not present in elastic fibers. 14.Nov.2024 SHIRIN N. AMIN 46  COLLEG E OF MEDICI NE 14.Nov.2024 SHIRIN N. AMIN 47  COLLEG E OF MEDICI NE Ground substance The ground substance of the extracellular matrix ECM is a highly hydrated (with much bound water), transparent, complex mixture of macromolecules , principally of three classes : glycosaminoglycans , proteoglycans, and glycoproteins. It fills the space between cells and fibers in connective tissue and, because it is viscous, acts as both a lubricant and a barrier to the penetration of invaders. 14.Nov.2024 SHIRIN N. AMIN 48  COLLEG E OF MEDICI NE 14.Nov.2024 SHIRIN N. AMIN 49  COLLEG E OF MEDICI NE 14.Nov.2024 SHIRIN N. AMIN 50  COLLEG E OF MEDICI NE Classification of C.T. Depending on the component that predominates in the tissue or a structural characteristic of the tissue. connective and supportive tissues are classified into main groups with several subgroups as below: 1. C.T. Proper. 2. C.T. with special properties. 3. Supporting C.T. 14.Nov.2024 SHIRIN N. AMIN 51  COLLEG E OF MEDICI NE 14.Nov.2024 SHIRIN N. AMIN 52  COLLEG E OF MEDICI NE C. T. Proper : C.T. proper: is of two types: 1- Loose (Areolar ) connective tissue: Loose connective tissue is very common and generally supports epithelial tissue. the loose connective tissue typically contains cells, fibers, and ground substance in roughly equal parts. The most numerous cells are fibroblasts , but the other types of connective tissue cells are also present , along with nerves and blood vessels. 14.Nov.2024 SHIRIN N. AMIN 53  COLLEG E OF MEDICI NE Collagen fibers predominate , but elastic and reticular fibers are also present, with a moderate amount of ground substance, loose connective tissue has a delicate consistency; it is flexible and not very resistant to stress. 14.Nov.2024 SHIRIN N. AMIN 54  COLLEG E OF MEDICI NE 14.Nov.2024 SHIRIN N. AMIN 55  COLLEG E OF MEDICI NE Location of loose connective tissue: It fills the spaces of the body just deep to the skin. It lies below the mesothelial lining of the internal body cavities. It is associated with the adventitia of blood vessels. It surrounds the parenchyma of glands. The loose connective tissue of mucous membrane (as in the alimentary canal) is called the lamina propria. 14.Nov.2024 SHIRIN N. AMIN 56  COLLEG E OF MEDICI NE 14.Nov.2024 SHIRIN N. AMIN 57  COLLEG E OF MEDICI NE 2-Dense connective tissue:  contains a greater abundance of fibers and fewer cells than loose connective tissue. It contains most of the components found in loose connective tissue except that it has more fibers and fewer cells. The orientation and arrangement of the bundles of collagen fibers in this tissue make it resistant to pressure. Dense connective tissue is less flexible and far more resistant to stress than loose connective tissue. 14.Nov.2024 SHIRIN N. AMIN 58  COLLEG E OF MEDICI NE Subtypes of dense connective tissue A/ Dense irregular connective tissue: In dense irregular connective tissue, bundles of collagen fibers appear randomly interwoven, with no definite orientation. The collagen fibers form a tough three-dimensional network, providing resistance to stress from all directions. It is often found closely associated with loose connective tissue. 14.Nov.2024 SHIRIN N. AMIN 59  COLLEG E OF MEDICI NE Fine networks of elastic fibers are often scattered among the collagen bundles. Fibroblasts (the most abundant cells of this tissue) are located in the narrow spaces that separate between collagen bundles. 14.Nov.2024 SHIRIN N. AMIN 60  COLLEG E OF MEDICI NE 14.Nov.2024 SHIRIN N. AMIN 61  COLLEG E OF MEDICI NE Location of dense irregular connective tissue It constitutes the dermis of the skin, sheathes of the nerves, the capsules of organs e.g. the spleen, testis, ovary, kidney, and lymph nodes. 14.Nov.2024 SHIRIN N. AMIN 62  COLLEG E OF MEDICI NE B/ Dense regular connective tissue: Fibers are arranged according to a definite pattern, with fibers and fibroblasts aligned in parallel for resistance to prolonged or repeated stresses exerted in the same direction. Location: Tendons, ligaments and aponeuroses. 14.Nov.2024 SHIRIN N. AMIN 63  COLLEG E OF MEDICI NE 14.Nov.2024 SHIRIN N. AMIN 64  COLLEG E OF MEDICI NE 14.Nov.2024 SHIRIN N. AMIN 65  COLLEG E OF MEDICI NE Reticular C.T. In reticular tissue fibers of type III collagen form a delicate 3D network that supports various types of cells. The fibrous network of this specialized connective tissue is produced by modified fibroblasts called reticular cells that remain associated with and partially covering the fibers. The fibers provides a framework with specialized microenvironments for cells in hemopoietic tissue and some lymphoid organs (bone marrow, lymph nodes, and spleen). 14.Nov.2024 SHIRIN N. AMIN 66  COLLEG E OF MEDICI NE Beside lymphocytes ,macrophages and other cells of the mononuclear phagocyte system are also dispersed within these reticular tissues to monitor cells formed there or passing through and to remove debris. 14.Nov.2024 SHIRIN N. AMIN 67  COLLEG E OF MEDICI NE 14.Nov.2024 SHIRIN N. AMIN 68  COLLEG E OF MEDICI NE Adipose Tissue A/ white (unilocular) adipose tissue: This type of adipose tissue appears white because, it consists of large number of unilocular fat cells, each of which contains a single lipid droplet. The white adipose tissue is heavily supplied with blood vessels, which form capillary networks throughout the tissue. It is found in adults. 14.Nov.2024 SHIRIN N. AMIN 69  COLLEG E OF MEDICI NE 14.Nov.2024 SHIRIN N. AMIN 70  COLLEG E OF MEDICI NE B/ Brown (multilocular) adipose tissue: Brown adipose tissue (Brown fat) is composed of multilocular fat cells, which store fat in multiple droplets. It may appear reddish- brown because of its extensive vascularity and its abundant mitochondria. Location: Multilocular fat is found infants. 14.Nov.2024 SHIRIN N. AMIN 71  COLLEG E OF MEDICI NE Mucoid C.T. Mucoid (or mucous) connective tissue is another embryonic type of connective tissue, found mainly in the umbilical cord and fetal organs. With abundant ground substance composed chiefly of hyaluronic acid, mucoid tissue is jellylike with sparse collagen fibers and scattered fibroblasts. Mucoid tissue is the principal component of the umbilical cord, where it is referred to as Wharton’s jelly. A similar form of connective tissue is also found in the pulp of young teeth. 14.Nov.2024 SHIRIN N. AMIN 72  COLLEG E OF MEDICI NE 14.Nov.2024 SHIRIN N. AMIN 73  COLLEG E OF MEDICI NE 14.Nov.2024 SHIRIN N. AMIN 74