Connective and Supportive Tissues PDF

Connective and Supportive Tissues Connective and supportive tissues connect other tissues provide a framework support the entire body by means of cartilage and bones. These tissues also play an important role in Thermoregulation Defense and repair mechanisms Reservoir for v...

Connective and Supportive Tissues Connective and supportive tissues connect other tissues provide a framework support the entire body by means of cartilage and bones. These tissues also play an important role in Thermoregulation Defense and repair mechanisms Reservoir for various hormones and cytokines.  The basal lamina separates all connective tissues from non-connective tissues. Cells of connective and supportive tissues are devoid of basal lamina except adipose tissue, as with muscles. CLASSIFICATION Four criteria are used to classify connective tissues- Predominant cell type (s) Type of fibrous components of the matrix, Number of fibers in a unit volume of the matrix, Orderliness of the matrical components Connective and supportive tissues  Mesoderm- Embryonal connective tissue Mesenchymal Tissue Mucus Tissue Adult Connective Tissue Proper Connective Supportive Tissue Blood Tissue Cartilage Bone Erythrocytes Loose Dense Hyaline Woven Agranulocytes Areolar Irregular Elastic Lamellar Granulocytes Adipose Regular Fibrous Platelets Reticular Elastic Plasma Classes of Connective Tissue COMPOSITION Connective and supportive tissues are composed of Cells – Mesenchymal cells, Fibrocytes and fibroblast, Reticular cells, Adipocytes, Pericytes, Mast cells, Macrophages, Plasma cells, pigment cells, other cells of loose connective tissue. Fibers – Collagen Fibers, Elastic Fibers and Reticular Fibers Amorphous Ground substance – Hydrated gel composed of glycosaminoglycans (GAGs), and proteoglycans, plasma constituents, metabolites, water, and ions. Connective and supportive tissues CONNECTIVE TISSUE CELLS  Mesenchymal Cells Mesenchymal cells are irregularly shaped with multiple processes. They are smaller than fibroblasts and have fewer cytoplasmic organelles. The large, oval nucleus has a prominent nucleolus and fine chromatin. The mesenchymal cell population serves as a reservoir of pluripotent cells that can differentiate into other types of connective tissue cells as needed. Connective and supportive tissues  Fibrocytes and Fibroblasts The most common cell of connective tissue is the fibrocyte. Fibrocytes are generally elongated and spindle-shaped, with processes that connect adjacent cells and fibers. Their heterochromatic nucleus is surrounded by a scant amount of pale cytoplasm. Secretory vesicles in the cytoplasm discharge their contents (e.g., procollagen, proteoglycans, proelastin) into the surrounding microenvironment. Fibrocytes maintain the connective tissue matrix by forming the fibers and constantly renewing the ground substance. Fibroblasts The fibroblast has a larger, more euchromatic nucleus and more abundant, basophilic cytoplasm than the fibrocyte. More active connective tissue matrix production. At the EM level, abundant rER and a prominent Golgi complex are present in the cytoplasm. In certain situations, fibroblasts may differentiate into adipose cells, chondroblasts, or osteoblasts. Myofibroblasts are fibroblasts that contain actin filaments associated with dense bodies; hence, they resemble smooth muscle cells. It is believed that myofibroblasts play a role in contraction of the wound during healing. Connective and supportive tissues  Reticular Cells Reticular cells are similar in appearance to the fibrocytes. They are stellate-shaped cells with a spherical nucleus and basophilic cytoplasm. Reticular cells produce reticular fibers, which form the fine structural network of organs such as the lymph nodes, spleen, and bone marrow. These cells are fixed in the tissue and are capable of phagocytosis. Reticular cells should not be confused with the reticulocyte, an immature erythrocyte. Connective and supportive tissues  Adipocytes (Fat cells) Adipocytes are also referred to as fat cells or adipose cells. Individual adipocytes or clusters containing multiple cells are normal components of loose connective tissue, but when the fat cells outnumber other cell types, the tissue is called adipose tissue. Mature unilocular adipocytes are spherical or polyhedral cells that measure up to 120 µm in diameter. Most of the cell is occupied by a single, large nonmembrane- bounded lipid droplet surrounded by a thin layer of cytoplasm. Connective and supportive tissues  Conti… The cell nucleus is displaced to the periphery by the lipid droplet, which is surrounded by cytoplasm that contains a small Golgi complex, mitochondria, rER, and microfilaments. In contrast, mature multilocular adipocytes contain a more centrally located nucleus with multiple lipid droplets. The high concentration of cytochrome in the mitochondria is primarily responsible for the brown color. Lipids can be preserved and stained with certain agents, such as osmium tetraoxide or Sudan III stain.  Pericytes (Rouget cells or Periendothelial cells) Pericytes are elongated cells that are located adjacent to the endothelium lining capillaries and postcapillary venules. The cells are surrounded by the basal lamina of the blood vessel and make frequent contact with the underlying endothelial cells by extending processes through the lamina. Pericytes resemble fibrocytes in appearance but have contractile filaments similar to smooth muscle. Proposed functions of pericytes include regulating capillary blood flow serving as multipotent mesenchymal cells with specific ability to form vascular smooth muscle cells Phagocytosis regulating new capillary growth Pericytes also have the ability to differentiate into adipocytes, osteoblasts, and phagocytes. Connective and supportive tissues  Mast cells are large, polymorphic, Mast Cells spherical or ovoid cells that contain a prominent, centrally located nucleus. Numerous secretory granules are present in the cytoplasm. These cells can be identified with immunocytochemistry or metachromatic stain (e.g., toluidine blue) that stain heparin containing granule red. The cytoplasm is occupied by an extensive Golgi complex, cisternae of rER, free ribosomes, and mitochondria. Mast cell granules contain histamine, heparin, and various proteases. Mast cells can be activated by physical stimuli such as trauma or sunlight, immunogenic and neurogenic stimuli. Mast cells are common in loose connective tissue, especially around nerve endings and microcirculation. The cells are found in the dermis of the skin and connective tissue of the respiratory tract and gastrointestinal (GIT) system. Connective and supportive tissues Macrophages are phagocytic cells that are scattered throughout the body and form the mononuclear phagocyte system. Macrophages Macrophages are large, ovoid, or spherical cells that contain cytoplasmic vacuoles and are readily distinguishable with the light microscope. At the EM level, characterized by numerous lysosomes, phagosomes, phagolysosomes, and pseudopodia (footlike extensions of the plasmalemma), abundant ribosomes, rER, smooth ER mitochondria, and a Golgi complex Mobile macrophages wander through the tissues performing their phagocytic function while fixed macrophages remain in one location. The fixed macrophage of connective tissues is also known as the histiocyte. Other macrophages located in specific tissues include the stellate macrophage of the liver (Kupffer cell), the microglial cell, the intraepidermal macrophage (Langerhans cell), alveolar macrophage, and the osteoclast. Acute and chronic inflammation. Multinucleated giant cells. Connective and supportive tissues  Plasma Cells Plasma cells are spherical, ovoid, or pear-shaped cells with a spherical, eccentric nucleus. The chromatin is often arranged in peripherally located clumps or in centrally converging strands give the nucleus a cartwheel” appearance. The cytoplasm is intensely basophilic, and a negatively stained Golgi region is usually present. At the fine-structural level, in addition to an extensive Golgi complex, the cytoplasm has an abundant rER with dilated cisternae containing slightly granular and moderately electron dense material as well as spherical inclusions referred to as Russell bodies. Free ribosomes and mirochondria are also present in the cytoplasm. Plasma cells are most numerous in lymphatic tissue, especially in the center of medullary cords of lymph nodes, abundant in bone marrow, the loose connective tissue underlying the epithelium of the gastrointestinal tract, the respiratory system, and the female reproductive system. Plasma cells do not originate in loose connective tissue but develop from B lymphocytes that immigrate into the connective tissue from the blood; they produce circulating or humoral antibodies. Connective and supportive tissues Connective and supportive tissues  Pigment Cells Cells in connective tissue may contain pigments, including melanin in domestic animals or pteridines and purines in fish and amphibians. When present in large numbers, the cells impart color to the connective tissue. Occur in various locations such as the dermis, uterine caruncles of sheep, meninges, choroid, and iris. Connective and supportive tissues CONNECTIVE TISSUE FIBERS Connective and supportive tissues  Collagen fibers Collagen is the principal fiber type in mature connective tissue. Fresh collagen fibers are white, and in histologic preparations, they stain with acid dyes, Thus, they are red to pink in hematoxylin and eosin (H&E) stained sections, red with van Gieson’s method, blue in Mallory and Masson’s triple stains, and green when light green stain is used. Type I collagen fibers accounts for 90% of the body collagen. The fibers are flexible and can adapt to the movements and changes in size of the organs with which they are associated. Collagen fibers are characterized by a high tensile strength and a poor shear strength, and stretch is limited to approximately 5% of their initial length. Consequently, they are found wherever high tensile strength is required, such as in tendons, ligaments, and organ capsules. Connective and supportive tissues  Reticular Fibers In routine histologic preparations, reticular fibers cannot be distinguished from other small collagen fibers, These fibers can be identified only with certain silver impregnations (thus the term argyrophilic or argentaffin fibers) or with the periodic acid Schiff (PAS) reagent. These fibers are actually individual collagen fibrils (type III collagen) coated by proteoglycans and glycoproreins. This coating increases the affinity of the fibers for silver salts. When individual reticular fibers are bundled to form collagen fibers, the coating is supposedly displaced and the argyrophilia decreases. Reticular fibers form delicate, flexible networks around capillaries, muscle fibers, nerves, adipose cells, and hepatocytes and serve as a scaffolding to support cells or cell groups of endocrine, lymphatic, and blood-forming organs. They are an integral part of basement membranes. Connective and supportive tissues  Elastic Fibers Elastic fibers and/or sheets (laminae) are present in organs in which normal function requires elasticity in addition to tensile strength. Elastic fibers can be stretched as much as two and one-half times their original length, to which they return when released. Found in the pinna of the ear, vocal cords epiglottis, lungs, ligamentum nuchae, dermis, aorta, and muscular arteries. Elastic fibers are one of the most resilient connective tissue fibers, withstanding chemical maceration and autoclaving. Elastic fibers usually occur as individual, branching, and anastomosing fibers. Their diameters vary within a wide range, from 0.2 to 5.0 µm in loose connective tissue to as large as 12µm in elastic ligaments, such as the ligamentum nuchae in the neck. In H&E-stained histologic sections, the larger elastic fibers in elastic ligaments are readily distinguished as highly refractile, amorphous, light blue strands; they are stainable by certain selective dyes, such as orcein and resorcin-fuchsin. Connective and supportive tissues  Amorphous Ground Substance The cells and fibers of connective tissue are embedded in an amorphous ground substance composed of glycosaminoglycans (GAGs), proteoglycans, plasma constituents, metabolites, water, and ions. The ground substance forms a hydrated gel that, by virtue of its high water content, has unique properties of resiliency. Seven major types of GAGS can be distinguished, namely, Hyaluronan (hyaluronic arid) vitreous humor of the eye, synovial fluid; umbilical cord, loose connective tissue, skin, and cartilage. Chondroitin-4-sulfate and chondroitin 6 are abundant in cartilage arteries, skin, and cornea. A smaller amount is found in bone. Dermatan sulfate - skin, tendon, ligamentum nuchae, sclera, and lung. Continued… Connective and supportive tissues amorphous Ground Substance Keratan sulfate - cartilage, bone, and cornea. Heparan sulfate - arteries and the lung. Heparin is found in mast cells, the lung, the liver, and skin. Proteoglycans fill space in the connective tissue matrix and impart its unique biomechanical properties, - regulate the passage of molecules and cells in the intercellular space, - play a major role in chemical signaling between cells and may bind and regulate the activities of other secreted proteins. Proteoglycans in low concentrations are not deterred in H&E- stained sections, but when present in higher concentrations, as in hyaline cartilage, they stain with basophilic dyes. Connective and supportive tissues  EMBRYONIC CONNECTIVE TISSUES  Mesenchyme Composed of irregularly shaped mesenchymal cells and amorphous ground substance Cell processes contact adjacent cells and thus form a three- dimensional network Mesenchymal cells undergo numerous mitotic cell divisions and continuously change their shape and location to adapt the transformations that occur during embryonic growth During early development, mesenchyme does not contain fibers, and the abundant amorphous ground substance fills the wide intercellular spaces. Mesenchyme gives rise to various types of adult connective tissues, as well as blood and blood vessels. Connective and supportive tissues  Mucous Connective Tissue Found primarily in the embryonic hypodermis and umbilical cord It is characterized by stellate fibroblasts that form a network. The large intercellular spaces are occupied by a viscous, gel-like amorphous ground substance that has a positive reaction for glycosaminoglycans or proteoglycans. Collagen fibers are also present. Connective and supportive tissues  ADULT CONNECTIVE TISSUES- Connective Tissue Proper Loose Connective Tissue Areolar Adipose Reticular Dense Connective Tissue Regular Irregular Elastic  Areolar Connective Tissue Description Gel-like matrix with: all three fiber types (collagen, reticular, elastic) for support Ground substance is made up by glycoproteins also made and secreted by the fibroblasts. Cells – fibroblasts, macrophages, mast cells, white blood cells, adipocytes Highly vascular tissue Function Wraps and cushions organs Holds and conveys tissue fluid Important role in inflammation Main battlefield in fight against infection  Areolar Connective Tissue Location Widely distributed under epithelia Packages organs Surrounds capillaries  Adipose Tissue Description Closely packed adipocytes Have nucleus pushed to one side by fat droplet Function Provides reserve food fuel Insulates against heat loss Supports and protects organs Location Under skin Around kidneys Behind eyeballs, within abdomen and in breasts  Reticular Connective Tissue Description – network of reticular fibers in loose ground substance Function – form a soft, internal skeleton (stroma) – support other cell types Location – lymphoid organs Lymph nodes, bone marrow, and spleen  Dense Irregular Connective Tissue Description Primarily irregularly arranged collagen fibers Some elastic fibers and fibroblasts Function Withstands tension Provides structural strength Location Dermis of skin Submucosa of digestive tract Fibrous capsules of joints and organs  Dense Regular Connective Tissue Description Primarily parallel collagen fibers Fibroblasts and some elastic fibers Poorly vascularized Function Attaches muscle to bone Attaches bone to bone Withstands great stress in one direction Location Tendons and ligaments Aponeuroses Fascia around muscles  Elastic Connective Tissue Description Dense regular connective tissue Containing a high proportion of elastic fibers Function Allow recoil of tissue following stretching Maintain pulsatile flow of blood through arteries Aid passive recoil of lungs following inspiration Location Walls of large arteries Within certain ligaments associated with vertebral column Within walls of the bronchial tubes