HISTO_LC6_CONNECTIVE TISSUE.pdf

UNIVERSITY OF NORTHERN PHILIPPINES HISTOLOGY LC6 CONNECTIVE TISSUE COLLEGE OF MEDICINE, BATCH 2026...

UNIVERSITY OF NORTHERN PHILIPPINES HISTOLOGY LC6 CONNECTIVE TISSUE COLLEGE OF MEDICINE, BATCH 2026 Transcribers: Gallego, Gutierrez, Labingdalawa, Malonzo Dr. Nicanor B. Lacuesta Jr.| Oct. 2022 Editors: Gallego, Gutierrez, Labingdalawa, Malonzo o Serves a medium for the exchange of wastes and CONNECTIVE TISSUE nutrients between blood vessels and cells I. CONNECTIVE TISSUES o Provides nutrition for the epithelial tissue A. Function B. Origin B. ORIGIN C. Classic Components Mesoderm II. GROUND SUBSTANCE Mesodermal cells migrate, surround, and invade A. Glycosaminoglycans B. Proteoglycans developing cells to become mesenchymal cells C. Multiadhesive Glycoproteins o Oval nucleus, prominent nucleoli, fine III. FIBERS chromatin, sparse cytoplasm –extends as thin A. Collagen Fibers processes away from the nucleus B. Reticular Fibers o Point of origin of all connective tissue cells, C. Elastic Fibers blood, and blood vessels IV. CELLS OF CONNECTIVE TISSUE A. Fibroblasts C. THREE CLASSES OF COMPONENTS B. Macrophages C. Mast Cells 1. Ground Substance D. Plasma Cells 2. Fibers E. Adipose Cells 3. Cells F. Leukocytes V. TYPES OF CONNECTIVE TISSUE II. GROUND SUBSTANCE A. Loose Connective Tissue B. Dense Connective Tissue Viscous, colorless, transparent, and homogenous C. Elastic Tissue D. Mucous Tissue Fills space in between cells and fibers VI. REFERENCES Acts as a lubricant VII. APPENDIX Barrier to foreign particles Difficult to examine in fresh and fixed samples due to high water content I. CONNECTIVE TISSUE Highly hydrated so when mounted in a slide, it will desiccate and only spaces will be observed. Provides and maintains the form of the body Major constituent is extracellular matrix – protein fibers, ground THREE CLASSES OF COMPONENTS substance, tissue fluid A. GLYCOSAMINOGLYCANS (GAGs) o Tissue fluid: Also known as mucopolysaccharides ▪ Similar to blood plasma in ion contents and Linear polysaccharides diffusible substances Repeating disaccharide units made up of uronic acid and ▪ Contains a small percentage of plasma proteins hexosamine of low molecular weight o Hexosamine: glucosamine or galactosamine ▪ Insignificant quantity under normal o Uronic: Glucuronic or iduronic acid circumstances, hence negligible Largest, almost unique, most ubiquitous - heparan sulfate (100s- ▪ Increase in tissue fluid leads to edema 1000s kDa) Intensely hydrophilic and act as polyanions (hydroxyl, carboxyl, A. FUNCTION and sulfate groups): makes the ground substance highly hydrated Structural Binds great number of cations (sodium),thus intensely hydrated o Encapsulate and provides internal structure to organs structures o Tendons, ligaments, and areolar tissue around organs (Table 1. see APPENDIX) o Specialized types: bone and cartilage Defense B. PROTEOGLYCANS o Due to content of phagocytic and immunocompetent Composed of a protein core to which various numbers and cells combinations of GAGs are covalently attached o Cells that produce intermediates of inflammation Carbohydrate portion constitutes 80-90% of the dry weight o A physical barrier – prevents dispersion of bacteria in the Proteoglycans bind to collagen owing to electrostatic interaction body between their acid groups and the basic amino acid residues of Nutrition collagen o Due to the close relation with blood vessels Synthesis of protein moiety begins in the RER Page 1 of 7 [HISTOLOGY] LC6 CONNECTIVE TISSUE – Dr. Nicanor B. Lacuesta Jr. Glycosylation is initiated in the RER and completed in the Golgi Acidophilic complex where sulfation also occurs o Pink - eosin o Blue - Mallory’s trichrome stain C. MULTIADHESIVE GLYCOPROTEINS o Green - Masson’s trichrome stain Have multiple binding sites for cell surface receptors (integrins) o Red - Sirrius red and other matrix macromolecules Very large molecules with branched oligosaccharide chains CATEGORIES OF COLLAGEN Important roles for the adhesion of cells to their substrates 1. Fibrillar Collagen (Types I, II, III) Functions: to provide three-dimensional STRUCTURAL GLYCOPROTEINS frameworks for tissues and organs 1. Fibronectin Have subunits that aggregate to form large fibrils (MW 235 - 270 kDa), dimeric clearly visible in the electron or light microscope Synthesized by fibroblasts and epithelial cells Collagen I is the most-abundant and widely Has binding sites for cells, collagen, and distributed type that forms large, eosinophilic glycosaminoglycans bundles called the collagen fibers Helps mediate normal cell adhesion and migration 2. Sheet Forming Collagen (Type IV) 2. Laminin Subunits produced by epithelial cells and are the Large (200-400 kDa), trimeric, cross-shaped major structural proteins of external laminae and glycoprotein the basal lamina in all epithelia Detected in the basal laminae Partially responsible for the adhesion of epithelial 3. Linking/Anchoring Collagen (Type VII) cells to basal lamina Short collagens that link fibrillar collagens to one another (forming larger fibers) and to other 3. Integrin components of the ECM. Act as matrix receptors for specific sequences on Type VII collagen forms anchoring fibrils that link laminin, fibronectin, some collagens, and certain into the basement membrane. other ECM proteins Heterodimers of two transmembrane polypeptides: Synthesis of collagen is very widespread among many cells the α and β chain though originally thought to be restricted to fibroblasts, chondroblasts, osteoblasts, and odontoblasts III. FIBERS Distributed unevenly throughout the body Principal amino acids composing collagen: Predominant type determines the property of connective tissue o Glycine (33.5%) o Proline (12%) THREE MAIN TYPES o Hydroxyproline (10%) A. COLLAGEN FIBERS Constitute a family of proteins selected during evolution Amount of collagen in a tissue can be determined by for their ability to form various extracellular fibers, measuring the hydroxyproline content sheets, and networks, all of which are extremely strong and resistant to normal shearing and tearing forces. 2 amino acids characteristic of collagen protein: Key element of all connective tissues, as well as hydroxyproline and hydroxylysine epithelial basement membranes and the external Not incorporated in the protein itself but results from laminae of muscle and nerve cells. the hydroxylation of the proline and lysine in the nascent Most abundant protein in the human body (30% dry collagen polypeptide in the RER during synthesis weight) 28 types have been described but the most important, STRUCTURE OF COLLAGEN best studied, and most common types are types I, II, III, 1. Tropocollagen IV, V, VII, IX, XII, XIV (Table 2. see Appendix) Protein unit that polymerizes to form collagen fibrils Degradation is achieved by collagenases Elongated (280 nm in length and 1.5 nm in width) Most abundant fibers in connective tissues Consists of 3 unit polypeptide chains intertwined in Causes tissue to become white a triple helix Birefringent Difference of chemical structures of these Inelastic and have a tensile strength greater than steel polypeptide chains account for the different types Consist of closely packed thick fibrils (75 nm thick) of collagen Can be organized in parallel array forming bundles A secreted collagen into the extracellular matrix Better studied in spread preparations and appear as Tropocollagen molecules polymerized elongated and tortuous cylindric structures indefinite longitudinally and also side-side to form fibrils, and length; diameter of 120 µm these are strengthened by numerous intermolecular bonds Page 2 of 7 [HISTOLOGY] LC6 CONNECTIVE TISSUE – Dr. Nicanor B. Lacuesta Jr. Tropocollagen molecules aggregate into Hydroxylation begins after the peptide chain has microfibrillar subunits packed together to form reached a certain minimum length and is still bound fibrils to the ribosomes Aggregation and packing is achieved by hydrogen Enzymes: peptidyl proline hydroxylase and peptidyl and hydrophobic interactions lysine hydroxylase Structure is reinforced by covalent cross links, 3. Glycosylation of hydroxylysine catalyzed by lysyl oxidase Different collagen have different amounts of carbohydrate (galactose or glycosylgalactose linked 2. Fibrils to hydroxylysine) Thin and elongated structures 4. Alpha chain is synthesized with registration peptides (NH and Variable diameter (20 to 90 nm) COOH terminal ends) assemble to form the procollagen Traverse striations (periodicity of 64 nm) which is transported into the extracellular environment o Determined by the overlapping Registration peptides ensure proper positioning of arrangement of subunit tropocollagen the alpha chains, makes the procollagen soluble, molecules and prevents premature assembly and precipitation o Dark band retain more stain due to more in the cell free chemical groups 5. Registration peptides are removed by procollagen peptidases In types I and III – fibrils associate to form fibers to turn procollagen into tropocollagen o Type I - Fibers can associate to form 6. Fibrils aggregate to spontaneously form fibers bundles 7. Fibrilllar structures are reinforced by covalent crosslinks, o Type II - Can occur as fibrils that do not catalyzed by lysyl oxidases form fibers o Type IV - Does not form fibrils or fibers but occur as unpolymerized or sparsely polymerized procollagen molecules Type I, II, and III forms fibrils that are called interstitial collagens Type IV and V do not form fibrils Figure 1. Tropocollagen Helix Figure 3. Collagen Synthesis B. RETICULAR FIBERS Extremely thin (0.5 to 2 µm) Figure 2. Dark bands coincide in the areas where that have the free ends; Extensive network in some organs these are the ones that would retain more stain because of free chemical Nonvisible in H&E preparations ends in the areas. The light band doesn’t have free ends so they stain a lot Stained black by silver salts (agrophillic) less. PAS (Periodic Acid Schiff) positive o Staining due to high content of glycoproteins COLLAGEN SYNTHESIS Have 6-12% hexoses compared to 1% in collagen 1. Polypeptide alpha chains are assembled on the Composed mainly of type III collagen polyribosomes in RER and injected into the cisternae 2. Hydroxylation of proline and lysine occurs Page 3 of 7 [HISTOLOGY] LC6 CONNECTIVE TISSUE – Dr. Nicanor B. Lacuesta Jr. Formed by loosely packed, thin (45nm) fibrils bound o Produced by fibroblasts in skin, tendon, smooth together by small interfibrillar bridges (proteoglycans and muscle glycoproteins) o Resistant to boiling, extraction with dilute acids and Weak birefringency alkali and not digested by trypsin Abundant in smooth muscle, endoneurium and the o Has a tertiary and quaternary structure, stabilized by framework of hematopoietic cells (bone marrow), spleen, hydrophobic interactions between the nonpolar and lymph nodes peptide chains Constitute a network around cells of parenchymal organs Abundance of reticular fibers in embryogenesis, inflammatory processes, wound healing but is replaced eventually by regular collagen fibers Create a flexible network in organs subjected to increase volume Figure 5. Elastic connective tissue is found in the stroma of the lungs and in the walls of the large arteries. Figure 4. Prominence of networks of delicate, black reticular fibers. These are mostly supportive stroma in most lymphoid and hematopoietic organs and endocrine glands. The fibers consist of type III collagen. Cell nuclei are also dark but cytoplasm is unstained. Figure 6. Elastic fibers add resiliency to connective tissue. Such fibers may C. ELASTIC FIBERS be difficult to discern in H&E stained tissue, but elastin has a distinct, darker- Fibers branch and unite with one another into an irregular staining appearance with other staining procedures. network Characteristic yellow color in fresh samples IV. CELLS OF CONNECTIVE TISSUE Capable of stretching to 150% of their length and yields very easily to traction but readily returns into original shape when A. FIBROBLASTS relaxed Most commonly found cells Methods to demonstrate: Synthesizes fibers and amorphous intercellular substrates. o Resorcin fuschin : purple 2 different morphological types: o Aldehyde fuschin : black o Younger, more actively synthesizing cell (fibroblast) o Orcein : dark blue o Abundant and irregularly shaped cytoplasm; nucleus is 2 components: ovoid, large and pale staining, with fine chromatin, o Amorphous central region containing elastin prominent nucleolus; cytoplasm rich in RER, well o Sheath of 14 nm tubular microfibrils developed Golgi complex Development: o Mature, quiescent (fibrocyte) o Microfibrils appear first o Found in the already formed or mature formed tissue o Amorphous material fills the space in tube o Smaller cell, spindle shaped, fewer processes; nucleus is Amino acid composition resembles collagen but has greater smaller, darker; acidophilic cytoplasm; less well- quantity of valine and alanine developed RER and Golgi complex Two unusual amino acids: desmosine and isodesmosine When actively stimulated, mature cells may revert to younger, (formed by covalent reactions among 4 lysine residues) thus active form (i.e., wound healing) crosslinks elastin and is thought to give its elastic properties Synthesize collagen reticular and elastic fibers, Occurs in a nonfibrillar form as fenestrated membranes in glycosaminoglycans, and glycoproteins some walls of blood vessels Fibroblasts rarely undergo division Elastin Mitoses are only observed when the organism requires additional o Secreted as pro-elastin (MW 70,000) which fibroblasts (tissue damage) polymerizes to form elastin Page 4 of 7 [HISTOLOGY] LC6 CONNECTIVE TISSUE – Dr. Nicanor B. Lacuesta Jr. E. ADIPOSE CELLS Specialized for storage of neutral fats or heat production Important for cushioning internal organs, body heat F. LEUKOCYTES (White Blood Cells) Leave the blood and migrate to the tissues where they become functional and perform various activities related to the immunity All are rather spherical white suspended in blood plasma, but they become amoeboid and motile after leaving the blood vessels and invading the tissues. Figure 7. Large fibroblasts in a section of umbilical cord V. TYPES OF CONNECTIVE TISSUE Connective Tissue Proper: A. LOOSE CONNECTIVE TISSUE Areolar tissue More abundant type Fills space between fibers and muscle sheaths Supports epithelial tissue Composed of all main components of connective tissue proper (fibers, ground substances, and cells) and the most abundant cells are fibroblast and macrophages o All these three components are in almost equal amount B. DENSE CONNECTIVE TISSUE Same component as loose but with a clear predominance of Figure 8. Fibroblast vs. Fibrocyte collagen fibers B. MACROPHAGES Have fewer cells with fibroblasts still being the most common Phagocytic capacity Less flexible and resistant to stress Derive mainly from precursor cells: monocytes–where they are Can be: transported to become mature macrophages in tissues o Dense irregular Can proliferate locally to produce more macrophage cells ▪ without definite orientation Ingestion of particles and their digestion by the lysosome ▪ fibers are going haywire o Dense regular C. MAST CELLS ▪ tissue 3D network and provide resistance to Oval to round connective tissue cell (20-30 µm) stress from all directions (tendons) Cytoplasm filled with basophilic granules ▪ has one single direction Nucleus is small spherical and centrally situated Can be seen in tendons, ligaments, and binds to your organs Metachromatic together. Release the intermediates of your inflammation, leukotrienes (one of defensive mechanism of CT, macrophages and mast cells) Contain specific receptor for IgE (IgE-mediated response – allergic reactions i.e. allergic rhinitis due to the presence of mucosal mast cells) Contain specific receptor for IgE (IgE-mediated response – allergic reactions) Two populations: o Connective tissue mast cells: Proteoglycan is heparin o Mucosal mast cells: Proteoglycan is chondroitin sulfate D. PLASMA CELLS Large ovoid cells, with a basophilic cytoplasm, rich in RER Nucleus is spherical and eccentrically placed with compact coarse heterochromatin Figure 9. Dense regular connective tissue. Long, parallel bundles of collagen Responsible for the synthesis of antibodies fibers fill the spaces between the elongated nuclei of fibrocytes (formed o These are more specific immune responses directed towards several antigens mature tissue). Page 5 of 7 [HISTOLOGY] LC6 CONNECTIVE TISSUE – Dr. Nicanor B. Lacuesta Jr. E. MUCOUS TISSUE Abundance of amorphous ground substance composed chiefly of hyaluronic acid Ground substance makes your mucous tissue jelly-like tissue containing collagen fibers and few elastic or reticular fibers Principal component of the fetal umbilical cord where it is referred to as Wharton’s jelly Cells found here are mainly fibroblasts Principal component of the umbilical cord (where it is referred to as Wharton’s jelly), also found in the pulp of young teeth Figure 10. Dense irregular connective tissue showing the randomly arranged large collagen bundles. The arrangement of collagen strengthens the tissues and resists tearing from all directions. C. ELASTIC TISSUE Composed of thick, parallel elastic fibers With a surrounding small amount of loose connective tissue, flattened fibrocytes Occurs in the yellow ligament of the vertebral column and in the suspensory ligament of the penis Figure 13. Section of umbilical cord showing large fibroblasts surrounded by a large amount of very loose ECM containing mainly ground substances very rich in hyaluronan, with wisps of collagen. VI. REFERENCES Mescher, A.L. (2016). Junqueira’s Basic Histology Atlas of Histology. McGraw Hill Education. Figure 11. Elastic tissue. Note the thick, parallel elastic fibers D. RETICULAR TISSUE Specialized loose connective tissue variation, provides the architectural framework of the myeloid and lymphoid hemopoeitic cells Reticular cells - fibroblasts specialized in the production of reticular fiber constituents Figure 12. Reticular tissue. Diagram shows the fibers and reticular cells. Silver-stained section of lymph node in which reticular fibers are seen as irregular black lines. Reticular cells are also heavily stained and dark. Most of the smaller, more lightly stained cells are lymphocytes passing through the lymph node. Page 6 of 7 [HISTOLOGY] LC6 CONNECTIVE TISSUE – Dr. Nicanor B. Lacuesta Jr. VII. APPENDIX Table 1. Glycosaminoglycans are named depending on the repeating disaccharide unit Table 2. Types of Collagen Page 7 of 7