Connective Tissue - OS 201 Exam 01

CONNECTIVE TISSUE OS 201 Donnel Alexis Rubio, MD, FPOA | September 12, 2022 Exam 01-Trans 03...

CONNECTIVE TISSUE OS 201 Donnel Alexis Rubio, MD, FPOA | September 12, 2022 Exam 01-Trans 03 OUTLINE C. FUNCTION I. Introduction III.Connective Tissue Support and movement A. Origin Proper Transporting fluid B. Classification A. Loose CT Protection (vital organs and immunity) C. Function B. Dense Irregular CT Supports and binds other tissues II. General Structure C. Dense Regular CT Energy storage A. Fixed/Resident IV. Summary II. GENERAL STRUCTURE Cells V. References B. Free/Wandering VI. Appendix Components: Cells → Connective tissue cells: fibroblasts, adipocytes, etc. C. Extracellular Matrix ○ Grouped into two categories: Fixed Resident Cells I. INTRODUCTION ★ Permanent residents of connective tissue Remember the four basic types of tissue: ★ Long-lived, stable groups of cells that show → Epithelium little movement → Connective tissue ★ Includes undifferentiated mesenchymal cells, ○ Connective tissue proper fibroblast, adipocytes, and macrophages ○ Cartilage Free or Wandering Cells ○ Bone ★ Temporary population of motile cells which ○ Blood move into the connective tissue from blood → Muscle tissue in response to specific stimuli → Nervous tissue ★ Short-lived and are continually replaced A. ORIGIN ★ Includes the plasma cells, Neutrophils, Eosinophils, Basophils, Monocytes, and Derived from embryonic mesenchyme (Fig.1) Mast Cells → Mesenchyme: primitive connective tissue → Extracellular matrix: collagen and elastin fibers, → Maturation and proliferation of mesenchyme gives rise ground substance (GAGs and glycoproteins), and to: tissue fluid ○ Connective tissue ○ Muscle A. FIXED/RESIDENT CELLS ○ Vascular and Urogenital Systems 1. Undifferentiated Mesenchymal Cells ○ Serous membranes of body cavities Originate from the embryonic mesoderm B. CLASSIFICATION Structure: 1. Connective Tissue Proper → Fusiform or stellate-shaped → Have large nuclei Loose connective tissue → Viscous ground substance Dense connective tissue → Few collagen fibers → Regular Difficult to distinguish from fibroblasts under light → Irregular microscopy 2. Specialized Connective Tissue → Usually smaller than the latter and is often associated with or are close to capillaries in contrast to Cartilage collagenous fibers Bone Give rise to differentiated cells that are used in repair and Adipose tissue formation of new tissue Hematopoietic tissue Lymphatic tissue Blood Figure 2. Mesenchymal tissue of a developing fetus. Fusiform (left) and Stellate (right) embryonic mesenchyme. 2. Fibroblast Principal and most common cell of connective tissue proper Found in all connective tissue Figure 1. Classification of connective tissue (enlarged image in appendix). Active form of a fibrocyte E01-T03 TG 11: Domingo, E., Domingo, F., Dungala, Dychiao, Evangelista, TE: Enano TH: Flores Last date edited: 07/15/2023 1 of 10  Derived from mesenchymal cells → Made of a family of cells called mononuclear Deployed along collagen fibers phagocyte system along with other monocyte-derived Structure: cells → Large, ovoid, euchromatic nucleus → Macrophage-like cells have different names in different → Prominent nucleolus organs as seen in Table 2. → More abundant and basophilic cytoplasm Table 2. Mononuclear Phagocyte System → Fusiform or spindle-shaped Cell Type Major Locations Main Function Function: produces and maintains most of the extracellular matrix (ECM) Precursor of Monocyte Blood → Collagen macrophages → Elastic and reticular fibers Production of → Glycosaminoglycans (GAGs) of ground substance cytokines, → Proteoglycans Connective tissue, chemotactic factors → Glycoproteins (e.g. laminin, fibronectin, etc.) lymphoid organs, & other molecules lungs, bone marrow, Table 1. Fibroblast vs. Fibrocyte Macrophage that participate in pleural and Fibroblast Fibrocyte inflammation peritoneal (defense), antigen Active cell Quiescent cell cavities processing, and More abundant and basophilic presentation Smaller than a fibroblast cytoplasm Liver Same as Kupffer cell Large, ovoid euchromatic Darker heterochromatic (perisinusoidal) macrophages nucleus nucleus Central nervous Same as Microglial cell Prominent nucleolus Spindle-shaped system macrophages Antigen processing Langerhans cell Epidermis of skin and presentation Lymph nodes, Antigen processing Dendritic cell spleen and presentation Osteoclast (from Localized digestion fusion of several Bone of bone matrix macrophages) Multinuclear In connective tissue Segregation and giant cell under various digestion of foreign (several fused pathological bodies Figure 3. Fibroblasts (left) and fibrocytes (right) stained with H&E. macrophages) conditions 3. Adipocytes Found in all the members of connective tissue proper[2026 Derived from the mesenchyme Trans] Specialized for the cytoplasmic storage of lipids (white Relatively more abundant in the lymph node, spleen, adipose) and heat generation (brown adipose) lymphatic tonsils, and lamina propria of the digestive Abundant along the course of blood vessels tract[2026 Trans] Serve as a cushion and protect the skin as well as the Structure: other organs → Oval or kidney shaped, eccentrically located nucleus Structure: → Irregular surface cytoplasm → Nucleus flattened to one side → Abundant vacuoles → “Signet ring” appearance → Large Golgi apparatus, RER and SER, mitochondria, secretory vessels, and lysosomes Microscopic Characteristics: → Light Microscope: Difficult to distinguish unless they show obvious evidence of phagocytic activity Figure 4. Adipocytes. 4. Macrophage Well-formed phagocytic ability Specialized in turnover of protein fibers and removal of dead cell tissue debris/particulate Derived from monocytes Figure 5. Macrophage (M) under light microscope [Ross, 2011] E01-T03 TG 11: Domingo, E., Domingo, F., Dungala, Dychiao, Evangelista, TE: Enano TH: Flores Last date edited: 07/15/2023 2 of 10  → Electron Microscope: Surface shows numerous folds and finger-like projections ○ Folds engulf substance to be phagocytized Figure 8. Lymphocytes [Eroshchenko, 2008] 3. Plasma cell Arise from B-lymphocytes Structure: Figure 6. Macrophage under electron microscope [Junqueira, 2013] → Oval cells → Round eccentric nucleus B. FREE/WANDERING CELLS ○ Described as “clock-faced” (dark spots of 1. Monocyte heterochromatin resemble the numbers around the clock)[2026 Trans] Free cells of the connective tissue → Basophilic cytoplasm in H&E stain Origin of macrophages → A clear perinuclear area, aka perinuclear hof, beside → Functions as antigen-presenting cells (APCs) of the the nucleus is usually observable (contains large Golgi immune system bodies) [MSS Review, 2020 as cited in the 2025 Trans] Structure: → More abundant in infected tissues[2026 Trans] → Round cells Function: produces antibodies[2026 Trans] → Eccentric bean shaped nucleus → Grayish blue cytoplasm → Agranular[2026 Trans] → 12-15 μm in diameter[2026 Trans] → Basophilic cytoplasm[2026 Trans] → Small lysosomal azurophilic granules stain the cytoplasm[2026 Trans] Figure 9. Plasma cells [Junqueira, 2013] 4. Mast cell Figure 7. Monocyte [Eroshchenko, 2008] 2. Lymphocyte Derived from progenitor cells in the bone marrow[2026 Trans] Especially numerous in connective tissue, skin, and Main functional cell of the lymphatic system mucous membrane Structure: Absent in brain and spinal cord → Spherical shape Structure: → 7-9 μm → Large ovoid, with spherical nucleus → Intensely stained large nucleus → Cytoplasm filled with large basophilic granules → Agranular[2026 Trans] → Although histologically similar, they are distinct from 3 Types: basophils[2026 Trans] → T-lymphocytes Mast cell granules: ○ Responsible for cell-mediated immunity → Composed of: heparin, histamine, eosinophil and → B-lymphocytes neutrophil chemotactic factors ○ Produces antibodies → Exhibits metachromasia, i.e. a characteristic wherein ○ Responsible for humoral immune system[2026 Trans] the granules take a different color from that of the ○ Mature into plasma cells that produce antibodies[2026 staining dye[2026 Trans] Trans] Function: Secretion of mast cell granules causes → Natural killer (NK) cells hypersensitivity reaction, allergy, or anaphylaxis ○ Similar to macrophages[2026 Trans] ○ Programmed to kill virus-infected cells and tumor cells E01-T03 TG 11: Domingo, E., Domingo, F., Dungala, Dychiao, Evangelista, TE: Enano TH: Flores Last date edited: 07/15/2023 3 of 10  Production of Lymphocytes Immunologic immunocompetent cells (B (several types) (defense) cells, T cells, etc.) Participation in allergic and vasoactive reactions, Eosinophilic Immunologic modulation of mast cell leukocytes (defense) activities and the inflammatory process Neutrophilic Phagocytosis of foreign Defense leukocytes substances, bacteria Secretion of cytokines and other molecules, phagocytosis of ECM Macrophages Defense components and debris, antigen processing and presentation to other cells Mast cells and Liberation of Defense basophilic pharmacologically active (allergic leukocytes molecules (e.g. Histamine) reactions) Energy Adipocytes Storage of neutral fats reservoir, heat production C. EXTRACELLULAR MATRIX Figure 10. Mast cell [Young, O’Dowd, & Woodford, 2014). Composition 5. Eosinophil → Ground Substance Found in blood → Basement Membrane Composes only 1-4% of leukocytes → Fibers (connective tissue proper) Structure: ○ Collagen → Round ○ Reticular fibers → With bilobed nucleus ○ Elastic fibers → Pink, coarse, eosinophilic cytoplasmic granules Function: associated with allergic reactions, parasitic infections, and chronic inflammation Figure 12. Extracellular matrix [Junqueira, 2013] Figure 11. Eosinophil [Ross, 2011] 1. Ground Substance 5. Summary of Functions Part of extracellular matrix (ECM) located in the spaces between the cells and fibers Table 3. Functions of Cells in Connective Tissue Proper[2026 Trans] Viscous clear substance with a slippery feel Representative Representative High water content Cell Type Product/Activity Function Little morphologic structure Fibroblasts, Amorphous under a light microscope chondroblasts, Production of fibers and Acts as a lubricant and barrier against invaders Structural osteoblasts, ground substance odontoblasts Immunologic Plasma cells Production of antibodies (defense) E01-T03 TG 11: Domingo, E., Domingo, F., Dungala, Dychiao, Evangelista, TE: Enano TH: Flores Last date edited: 07/15/2023 4 of 10  ○ Laminin Contains binding site for Collagen Type IV, Heparan sulfate, Heparin, and actin Most abundant constituent of the basal lamina of the epithelia ○ Tenascin Appears during embryogenesis but synthesis is turned off in mature tissues Reappears during wound healing, musculotendinous junctions, and malignant tumors ○ Osteopontin Seen in the ECM of the bone Binds to osteoclasts and connects them to the underlying bone surface Important for the sequestration of calcium and the promotion of calcification in the ECM Figure 13. Ground substance. Illustration of composition (top); Ground substance stained pink between collagen fibers stained in blue (bottom) [Young, O'Dowd, Woodford, 2014] Composed of: → Glycosaminoglycans (GAG) ○ Also known as mucopolysaccharides ○ Long polysaccharide made of repeating disaccharide units, which are mostly negatively charged due to the presence of sulfate groups ○ Composition of disaccharide units: Uronic Acid - can either be ★ Glucuronic Acid ★ Iduronic Acid Hexosamine - can either be: ★ Glucosamine ★ Galactosamine ○ Binds large amounts of water molecules and Figure 14. Examples of Multi-Adhesive Glycoproteins cations Provides GAGs with space-filling, cushioning, 2. BASEMENT MEMBRANE and lubricant functions Sheet-like arrangement of ECM proteins Allows diffusion of molecules Acts as an interface between the support tissues and ○ Examples: epithelial or parenchymal cells Hyaluronic acid Term derived from the initial recognition of membranes ★ Largest, almost unique, and most ubiquitous lying beneath the basal cells of epithelia ★ Composed of D-glucuronic acid & → External lamina is used instead for muscles and D-glucosamine nervous tissue ★ Found in joints and cartilage → Composed of two layers: basal lamina and the Dermatan sulfate reticular lamina Chondroitin sulfate → Basal lamina is further divided into two: lamina lucida Keratan sulfate and lamina densa Heparan sulfate Functions: → Proteoglycans → Provides physical binding of the epithelium to the ○ GAG + core protein underlying tissue and physical support → Multi-Adhesive Glycoproteins → Controls epithelial growth and differentiation ○ Large molecules with branched oligosaccharide ○ Forms a barrier to downward epithelial growth chains which is only breached if the epithelium undergoes ○ Involved in the interaction of the cells with the ECM malignant transformation ○ Function: adhesion of cells to their substrate → Permits the flow of nutrient, metabolites, and other ○ Fibronectin molecules to and from the epithelium Most abundant glycoprotein in the CT ○ Epithelium is devoid of blood vessels Found in the basal lamina of epithelia and → Selective barrier to the passage of molecules from one external lamina that envelopes smooth and compartment to another striated muscles ○ Regulates permeability between compartments E01-T03 TG 11: Domingo, E., Domingo, F., Dungala, Dychiao, Evangelista, TE: Enano TH: Flores Last date edited: 07/15/2023 5 of 10  Components ○ Major structural proteins of external laminae and → Glycosaminoglycan (heparan sulfate) basal lamina of epithelium → Type IV Collagen → Linking/Anchoring Collagen → Structural glycoproteins ○ Collagen Type VII ○ Fibronectin ○ Short collagen that links fibrillar collagen to one ○ Laminin another ○ Nidogen-1 Table 4. Examples of Clinical Disorders Resulting from Defects in Collagen Synthesis Disorder Defect Symptoms Faulty transcription or Ehlers-Danlos Aortic and/or translation of collagen Type IV intestinal rupture type III Increased skin Ehlers-Danlos Faulty lysine hydroxylation elasticity, rupture Type VI of eyeball Increased Ehlers-Danlos Decrease in procollagen articular mobility, Type VII peptidase activity frequent luxation Lack of vitamin C, a Ulceration of Scurvy required cofactor for prolyl gums, Figure 15. Basement membrane surrounding the renal tubules hydroxylase hemorrhages 3. FIBERS Spontaneous Elongated structures formed from proteins that polymerize Osteogenesis Change of 1 nucleotide in fractures, cardiac after secretion from fibroblasts imperfecta genes for collagen type I insufficiency Predominant fiber type determines specific tissue properties Osteogenesis imperfecta Collagen → Also known as the “Brittle Bone Disease” Most abundant protein in the body → Genetic disorder that stems from a lack of Type I → Makes up 30% of its dry weight Collage → Abundant in bone, dermis, and cartilage → Results in bones that break easily → 25 types of collagen → Symptoms may range from mild to severe: Synthesized by the fibroblasts ○ Blue to white eyes Composed of ○ Loose joints → Glycine - 33.5% ○ Short stature → Proline - 12% ○ Hearing problems → Hydroxyproline - 10% ○ Breathing problems Bundle 1-20 μm in diameter elongated, tortuous, ○ Teeth problems cylindrical Made of fibrils 75 nm in diameter Stains: → Pink with eosin (H&E) (Fig.16) → Blue with Mallory’s Trichrome stain (Fig.16) → Green with Masson’s stain → Red with Sirius Red Figure 16. Collagen fibers stained with Eosin (left) and Mallory’s Trichrome stain (right). Grouped by structures formed by interacting subunits: → Fibrillar Collagen ○ Collagen Types I, II, and III ○ Subunits aggregate to form large fibrils ○ Collagen Type I Most abundant and widely distributed Forms large and eosinophilic collagen fibers Often densely fill connective tissue forming tendons, organs, capsules, and dermis → Sheet-forming Collagen ○ Collagen Type IV Figure 17. Osteogenesis Imperfecta Type I E01-T03 TG 11: Domingo, E., Domingo, F., Dungala, Dychiao, Evangelista, TE: Enano TH: Flores Last date edited: 07/15/2023 6 of 10 Reticular Fibers Type III Collagen Abundant in smooth muscle covering the spleen and liver Forms an extensive branching network (reticulum) or an irregular anastomosing network → Provides a supporting framework for the cellular constituents of various tissues and organs Fibrils → 35 nm in diameter Bundle → 0.5 - 2 μm in diameter Stains: → Black with silver (Ag) stain → Red/orange with Periodic Acid-Schiff (PAS) Figure 19. Random Coiling of Elastic Fibers Figure 20. Photomicrograph of Elastic Fibers Stained with Resorcin-Fuchsin Marfan Syndrome Figure 18. Photomicrograph of lymph node in silver preparation showing the → Genetic disorder of the connective tissue specifically reticular fibers forming an irregular anastomosing network on the formation of fibrillin (pointed by black arrows) → Patient usually have Elastic Fibers ○ Tall habitus (body type) Thinner than collagen fibers ○ Disproportion in long extremities relative to the → Fibril trunk ○ 10 nm in diameter ○ Chest bone deformities → Bundle ○ Flexible joints ○ 0.2 - 1 μm in diameter ○ Scoliosis Arranged in branching pattern to from a 3D network → Most serious complications involve heart and aorta Interwoven with collagen fibers ○ Increased risk of mitral valve prolapse and aortic → Limits distensibility of the tissue aneurysm → Prevents tearing from excessive stretching May form sheets and laminae Stains: → Unstained in H&E and Masson → Brownish-red with Orcein & Weigert → Black/Dark Blue with Resorcin-Fuchsin Abundant in the large blood vessels of the aorta and the lungs Composed of two structures: → Central core ○ Made of cross-linked elastin ○ Contains two unusual amino acids: Desmosine Isodesmosine → Surrounding fibrillin ○ A glycoprotein Allows tissues to respond to stretch and distention Elasticity is due to its unusual polypeptide backbone that causes random coiling (Fig. 19) Elastin is synthesized by the same pathway as collagen Figure 21. Marfan Syndrome E01-T03 TG 11: Domingo, E., Domingo, F., Dungala, Dychiao, Evangelista, TE: Enano TH: Flores Last date edited: 07/15/2023 7 of 10  III. CONNECTIVE TISSUE PROPER Ordered and densely packed arrays of fiber and cells A. LOOSE (AREOLAR) CONNECTIVE TISSUE Parallel collagen fibers separated by very little ground substance having very few blood vessels [Junqueira, 2018] Characterized by densely packed collagen bundles fixed according to a definite pattern, with fibers and fibroblasts aligned in parallel Consists mostly of type I collagen bundles and fibroblasts aligned in parallel [Junqueira, 2018] The cells that produce and maintain the fibers are packed and aligned between fiber bundles [Ross and Pawlina, 2016] Function: provide great resistance to prolonged or repeated stresses from the same direction → E.g. tendons, aponeuroses, ligaments IV. SUMMARY Figure 22. Mammary Gland. Shows Loose Connective Tissue (LCT) surrounding the Glandular Epithelium (GE) and Dense Irregular Connective Tissue (DICT). Characterized by loosely arranged fibers and abundant cells Thin and sparse collagen Forms layer beneath the epithelial lining of organs and filling the spaces between fibers of muscle and nerve [Junqueira, 2018] Transient wandering cells that migrate from local blood vessels in response to specific stimuli [Ross and Pawlina, 2016] → Site of inflammatory and immune reactions Characteristics: → Few fibers → Abundant cells → Abundant ground substance Function: diffusion of oxygen & nutrients from vessel B. DENSE IRREGULAR CONNECTIVE TISSUE Randomly interwoven bundles of collagen fibers [Junqueira, Figure 24. Review of Supporting/Connective Tissue [Young et al., 2014]. 2018] (enlarged figure in appendix) → Predominantly Type I [Junqueira, 2018] V. REFERENCES Contains mostly collagen fibers arranged in various directions Rubio, D. (2022). Connective Tissue [Powerpoint Presentation] UPCM 2026 Trans. (2022). Connective Tissue. Characteristics: Mescher, A. (2013). Junquiera’s Basic Histology: Text and Atlas (13th ed). → Abundant fibers McGraw-Hill Education → Few cells Ross, M. (2011). Histology: A text and Atlas (6th ed). Lippincott, Williams, → Relatively few ground substance and Wilkins Function: provides significant strength and resistance Young, B., O’Dowd, G. & Woodford, P. (2014). Wheater’s Functional Histology: A Text and Color Atlas.(6th ed). Churchill Livingstone. from all directions due to its rough 3D collagen network [Junqueira, 2018] Closely associated with loose connective tissue (see previous figure) → E.g. deep dermis layer of skin, capsules surrounding organs C. DENSE REGULAR CONNECTIVE TISSUE Figure 23. Dense Regular Connective Tissue E01-T03 TG 11: Domingo, E., Domingo, F., Dungala, Dychiao, Evangelista, TE: Enano TH: Flores Last date edited: 07/15/2023 8 of 10  VI. APPENDIX Figure 1. Classification of connective tissue. Figure 24. Review of Supporting/Connective Tissue [Young et al., 2014]. E01-T03 TG 11: Domingo, E., Domingo, F., Dungala, Dychiao, Evangelista, TE: Enano TH: Flores Last date edited: 07/15/2023 9 of 10  Appendix Figure 1. Composition and distribution of Glycosaminoglycans in connective tissue and their interactions with collagen fibers [Junqueira, 2018] Appendix Figure 2. Collagen Types [Junqueira, 2018] E01-T03 TG 11: Domingo, E., Domingo, F., Dungala, Dychiao, Evangelista, TE: Enano TH: Flores Last date edited: 07/15/2023 10 of 10