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Connective Tissue

Lecture IV

Bismark Oliver C. Lemana, M.Sc. Biological Sciences Department, College of Science University of Santo Tomas, Manila

• Originated from mesenchyme (mesoderm) – Surrounds and penetrates organs

• General function: – Body form maintenance

– Provides matrix

– Body support

• Components – Cell, fibers and ground substance

– Extracellular matrix

Connective Tissue

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• Function:

– Structural

– Reservoir for growth and differentiation hormones

– Nutrient – waste exchange

Extracellular matrix

• Mesenchymal Origin – Retained in connective tissue proper

• Fibroblasts

• Hematopoietic Stem Cells – Bone marrow derived

– Moves to different areas through blood • Mast cells, macrophages, plasma cells

Leukocytes Transient cells

Cellular Components

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Hematopoietic

Stem Cells

Mesenchymal Cells

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• Synthesis of extracellular Matrix

– Collagen, elastin, glycosaminoglycans, proteoglycans, multiadhesive proteins

• Stages of activity: (synthesis state)

– Active (Fibroblast)

• RER and Golgi complex rich

• Growth factors and differentiation

– Quiescent (Fibrocyte)

• Less RER

Fibroblasts

Fibroblast

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• Storage of fats

– Insulation

• Production of heat

Adipocytes

• Bone marrow -> Monocytes -> Macrophage • Defense/Removing elements against:

– Cell debris, abnormal ECM, neoplastic cells, bacteria

• May present immune response – Antigen-presenting cells

• Posses tumor cell-killing capabilities Activated macrophages

Increased phagocytotic capacity and intracellular digestion

Enhanced lysosomal enzyme activity

Macrophage

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Macrophage

• Monocyte derived cells

• Lymphocyte activation

• Monocyte differentiation:

– Increased cell size

– Increased protein synthesis

– Increase in # of golgi complexes and lysosomes

Mononuclear Phagocyte

System

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Mononuclear Phagocyte

System

• Originated from bone marrow (progenitor cells) • Inserted in the connective tissue proper • Main functions:

– Inflammatory response – Innate immunity – Tissue repair

• Bioactive secretions – Heparin – Histamine – Serine proteases – ECF-A and NCF – Leukotrienes (SRS-A)

Mast Cells

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• Ovoid in shape with basophilic cytoplasm

– Rich in RER

• Originated from B lymphocytes

• Function:

– Production of antibodies

IgE

• Class of an antibody

• Anti-allergy and anti-parasite antibody

Plasma Cells

Plasma Cells

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Immediate hypersensitivity

reactions

• White blood cells

• Wandering cells of connective tissues

– Migrates through diapedesis

– Increased activity during inflammation

Leukocytes

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• Polymerization of proteins

– Collagen, reticular (collagen proteins)

• Tendons, aponeuroses, organ capsules, meninges

– elastic fibers (elastin proteins)

Stroma

– Supporting tissue of organs

– Trabeculae and walls of organs

Fibers

Stroma

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• Most abundant type of fiber in humans – 30% dry weight

• Protein derived • Structural functionality

– Skin, bone, cartilage, smooth muscles and BL

• Characterized into: – Forms fibrils – Fibril-associated – Forms anchoring fibrils – Forms network

Collagen

• Visible under light microscopes

• Type I is the most abundant

• Composition of the following structures

– Tendons

– Organ capsules

– Dermis

Long Fibril-forming

Collagen

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Long Fibril-forming

Collagen

• Fibril binding collagen

– Collagen to collagen

– Collagen to ECM compounds

• FACIT

– Fibril-associated collagen with interrupted triple helices

– Non-fibril forming type

Fibril-Associated

Collagen

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• Binding basal lamina with reticular fibers of connective tissues

Anchoring Fibril-Forming

Collagen

• Major structural component of BL

– Type IV

Network-Forming

Collagen

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• Occurs in many types of cells

• Procollagen αchains – Collagen precursor

– Forms triple helices in ER from protein synthesis

• Triple helix – Homotrimetric

– Heterotrimetric

• Combinations may affect the collagen type produced

Collagen Synthesis

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• Osteogenesis Imperfecta – Mutation of genes of type I collagen – Change in the position of Glycine

• Progressive Systemic Sclerosis – Over accumulation of collagen (fibrosis) – Hardening of affected organ – Functional impairment

• Kelloids – Local swelling due to abnormal collagen amount skin

• Scurvy – Vitamin C deficiency – Degeneration of connective tissue

Collagen Associated

Diseases

• Mainly composed of Collagen III • Argyrophilic

– High affinity to silver salts

• “flexible” in nature – Can change in form or volume

• Eg. Arteries, small intestines and uterus

• Reticular cells – Fibroblast-like cells: production of RF

Ehlers-Danlos Type IV disease • Deficiency in Type III collagen • Artery and Small Intestine rupture

Reticular Fibers

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Reticular Fibers

Adrenal cortex Lymph node

• Thinner than collagen

• Network forming fibers

• Found in organs subject to stretching or bending

– Eg. Arteries

Elastic Fibers

mesentery dermis Smooth muscle

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Elastic Fiber

Formation

1. Formation of fibrillin • Microfibril

accumulation

2. Deposition of elastin • Increase in fiber

size

3. Further accumulation of Elastin

• Formation of mature Elastic fiber

• Microfibril and fibrillin – Non-elastic precursor; highly resistant to pulling forces

– Holds the lens of the eye

• Elastin – Matures in ECM

– Glycine and proline rich • Rubber-like capabilities

Combination of fibrillin and elastin can form variable types of fibers depending on their function

Elastic fiber

precursors

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• Desmosine and isodemosine

Elastin Cross-link

• Highly water-based

• Complex of:

– Anionic macromolecules (glycosaminoglycans and proteoglycans

– Multiadhesive proteins (laminin, fibronectin, etc…)

• Function:

– Strength and rigidity of the matrix

– Acts as lubricant and barrier to foreign bodies

Ground Substance

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• Composition:

– Hexosamine (galactosamine/glucosamine)

– Uronic acid (glucoronic/iduronic)

• Hyaluronic acid

– largest, most abundant GAG

– Functions:

• Diffusion of molecules in connective tissues

• Lubrication to organs

Glycosaminoglycans

Glycosaminoglycans

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• Synthesized in RER, mature in Golgi, secreted via exocytosis

• Functions:

– Structural and anchoring proteins

– Bind and sequester signalling proteins

• Fibroblast growing factors

Proteoglycans

Proteoglycans and

Glycoproteins

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Connective Tissues

• Areolar tissue

• Features: – Flexible, highly vascularized, not very resistant to

stress

• Function: – Supports structure subject to pressure and low

friction (epithelia)

• Location: – Papillae of the dermis, lining of the pleural and

peritoneal cavities,

Loose Connective

Tissue

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• Adapted for resistance and protection

• Similar with LCT but:

– More collagen

– Less resistant to stress

• Two types:

– Dense irregular

– Dense regular

Dense Connective

Tissue

• Collagen arranged in bundles but without any definite orientation

• Collagen bundles are arranged in a 3-dimensional network

– More resistant to stress

• Found always in association with LCT

Dense Irregular

Connective Tissue

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LCT and DICT

Mammary gland Esophagus

Blood vessels Mesothelial Cells

• Has a definite pattern

• Linear orientation of the fibroblast

• Offers greater resistance to traction forces

Dense Regular

Connective Tissue

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• Type III Collagen

• Framework to hematopoietic and lymphoid organs

– Bone marrow, lymph node, spleen

The mononuclear phagocyte system are dispersed in the

trabeculae to monitor the flow of materials and prevent foreign bodies through phagocytosis

Reticular Tissue

Reticular Tissue

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• Found in umbilical cord (Warton’s Jelly) and fetal tissues

Mucous Tissue