Connective Tissue Histology (10/16c) [Biomedical] Flashcards
Functions of CT
Maintains/supports structure and communicates
Mediates exchange metabolic waste, nutrients, etc
Plays a role in immune response, inflammation and tissue repair
Classifications of CT - Connective Tissue Proper
Loose (Areolar) CT
Dense CT
- Irregular
- Regular
Classifications of CT - Specialized CT
Adipose — modified loose CT
Cartilage
Bone
Hematopoietic tissue (bone marrow)
Components of CT
Extracellular Matrix
- ground substance
- fibers
Cells
- resident
- visiting
Extracellular Matrix (ECM) Components
Ground Substance — largely proteoglycans, attract water to create a hydrated gel
Fibers — embedded throughout the ground substance
ECM Function
Dictates:
- water in the CT
- types of fibers produced
- how much of the fibers are produced
ECM - Ground Substance Components
Proteoglycan aggregates (proteins, GAGs, linked to hyaluronic acid) - GAGs are long-chained polysaccharides with high negative charge that attract water
Structural Glycoproteins
- Fibronectin, fibrillin, etc are proteins that bind cells (fibroblasts) to fibers
ECM - Fibrous Proteins
Collagen Fibers
- Types I-IV
Elastic Fibers
- Elastin and fibrillin
ECM - Collagen Fiber Type I
Most common type
Bone, ligament, tendon, fascia, joint capsules, etc.
Bundled, cross-linked, highly organized structure makes it exceptionally strong and resilient to tensile forces
Several fibrils put together to form one collagen fiber, crosslinked by glycoproteins (fibronectin)
EX: looks like fettuccine
ECM - Collagen Fiber Type II
Within hyaline and elastic cartilage
Not bundled, no highly regular appearance (more deformable)
Feathery looking
More cellular/more ground substance allows for recoil and bounce back of shape
ECM - Collagen Fiber Type III
Reticular Fibers
Lymph tissue, bone marrow, blood vessels (BV’s), immature wound beds
Branched in a mesh-like appearance
ECM - Collagen Fiber Type IV
Occurs in basal laminae (epithelial cell basement membrane)
Support of tissue layer and ability to filter
ECM - Elastic Fibers
Made of elastin and fibrillin
Found in lungs, blood vessels, skin, ligaments
- Ligamentum nuchae and flavum in the spine, abundance of elastin)
Fibrillin is the protein that bind elastin fibers together
Can be relaxed or stretched, allows for elastic recoil
Wavy appearance, somewhat in parallel but not in bundles
Resident Cells
Fibrocytes or fibroblasts (if active)
- Fibroblasts produce ground substance, fibers, and everything else in CT (“workhorse of the CT”)
Mesenchymal Cells (AKA stem cell or pericyte) - immature or precursor fibroblast
Visiting Cells
Produced in bone marrow and travel to the tissue
All involved in immune response within CT
Macrophage — phagocytic, antigen presenting and cytokines
Mast Cell — inflammatory mediator, produce/secrete vasoactive substances, heparin, histamines
Plasma Cells — B lymphocytes, antibody (immunoglobulin) production
CT Proper — Loose CT (areolar)
Functions — vehicle by which blood vessels travel to transfer nutrients/waste with epidermal layer, packs the space between/around organs to absorb forces and provide protection
Characteristics — most abundant CT proper, sparse elastin and collagen fibers, increased cells and ground substance
CT Proper — Dense Irregular CT
Functions – withstand tension from different directions but also somewhat flexible
Characteristics – densely packed with collagen (irregularly arranged), some elastic fibers as well
Found in the dermal layer, sheaths around tendons, bursa and nerves
CT Proper — Dense Regular CT
Functions – to provide maximum tensile strength
Characteristics — collagen in dense parallel bundled arrangement
Found in the ligaments, musculotendinous units and aponeuroses
Disorders of Elastin
Can be damaged by UV light (affects skin elasticity)
Loss of elastin in respiratory system causes emphysema
Disorders of Collagen - Ehlers Danlos Syndrome
10 clinical/genetic variations
Autosomal dominant, recessive, x-linked recessive
Collagen defect– lacks tensile strength
Most common clinical symptoms – joint hypermobility, large joint dislocation, and skin hyperelasticity
Disorders of Collagen - Osteogenesis Imperfecta
1/20,000 incidence — defect in Type I collagen
Autosomal dominant and spontaneous mutation
Wide range of clinical manifestations
Brittle bones is very common
Fracture incidence decreases after puberty
