Connective Tissue Flashcards
Define ‘connective tissue’
- Links muscles, nerves and epithelial tissues in a structural way
- Provides support in metabolic and physiological ways
Name 5 types of specialised connective tissue in the body
- Lymphatic tissue
- Blood
- Cartilage
- Adipose tissue
- Bone
Describe the composition of the extracellular matrix of connective tissue
- GROUND SUBSTANCE containing hyaluronic proteoglycan aggregates
- FIBRES consisting of collagen, reticular and elastin
- CELLS such as fibroblasts, mast cells, leukocytes, mesenchymal and plasma cells
What cell types may be present in connective tissue?
- Fibroblasts
- Mesenchymal cells
- Mast cells
- Leukocytes
- Plasma cells
How might connective tissues differ from eachother?
- Types of cells which they contain
- Abundance/density of certain cell types
- Constitution of extracellular matrix (e.g. fibre content/arrangement, ground substance composition)
Describe the classification of connective tissues
- EMBRYONIC > mesenchymal, mucous (umbilical cord)
- PROPER > loose, dense irregular, dense regular
What is meant by connective tissue being ‘mesenchymally derived’?
- Mesenchymal cells are MULTIPOTENT PROGENITOR CELLS derived from the middle germ layer, the MESODERM
- Mesenchymal cells are undifferentiated and have the potential to become a range of cells; cell type depends on the type of connective tissue
Describe the structure of mesenchymal cells
- SPINDLE SHAPED
- Cytoplasmic projections give tapered appearance
- Abundant viscous (almost gelatin-like) extracellular matrix
Explain the structure of the ground substance in connective tissue
- Hyaluronic proteoglycan aggregates
- Hyaluronic acid molecules form linear aggregates each with many proteoglycan monomers (interwoven within a network of collagen fibres)
- High density of -ve charge attracts water molecules forming a hydrated gel
What is RETICULIN?
- Type III collagen
- Fibrils form fibres around muscle and nerves and within lymphatic tissues and organs
Describe the structure of type I collagen
- Periodic banding repeated every 68nm
- Triple helix of α chains with repeating GLY-X-Y amino acid sequence
- Each fibre is 300nm long, 1.5nm wide
Explain why fibroblasts contain an abundance of RER
- Fibroblasts secrete PROCOLLAGEN which form collagen fibrils in the extracellular matrix
- Lots of RER needed for protein synthesis of procollagen
List 3 locations in the body where you would find LOOSE connective tissue
- Submucosa of gut wall
- Mammary gland
- Adipose tissue
How could you distinguish reticular fibres in connective tissue?
- Irregular anastomosing network
- Stain dark blue/brown
Explain the signs and symptoms of Marfan’s Syndrome
- Autosomal dominant
- Abnormal expression of fibrillin gene so results in abnormal elastin tissue
- Sufferers are abnormally tall, exhibit arachnodactyly and frequent joint dislocation
- Can be at risk of catastrophic aortic rupture
Describe the structure and staining of elastic fibres
- Composed of elastin, surrounded by microfibrils called FIBRILLIN
- Amorphous appearance (low electron density)
- Fibrillin fibres are more electron dense so stain darker and lie at the periphery and within elastic fibres
- Elastic fibres stain BLACK
Where in the body would you find elastic fibres?
- Tunica media of arterial walls
- Dermis
- Sites containing elastic cartilage
What are the features of loose connective tissue?
- Loosely arranged fibres
- Large matrix:fibre ratio
- Allows elasticity and movement
Describe the composition of loose connective tissue
- Non branching collagen fibres (type I and type III/reticular)
- Branching elastic fibres
- Small blood vessels
- Mast cells
- Fibroblasts
Explain the arrangement of dense irregular connective tissue in the dermis and how this relates to function
- Bundles of collagen are densely packed and irregularly arranged (orientated in multiple directions)
- Skin can RESIST FORCES in multiple directions to prevent tearing
- Elastic fibres allow a degree of stretch and RESTORATION of shape after skin is bent or folded
Describe the arrangement and composition of DENSE REGULAR connective tissue
- Mainly type I collagen
- Collagen bundles lie parallel in one direction (in line with direction of tensile force)
- Elongated flattened fibroblasts arranged in rows between fibres
What is the role of fibroblasts?
- Synthesise and secret extracellular matrix composed of ground substance and fibres
- Important in wound healing and the formation of scar tissue
Describe the structure of a macrophage
- Kidney shaped nucleus
- Cytoplasmic extensions on surface
- Abundant dark staining LYSOSOMES
- Contain phagocytic vesicles
Explain the role and function of macrophages in the immune response
- Move into loose connective tissue where there is local inflammation
- PHAGOCYTIC so can degrade foreign organisms and cell debris
- Contain many lysosomes (digestive enzymes) for breakdown of engulfed material
- Professional antigen presenting cells so can present foreign antigens to T lymphocytes in immune response
