week 7

• What is connective tissue?


  They support, connect or separate different types of tissues and organs
• Three major components of connective tissue

  Fluid or ground state component

  Fibres

  Cells
• Where is there no connective tissue?

  The central nervous system
• What is the fluid or ground state?

  Area between any of the solid aspects
• Types of connective tissues

  Adipose tissue

  Cartilage

  Bone

  Blood

  Loose connective tissue (under the skin)

  Fibrous connective tissue (forming a tendon)
• ECM


  Extracellular matrix

  
  

  Consists of cells separated by varying amounts of extracellular substance

  
  

  The proportion of cells is in the minority
• Major cells that make up connective tissues

  Fibroblasts

  Chondrocytes

  Osteoblasts

  Adipocytes
• Three types of fibres in connective tissue

  Collagen fibres

  Elastic fibres

  Reticular fibres
• Collagen fibres


  Most abundant

  
  

  Tough and flexible, resistant to stretching. Incredibly strong.

  
  

  Tendons are 90% collagen

  
• Elastic fibres


  Found where tissue can be stretch (e.g. ear cartilage)

  
  

  Individual microfibrils are embedded in the matrix (matrix is 90% of the fibre)

  
• Reticular fibres


  Type of collagen (3D scaffold)

  
  

  Delicate, fine networks that give support to individual cells

  
• Extracellular matrices


  Glycoproteins

  Proteoglycans

  Haluronic acid
• What controls the composition of the ECM?

  It is according to the function of tissue

  
  

  ECM is usually mae by the cells wihin it

  
  

  All connective tissue within the body is continuous with all other connective tissue
• Loose connective tissue


  Blood, fat

  
  

  They allow movement, loosely arranged collagen fibres.

  
  

  They form a close association with epithelium
• Histology of fat cells


  They look empty, as fats are extracted during histological processing of tissue
• Where is blood derived?

  Mesoderm (bone marrow in adults)
• What is the matrix of blood?

  The liquid, plasma

  
  

  Plasma is dissolved proteins in water
• Dense connective tissue


  ECM are densely packed collagen fibres with sparse cells

  
  

  Have fibroblasts

  
  

  Two types: dense irregular and dense regular
• Dense irregular connective tissue


  Woven patterns of fibres, that resists tension/stress from any direction

  
  

  E.g. dermis of the skin, non-lactating breast
• Dense regular connective tissue

  Thickly packed parallele fibre bundles, few fibroblasts

  
  

  They resist force in one direction

  
  

  e.g. tendons, ligaments, bone, some organs
• Where are most connective tissues derived from?

  Mesoderm

  
  

  But some skeletal components of the head are derived from the neural crest cells
• Mesenchyme


  Embryonic connective tissue - gives rise to most of the body's connective tissues, bones, lymphatic and circulatory systems

  
  

  It is comprised of the extracellular matrix

  
  

  Cells of the mesenchryme are able to migrate through this tissue, allowind development of structures
• The epithelial-mesencyhmal relationship


  Helps form nearly every organ in the body

  
  

  Mesenchymal cells can migrate esily, while epithelial cells cannot

  
  

  Epithelial cells can change into more mobile mesenchymal cells, critical for embryogenesis - but this is bad for cancers
• Mesenchymal cells


  Migrate as individual cells, if provided with the proper extracellular environment
• What is the skeleton of sharks and rays made up of?

  Entirely of cartilage
• Chondrocytes


  Cells that secrete cartilage matrix (ground substance)

  
  

  Form the cartilage tissue, that will be the template that undergoes osteophication and form bone

  
  

  Not capable of cell division
• Where is cartilage form?

  Areas where compression/load is resisted. Needs structure, but flexibility
• Hyaline cartilage


  Resists compression, is flexible

  
  

  Found in the trachea and bronchi, end of bones and inside synovial joints

  
  

  Keeps airways open, creates frictionless movement
• Stem cell research into cartilage

  Very important, as it doesn't regenerate very well

  
  

  It also isn't vascularised, so it won't have the rejection of tissue
• Fibrocartilage


  Intervertebral discs

  Transitional between dense connective tissue and hyaline cartilage

  
  

  Tough and resists compression

  
  

  Chondroctyes or single or in pairs
• Elastic cartilage


  Found in external ear, auditor tube, larynx
• How do we make cartilage?

  1) Paraxial mesoderm forms somites, gives rise to the sclerotome from which cartilage is derived. These cells undergo ossification via endochondral ossification

  
  

  2) Cranial NCC form bones through intramembranous ossification. NCC cells condense and change shape to form osteoblasts
• Endochondroal ossification


  Initial chondroification

  
  

  It follows the initial patterning of the cartilage deposition - cartilage growth is primarily a maturation-based process
• Development of bone


  The axial skeleton is initially deposition as cartilage, then acts as a template for later bone formation
• Labelling cartilage in report

  You can say what structure it will become (e.g. this is cartilage that will form a vertebrae)
• Endochondrol ossification


  Making cartilage into bone

  
  

  Occurs during later foetal development

  
  

  Bone tissue is created from te cartilage template
• What drives the endochondral ossification?

  Hedgehog signalling pathway
• Achondroplasia


  Reduced proliferation of chondrocytes in te epiphyseal plate of long bones

  
  

  Results in dwarfism
• Disorders of cartilage


  Osteoarthritis

  Achondroplasia

  Spinal disc herniation

  Relapsing polychondritis
• treatment of cartilage


  Currently, limited repair capabilities as there is no blood supply

  
  

  But stem cell could be very useful in the future