#13337 - Connective Tissue - Organisation of the Body

Connective tissue

Definition: association of the extracellular matrix and the various cell types within it. It varies in type and amount in different locations of the body.

Functions:

Mechanical

-supporting matrix for highly organised structures such as the blood, nerve, lymp

-force transmitter- tendon-MUSCLE to bone, ligaments- bone to bone

-facilitates movement between structures

Metabolic

-route for exchange between metabolites and regulatory molecules- between the blood and tissues between blood and tissues

-storage of fat- subcutaneous and mesentries

Defense

-fat in the superficial fascia forms an insulating layer. Fat in the loculi of loose connective tissue of the dermis provides cushioning and padding

-Inflammation- macrophages and mast cells of the connective tissue- inflammation- local response to bacteria

Repair- after injury fibroblasts lay down collagen fibres- scar tissue

STRUCTURE

-cells

Fibroblasts-STRUCTURAL ROLE: embryonic mesenchyme- secrete most of the extracellular matrix components (fibres and ground substancs)

-GAG, PROTEOGLYCANS, COLLAGEN, ELASTIC, GLYCOPROTEINS , GROWTH FACTORS

-Secrete fibroblast growth factors- mutation in FGF3R leads to Achondroplasia

-plays a role in wound healing

-active and quiescent forms are distinct-

-active fibroblasts have euchromatin and a prominent nucleolus and ovid shaped nuclei

-queicsent fibroblasts have fusiform cells, less ERcytoplasm is elongated into a thin line

-Secretes glycogen in a particular orientation

Macrophages: DEFENCE-phagocytosis, antigen presentation, cytokine secretion

- resident phagocytic cells- blood monocytes-engulf and remove invading organisms and dead cells- secrete cytokines the local inflammatory response – recruit other phagocytic cells such as leucocytes from the blood stream

-specialised roles in certain tissues: Kuppfer cells (liver), microgilia (CNS), Langerhan’s cells (epidermis),osteoclasts in bone

Mast cells

-contain secretory granules containing bioactive molecules-histamine, serotonin, tumour necrosis factor, proteases, heparin, prostaglandins

-activation of IgE receptors on cell surface- activation of mast cells, release the mast cells granules- vasodilation, increase capillary permeability, breakdown of ECM- inflammatory response

adipose cells

- white adipose cells- single large droplet of lipid- energy storage, insulation, padding and shock absorber

- brown adipose cells- fat globules are smaller and numerous-heat productions

Matrix- ground substance

GAG-long unbranched polysaccharide chains- repeating disaccharide units- amino sugar- N-acetylglucosamine) chondroitin sulphate, keratin sulphate

-Highly anionic- attract sodium ions and water which leads to swelling, turgor and resists compression in joints

-stornly hydrophilic-porous hydrated gels

proteoglycans- covalent linkage GAG to core protein-aggrecan found in cartilage-control the activity of growth factors

glycoproteins- laminin and fibronectin- EXTRACELLULAR matrix –cells can attach to and move through the matrix- bind to integrins

-integrin receptors in the plasma membrane link the cytoskeleton to extracellular glycoproteins and collagen

Fibres

-Collagen-

-made up of three alpha helix chains, rod like super helix- fibrils, fibres

-Type 1: found in tendons and bones- resists tension

-type 2: found in hyaline cartilage- reisist pressure

-Type 3: found in skin, muscles and vessels- resists deformation on expansion

- type 4 sheets basal lamna

-collagen is arranged in a staggered fashion that is cross linked to form fibrils and many of these fibrils are linked together to form fibres- banded appearance- electron microscopy- collagen is stained using H&E stain- pink stain

Collagen Type I biosynthesis:

• Preprocollagenα chains synthesised

• Signal peptide cleaved to form procollagen

• Hydroxylation of specific prolyl and lysyl residues by peptidylproline/lysine hydroxylases

  • Requires Vitamin C as cofactor

• Glycosylation of hydroxylysines: glucosyl/galactosyl groups added

• Self-assembly of procollagen triple helix with N and C registration peptides

• Secretion

• Procollagen Peptidase catalyses formation of Tropocollagen(a triple helix) from α chains

• Tropocollagenself-assembles to form fibrils, which self-assemble to form fibres

• Lysyl oxidase catalyses cross-link formation, stabilising the fibres

reticular fibres-

- type 3 collagen fibres- shorter and thin fibres- form a delicate meshwork- the fibres are held by glycoproteins and GAG

-holding tissue elements together- evident in haemopoietic tissue- the reticular fibres stain positive by a -silver stain

elastin fibres-

-Formed from oxytalan which is made up of fibrillin. Deposition of Elastin on the oxytalan forms eualinin and deposition of further elastin leads to elastic fibres. Mutation of fibrillin- leads to marfan syndrome- aortic rupture

highly branched, elasticity- recoil after stretching- lungs, blood vessels, skin- tropoelastin-crosslinked- elastin formed fibrillar structure that is associated with the glycoprotein elastin embedded scaffold –

-muation in one of the fibrillin glycoproteins- leads to loss of integrity of the elastic fibres- tendency to rupture

Types:

Loose connective tissue- makes up most of body

-delicate, flexible, well vascularised- not very resistant –supports structures under pressure and low friction

-fills space between

-muscle cells

-supports epithelial tissue

-sheats lympathic and blood vessels

-hypodermis of the skin

-loosely arranged fibres, large number of cells, large amount of ground substance. Dense ssue- more numerous and thicker fibres, few cells and a small amount of ground substance.

-found underneath epithelial cells, around muscle...