Okay so not quite an essay...
"Discuss intercellular
matrices of connective tissues"
General classes of connective tissue
- loose/dense - density of fibres
- irregular/regular - meshwork or parallel bundles of
fibres.
- Bone - tensile and compressive strength
- cartilage - friction free movement, strength
- adipose tissue - storage of lipids
Cells of connective tissue
Fixed cells
fibroblasts - secrete ground substance and
fibres, relatively long lived
adipose cells - fat storage
mesenchymal cells - precursors of cell in
development, may remain to replace those as
necessary
Free cells
short lived, defensive
macrophages - phagocytosis of old cells and
foreign organisms
Substances in matrix
- Ground substance
- cells and fibres embedded in highly hydrated gel
- nutrients and waste products pass through aqueous
phase easily between blood and parenchymal cells
of tissues.
- Gel restricts movement of bacteria
- hyaluromidase, excreted by some bacteria break
down hyaluranic acid and allows bacteria to pass
through gel.
- Collagen
- 12 types of fibre
- each fibril made of 3 polypeptide (-helices
- Type 1
- fibrils 50-90 nm in diameter
- occur in dermis, bone, tendon, fascia
- strong - breaking force several hundred kg per
square cm
- Type II
- In hyaline and elastic cartilage, nucleus
pulposus and vitreous body of eye
- thin fibrils abundant in ground substance
- Type III
- abundant in loose connective tissue, walls of
blood vessels, stroma of glands, spleen, kidneys,
uterus
- Types I,II & III microscopically visible
- Type IV
- restricted to basal lamina of epithelia
- meshwork of filaments provides selective
filtration barrier for macromolecules.
- Fibrillin
- 8-10 nm diameter glycoprotein
- defective in Marfan syndrome gives long limbs,
progressive dilation of aorta, poss. leading to
fatal rupture
- Elastic Fibres
- core of elastin surrounded by fibrillin
- branching pattern in loose connective tissue
- fenestrated sheets or coarse fibres elsewhere.
- Adhesive glycoproteins
- fibronectin
- binding domains for collagen, cells and
glycosaminoglycans
- Laminin
- most abundant constituent in basal lamina
of epithelia.
- Influences phenotype of epithelial cells.
- Thrombospondin
- most abundant protein in blood platelets
- can bind to heparin, collagen,
fibronectin, fibrinogen.
Types of connective tissue
- Serous membranes
- e.g. peritoneum
- thin layer of loose connective covered by
mesothelium
- Reticular
- Form of loose connective tissue
- mainly type III collagen fibres forming
wide-meshed network.
- stroma of bone marrow, spleen, lymph node and
thymus
- Mucous connective tissue
- nearly completely in embryo
- v. large amounts of ground substance
- Dense irregular
- e.g. dermis of skin
- coarse fibre bundles woven into tight meshwork.
- Dense regular
- cylindrical cords or flat sheets of collagen
fibres.
- E.g. tendons, aponeuroses
- Cartilage
- Hyaline
- matrix contains 40% (dry weight)
collagen,
- Mainly type II collagen, which are
thinner fibres than type I
- cells (chondrocytes) in individual
lacunae
- Fibre increase in diameter from lacunae
into matrix
- proteoglycans present in high
concentrations and form firm gel
- principle proteoglycans are keratan
sulfate and chondroitin sulfate
- Fibrocartilage
- closely resemble dense regular connective
tissue
- found at insertion of ligaments and
tendons, intervertebrate disks
- cells in lacunae have thin capsules
- chondrocytes in small amount of
connective tissue in rows between
parallel collagen type-I fibres.
- Elastic cartilage
- e.g. external ear
- more opaque and yellowish in colour
- less abundant matrix
- much of matrix is elastin fibres
- develop from areas of primitive
connective tissue
- Bone
- Compact or cancellous (spongy)
- Matrix is 35% organic matrix, 65% inorganic
salts. (Dry weight)
- Lacunae formed circumferentially around blood
vessels (Haversian canals)
- Organic matrix
- is 90% collagen in ground substance rich
in proteoglycans.
- Collagen predominantly type-I, but with
greater crosslinking for strength.
- Inorganic salts
- are calcium phosphate (thought to be Ca10{PO4}6)
- Occur as rod like crystals 40nm long and
1.5-3 nm thick.
- Occur at 60-70 nm intervals that reflect
geometry of collagen fibres
ŠNick Manville 23/11/97.