Transcript Connective tissue 2 Dr. Maria Zahiri Formation of Type I collagen

Connective tissue 2
Dr. Maria Zahiri
Formation of Type I collagen
Within the cell
During translation, two types of peptide chains are formed on ribosomes along the RER. (the
alpha-1 and alpha-2 chains)
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These peptide chains (known as preprocollagen) have registration peptides on each end and
a signal peptide.
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The preprocollagen is then released into the lumen of the RER. Thereafter the signal
peptides are cleaved inside the RER and the peptide chains are now called pro-alpha
chains.
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Hydroxylation of lysine and proline amino acids occurs inside the lumen. This process is
dependent on ascorbic acid (Vitamin C) as a cofactor. Further glycosylation of specific
hydroxylysine residues occurs.
Triple helical structure is formed inside the endoplasmic reticulum from each two alpha-1
chains and one alpha-2 chain. This is called procollagen.
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Procollagen is transported into the golgi apparatus, where it is packaged and secreted by
exocytosis.
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Outside the cell
the registration peptides are cleaved and tropocollagen is formed by
procollagen peptidase.
These tropocollagen molecules gather to form collagen fibrils, via covalent
cross-linking by lysyl oxidase which links hydroxylysine and lysine residues.
Multiple collagen fibrils form into collagen fibers.
Collagen may be attached to cell membranes via several types of protein,
including fibronectin and integrin.
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(a) Connective tissue proper: loose connective tissue, areolar
Description: Gel-like matrix with all
three fiber types; cells: fibroblasts,
macrophages, mast cells, and some
white blood cells.
Elastic
fibers
Function: Wraps and cushions
organs; its macrophages phagocytize
bacteria; plays important role in
inflammation; holds and conveys
tissue fluid.
Collagen
fibers
Location: Widely distributed under
epithelia of body, e.g., forms lamina
propria of mucous membranes; surrounds
capillaries.
Fibroblast
nuclei
Epithelium
Lamina
propria
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Photomicrograph: Areolar connective tissue, a
soft packaging tissue of the body (300x).
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(d) Connective tissue proper: dense connective tissue, dense regular
Description: Primarily parallel
collagen fibers; a few elastic fibers;
major cell type is the fibroblast.
Collagen
fibers
Function: Attaches muscles to
bones or to muscles; attaches bones
to bones; withstands great tensile
stress when pulling force is applied
in one direction.
Location: Tendons, most
ligaments, aponeuroses.
Nuclei of
fibroblasts
Shoulder
joint
Ligament
Photomicrograph: Dense regular connective
tissue from a tendon (500x).
Tendon
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(e) Connective tissue proper: dense connective tissue, dense irregular
Description: Primarily
irregularly arranged collagen
fibers; some elastic fibers;
major cell type is the fibroblast.
Function: Able to withstand
tension exerted in many
directions; provides structural
strength.
Location: Fibrous capsules of
organs and of joints; dermis of
the skin; submucosa of
digestive tract.
Fibrous
joint
capsule
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Nuclei of
fibroblasts
Collagen
fibers
Photomicrograph: Dense irregular
connective tissue from the dermis of the
skin (400x).
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(f) Connective tissue proper: dense connective tissue, elastic
Description: Dense regular
connective tissue containing a high
proportion of elastic fibers.
Function: Allows recoil of tissue
following stretching; maintains
pulsatile flow of blood through
arteries; aids passive recoil of lungs
following inspiration.
Elastic fibers
Location: Walls of large arteries;
within certain ligaments associated
with the vertebral column; within the
walls of the bronchial tubes.
Aorta
Heart
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Photomicrograph: Elastic connective tissue in
the wall of the aorta (250x).
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What kind of tissue does this represent?
Loose (areolar) connective tissue
Where in the body can you find this tissue?
delicate thin layers between tissues; present in all mucous
membranes
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What kind of tissue does this represent?
Adipose tissue
Where in the body can you find this tissue?
fat
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What kind of tissue does this represent?
Dense connective tissue
Where in the body can you find this tissue?
tendons; ligaments
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Classification of connective tissue
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Emberyonic (mesenchyme)
Adult ( Loose- Dense)
Dense( Regular- Irregular)
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Elastic Fibers
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Staining (orsein)
1- oxytalan: microfibrils ( GP: fibromodolin, fibrilin)
2- Oxytalan+ elastin= elaunin
3- Elaunin + elastin in core= elastic
 aa of elastin: Gly, Pro, Desmosin - isodesmosin
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Disorders: marfan syndrom
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Ground Substance
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An amorphous gel-like material
it is not visible on slides, because it is removed during the
preparation process
composed of Glycosaminoglycans (GAG), Proteoglycans and multi
adhesive Glycoproteins
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Glycosaminoglycans (GAGs) or mucopolysaccharides
 GAGs are negatively charged, long, rod-like chains of repeating
disaccharides (hexosamine + uronic acid) that have the capability of
binding large quantities of water(hydrophilic)
 Hexosamine: Glocose amine or Galactose amine
 uronic acid: glocoronic acid or iduronic acid
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Different Types of GAGs
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Proteoglycan complex
Constitute a family of macromolecules each
is composed of a protein core to which GAGs
are covalently bonded
(heparin( mast cell), Agrecan(ECM),
Syndecans and fibroglycan(cell surface)
They have large volume like a bottle brush
Function:
-Cell Binding to ECM
.
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Glycoproteins
 They have binding site for several components of extracellular
matrix as well as for:
integrin molecules of the cell membrane that facilitate the attachment
of cells to the extracellular matrix
 (Fibronectin, Laminin, Chondronectin, Osteonectin, Entactin,
Tenascin)
Fibronectin is a v-shaped macromolecule that has binding site for
• extracellular components
• integrins of cell membrane,
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Laminin is very large has three polypeptide chains, it is located in basal
lamina and has binding site for:
heparan sulfate, type IV collagen, entactin and cell membrane
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 Tenacin
composed of 6 chains, it is distributed just in
embryonic tissue and marks migratory pathway of some
cells
 Entactin bind to laminin and type IV collagen
 Chondronectin
and Osteonectin are similar to
fibronectin and have binding sites for collagen type II
and type I respectively
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Integrins (Transmembrane Linkers)
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
Integrins are transmembrane proteins but unlike other cell surface
receptors, they are linked to cytoskeleton and structural member of
extracellular matrix such as collagen so they also called
Transmembrane Linkers
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Integrins are much more numerous than usual receptors
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they bind to extracellular component by weak bonds
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Fluid
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Edeme phenomen
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Specific connective tissue
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Adipose tissue
Bone and cartilage
Blood
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Adipose tissue (Fatty tissue)
A kind
of connective tissue with many adipocytes
Forms one of the largest “organs” of body
 15-20%
of body weight in men
 20-25% of body weight in women
Over
2 times as much stored energy as glycogen
Subcutaneous adipose shapes body
Shock absorber in soles of feet and palms
Thermal insulation
Fills space between organs
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Two Types of Adipose Tissue
 Yellow, White
 cells
or unilocular
with one large fat droplet in cytoplasm
 Brown
or multilocular
 cells
with numerous smaller lipid droplets in cytoplasm and
many mitochondria
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Unilocular Adipose Tissue
 White
to dark yellow depending on diet
 Most common form in adults
 Cells 50-150 mm diameter
 Nuclei eccentric and flattened
 Lipid droplet has no membrane
 Heavily vascularized
 Cell number constant after early postnatal period
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Multilocular Adipose Tissue
 multiple
droplets
 vascularization and many mitochondria,
 Central nucleus
 Has a lobular organization like glands
 Production of body heat by many mitochondria
 In human neonate, produces heat
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‫‪Dr. Maria Zahiri‬‬
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