connective tissues and extracellular matrix 2014-9
TRANSCRIPT
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Connective Tissues and Extracellular
Matrix
Prof. F.L. Chan
School of Biomedical Sciences
PFOS1(23)
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Organ = parenchymal tissue + stromal tissuee.g Mammary gland = glandular tissue (functional part) +
connective tissue, fat cells, blood vessels, lymphatics and
nerves (supporting part)
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- Epithelia are avascular (no blood vessels). Epithelial cells arefunctionally dependent on the underlying connective tissue for
exchange of oxygen, nutrients and supply of trophic factors (e.g.
growth factors), and removal of waste.
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General functions of connective tissues
The diversified functions of connective tissues depend on:Variety of cell typesTypes of extracellular fibersComponents of ground substance
1. Support and binding of other tissues(e.g. epithelia, blood vessels and nerves)
2. Exchange of materials (via blood
vessels) and holding body fluids3. Protection: defending the body againstinfection (by white blood cells/leukocytes)
4. Storage of fat as reserve and insulation(by adipose tissue)
5. Wound healing
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Characteristics of connective tissues
Found throughout the body and widespread in many
primary tissues and organs Connective tissues consist of cells and extracellularmatrix which includes extracellular fibers, groundsubstance (gel-like non-structural material) and tissue
fluid Connective tissue comprises a very diverse group of
tissues with various functions
All connective tissues are derived from embryonic
tissue mesenchyme
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Types of connective tissues
1. Embryonic connective tissue
a. Mesenchyme
b. Mucous connective tissue (e.g. Whartons jelly in
umbilical cord)2. Connective tissue proper
a. Loose (areolar) connective tissue
b. Dense connective tissues: regular and irregular
3. Specialized connective tissues
a. Bone
b. Cartilage
c. Blood
d. Reticular tissues: in hemopoietic (hematopoietic)and lymphatic tissues
e. Adipose tissue
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Different types of connective tissues have a
common embryonic origin: mesenchyme
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e.g. Loose (areolar) connective tissue:- A model connective tissue
- A common connective tissue type underlies all epithelia, surrounds
blood vessels and nerves
A. Cell types:
- Fibroblasts
- Fat cells (adipocytes)
- Mast cells
- Macrophages- Plasma cells
- Lymphocytes
B. Extracellular matrix:- Collagen fibers
- Elastic fibers
- Ground substance
(tissue fluid, proteoglycans &glycoproteins)
Basic organization of connective tissues
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Loose and dense connective tissues
e.g. in mammary gland
Dense irregularconnective tissue
Loose connective
tissue
Mammary gland
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Loose (areolar) connective tissues
Fine network of
collagen/elastic/reticular fibers,
with fluid-filled spaces Cells: fibroblasts & blood-borne
cells
Functions: most general
functions of connective tissuese.g. support and binding
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Dense irregular connective tissues
Large amount of collagen fibers, hightensile strength/elasticity
Fibers in random direction or layers
Cells: mostly fibroblasts
Functions: provides structuralstrength/elasticity
Examples:
dermis of skin, submucosa of
digestive tract, fibrous capsules
of joints, fascia
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Dense regular connective tissues
Dense parallel orientation ofcollagen fibers to withstand
tensile forces in one direction
Cells: fibroblasts
Functions: to attach muscles to
bones; bones to bones
Examples: Tendons, ligaments
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Adipose tissue (white)
Large number of adipocytes,few fibers
Functions:
Tissue for energy reserve and
insulation Endocrine function in regulation
of energy metabolism and
homeostasis
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Brown adipose tissue
- Tissue contains more blood supply; fat cells contain more mitochondriaand many lipid droplets.
- It is present in aorta, kidney, neck and more abundant in the newborn.
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Reticular connective tissues
Locations: all lymphoid organs,
hemopoietic tissue (bone marrow), liver
Rich in reticular fibers (type III
collagen; stained by silver staining) whichform a branched network to house various
cell types for cell-cell interactions
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Connective tissue cells
B. Transient connective tissue cells
(blood-born, immune functions):
1. Lymphocytes2. Plasma cells (production of antibodies)
3. Monocytes
4. Granular leukocytes:
neutrophils, eosinophils, basophils
A. Fixed connective tissue cells:
1. Fibroblasts (or myofibroblasts)
2. Macrophages3. Adipocytes
4. Mast cells
5. Reticular cells in reticular tissues
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Connective tissue cells
F = fibroblast; L = lymphocyte; P = plasma cell
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Fibroblasts
Functions: synthesis of
extracellular matrix
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- Phagocytic cells derived from monocytes in blood- Free-moving in blood and tissues, or fixed in organs (e.g.
lymph node, spleen, liver, skin)
- Functions: phagocytose pathogens (e.g bacteria), dead
cells, RBC etc; defense and immune responses
Macrophages
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Adipocytes (fat cells)
- Cells contain a single large lipid droplet, with nuclei squeezedon periphery
- Functions: synthesis and storage of fat, and endocrine
regulations
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Mast cells
Cellular granules contain vasoactive and immunoreactive substances
e.g. histamine, heparin Functions: mediate inflammation and allergic reactions
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- Cells with a darkly stained nucleus and small amount of cytoplasm- Functions: various immune responses for defense and inflammation
Lymphocytes
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Plasma cells
Cells with well-developed Golgi apparatus and RER Cells are active in antibody synthesis and differentiated from B-
lymphocytes
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MonocytesCells of Mononuclear Phagocytic System:
- Macrophages (histiocytes) in connective tissues, peritoneal cavity- Kupffer cells in liver
- Alveolar macophages in lungs
- Macrophages in lymphoid organs
- Osteoclasts in bone
- Microglia in CNS
- Langerhans cells in epidermis
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3 Major types of connective tissue fibers:
A. Collagen fibers (Types I, II collagens)
- Tough fibers arranged in bundles; provides great
tensile strengthB. Reticular fibers (Type III collagen + proteoglycans)
- rich in hemopoietic (bone marrow) and lymphoidtissues, & liver
- small and branched collagen fibers that form delicatenetworks to house cells for better cell-cell interactions
C. Elastic fibers (elastin) and microfibrils (fibrillins)
- long, thin fibers that allow for stretching- rich in dermis, large blood vessels & elastic cartilage
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Connective tissue fibers (I)
Collagen fibers
Collagen fibers and fibrils
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Ultrastructure of collagen fibrils and their association
with proteoglycans
Collagen fibrils show a characteristic 67-68 nm cross-striation
pattern
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Connective tissue fibers (II)
Areolar connective tissue Aorta
Elastic fiber
Elastic fibers
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Ultrastructure of elastic fibers
Microfibrils
Elastic fiber
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Extracellular matrix = connective tissue fibers + ground substance
Ground substance is a viscous and clear substance in fresh connectivetissues and contains mainly tissue fluid, proteoglycans, glycosaminoglycansand glycoproteins.
It appears as empty spaces in histological sections but reacts to PAS
reaction. At EM level, it appears as amorphous substance.
Functions: very diverse from tissue support, molecular filter, cell adhesion,
cell-matrix interactions to wound healing.
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Major components of ground substance
1. Proteoglycans = core protein + glycosaminoglycans (GAGs)
2. Hyaluronic acid (hyaluronan)
3. Glycoproteins e.g. fibronectin adhesion proteins
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A proteoglycan molecule as seen under electron microscope
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Glycosaminoglycans (GAGs)
- GAGs are unbranched long chains of polysaccharides
made up of repeating disaccharide units and components of
proteoglycans
Family of GAGs:
- Chondroitin 4-sulfate
- Chondroitin 6-sulfate
- Dermatan sulfate
- Heparan sulfate
- Heparin- Hyaluronic acid (hyaluronan)