connective tissues and extracellular matrix 2014-9

7/25/2019 Connective Tissues and Extracellular Matrix 2014-9

1/33

Connective Tissues and Extracellular

Matrix

Prof. F.L. Chan

School of Biomedical Sciences

PFOS1(23)


2/33

Organ = parenchymal tissue + stromal tissuee.g Mammary gland = glandular tissue (functional part) +

connective tissue, fat cells, blood vessels, lymphatics and

nerves (supporting part)


3/33

- 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.


4/33

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


5/33

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


6/33

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


7/33

Different types of connective tissues have a

common embryonic origin: mesenchyme


8/33

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


9/33

Loose and dense connective tissues

e.g. in mammary gland

Dense irregularconnective tissue

Loose connective

tissue

Mammary gland


10/33

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


11/33

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


12/33

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


13/33

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


14/33

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.


15/33

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


16/33

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


17/33

Connective tissue cells

F = fibroblast; L = lymphocyte; P = plasma cell


18/33

Fibroblasts

Functions: synthesis of

extracellular matrix


19/33

- 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


20/33

Adipocytes (fat cells)

- Cells contain a single large lipid droplet, with nuclei squeezedon periphery

- Functions: synthesis and storage of fat, and endocrine

regulations


21/33

Mast cells

Cellular granules contain vasoactive and immunoreactive substances

e.g. histamine, heparin Functions: mediate inflammation and allergic reactions


22/33

- Cells with a darkly stained nucleus and small amount of cytoplasm- Functions: various immune responses for defense and inflammation

Lymphocytes


23/33

Plasma cells

Cells with well-developed Golgi apparatus and RER Cells are active in antibody synthesis and differentiated from B-

lymphocytes


24/33

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


25/33

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


26/33

Connective tissue fibers (I)

Collagen fibers

Collagen fibers and fibrils


27/33

Ultrastructure of collagen fibrils and their association

with proteoglycans

Collagen fibrils show a characteristic 67-68 nm cross-striation

pattern


28/33

Connective tissue fibers (II)

Areolar connective tissue Aorta

Elastic fiber

Elastic fibers


29/33

Ultrastructure of elastic fibers

Microfibrils

Elastic fiber


30/33

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.


31/33

Major components of ground substance

1. Proteoglycans = core protein + glycosaminoglycans (GAGs)

2. Hyaluronic acid (hyaluronan)

3. Glycoproteins e.g. fibronectin adhesion proteins


32/33

A proteoglycan molecule as seen under electron microscope


33/33

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)

connective tissues and extracellular matrix 2014-9

Documents