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Histology of the Connective Tissue
By
Safaa El Bialy (MD, PhD)
Objectives
• List the structural and functional characteristics of connective tissue and distinguish it from other basic tissue types.
• Describe the functions carried out by different types of connective tissue.
• Describe the three fundamental components found in all connective tissues.
• Describe the biochemical composition and the sites of synthesis of the extracellular matrix components.
• Define the structure and function of the connective tissue cell.
Embryonic Origin (FYI)
All connective tissue cell types are derived from embryonic mesenchyme (mesoderm)
Mesenchyme is characterized morphologically by a prominent ground substance matrix containing a loose aggregate of collagen fibrils and unspecialized cells
Connective Tissue
• Is one of the 4 basic tissues of the body. • CT forms a framework, connecting, supporting and packing tissues of
the body.• It also plays a dynamic role in the development, growth, defense and
homeostasis of other tissue types.
• Structurally it is made up of :1. Cells2. Extracellular matrix * Fibers * Ground substance: Viscous material of glycoproteins and proteoglycans
Types of cells in connective tissue
1. Residents:•Fibroblasts •Reticular cells (type of fibroblast that synthesizes type III collagen)•Mesenchymal cells •Fat cells 2. Visitants:•Macrophages•Mast cells•Plasma cells•Leukocytes•Melanocytes
Fibroblasts
• Fibroblasts • Most common cells in CT• Spindle shaped with elongated
nuclei• Synthesize most components of
connective tissue (Extra-cellular matrix, proteins etc)
• Involved in wound healing• Adipocytes• Also called “Fat Cells”• Nucleus pressed against the cell
membrane “Signet ring”• Functions:
1. energy reserves,
2. insulation,
3. protection and support
Macrophages• Macrophages (Histiocytes)• Almost as numerous as fibroblasts• Most abundant in richly vascularized
areas• Derived from monocytes in bone marrow
and mature to macrophages in CT• Important agent of defense.• secrete :
1. enzymes
2. two proteins of complement system,
3. an important antiviral agent, interferon• Langerhan’s cells in epidermis, kupffer
cells in liver, microglial cells in CNS and osteoclasts in bone all derive from monocytes and are macrophages like cells).
Mast cells• Mast means well fed. Their
cytoplasm is full of coarse granules
• Spherical, central nucleus• Metachromatic granules• Secrete:• Histamine: increase vascular
permeability and smooth muscle contraction
• Heparin: anticoagulant• Tend to occur in small groups
around blood vessels (particularly in dermis, digestive and respiratory tracts)
PLASMA CELLS
• Resemble to lymphocytes• Basophilic cytoplasm due to rough
ER• Eccentric nucleus• Cartwheel appearance• Cytoplasm contains a clear, rounded
area (site of centrosphere and Golgi apparatus
• Frequently found in serous membranes and lymphoid tissue and plentiful in sites of chronic inflammation
• Principle function is the production of antibodies which are synthesized in RER
• Rare in most connective tissues
Leucocytes
•Wandering cells
•leukocytes that migrate from the blood vessels by diapedesis
•This process increases greatly during inflammation
•Neutrophils
•Eosinophils
•Basophils
•Lymphocytes
•Monocytes
•macrophages
Extracellular Matrix• Extracellular matrix (Fibers & Ground substance) is synthesized and
secreted mainly by the fibroblasts • Fibers
Prime function is a support and a strengthening role in1. Fibrous capsule of organs2. Penetrating trabeculae of organs3. Dermis of skin4. Ligaments & tendons5. Cartilage & bone
• Ground substance 1. Acts as a molecular sieve & stops the spread of noxious substances 2. Cellular nutrition & waste removal 3. Plays a vital role in aging. Its amount diminishes with age and wrinkles start appearing.
Fibrous Components
• Connective tissue fibers are long, slender protein polymers that are present in variable proportions in different types of connective tissue.
• In many cases the predominant fiber type is responsible for conferring specific properties on the tissue.
• We have three types of fibers:• Collagen Fibers• Reticular Fibers • Elastic Fibers
Collagen• Collagen is the most abundant
protein in human body forming 30% of its dry weight
• Collagen Producing Cells:• 1. Fibroblast: More than one type
of collagen• 2. Chondroblast: Type II collagen• 3. Osteoblast:Type I• 4. Reticular cell:Type III• 5. Smooth muscle:Type I & III
Synthesis of Collagen (FYI)
Mother cell
Procollagen (Triple-helical units)
Procollagen peptidase
Collagen fibril
Collagen fiber
Extracellular
Intracellular
Reticular Fibers
• These fibers look very similar to collagen but are thinner (0.5-2 um).
• More highly glycosylated.• Form delicate silver-staining
network instead of thick bundles.• Composed mainly of type III
collagen and glycoprotein.• Reticular lamina of basement
membrane (Slide # 6 in epithelial tissues) and around adipocytes, smooth muscle (slide # 29 in muslce tissue) and nerve fibers.
• Reticular fibers constitute a network around the parenchymal cells of various organs (liver, endocrine glands)
Lymph NodeReticular cells and fibers
Elastic Fibers (Connective tissue)
Elastic fibers consist of an amorphous protein called elastin and numerous protein microfibrils embedded in it.
Diameter range 0.1-10um.
Add resilience to connective tissue
Collagen fibers
Elastic fibers
Elastic Fibers
• Elastic fibers are collected in thick, wavy, parallel bundles & separated by loose collagenous tissue with fibroblasts.• Ground substance is sparse.• Elastic connective tissue provides flexible support.•ligamentum flava of the vertebral •column•suspensory ligament of the penis•elastic lamina of blood vessels.
Elastic laminae
Wall of Aorta
Medical application (FYI)
• Marfan syndrome:• Lack of fibrillin which is necessary for the deposition of elastic fibers
• Lack of resistance in tissues rich in elastic fibers
• Aortic aneurysm is common
Ground SubstanceGlycosoaminoglycans • GAGs are polysacharides that
contain aminosugars.• Hyaluronic acid is the largest GAG.Proteoglycans:• They are made up of a core protein to
which glycosoaminoglycans (GAGs) are attached.
Glycoproteins: • Fibronectin-mediates the attachment
of cells to the extracellular matrix.• Laminin-a component of basal
laminae that mediates the attachment of epithelial cells.
Tissue fluids:• plasma proteins of low molecular
weight• Salts:
Proteoglycans Glycoproteins
Connective Tissue Types
1. Embryonic connective tissue
2. Adult connective tissue:
A. Connective Tissue Proper:
1. Loose connective tissue
2. Dense connective tissue
a) Dense regular connective tissue
b) Dense irregular connective tissue
B. Reticular connective tissue
C. Elastic connective tissue
D. Mucous connective tissue
Connective tissue
Embryonic Adult
Mesenchyme Mucous Loose (areolar)
DenseSpecialized
Irregular RegularReticular Adipose Elastic
Mesenchyme
• Mesenchyme is embryonic connective tissue.
• Its stellate and fusiform cells (mesenchymal cells) are derived from mesoderm.
• loosely associated cells and are surrounded by a large extracellular matrix
• They give rise to all the connective tissue of the body.
• These are multipotential cells and persist in adults to give rise to new generations of connective tissue cells especially during wound healing, bone repair and tissue fibrosis
Mucous Connective Tissue
• Resembles embryonic mesenchyme and is rarely found in adults
• Found mainly in the umbilical cord and nucleus pulposus of the intervertebral discs
• This tissue has very few cells (fibroblasts) & fibers.
• Lots of ground substance (mainly hyaluronic acid)
• This tissue yields readily to pressure and returns to its original shape, so it is useful for protecting underlying structures from excess pressure.
Loose Connective Tissue
• Very common type• Support structures under some
pressure and low friction• Fibroblasts and macrophages
are predominant• Collagen, elastic and reticular
fibers are present• Supports epithelial tissues,
small blood vessels and lymphatics
• Fills spaces between muscle and nerve fibers
• Papillary layer of dermis and hypodermis
Dense Connective Tissue
• Same components as loose CT• Fewer cells with predominance of
collagen fibers over ground substance
• Less flexible and more resistant• Collagen fibers arranged in bundles
without a definite orientation → dense irregular CT (dermis, wall of GIT, organ capsules)
• Often found with loose CT• Collagen fibers arranged according
to a definite pattern → Dense regular CT (tendons and ligaments)
Loose connective tissue
Dense connective tissue
Connective Tissue
Fibroblasts
Extracellular matrix
Mammary Glands
Epithelial tissue
Lesser amount of collagen fibers
Larger amount of collagen fibers
Special Types of Connective Tissues
• Adipose tissue• Blood & lymph• Cartilage• Bone
Adipose tissue
• Specialized type of CT• Adipocytes or fat cells
predominate• 15-20% of male body weight
and 20-25 % of female body weight
• Largest repository of energy• Key regulator of body’s
energy metabolism
Adipose tissue
Cartilage
Perichondrium
Chondroblasts
Chondrocytes
Lacuna
Cartilage matrix
Isogenous group
of chondrocytes