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THE GROUND TISSUES
EPITHELIAL TISSUES
CONNECTIVE AND
SUPPORTIVE TISSUES
MUSCLE TISSUES
NERVOUS TISSUE
HISTOLOGY 1.5.:
CONNECTIVE AND SUPPORTIVE TISSUES
A diverse group of tissues that share a common origin from the
mesenchyme of the embryo.
They provide structural and metabolic support for other tissues and
organs throughout the body, bind the tissues to form organs, and the
organs to form organ systems and organism.
They contain blood vessels and mediate the exchange of nutrients,
metabolites and waste products between tissues and
the circulatory system.
THUS:
•Origin: from the mesoderm
•Blood supply: densely vascularized
•Nerve supply: densely innervated
Tissue components of the connective and supportive tissues:
• Cells of great variety (fixed and free cell types, see later)
• Extracellular matrix (ECM) - ground substance
- fibers (collagen, elastic, reticular)
Extracellular matrix (ECM)
I. THE GROUND SUBSTANCE
A highly hydrated gel in which the cells and fibers are embedded
Molecular components:
Proteoglycan consisting of dimeric glycosaminoglycans (GAGs)
bound to a protein core:
chondroitin sulphate (cartilage, arteries, skin, cornea)
keratane sulphate (cartilage, bone, cornea)
heparane sulphate (arteries, lung)
dermatan sulphate (skin, tendon,ligaments, sclera, lung)
hyaluronic acid (vitreous humor of eye, synovial fluid, loose CT,
skin, cartilage, umbilical cord)
Hydrophilic side chains of GAGs bind a considerable amount
of extracellular fluid – water reservoir of the organism.
It is a part of the connective and supportive tissues not visible in
histological preparates, unless special staining methods are applied:
• Toluidine-blue
• PAS staining
• Alcian-blue staining
Extracellular matrix (ECM)
II. CONNECTIVE TISSUE FIBERS
1. COLLAGEN fibers
The most abundant protein in the body.
H.E-stained light micrograph
Scanning electron micrograph
Two isolated fibers
artificially coloured
in the computer
(SEM)
Cross-striation
observed in the
transmission
electron microscope
Synthesis of collagen fibers:
• Takes place in the rER of fibroblasts:
pro-a-chains form triple helices
• These procollagen molecules are transferred to the Golgi complex
• Tropocollagen molecules are released
via exocytosis from Golgi-vesicles
• Tropocollagen molecules are assembled to form
collagen fibers in ECM
Properties of collagen fibers
• Non-branching bundles of changing thickness
• High tensile strength
• Poor sheer strength
• They can be stretched to approximately 5 % of their initial length
SYNTHESIS OF COLLAGEN FIBERS BY FIBROBLASTS
Specific staining for the visualization of collagen fibers:
Azan staining stains the collagen fibers selectively in blue colour
other tissue componenst are stained red
TYPES OF COLLAGEN FIBERS
Type I.: 2 a1 chains + 1 a2 chain
the most common (bone, skin,tendon, ligaments)
Type II.: 3 a1 chains
predominates in cartilage
Type III.: 3 a1 chains
in embryonic CT and skin
Type IV.: still unknown composition
in the basal laminae of adults
Type V.: still unknown composition
mainly in the embryo
2. ELASTIC FIBERS
They are present in organs whose normal function requires elasticity
in addition to tensile strength
Wall of the aorta stained with H.E.
and
resorcin fuchsin,
specific staining for elastic fibres
SYNTHESIS OF ELASTIC FIBERS:
• Takes place in the rER of fibroblasts (and smooth muscle cells):
tropoelastin molecules
• Transformed to elastin, cross-linked and assembled in the
extracellular space
• Microfibrils secreted prior to elastin provide scaffolding on which
elastin forms fibers and sheets
PROPERTIES OF ELASTIC FIBERS
• Occur in the form of individual, branching and anastomosing fibers
•They can be stretched 2.5 times of their original length
to which they return when released
SYNTHESIS OF ELASTIC FIBRES BY FIBROBLASTS
3. RETICULAR FIBERS
Individual collagen fibers coated by proteoglycans and glycoproteins.
This coating causes their affinity for silver salts.
They form delicate flexible networks around capillaries, muscle fibers,
nerves, adipose cells and hepatocytes.
Serve as scaffolding in endocrine, lymphatic and blood cell-forming
organs.
Reticular fibers around hepatocytes
and around kidney tubules (as part of
basement membrane)
SYNTHESIS OF RETICULAR FIBRES BY FIBROBLASTS
CELL TYPES OF THE CONNECTIVE TISSUES
I. Fixed cells:
fibrocytes
fibroblasts
mesenchymal cells
adipose cells
II. Free cells:
macrophages
mast cells
plasma cells
melanocytes
blood-derived cells
(lymphocytes, monocytes,
eosinophils,neutrophils)
I. FIXED CELLS
I.1. Fibrocytes, fibroblasts:
The most common fixed cell types.
Fibroblast: metabolically more active
(see before: synthesis of ECM components)
(purple arrows).
Fibrocyte: metabolically less active,
more slender cell and nucleus, less cell
organelles (green arrows)
I. FIXED CELLS
I.2. Mesenchymal cells
Pluripotent undifferentiated cells around blood vessels:
Serve as a reservoir of cells that can differentiate into other
connective tissue cell types.
I. FIXED CELLS:
I.3. Adipose cells:
LM
SEM
TEM
Adipose cells, single or in groups are normal
components of the connective tissue (they may
form a separate tissue: adipose tissue).
Spherical or polyhedral cells with a large lipid
droplet surrounded by a thin cytoplasmic rim.
II. FREE CELLS:
II.1. MACROPHAGES (histiocytes): in non-reactive CT are fixed,
upon stimulation they become motile.
Phagocytotic cell type, rich in hydrolytic enzymes.
LM
SEM
TEM
THE MONONUCLEAR PHAGOCYTE SYSTEM
Connective tissue:
Liver:
Lung:
Lymph nodes:
Spleen:
Bone marrow:
Serous cavities:
Bone:
Central nervous system:
Skin:
Synovia:
histiocytes
Kupffer-cell
alveolar macrophage
free and fixed macrophages
free and fixed macrophages
fixed macrophages
pleural and peritoneal macrophages
osteoclasts
microglial cells
histiocytes
type A cells
II.FREE CELLS:
II.2. Mast cells: around blood vessels in skin and intestine.
TEM
LM
LM
Large metachromatic granules:
histamine, heparin, serotonin
II. FREE CELLS:
II.3. Plasma cells:
In the loose CT of gastrointestinal tract,
respiratory system and female
reproductive system, in the lymphatic
tissue.
They develop from B-lymphocytes,
produce antibodies.
LM
TEM
II. FREE CELLS
II.4. Melanocytes
Large pigmented cells of neural crest-origin. They occur in the dermis
of skin, meninges, choroid and iris.
II. FREE CELLS:
II.5. Other free cells temporarily occurring in the CT
Lymphocytes,
monocytes,
granulocytes
(in details see the chapter „Blood” later)