Download Reticular Connective Tissue

Connective Tissue
- largely a category of exclusion
- structure and support
- mesodermal origin
- blood, cartilage, bone =>
substantially different
not CT proper
different embryonic origin
=> often treated as a separate category
- most abundant protein in CT = collagen
Collagen
- main protein in connective tissue
- most abundant protein in mammals
- fibrous => different from enzymes
- great tensile strength
- strengthens blood vessels
- cornea and lens = crystalline collagen
- skin strength and elasticity
- degradation of collagen = wrinkles
Collagen II
- three topocollagens => triple helix (Madras helix)
- polypeptide composition
- 28 forms of collagen
- 90% of the body made of I, II, III, IV
I = bone
II = cartilage
III = reticular fibers
IV = basement membrane
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Other Fibers
Reticular
Elastic
- delicate, thin
- form network not bundles
- not visible in H&E stain
!special stains required,
i.e. silver
! consist of tropocollagen
- support individual cells
- coloration only appears in
thick elastic fibers
- consist of myofibril embedded
in amorphous matrix
- matrix accounts for 90%
- consists of elastin
- can stretch to 150% its size
Ground Substance
= in cavities/ clefts between fibers
- soluble in most solvents used to prepare tissues
Proteoglycans
- 5% proteins + 95% polysaccharides (covalently linked)
= Hyaluronan, Chondroitin sulfate, Dermatan sulfate,
Heparan sulfate, Keratan sulfate
-carbohydrates bind water and cations
= diffusion of substances of low molecular weight, i.e. gases,
ions and small molecules
- exclusion of large molecules
= inhibits spread of microorganisms
=> some of the more invasive types produce the enzyme
hyaluronidase, which depolymerizes hyaluronic acid.
Fibrocytes
Cell types
- most common cell type
- "true" connective tissue cells
- only their oval, sometimes flattened nuclei are visible
- do not contain many organelles
- stimulated = transformed into a fibroblast
protein synthesis to repair tissue damage
- amoeboid movement
Reticular cells
- larger than an average fibrocyte
- "fibrocytes" of reticular connective tissue
- form network of reticular fibres
Adipocytes
- fixed cells, very narrow rim around a large central
- main function???????
- endocrine function - secretion of leptin
Macrophages
- arise from monocytes
- phagocytosis of foreign particles
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Connective Tissue Classification
Two different types of Classification accepted:
Connective tissue proper
ACT, FCT
Loose Connective tissue
ACT, RCT, adipose
Specialized connective
tissue
Dense connective tissue
Regular, irregular, elastic (FCT)
Blood, bone, cartilage, adipose,
RCT
Cartilage
Hyaline, fibrocarilage, elastic
Embryonic connective
tissue
Mesenchymal and mucous CT
Other
Bone, blood, embryonic
Loose Connective Tissue
Areolar Connective Tissue
- most widely distributed in vertebrates
- underneath epithelium of all tissues
w/ openings
- pliable, mesh-like tissue
- fluid matrix
- functions: cushion/ protect organs
- widely dispersed fibroblasts
- cells separated by a gel-like
gelatinous ground substance
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Reticular Connective Tissue
- network of reticular fibers (fine III
type collagen), thin branching
- fibers synthesized by reticular
cells
- identified by staining with silver or
PAS (carbohydrates)
- resembles ACT
- forms framework supporting
blood cells in lymph nodes, spleen
and bone marrow
- architectural framework of liver,
adipose tissue, bone marrow,
spleen, basement membrane
Adipose Connective Tissue
- composed of adipocytes
-derived from lipoblasts
-store energy in the form of fat
-cushions and insulates the body
-two types of adipose tissue exist:
WAT and BAT
- serves as an important endocrine
organ by producing leptin and
resistin
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