- 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
- 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
- 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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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
= 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
- 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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Two different types of Classification accepted:
Connective tissue proper
ACT, FCT
Specialized connective tissue
Blood, bone, cartilage, adipose,
RCT
Embryonic connective tissue
Mesenchymal and mucous CT
Loose Connective tissue
ACT, RCT, adipose
Dense connective tissue
Regular, irregular, elastic (FCT)
Cartilage
Hyaline, fibrocarilage, elastic
Other
Bone, blood, embryonic
- 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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- 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
- 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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