Features of CT
- abundant ECM
- Few cells, widely spaced
- highly vascularized
Embryonic CT types and characteristics
- mesenchyme: precursor to bone, muscle, cells in jellylike matrix with some reticular fibers
- mucous CT: only in umbilical cord (Wharton’s Jelly) and parts of the embryo; large blood vessels along it; large, stellate fibroblasts
Loose CT
Lots of ground substance, few fibers, scattered cells
-Areolar ct: papillary layer of dermis, superficial fascia of mesothelium in body cavities, mucous membrane, around blood vessels and peripheral nerves
-cellular CT: lamina propia; more cells than areolar, deep to epithelium
Dense irregular CT
- less ground substance and more collagen
- collagen bundles in many directions; directions correlate to stress areas
- reticular layer of dermis, capsules of organs, sheaths of tendons and nerves
Dense Regular CT
- groups of parallel collagen fibers (different groups can be in dif directions)
- tendons, ligaments, aponeuroses, stroma of cornea
Dense regular elastic
- little collagen but a lot of elastin
- coarse, fibrous bundles (ligamenta flava, suspensory ligament of penis)
- fenestrated sheets of elastic tissue in the tunica media of large arteries
Adipose CT
Mainly made of adipocytes
- white fat: synovial joins, orbit, heal, butt
- brown fat: around kidneys, adrenals, aorta (heat)
Synthesis of collagen
- 3 alpha chains (with gly as 3rd residue and Pro, hydroxy Pro, and hydroxylys) combine with propetides @ ends to prevent self-assembly [occurs in RER]
- Golgi packages procollagen into secretary vesicles for exocytosis
- ECM: cleavage of propeptides (tropocollagen) and self assembly of fibrils (68 nm banding pattern)
- fibrils can aggregate into fibers and fiber bundles
Collagen Type I
- dermis, ligament, tendon, organ and joint capsules, cornea, teeth, bone, loose CT
- most common (90%)
- Made by fibroblasts in CT proper
- stains pink w/ H&E or blue/green w/ trichrome
- banded fibrils form fibers
Collagen Type II
- hyaline and elastic cartilage, vitreous body of eye
- made by chondroblasts and chondrocytes
- thin fibrils (NOT fibers)
Collagen Type III
- supporting network for soft organs, underlying basal lamina of epithelium
- Reticular fibers (network of thin fibrils)
- PAS positive and silver stain
- made by fibroblasts in loose CT and by Reticular cells, smooth muscle cells, and Schwann cells
Collagen Type IV
- lamina densa of basal lamina
- propeptides not removed, so they don’t aggregate into fibrils and form a mat instead
Collagen Type VII
- lamina reticularis of basement membrane
- anchor basal lamina of stratified epithelium of skin, cornea, esophagus
- anchoring fibrils (bound to lamina densa and type I and III fibrils)
Elastic fiber structure
-protein elastin core surrounded by fibrillin (glycoprotein)
Ground substance composition
-mainly made of GAGs and glycoproteins
What gives the ground substance its gel like consistency?
Hydrated GAGs
Test tube brush appearance
GAGs attach to a core protein, forming strongly negative proteoglycans
Adhesive glycoproteins
- fibronectin, laminin, chondromectin, osteonectin
- promote attachment of ECM components to one another and attachment of cells to ECM
- bind to transmembrane proteins in integrin family
Fixed cells in CT
- fibroblasts (most abundant): make collagen, elastic and reticular fibers
- derived from mesenchymal stem cells
- spindle shaped w/ flattened, oval nuclei and basophilic cytoplasm and extensive RER when active
- sparse cytoplasm and little RER when inactive
- macrophages
- mast cells (large and ovoid)
- adipocytes
Transient cells in CT
- lymphocytes (lamina propria, lymph notes)
- monocytes (not usually found b/c turn into macrophages)
- plasma cells (in GI/resp tracts)
- granulocytes (proliferate rapidly during immune response)
