role of the dermis
support the epidermis and bind to the hypodermis
what are the 2 layers of the dermis and classify them.
papillary layer: loose irregular CT
reticular layer: dense irregular CT
what is the hypodermis?
loose CT usually infiltrated with fat cells (adipose)
role of connective tissue
- carry nerve and blood vessels that provide innervation and blood supply to the epidermis and other epithelia (communication/transport)
- provide support and connecting framework to other tissues of the body
structural composition of CT
extracellular fibers, amorphous ground substance (called extracellular matrix), and a population of different types of connective tissue cells
what are the different varieties of CT
- loose CT (e.g. papillary layer)
- dense CT (e.g. reticular layer)
- supporting CT (e.g. cartilage and bone)
- CT with special properties (e.g. hemopoietic-bone marrow)
what is the evolution of CT cells?
- mesenchymal cell
- -blast (e.g. fibroblast, lipoblast, chondroblast)
- -cyte (e.g. fibrocyte, lipocyte, chondrocyte)
what is the chromatin level (or packing) of the different levels of CT cell evolution? what does this tell us?
- mesenchymal: euchromatin (pale), so is very active
- fibroblast: euchromatin and heterochromatin (pale and dark), so active, but less
- fibrocyte: heterochromatin (dark), so not very active
CT is derived from _____
mesenchyme
most epithelial tissues is derived from ________
ectoderm and endoderm
most common CT cells
fibroblast, adipocyte, mast cells/macrophage/lymphocyte
function of fibroblast
secrete collagen and other elements of ECM
function of adipocytes
store fat
CT matrix is made of what?
ground substance and fibers
what is the ground substance made of in “normal” CT?
- water
- structural glycoproteins (e.g. fibronectin)
- proteoglycans
- glycosaminoglycans (GAGs)
what is the ground substance of bone?
includes minerals
what is the ground substance of blood?
fluid called plasma
what are the different fibers and their general function?
collagen fibers (confer tensile strength with flexibility) and elastic fibers (confer resiliency)
what are the different collagen fibers and where we find them?
1: dermis, tendon
2. hyaline cartilage
3: reticular fibers
4: basement membrane
5: fetal tissues
where is elasin found?
elastic cartilage and arteries
how is collagen synthesized?
- from a1 and a2 gene in nucleus, which is transcribed
- synthesis and clipping of preprocollagen (in RER)
- hydroxylation of lysine and proline residues (in rER)
- attachment if glucosyl and galactosyl to hydroxylysyl residues
- assembly of procollagen molecules (triple helix)
- packing and secretion in Golgi
- procollagen peptidase in extracellular space, so causes self aggregation
how does collagen aggregate?
- formation of microfibrils of tropocollagen (in a stepwise, overlapping manner)
- collagen fibril
- collagen fibers
- packed into a bindle of fibers
what explains the periodicity of the tropocollagen packing?
the stepwise overlapping
in cartilage, the ECM allows the tissue to _________
support mechanical stress without distortion and also provides support to adjacent soft tissues
