Biomedical Engineering Reference
In-Depth Information
be classified into different types: simple squamous epithelium (e.g.,
lung,heart,andbloodvessels),simplecuboidalepithelium(e.g.,kid-
ney tubules and ducts of glands), simple columnar epithelium (e.g.,
gastrointestinaltractandgallbladder),ciliatedcolumnarepithelium
(e.g., upper respiratory tract and uterus), glandular epithelium (e.g.,
endocrine glands), stratified squamous epithelium (e.g., epidermis
and esophagus), and transitional epithelium (e.g., urinary bladder).
Epithelial cells have diverse functions in absorption, secretion, sen-
sory system, transport, andprotection.
24.2.1
Extracellular Matrix and Growth Factors
Epithelialtissuesareusuallyseparatedfromtheunderlyingconnec-
tivetissuesbyabasementmembrane.Thebasementmembraneisa
specializedECMfoundinmosttissues.Itservesasabarrierandpro-
vides structural support for the epithelial cell layer.
8
Its constitutive
components bind to cell membrane receptors to initiate outside-in
signaling.
9
The molecular compositions of all basement membranes
are not static, varying from tissue to tissue and during develop-
ment and disease. All basement membranes contain laminins, type
IVcollagen,heparan sulfateproteoglycans, andentactin-1/nidogen-
1.
10
Type IV collagen is the most abundant protein in basement
membranes.
8
Matrigel, a solublized basement membrane derived
from mouse sarcoma, is commonly used in cell culture. Laminin-
1 trimer is a major component of Matrigel. Compared with other
organs,suchaskidney,pancreas,andlung,theliverhassomeunique
features. Mature hepatocytes lack a basement membrane, and the
ECMconstitutesonlyaminorpartofthenormalliver.
11
Inthespace
ofDisse,betweenendothelialcellsandhepatocytes,thereisonlylit-
tle matrix, in which fibronectin is the most abundant component. In
addition, collagen types I, III, IV, V, and VI are also present in the
space of Disse.
11
This is different from other epithelial tissues in
which collagen type I is restricted to the stroma and not directly
in contact with epithelial cells. A better understanding of tissue-
specific basement membrane compositions and structures will help
design suitable scaffoldsfor variousepithelial tissue engineering.
The basement membrane sequesters growth factors and
cytokinesandconsequentlyinfluencestheirlocalconcentrationand
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