7 nots - 1 Type VII collagen and anchoring fibrils...

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September 29, 2008 Lecture 7
Type VII collagen and anchoring fibrils
www.lab.anhb.uwa.edu.au/. ../Integum.htm
The epidermis
The most superficial part of the epidermis is formed by the stratum corneum. Nuclei are
not visible in this layer. Cell outlines may be visible at high magnification or, in the form
of artifacts, as cracks or clefts in the stratum corneum. The stratum granulosum is
formed by a single layer of very dark and flattened cells in thin skin. Several layers of
cells containing keratohyalin granules are visible in thick skin. Polyhedral cells with clear
outlines form the stratum spinosum . The stratum basale is formed by a single layer of
cuboidal or columnar cells and delimits the epidermis from the dermis.
At high magnification, the basal cytoplasm of the basal cells seem to interdigitate with
the underlying dermis. Similar to the dermal papilla, this irregular border at the cellular
level, the dermal-epidermal junction, anchors individual basal cells firmly to the
underlying dermis.
The Dermis
The dermis is the thick layer of connective tissue to which the epidermis is attached. Its
deepest part continues into the subcutaneous tissue without a sharply defined boundary.
Its thickness is for this reason difficult to determine but 1-2 mm is a good guestimate for
"average" skin. The dermis may be divided into two sublayers (again without a sharp
boundary):
The papillary layer (contains anchoring fibrils composed of type VII collagens)
consists of loose, comparatively cell-rich connective tissue, which fills the hollows at the
deep surface (dermal papillae) of the epidermis. Capillaries are frequent. Collagen fibres
appear finer than in the reticular layer. The reticular layer appears denser and contains
fewer cells. Thick collagen fibres (5-10 μm) often aggregate into bundles (up to 100 μm
thick). The fibres form an interlacing network , although their predominant direction
is parallel to the surface of the skin. A preferred orientation of the collagen fibres is not
visible in the sections, but the main orientation of the fibres differs in skin from different