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Dermis (corium)
The dermis is the layer ofthe skin underlying theepidermis.
It is ofmesodermal origin
It supports the epidermis
thickness= 0.5-3 mm
dermis is divided intotwo layers:
a superficial papillary layer
and a deeper, moreextensive reticular layer
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The papillary layer
The dermal papillary layer isuneven and forms dermalpapillae, which interdigitate withthe epidermal downgrowths(interpapillary pegs) and ridges ofthe overlying epidermis.
It is Thinner than the reticularlayer.
This dermal layer is composed ofthin, loosely arranged fibers andcells, and contains capillary loopsand Meissners corpuscles, which
are fine-touch receptors. Vascular papillae
Nervous papillae
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The reticular layer
The dermal reticular layerconstitutes the major portionof the dermis.
It is dense irregular connectivetissue
It is composed ofdensebundles of collagen fibers andthick elastic fibers and maycontain pacinian corpuscles(pressure receptors) andKrause end-bulbs (cold
receptors) in its deeperaspects.
It also contains: hair follicles,sweat and sebaceous glands.
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Hair and Hair Follicle
Hair is an elastic keratinizedthread derived from aninvagination of the epidermalepithelium.
Location of hair?
A hair follicle is aninvagination of the epidermisextending deep into thedermis.
Hair consists of two parts: The hair shaft is a long, slender
filament that extends abovethe surface of the epidermis.
hair root: it is embedded inthe skin
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Hair and Hair Follicle (cont..)
Hair follicle: it is tubularsheath that surrounds thehair root and is made bydermal and epidermalelements
The hair bulb is theterminal expanded regionof the hair follicle in whichthe hair is rooted.
Hair bulb is deeply indented
by a dermal papilla, whichcontains a capillary networknecessary for sustaining thefollicle.
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Structure of hair
Hair has epithelial cells arranged inthree concentric regions:
1. Medulla: it forms the central axisof hair . Consists of two or morelayers of shrunken, moderatelykeratinized , cuboidal cells.
2. Cortex: if forms the main bulk ofthe hair. It contains long,flattened, heavily keratinized cellswhich are very closely packed.
3. Cuticle: it is made by the mostperipheral cells of the hair. It
consists of single layer offlattened, clear, keratinized cellswhich partially overlap each other.
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The arrector pili muscle
The arrector pili muscleattaches at an oblique angle tothe middle of hair follicle.
It extends superficially tounderlie sebaceous glands,
passing through the reticularlayer of the dermis andinserting into the papillarylayer ofthe dermis.
Function: The contraction ofthis smooth muscle causes
erection of the hair. Innervation: sympathetic
nerve fibers.
