The Skin
The Skin
- It ls the largest organ in the body.
- it ls forms a protective layer to the surface of the whole body.
- it is very important of processes of excretion of sweat and regulation of heat.
- Types of skin
1: Thick skin In the palms of hands and soles of foot.
2: Thin skin present in other body areas.
- Structure of skin
- A : Epidermis : Consist mainly a stratified squamous keratjnized epithelium offour types of cells and four-five layers
* Keratinocyte : is the predominant cell type in the epidermis , the outermost
layer of the skin, constituting 90% of the cells found there.
1: Stratum Germinativum : a single layer of short columnar or cuboidel cell
resting on the basment membrane.
2: Stratum Spinosum : consist of cuboidel cell with central nucleus in 4-8
layers.
Malpighi on layer : which consist of both the stratum germinativum and stratum
spinosum.
3. : Stratum Granulosum consist of 2-4 layers of flattened cell with fıttend
necleus contain Basophillc granules in the cytoplasm.
4 : Stratum Lucidum : Thin layer extremely flattened cell unnucleated contain
filament keratine hyaline and granules.
5. : Stratum Corneum : consist of 15-20 layers of flattend unnucleated keratinized
cell(the scales)
* Melanocyte :- are melanin-producing cells located in the bottom layer (the
stratum basale) of the skin's epidermis. Melanin is the pigment primarily
responsible of skin color ·
- langerhans : antigen-presenting immune cells of the skin .They are present ın
all layers of the epidermis, but are most prominent In the
stratum spinosum . They also occur in the papillary dermis, particularly around
blood vessels.
- Merickle : found in the, stratum basale (at the bottom of sweat duct ridges)
of the epidermis . Most often, they are associated with sensory nerve endings,
when they are known as merkel nerve endings.
- B : Dermis : consist of areolar connective tissue.
in Amphibia : the dermis consist of two layers :-
1 : stratum spongiosum : which contain areolar connective tissue which rich of
nerve ending, blood vessels.
2 : stratum compactum : which contain fibro connective tissue and poisonous gland
and mucus gland.
- In mammalian : this layer ls areolar connective tissue which rich of nerve
ending, blood vessels, elastic and collage nous fibers, hair follicle and some
glands.
- C :- Hypodermis : connective tissue rich in fat cell or adipose connective tissue.
* Gland of the skin :-
- sebaceous gland :- this is a branched alveoıar gland(holocrine). They are
embedded in dermis over most of the body surface . they are not found in the
glabrous skin of the palms of hands and soles of foot .
- sweat gland : this ls a coiled tubular gland (merocrine). whose ducts open at
the skin surface.
* Skin has Sens organs to receptor the stimuli :-
- Free nerve ending : to touch.
- pacinian corpuscle : to pressur
- Meissenar corpuscle : to touch.
- Kraws corpuscle to : colding.
- Ruffini corpuscle : to heating.
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Lab 1 photo :
Drowing photo
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