Brief introduction about structure of skin.

1. THE ULTRA STRUCTURE
OF EPIDERMIS
Dr. Rahul pratap s chouhan
( Dermatology resident 1st year)
Ananta institute of medical sciences
& research center, Rajsamand.

2. EPIDERMIS
-It is the outermost layer of the skin, and its size varies as per
the location.
-It is thinnest over the eyelid measuring less than 0.1 mm, and
thickest over the palms and soles, measuring approximately
1.5 mm.
-It is stratified squamous epithelium. Keratinocytes constitute
more than 95% of epidermal cells.
-The “brick like” shape of keratinocyte is provided by
cytoskeleton made of keratin intermediate filaments.

3. SURFACE OF THE EPIDERMIS
-The surface of skin is laced with multiple network of fine
grooves called sulci cutis.
-Cristae cutis are slightly elevated areas or mounds that
surround these grooves.
-The pores of sweat glands derived from the skin, open into the
cristae cutis.
-Depending on the body location, the orientation of sulci cutis
varies, these are known as dermal ridge patterns or
dermatoglyphics. They comprises fingerprints and sole patterns
which are unique to each individual.

5. On morphological grounds,
the epidermis can be divided into four distinct
layers:
1. Stratum basale
2. Stratum spinosum
3. Stratum granulosum
4.Stratum corneum

8. 1.STRATUM BASALE
-Lowermost layer that rests directly on the basement
membrane zone.
- It consist of one layer thick keratinocytes( cells that
secrete the structural protein called keratin) and
melanocytes which house melanosomes that secrete
the pigment melanin.
-The keratinocytes in this layer are columnar in shape,
nucleated, and have a dense cytoplasm.

9. -The cell cycle in this germinative layer gets completed in
18-20 days.
Clinical significance: Basel cell carcinoma initiate in the
actively mitotic cells of the basal layer.

10. 2.STRATUM SPINOSUM
-This layer comprises of keratinocytes which are
polygonal, nucleated, 8-10 layers thick and connected
by unique intercellular bridges called “desmosomes”.
-This desmosomes appear as “prickles” under the
microscope, hence called “prickle-cell-layer” to this
spinous layer.
Clinical significance:
The autoimmune bullous disease pemphigus affects
desmosomes and cause histological cleft at this level.

11. 3.STRATUM GRANULOSUM
-When keratinocytes migrate upward from the stratum
spinosum, their cytoplasm develops keratohyaline
granules, thus the name “granular” cell layer.
-This layer is three to five layers thick, and contains
diamond-shaped keratinocytes.
*The bottom three layers, viz. basal, spinosus, and
sometimes granular layers are often clubbed together
and called the stratum malphighi.

12. 4.STRATUM CORNEUM
-This is the outermost cell layer.
-The keratinocytes in this layer become enucleated
and flattened and are called corneocytes.
-This layer can be 20-25 layers thick depending on
the body part involved
-Epidermis over palms and soles has an additional
translucent cell layer between the stratum corneum
and granulosum called strartum lucidum.

13. Clinical significance:
-Damage to this layer causes damage to the “skin
barrier”, occurring in disease like atopic dermatitis and
psoriasis.
*Epidermal turnover time(Keratinization): Migration of a
keratinocyte from basal layer to the outermost layer(52-
75 days).

14. Apart from the keratinocytes, the epidermis
houses other cells like:
1. Melanocytes
2. Langerhans cells
3. Merkel cells

15. 1.MELANOCYTES
Melanin producing basal cell layers, With dendritic projections
into surrounding keratinocytes.
Epidermal-melanin unit: one melanocyte integrates with 36
keratinocytes.
Clinical significance:
1. Damage to or dysfunctional melanocytes lead to the
depigmentation disorder, vitiligo.
2. Melanocytic nests also cause various types of melanocytic
nevi(moles), which may undergo malignant transformation to
melanoma.

16. EPIDERMAL-MELANIN UNIT

18. SKIN COLOR
The skin color varies with the type of melanin:
1. Brown(pheomelanin)
2. Black(eumelanin)
Skin color also depend on concentration of
melanosomes in the epidermis.

19. 2.LANGERHANS CELLS
-These are dendritic cells, akin to melanocytes, and are
specialized macrophages.
-They trap antigens and present them to T-lymphocytes,
thereby behaving as “antigen presenting cells” with a definitive
role in immune surveillance.
-Tennis-racquet-shaped granules present in the cytoplasm of
this cells.
-The immunohistochemical surface markers for these cells are
CD1a or CD207(langerin)

20. CLINICAL SIGNIFICANCE:
In allergic dermatitis, there is a significant increase in
the number of Langerhans cells, proving their role in this
T-cell-mediated disorder.

21. 3.MERKEL CELLS
-These are fine-touch sensitive, slowly adapting
mechanoreceptors(type 1 mechanoreceptors).
-They are oval-shaped located perifollicularly, and
contain granules.
-Merkel cells interact with neuropeptides and help in
sensory perception.

23. THANK YOU