intoduction to skin epidermis part one

1. EPIDERMIS
DR. SUBODH KUMAR SHAH

2. INTRODUCTION OF SKIN
 Skin is the largest organ in the body.
 In a 70-kg individual, the skin weighs over 5 kg and covers a surface area of approx.
2m2 .
 Human skin consists of a stratified, cellular epidermis and an underlying dermis of
connective tissue and beneath the dermis is a layer of subcutaneous fat.
 Mainly two kinds of human skin:
- Glabrous skin (non-hairy skin) and
- Hair-bearing skin

3. FUNCTIONS:
 The skin has very important vital functions for keeping the physiological and
biochemical conditions of the body in its optimum state. The most important
functions of the skin are:
 Regulates body temperature.
 Prevents loss of essential body fluids, and penetration of toxic substances.
 Protection of the body from harmful effects of the sun and radiation.
 Excretes toxic substances with sweat.
 Mechanical support.
 Immunological function mediated by Langerhans cells.
 Sensory organ for touch, heat, cold, socio-sexual and emotional sensations.
 Vitamin D synthesis from its precursors under the effect of sunlight and introversion of
steroids

4. INTRODUCTION OF EPIDERMIS
 Superficial layer of skin.
 Continually renewing, Stratified squamous epithelium that keratinizes
and give rise to derivative appendages.
 Keratinocyte make 95% of cell population.
 Approximately 0.4 to 1.5mm thick.
 Avascular .
 Project to dermis by rete ridges .
 Joined by complex basement membrane to dermis.

5.  Epidermal Appendages are:
1) Hair
2) Nail
3) Sebaceous Gland
4) Sweat Gland(Apocrine & Eccrine)
 Other cells of Epidermis are:
1) Melanocytes
2) Langerhan’s cell
3) Merkel cell

6. DEVELOPMENT
 Skin arises by juxtaposition of two major embryological
components:
i. Prospective epidermis- originates from surface area of early
gastrula.
ii. Prospective mesoderm- brought into contact with inner surface of
epidermis during gastrulation.
provides dermis.
induce differentiation of epidermal structures.
 Neural crests contribute: pigment cells.

7. DEVELOPMENT OF EPIDERMIS
 Epidermis develop from surface ectoderm of early gastrula.
 Development relies on Initiation signals.
 Notch and Wnt signalling pathways has opposing interplay with
Beta Catenin, Lef1 & Notch peptide.
 Signals from sonic Hedgehog pathways Bone Morphogenetic
Proteins(BMP’s).

8. LAYERS OF EPIDERMIS
From below up layers are-
1. Stratum Basale or Germinativum
2. Stratum Spinosum or Prickle layer
3. Stratum Granulosum
4. Stratum Corneum or Horny layer
Stratum Lucidium is extra layer below horny layer
found in thick skin of palms and soles.
Malpighian layer include basal and spinous cell.

10. STRATUM BASALE
Continuous layer generally one cell thick.
-may be 2-3 cell thick in glabrous and
hyperproliferative epidermis
Cuboidal with large,dark staining nuclei and a
dense cytoplasm.
Site of mitotically active cell and give rise to
other layer.

11. STRATUM SPINOSUM
 8 to 10 cell layer.
 Polyhedral cell with a round nucleus.
 Become flatter and develop organelles.
 They look shrunken and contain spine like projection in
histological section.
Contain numerous desmosome and Calcium dependent cell
surface modification.
Function: adhesion of epidermal cells and resistance to mechanical
stress.
 Limited mitosis occur.

12. STRATUM GRANULOSUM
2 to 5 cell layer
Named for basophilic keratohyalin granules.
Cytoplasm of granular layer and upper spinous layer
also contain lamellar granule or membrane coating
granule or Odland bodies .
Lamellar granules appear in intercellular space
between plasma membranes of adjacent cells.
Cornified envelope begins to form.
Keratinocyte of granular zone have keratin filament
and keratohyaline granule.

13. STRATUM LUCIDUM
On palms and soles there is stratum lucidum
in between stratum granulosum and stratum
corneum layers.
These cells are still nucleated, and may be
referred to as ‘transitional’ cells.

14. STRATUM CORNEUM
Outer most layer of skin(epidermis).
20 to 25 cell layer thick.
Cells (corneocyte) are flattened and have lost their
nuclei and cytoplasmic organelles.
Cells are stuck together by lipid in intercellular space.
Keratin filament aggregate into disulphide cross link
filament.
Contain highly insoluble cornified envelope.

15.  Stratum cornuem barrier is formed by a two-compartment
system of lipid depleted, protein enriched corneocyte
surrounded by a continuous extracellular lipid matrix.
 Desquamation: degradation of lamellated lipid + loss of
residual intercellular demosomal interconnection.

16. OTHER CELL OF EPIDERMIS
MELANOCYTE
-Melanosome contain melan
-Mostly basal
melanocyte to keratinocyte ratio
sun exposed part 1:1
sun protected part it is 1:10
-Dendritic
-No desmosome.
 Pale staining cytoplasm with ovoid nucleus and pigment containing
melanosomes.
 Melanosome contain melanin.

17. Merkel cells(0.2-5%)
-Mechanoreceptor in area of high
tactile sensitivity
-Basal cell
-No Dendrites
-Desmosomes
• Pale – staining cytoplasm with
lobulated nucleus.
• Margin of cells project cytoplasmic
‘spines’ towards keratinocytes.
• Contains neurosecretory granules.
Fig: Merkel cell in human epidermis. The dermis (d) with collagen fibres
is seen in the lower part of the picture;
b, basement membrane;
de, desmosomes making connections with adjacent basal keratinocyte;
g, spherical granules (see inset);
n, nucleus of Merkel cell; t, tonofi laments.

18. Lagerhan’s cell
-Antigen presenting cell.
-Suprabasal.
-Dendritic
-No desmosome.
-It recognizes, uptake, process and
present antigen to sensitize
lymphocyte and important in induction of
delayed hypersensitivity.
 On electron microscopy clear cytoplasm
with lobulated nucleus , well developed
ER(endoplasmic reticulum) ,golgi body and
lysosome.
 Rod or racquet shaped granules – Birbeck
granules.
Fig: Langerhans’ cell with its characteristically
indented nucleus, situated
between keratinocytes.
Inset: Langerhans’ cell granules showing racquet-
shaped profiles.