Normal histology of skin with pathological skin conditions , Special stains and IHC

1. NORMAL HISTOLOGY OF SKIN
Dr. Sunil Mitran
Department of Pathology
Moderator: Dr. Subhashini, Assistant Professor, Department of
Pathology, SVMCH&RC

2. INTRODUCTION
• The skin is considered the largest organ of the body and has many
different functions.
• The skin is divided into three main layers,
- The epidermis
- The dermis
- Hypodermis or subcutaneous tissue

3. Functions of
Skin
Protective function:
• It is the first line of defense. It protects our body from infection,
pathogens, and harmful UV irradiation.
Sensory function:
• Free nerve endings on the skin are sensitive to pain, touch, heat and
cold, resulting in either voluntary or reflex activities.
Secretory function:
• Sweat help in temperature regulation and sebum makes skin smooth.
Heat regulatory function:
• Sweating and cutaneous blood flow help in temperature regulation
Excretory function:
• Through secretion of the glands of the skin – water, salt, fatty
substance and urea are excreted
Synthetic function:
• Helps in synthesis of natural Vitamin D and melanin pigment also.
Water balance:
• Skin serve a useful means in regulating water balance of the body by
perspiration.

4. Epidermis
• The most superficial layer of the skin and lined by stratified squamous
keratinized epithelium
• The first barrier of protection from the invasion of foreign substance
• Contains Keratinocytes, Melanocyte, Langerhans cell, Merkel cells

5. Layers of
epidermis
• It is divided into 5 layers
from superficial to deep
• Stratum corneum
• Stratum lucidum
• Stratum granulosum
• Stratum spinosum
• Stratum basale
Superficial
Deep

6. Stratum basale
• Provides the germinal cells
necessary for the regeneration of
the layers of epidermis
• Separated from the dermis by a thin
layer of basement membrane
• After a mitotic division, a newly
formed cell will undergo a
progressive maturation called
keratinization as it migrates to the
surface.

7. Stratum Spinosum
• The cells that divide in the stratum
basale soon begin to accumulate many
desmosomes on their outer surface
which provide the characteristic prickles
of the stratum spinosum which is often
called the prickle-cell layer
• 5-10 layer thickness with keratinocytes
larger than basal cells

8. Acanthosis Acantholysis

9. Stratum Granulosum
• 1-3 layers of flattened cells.
• The progressive maturation of a
keratinocyte is characterized by the
accumulation of keratin, called
keratinization.
• The cells of the stratum granulosum
accumulate dense basophilic
keratohyaline granules. It contains
keratin, profilaggrin, loricrin and
trichohyalin proteins.
• These granules contain lipids, which along
with the desmosomal connections, help to
form a waterproof barrier that functions
to prevent fluid loss from the body.

10. Stratum Lucidum
• The stratum lucidum is normally only
well seen in thick epidermis and
represents a transition from stratum
granulosum from stratum corneum
• Location: Palms of the hand and soles
of the feet.

11. Stratum Corneum
• The stratum corneum is the outermost
layer of the epidermis, consisting of
dead cells (corneocytes) that lack
nuclei and organelles.
• Desquamation, the process of cell
shedding from the surface of the
stratum corneum, balances
proliferating keratinocytes that form in
the stratum basale
• Duration of desquamation- 2- 4weeks.

12. Stratum corneum
Hyperkeratosis Parakeratosis

13. Dyskeratosis Spongiosis

14. TERMS DEFINITION
Acanthosis Thickening of epidermis in stratum spinosum
Hyperkeratosis Thickening of stratum corneum
Parakeratosis Retained nucleus in stratum corneum
Spongiosis Intraepidermal intercellular edema
Dyskeratosis Abnormal, premature keratinization of keratinocytes
Acantholysis Disruption of intercellular junctions between epidermal
keratinocytes, resulting in acantholytic cell
Orthokeratosis Hyperkeratosis without parakeratosis
Exocytosis Presence of inflammatory cell within the epidermis in association
with spongiosis
Interface dermatitis Dense inflammatory infiltrate in dermo-epidermal junction

15. Types of epidermal cells
Keratinocytes
• They are responsible for keratin formation
• Formed of many layers that continuously
shed and regenerate every 2 – 4 weeks

16. Melanocytes
• Dendritic cell
• Found in between cells of the basal
layer
• They form melanin by tyrosinase from
tyrosine amino acid by converting it to
dioxyphenyl alanine
• Ratio of melanocytes to keratinocytes
– 1:10

17. Langerhans cells
• They are dendritic cells (antigen-presenting immune cells)
of the skin.
• Found in upper layer of stratum spinosum
• Have branched shaped & central nuclei
• Represent 3-8% of epidermal cells
• Difficult to see in routine section staining
• IHC S100, CD207a and EM will be useful for identification

18. Merkel cells
• Found in basal cell layer
• They are modified epidermal cells
because of sensory nerve fibers form
terminal disk under merkel cells
• Significance - mechanoreception

20. Dermis
• Thermoregulation
• Supply the avascular epidermis with
nutrients
• The dermis is typically subdivided into two
zones, a papillary dermis and a reticular
layer
• The dermis contains mostly fibroblasts
which are responsible for secreting
collagen, elastin, and ground substance
that gives support and elasticity of the
skin.

21. Papillary dermis
• The papillary dermis contain vascular
networks that have two important
functions.
• The first being to support the avascular
dermis with vital nutrients and
• Secondly to provide a network for
thermoregulation
• It also contains the free sensory nerve
endings and structures called Meissners
corpuscles also called mechanoreceptors
which is responsible for light touch

22. Reticular dermis
• The reticular layer of the dermis consists of mainly loose
connective tissue
• It is important in giving the skin it overall strength and
elasticity, as well as housing other important epithelial
derived structures such as gland and hair follicles

23. Type of cells in dermis
Fibroblasts
• It is a type of cell that synthesizes the extracellular
matrix and collagen.
• It plays a critical role in wound healing.
• They have a branched cytoplasm surrounding an
elliptical, speckled nucleus having two or more nucleoli.
• Inactive fibroblasts which is also called as fibrocytes, are
smaller and spindle shaped.

24. Mast cells
• It contains many granules rich in histamine and heparin. Although
best known for their role in allergy and anaphylaxis
• It plays important protective role as well as involved in wound healing
and defense against pathogens
• Inflammatory cells
Adipocyte – another component cell type in dermis
Apart from these cells, Dermis also composed of matrix components
such as collagen (strength), elastin(elasticity).
Type of cells in dermis

25. Skin Appendages
• Hair follicles and hair
• Sweat glands – Eccrine or merocrine sweat gland
Apocrine sweat glands
• Sebaceous glands
• Nails

26. Hair and hair follicles
• Hair – Produced by hair follicle which are made of hard keratinized
epithelial cells
• Melanocytes provide pigment for hair color

27. Hair anatomy
• Central medulla
• Cortex surrounds medulla
• Cuticle on outside of cortex most heavily keratinized

28. Associated hair structures
Hair follicle
• Dermal and epidermal sheath surround
hair root
Arrector pili muscle
• Smooth muscle
• pulls hair upright when cold or
frightened
Sebaceous gland

29. Sweat glands
Eccrine sweat gland Apocrine sweat gland
Merocrine secretion Secretion may contain pheromones and begins at
puberty and is stimulated during emotional distress
Empty directly onto skin surface Empty into hair follicle
Location: almost all over body especially abundant on
palms & soles
Location: armpits, groin, nipples
Clear, watery secretion Viscous, cloudy secretion- good nutrient source for
bacteria
Apocrine glands in the axilla
Eccrine glands in deeper reticular dermis and subcutaneous fat

30. Sebaceous glands
• Sebum discharged mostly into hair follicles (lubrication & bactericidal)

31. Nail
• It is scale like modifications of the
epidermis
• Heavily keratinized
• Stratum basale extends beneath the nail
bed
• Responsible for nail growth
• Lack of pigment makes them colorless

32. Cell type Location Characteristic
structures
Histochemical stain Immunostains
Keratinocyte Entire epidermis Tonofilament,
Desmosomes
Cytokeratin
Melanocyte Basal cell layer Melanosomes Fontana-Masson,
DOPA, tyrosinase
S100,MART-1,Melan
A
Langerhans cell Mid Epidermis Birbeck granules ATPase S100,CD1a,Langerin
Merkel cell Basal layer,
Buldge of hair follicle
Neurosecretory
granules
NSE CK20,Chromogranin,S
ynpatophysin
Fibroblast Entire dermis Spindle shaped with
prominent Rough ER
Masson trichome for
collagen
Vimentin,
Procollagen,CD34
Mast cell Perivascular space Scroll- containing
secretory granules
Giemsa, toludine blue C-Kit, Tryptase
Macrophage Perivascular space Lysosomes CD68,CD163
Eccrine/Apocrin
e gland
Epidermis and dermis Ducts and secretory
coils containing
granules
PAS for apocrine
gland
EMA, CEA
ROLE OF SPECIAL STAINS AND IHC

33. Skin biopsy
• Techniques of Skin biopsy – Punch biopsy, shave biopsy, saucerization
biopsy, wedge biopsy, Incisional biopsy, Excisional biopsy

34. REFERENCES
• Sternberg’s diagnostic surgical pathology
• Lever’s histopathology of the skin
• Wheater’s pathology

35. THANK YOU