skin

HISTOLOGY OF SKIN (Derma)(Integument)(Cutaneous layer)

Skin

Largest Single Organ( 15% to 20% of body weight)
Surface Area of (1.5 to 2 m²)
Composed of (Epidermis & Dermis)
Skin Appendages

Layers of Skin

Appendages of SkinHairNail Sweat glandsSebaceous glands

Functions of skin

Protection
Sensation
Thermoregulation
Metabolic
Cosmetic

Skin is a permeability barrier against excessive loss or uptake of water

Types of skinAccording to thickness of epidermis

Thick & Thin Skin

Layers of Epidermis

Stratum Basale
Stratum Spinosum
Stratum Granulosum
Stratum Lucidum
Stratum Corneum

Layers (strata) of Epidermis in (Thick Skin)

Layers of Epidermis in (Thin Skin)

Basale

Spinosumm
Granulosum
Corneum

Cytoskeleton in Stratum basale

• keratins, cytoskeletal intermediate filaments
• Desmosomes
• Hemidesmosomes

Desmosomes

Stratum Germinativum Combined zone of basal layer & cells Just above it that may still divide

Stratum Basale

Stratum Spinosum
Loss of intercellular junctions lead to blistering disorder (Pemphigus)

Stratum Granulosum& Stratum Lucidum (Thick skin)

corneum

lucidum
Granulosum
Spinosum

Keratohyaline Granules

Ultrastructural lamellar granulesexocytosis

Cells of skin

• Keratinocytes
• Melanocytes
• Langerhans cells (dendritic cells)
• Merkel cells(tactile cells)

Keratinocytes & other cells

Keratinocytes of stratum spinosum(Thickest layer with tonofibrils)

Psoriasis Changes in Epidermal turnover time

Melanocyte
Originate from neural crest
Give the skin it’s color
Present in stratum basale
Melanin granules migrate through the cytoplasmic extensions to enter keratinocytes

Melanocyte

Contain pigment (Eumelanin or Pheomelanin)
They have pale-staining, rounded cell bodies
Attached by hemidesmosomes to the basal lamina
lacking attachments to the neighboring keratinocytes
Keratinocytes are the main depots of melanin


Melanocytes are pale staining cells

Melanocyte Extensions

Melanosome Formation

Darkening of the skin (tanning) after exposure to solar radiation is a two-step process

Physicochemical reaction darkens preexisting melanin
Paracrine factors secreted by keratinocytes experiencing increased UV radiation

Main Factors Affecting Skin Color:

MELANIN

CAROTENE

SKIN THICKNESS

HEMOGLOBIN

Changes in pigmentation of the skin (Hypo- or Hyper-pigmented skin)

AlbinismDeficiency of tyrosinase enzyme lead to Hypopigmentation

Vitiligo Loss of skin melanocytes lead to Depigmentation

Mole Normal proliferation of melanocyte

Melanoma Dividing rapidly & malignantly transformed melanocytes

Langerhans Cells

Network of Langerhans Cells (APCs)

Merkel (Tactile cells)

Merkel (Tactile cells)

Granules

Nerve end

Dermal-Epidermal InterdigitationsPeg & socketRidges & grooves

Dermal-Epidermal Interdigitations

Irregular junction between the dermis and epidermis
Projections called (dermal papillae) interdigitate with invaginating (epidermal ridges)
To increase surface of contact & strengthen adhesion of the two layers

SEM  25

Finger& Foot prints (Dermatoglyphs)
loops, arches& whorls

Desmosomes &Hemidesmosomes

Dermo- Epidermal Junction Abnormality

Friction Blisters

Dermis

layer of connective tissue
Thickness varies with the region of the body
The surface of the dermis is very irregular

Papillary layer

Includes the dermal papillae
Consists of thin layer of loose connective tissue
Types I and III collagen fibers
Fibroblasts and scattered mast cells, macrophages & other leukocytes
From this layer, anchoring fibrils of type VII collagen insert into the basal lamina


Reticular layer
Much thicker than papillary layer
Dense irregular connective tissue (mainly bundles of type I collagen)
More fibers & fewer cells than the papillary layer
A network of elastic fibers is also present, providing elasticity to the skin
Between the collagen and elastic fibers are abundant proteoglycans rich in dermatan sulfate

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