SKIN : STRUCTURE AND FUNCTION

Dr. M. Joseph Department of Pathology

LHSC

Which is the largest organ of the body

Objectives

• Structure and function of various layers of skin

• Histologic changes in the epidermis - Spongiosis

- Hyperkeratosis

- Parakeratosis

- Acanthosis

- Lichenification

- Acantholysis

Skin Functions

1) Protection

2) Thermoregulation

3) Sensation

4) Metabolic

Skin Structure

Three Layers

a) Epidermis

b) Dermis

c) Subcutaneous adipose tissue Thickness of skin (for information only)

Epidermis +dermis = 1.5-4.0 mm

Epidermis only = 0.05-0.1 mm

Skin Structure

Basement membrane

Apocrine sweat gland

Epidermis: Keratinized stratified squamous epithelium

S. Corneum (4)

S. Granulosum (3)

S. Spinosum (2)

S. Basalis (1) Merkel cell

• 4 layers • >95% of epidermal cells are keratinocytes, • keratinocyte replication and maturation - keratinization • 3 specialized cells (Melanocyte, Langerhans cells, Merkel

cells)

Epidermis:4 Layers Under the microscope

• Stratum Corneum

• Stratum Granulosum

• Stratum Spinosum

• Stratum Basalis

Skin Types/Mucosa

Compact Thickened Stratum Corneum

Thin skin Thick skin, palm, sole

Mucosa

No stratum Corneum

Function of 3 Specialized Cells in Epidermis

Merkel cell

Melanocytes - melanin synthesis Langerhans cells - immunologic function Merkel cells -tactile function

Dendritic melanocyte –keratinocyte unit

Melanin production and Transfer

Melanin in Melanosome

Melanocyte

Keratinocyte

Melanosome caping keratinocyte nucleus- gives protection of DNA against UV injury

Melanocytes in dark and light skin

Dark skin White skin

The number of melanocytes per unit area of the skin are the same

Light skin Dark skin

Dark skin has increased production of melanosomes, and melanin More transfer of melanin to keratinocytes Slower rate of degradation of melanosomes

Dermis: upper papillary dermis and lower reticular dermis

• Collagen

• Elastic fibers

• Ground substance

• Nerves

• Blood vessels

Skin Vasculature

Skin Appendages (adnexal structures)

• Sweat glands

• Hair follicles

• Sebaceous glands

• Nail, hair

Skin Appendages

Apocrine sweat g l and

Pilo-sebaceous unit

ACNE

- structure including histology of pilosebaceous unit

- pathophysiology of acne

- correlate clinical lesions with pathology

Normal Pilosebaceous Unit

Hair follicle

Sebaceous gland

Acne: a disease of pilosebaceous unit Open comedone Closed comedone

The mouth of the dilated hair follicle is widely open in open comedone and closed in closed comedone. The lumen contains keratin, lipid and bacteria Rupture of closed comedones usually lead to inflammatory acne.

Open Comedones Closed Comedones(blackheads) (whiteheads)

Inflammed acne (pustular)

Acne: pathogenesis

• Primary event: development of comedones

• Androgen dependent

• Abnormal desquamation of keratinocytes in the pilosebaceous unit

• Increase in sebum production

• Overgrowth of Proprionibacterium acnes

• Rupture of comedones and Inflammation

Skin Structure (molecular level)

• Epidermal Desmosome

• Epidermal Basement Membrane Zone

Keratinocytes Desmosome

Desmosome

Plaque

Core

The molecular structure of thedesmosome

Desmoplakin 1 (245 kd) Desmoplakin 2 (215 kd)

Plaque

Core

Plakoglobin (85 kd)

Plakophilin 1,2,3 (75 kd) Keratocalmin (250 kd)

Desmoglein 1 (165 kd) Desmoglein 2 (Colon)

Desmoglein 3 (130 kd) Desmocollins: 1a, b 2a, b 3a, b

Other Plaque Components: Envoplakin, Perlplakin, and Corneodesmosin (Keratinocyte Envelops)

Pemphigus vulgaris antigen is Desmoglein 3, in core

Basement Membrane Zone

Hemidesmosome

Lamina lucida

Lamina Anchoringdensa fibrils

Bullous Pemphigoid antigen is in Hemidesmosome

Basement Membrane Zone

Bullous Pemphigoid antigens are BPAg1 and BP Ag2, in Hemidesmosome

Molecular Structure of Basement Membrane Zone

For information only

Epidermal Changes: Correlate Pathology with Clinical

Appearance

SPONGIOSIS: intercellular edema (1), may cause microvesicles (2)

2

1 Normal skin

Acute dermatitis (Spongiotic dermatitis)

Juicy papule Spongiosis

1) Hyperkeratosis: thickening of the stratum corneum

2) Parakeratosis: nuclei preserved 3) Acanthosis: epidermal hyperplasia (stratum spinosum thickened)

1&2

3

Normal skin

Psoriasis

Acanthosis Plaque lesion with a silvery scale Hyperkeratosis

Parakeratosis

Lichenification: thickening of the skin with increased skin markings

Normal skin Thickening of all layers of skin

Lichenification

Pemphigus vulgaris

Acantholysis: loss of desmosomal connection, keratinocytes round up and separate

Flaccid bulla with Intraepidermal bullafocal erosion

Objectives

• Structure and function of various layers of skin • Changes in the keratinocytes

- Hyperkeratosis, parakeratosis - Acanthosis - Spongiosis - Lichenification - Acantholysis

Post lecture reading: Interesting facts on structure & function….webCT Not examinable

QUIZ

1) Which cell produces melanin ?

2) Name the gland involved in acne ?

3) Name the odor producing gland ?

4) What is a desmosome ?

5) Function of Langerhan’s cell ?

6) Layers of basement membrane zone?

7) Where is vit D synthesized ?

1 2

Practice QUIZ

3

Thank You