SKIN : STRUCTURE AND FUNCTION Dr. M. Joseph Department of Pathology LHSC
Jan 04, 2016
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