development structure and function of skin.pdf

Development, strucutre and function of skin

1. Structure and function of
skin
Presenter:DR ANJALY A
Moderater:DR SRAVYA
Professor and HOD: DR GNR NETHA
DEPARTMENT OF DVL

2. INTRODUCTION
●Largest organ weighs over 5 kg
●Consists of stratified, cellular epidermis, underlying dermis separated by a
dermal epidermal basement membrane

4. DEVELOPMENT OF SKIN

5. EMBRYOLOGY OF EPIDERMIS

7. DEVELOPMENT OF DERMIS

9. ULTRA STRUCTURE OF THE SKIN
EPIDERMIS
●Stratified squamous epithelium
●Thickness - 0.4 mm on eyelids to 1.5 mm on palms and soles
●Contents
Keratinocytes, melanocytes,langerhans cells and merkel cells
Hair follicles,apocrine glands and sweat glands

10. LAYERS OF EPIDERMIS
1.Stratum corneum
2.Stratum lucidum
3.Stratum granulosum
4.Stratum spinosum
5.Stratum basale

12. STRATUM BASALE
•Stratum Basale
• Continuous layer ,generally one cell thick but can be 2 3- cell layer thick in glabrous
skin and hyperproliferative skin.
• Basal cells are small and cuboidal with large dark staining nuclei and dense
cytoplasm.
• It contains ribosomes, tonofilaments and melanosomes transferred from
melanocytes by phagocytosis.
• It contains three types of cells: stem cells, transient amplifying cells and post mitotic
cells.

13. STATUM SPINOSUM
• Aka prickle cell layer.
• Contains 8-10 layers of cells.
• Cells are polyhedral with a round nucleus.
• The cells in upper spinous layer are more larger and flattened and contains
"lamellar granules".
• They are named spinous for the spine like appearance which corresponds to
abundant desmosomes

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14. STRATUM GRANULOSUM
It is 2 5- cells thick.
• Contains intracellular granules of keratohyalin.
• lamellar granules or odland bodies
• They discharge their lipid component into intercellular space playing an important
role in barrier function and intercellular cohesion.

16. STRATUM LUCIDUM
●In palmoplantar skin it is an additional layer
●Present between S.granulosum and S.corneum
●It is electron-lucent because presence of Eleidin granules (refractile)
●These cells are still nucleated and may be referred as transitional cells.

17. STRATUM CORNEUM
●Outermost skin layer.
● cells(corneocytes) are flattened with no nuclei and cytoplasmic organelles.
●Filagrin helps in keratin filament aggregation and break down into individual amino acid
- natural moisturising factor
Mutation in filagrin gene -Ichthyosis vulgaris, Atopic eczema, systemic allergies.
● The corneocyte has a highly insoluble, cornified envelope within the plasma
membrane formed by soluble protein precursor called as involucrin and loricrin
●Contains several lipids

19. Changes from stratum basale to stratum corneum
●Shape of cells flattens
●Nucleus – Lost
●Water content
decreases
●Keratin increases
●Epidermal transit time
approx. 28 days

20. BASEMENT MEMBRANE ZONE
Composed of the hemidesmosome anchoring filament - anchoring fibril complex at
the dermo epidermal junction.
Serves as an important structure for the attachment of cells, template for tissue
repair, influences differentiation, morphogenesis and apoptosis of epithelual cells.
Four major ultrastructural subregions
●Basal keratinocyte
●Lamina lucida
●Lamina densa
●Sublamina densa

21. Basal keratinocyte
Hemidesmosome attaches basal keratinocytes to extracellular matrix
Hemidesmosome plaque consists of plectin, BP230, BP180 and integrins.
BPAg1:230-kDa protein
Attaches intermediate filaments to hemidesmosomal plaque
BPAg2:180-kDa protein
Transmembrane protein, interacts with BPAg1, integrin and plectin
intracellularly

22. Molecular structure of components of BMZ

23. Lamina lucida
Electron lucent region.
It has anchoring filaments that consists of laminins, BP180, nidogen and integrins.


●Contains laminibs, type IV collagen, nidogen and heparin sulfate proteoglycan
Sublamina densa
●Consists of collagen VII, which binds types I and IV collagen, laminin 332,microfibrls
and microtgread like fibers.
Lamina densa

25. Cells of epidermis
1.Keratinocytes
2.Melanocytes
3.Langerhan cells
4.Merkel cells

26. Keratinocytes
●Ectodermal in origin
●Composed of intermediate filaments, the predominant being keratin.
TYPES OF KERATIN
1.Acidic keratins:k9-k20, chromosome 17
2.Basic keratin: K1-K8, chromosome 12
The acidic and basic keratins are paired together

27. Keratin expression of various cells
Simple epithelia K8/K18
Stratified squamous epithelium and basal
layer
K5/K14
Spinous layer K1/K10
Basal keratinocytes in bulge of hair K15
Palmoplantar epidermis K9
Superficial interfollicular epidermis K2
Merkel cells K8,k18,k19,k20 K20 (specific)

28. INTERCELLULAR JUNCTIONS

29. Intercellular junctions
1.Desmosomes
Specialised regions of plasma membranes that link cells to each other and also
connect IF to the plasma membrane.
Rich in transmembrane glycoproteins called desmogleins and desmocollins
Desmogleins(Dsg1-3) and desmocollin(Dsc1-3)
Dsg1 and dsc1 are more in upper epidermis and Dsg 3 and Dsc3 are more
expressed in basal keratinocytes.

31. 2) Adherens junction

Electron dense transmembrane structures that
associate with actin skeleton.
• Their main component is calcium dependent E-
cadherin.
• The main linkage to actin cytoskeleton is via alpha
- catenin.

32. 3) Gap junction

● Comprise a cluster of intercellular connections known as connexons.
●They allow transfer of ion and molecules across the cell


4) Tight junction

●They are major regulator of permeability of epithelium key component of
skin barrier integrity.
●They are composed of transmembeane and intracellular molecules that
occludin, junction adheren molecule and and claudins.

33. MELANOCYTES
●Dendritic cells that are involved in pigment synthesis
●Derived from neural crest.
●Melanocytes are incontact with keratinocutes but do
not form junction with them at any level.
●One melanocyte is in contact with 36 keratinocutes
forming an epidermal melanin unit
●Density of melanocytes donot vary with races

34. Melanosome and melanin synthesis

35. Applied aspects
In vitiligo- melanocytes are destroyed
In albinism- number of melanocytes normal, but unable to synthesise fully
pigmented melanosomes
Freckles-localised increase in pigment by normal number of melanocytes.
Nevi- benign proliferation of melanocytes
Melanonas- manignant counterpart of nevi.

36. Langerhans cells
●Dendritic cells found in stratum spinosum
●Express langerin(CD207) , CD45, CD1a, S100, CD34, vimentin, actin
●Contain reniform nuclei with characteristic birbeck granules seen on electron
microscopy
●Play an important role in cutaneous immune mechanism, antigen
presentation, stimulation of Tcell response.
●Cells are implicated in the pathogenesis of allergic contact dermatitis,
cutaneous leishmaniasis, HIV infection
●In psoriasis, sarcoidosis, contact dermatitis- number reduced

38. Merkel cells
Slow adapting type 1 mechanoreceptor
Found in hairy skin and glaborous skin digits, lips, region of oral cavity, and outer
root sheath of hair follicle.

39. Hair follicle

40. Apocrine glands

Coiled tubular gland open above the sebaceous gland or directly on the skin surface.
Present on axilla, genital, areola, nipple, vermillion border of lips, perianal area
Modified apocrine glands
●External ear canal- ceruminous gland
●Eyelids- molls glands
●Breast- mammary glands

41. Sebaceous gland
1.Fully developed at birth, enlarge at puberty in response to increased
androgens
2.Found everywhete on skin except palms, soles and prepuce.
3.They consist of several lobules that empty into a sebaceous duct
4.Usually associated with hair follicle bit free sebaceous glands not associated
with hairs are found in specific locations
●Montgomery’s areolar tubercles
●Fordyce spots
●Meinomian glands
●Glands of zeis
●Tyson’s gland

42. DERMIS
Integrated system of fibrous filamentous and
amorphous connective tisse that accomodates
●Cellular components
●Connective tissue components
●Ground substance

43. Cellular components
●Fibroblast
●Lymphocytes
●Macrophages
●Mast cells
●Histiocytes

44. Connective tissue components
●Collagen
●Elastin
●Reticulin
●Major type is type 1 collagen(70%)



●Water, electrolutes, mucopolysaccrhide and plasma protein
Ground substance

45. Layers of dermis
1.Superficial papillary dermus
2.Deep reticular dermis
Both are separated by subpapillary plexus
of blood vessels

46. Papillary dermis v/s reticular dermis
Superficial 1/10th part of dermis Lower 9/10th part of dermis
Interdigitates with ridges of undersurface of
epidermis
Merges with subcutaneous fat
Small bundles of collagen fibers and elastic
fibers
Large diameter collagen fibres
Mature elastic fibres not found Mature elastic fibres form superstructure
around collagen bundles
Higher metabolic rate Lower metabolic rate

48. Ground substance
Supporting matrix of dermis consisting of PGs and GAGs
Bind large amount of water therby influencing dermal volume and compressibility
Bind to growth factors thereby influencing proliferation, tissue repair and
morphogenesis
Major PGs in adult dermis are chondroitin sulphate/ dermatan sulphate and
heparan and chondroitin-6 sulphate proteoglycan

49. Connective tissue matrix
Main fibrous connective tissue of dermus is made of collagen and elastic
connective tissue.
80-90% of collagen fibers of dermis is type 1 collagen
8-10%- type 2
●TypeI- reticular dermis
●Type III and V- papillary dermis and around adnexa
●Type IV-basal lamina
●TypeVI- interfibrillar spaces
●Type VII-anchoring fibrils between lamina densa and sublamina densa

50. Elastic tissue
It forms a continous network throughout the dermis that extend from lamina densa
of DEJ to the connective tissue of subcutis
Because of their elasticity, they maintain normal configuration of cella

51. Subcutaneous tissue

52. SUBCUTANEOUS TISSUE
Adipocyte is the primary cell
Consists of lobules of adipocytes separated by thin fibrous septa through which small
blood vessels pass
Provide insulation
Act as calorie reserve
Release hormine leptin which I nhibit insulin production
Regulates hunger and energy metabolism
Tissue remodelling and photocytosis

53. Functions of skin
1)Barrier function
●Permeability barrier
●Barrier to microorganisms and chemicals
●Barrier to UV radiation
2) Regulation of body temperature
3) sensory function
4) immunological function
5) vit D sunthesis
6) vit E secreation
7) transport of metabolotes and wound repair

54. Thank you