Nboost Doctor brochure - Flipbook - Page 13
What are the functions of the epidermis?
REASSESSING THE EPIDERMIS
Keratinocytes are characterised by structural components acquired throughout the epidermal cell
differentiation process:
What is the epidermis?
1. Intercellular junctions – seal adjacent
The epidermis is the outermost layer of the skin composed of multiple layers and several cell types.
Cell types
Stratum
corneum
Corneocytes
(dead keratinocytes)
1. Maintenance of homeostasis
Keratinocytes
2. Protection from infection, physical
damage and chemical injury via two
important barriers2
(found only in thick skin)
Stratum
granulosum
Functions
1
Dendritic cell
Stratum
spinosum
Lanherans
Merkel cell
Stem cell
Stratum
basale
Melanocyte
-
Corneocytes (Stratum Corneum) –
prevent the entry of foreign substances,
microorganisms and loss of water
Keratinocytes (Subjacent Layers) – seal the
cells and produce protective biomolecules
3. Thermoregulation and hydration3
4. UV protection and skin pigmentation4
Dermis
How does the epidermis change as we age?
The visible effects of ageing
on the epidermis
Thin skin
Appearance of wrinkles
Skin dryness
Uneven pigmentation
Increased vulnerability to injury
Enlarged pores and rough texture
Young
Old
Epithelium
Basement
membrane
Papillary
dermis
Hydration & Transepidermal Water Loss (TEWL)
Reduced expression of aquaporins (AQP), water channels in the
membrane,5 together with changes in the main component of the
skin’s natural moisturising factor, decreases the binding capacity
of water.6
© 2008 Mine et al.
2. Extracellular matrix – extracellular
3. Keratin cytoskeleton – internal structure
that confers keratinocytes high deformation
resistance 70 times more than other cells
A primary factor for preserving the skin barrier is
its capacity for cell renewal, which is affected by
keratinocyte’s differentiation and proliferation rate.
Maintenance of water-ion balance6,11
The epidermis plays a fundamental role in
internal homeostasis by controlling the
exchange of substances, especially water
and ions, with the external environment.
The epidermis has multiple biochemical
components with selective properties to
preserve this functionality.
During keratinocyte migration towards the
most superficial layers, increased acidity
causes filaggrin to become degraded into
small, free metabolites and amino acids,
forming natural moisturising factors (NMF).
Normal
epidermis
Dry, brittle and
scaly epidermis
Attack from
external factors
Epidermal
layer
AQPs are essential for maintaining waterion balance of the cell by transporting
water and small molecules of solute across
epidermal cell membranes.
Skin surface
lipids
Increased
transepidermal
water loss
Structure & thickness
Keratinocytes, become shorter and fatter as skin ages, while
corneocytes become larger as a result of decreased epidermal
turnover. The loss of dermal papillae and reduced interdigitation
between layers results in less resistance to shearing forces.7
Keratinocyte proliferation & differentiation
Largely due to the keratin cytoskeleton acquired throughout the
epidermal cell differentiation process, keratinocytes have a high
deformation resistance, contributing to their protective action.
This protection is reduced with age.8
Melanin & erythema
Reticular
dermis
Protection against mechanical and chemical
injury depends directly on the structural epidermal
integrity – a stratified arrangement of cell layers with
keratinocytes bonded by intercellular junctions and
extracellular matrixes.
keratinocytes
environment to support cell adhesion,
intercellular communication and regulation
of cell differentiation
Sublayers
Stratum lucidum
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Protective barrier against mechanical and chemical injury10
Uneven distribution of pigment cells, local loss of melanocytes
(decreasing at a rate ranging from 8 to 20% per decade),
and changes in their interaction with keratinocytes causes a
heterogeneity in skin color.9
Immunological defense12
Epidermal cells – including keratinocytes,
melanocytes, and Langerhans cells – can produce
multiple cytokines, reinforcing the epidermis as
a tissue that is immunocompetent and active in
creating an immunological barrier.
The epidermis has an active role in the inflammatory
response and in the preparation of more efficient
systemic immune responses with improved B- and
T-cell activation.
1
Blanpain C, Fuchs E. Epidermal homeostasis: a balancing act of stem cells in the skin. Nat Rev Mol Cell Biol. 2009 Mar;10(3):207-17 2Nguyen AV, Soulika AM. The Dynamics
of the Skin’s Immune System. Int J Mol Sci. 2019;20(8):1811. 3Russell-Goldman E, Murphy GF. The Pathobiology of Skin Ageing: New Insights into an Old Dilemma. Am J Pathol.
2020;190(7):1356-69. 4Brenner M, Hearing VJ. The Protective Role of Melanin Against UV Damage in Human Skin. Photochem Photobiol. 2008;84(3):539-49. 5Hara M, Verkman AS.
Glycerol replacement corrects defective skin hydration, elasticity, and barrier function in aquaporin-3-deficient mice. Proc Natl Acad Sci USA. 2003;100(12):7360-65.
6
Kezic, S., Kammeyer, A., Calkoen, F., Fluhr, J.W., Bos, J.D. Natural moisturizing factor components in the stratum corneum as biomarkers of filaggrin genotype: evaluation
of minimally invasive methods. Br. J. Dermatol. 2009; 161:1098–1104. 7Farage MA, Miller KW, Elsner P, Maibach HI. Characteristics of the Ageing Skin.
Adv Wound Care (New Rochelle). 2013;2(1):5-10. 8Lulevich V, Yang HY, Isseroff RR, Liu GY. Single cell mechanics of keratinocyte cells. Ultramicroscopy. 2010;110(12):1435-42.
9
Ortonne JP. Pigmentary changes of the ageing skin. Br J Dermatol. 1990;122(35):21-8. 10Lulevich V, Yang HY, Isseroff RR, Liu GY. Single cell mechanics of keratinocyte cells.
Ultramicroscopy. 2010;110(12):1435-42. 11Tzaphlidou, M. The role of collagen and elastin in aged skin: an image processing approach. Micron. 2004; 35:173–177.
12
Brazzini, B., Ghersetich, I., Hercogova, J., Lotti, T. The neuro-immuno- cutaneous-endocrine network: relationship between mind and skin. Dermatol. Ther. 2003;16: 123–131.
© Mine S, Fortunel NO, Pageon H, Asselineau D (2008) Ageing Alters Functionally Human Dermal Papillary Fibroblasts but Not Reticular Fibroblasts: A New View of Skin
Morphogenesis and Ageing. PLoS ONE 3(12): e4066. doi:10.1371/journal.pone.0004066
