The epidermis includes five main layers: the stratum corneum, stratum
lucidium, stratum granulosm, stratum spinosum, and stratum
germinativum.
LEARNING OBJECTIVE [ edit ]
Outline the progression of kerantinocytes through epidermal strata from deepest to most
superficial
KEY POINTS [ edit ]
The epidermis provides a protective waterproof barrier which also keeps pathogens at bay and
helps regulate body temperature.
The main cell types of the epidermis include stratifiedsquamous keratinzed epithelium, as well
as Merkel cells,melanocytes and Langerhans cells.
The main layers of the epidermis are: stratum corneum, stratum lucidium, stratum granulosm,
stratum spinosum,stratum germinativum (aka stratum basale).
Keratinocytes in the stratum basale proliferate during mitosis and the daughter cells move up the
strata changing shape and composition as they undergo multiple stages of celldifferentiation.
TERMS [ edit ]
keratinocyte
Keratinocyte is the predominant cell type in the epidermis, the outermost layer of the skin,
constituting 95% of the cells found there. Those keratinocytes found in the basal layer (Stratum
germinativum) of the skin are sometimes referred to as "basal cells" or "basal keratinocytes. "
stratum germinativum
The stratum basale (basal layer, sometimes referred to as stratum germinativum) is the deepest
layer of the five layers of the epidermis.
Merkel cells
Merkel cells or Merkel­Ranvier cells are oval receptor cells found in the skin of vertebrates that
have synaptic contacts with somatosensory afferents. They are associated with the sense of light
touch, discrimination of shapes, and textures.
Give us feedback on this content: FULL TEXT [ edit ]
The epidermis is the outermost layer of
the skin . It forms a protective barrier over
the body's surface which prevents
pathogens from entering . It is also
responsible for retaining water in the
body and absorbing nutrients.
Skin Overview
Skin layers, of both hairy and hairless skin.
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Human Skin
This image details the parts of the integumentary system.
The epidermis is the outermost layer and helps the skin regulate body temperature. It does
not contain any bloodvessels, and cells in the deepest layers are nourished bydiffusion from
blood capillaries extending to the upper layers of the dermis.
The epidermis can be further subdivided into five strata or layers:
1. Stratum corneum ­ corneocytes are surrounded by aprotein envelope (cornified
envelope proteins), filled with water­retaining keratin proteins, attached together
through corneodesmosomes and surrounded in the extracellular space by stacked layers
of lipids.
2. Stratum lucidum (only on palms and soles of feet).
3. Stratum granulosum ­ in this layer, keratinocytes lose their nuclei and
their cytoplasm appears granular. Lipids, contained in these keratinocytes within
lamellar bodies, are released into the extracellular space through exocytosis to form a
lipid barrier.
4. Stratum spinosum ­ Langerhans cells, immunologically­active cells, are located in the
middle of this layer.
5. Stratum germinativum (basale)­ composed mainly of proliferating and non­
proliferating keratinocytes, attached to the basement membrane byhemidesmosomes.
Melanocytes are present, connected to numerous keratinocytes in this and other strata
through dendrites. Merkel cells are also found in the stratum basale .
Layers of the Epidermis
The epidermis is made up of 95% keratinocytes but also contains melanocytes, Langerhans cells,
Merkel cells, and inflammatory cells.The stratum basale is primarily made up of basal keratinocyte
cells, which can be considered the stem cells of the epidermis. They divide to form the keratinocytes
of the stratum spinosum, which migrate superficially.
The epidermis consists of stratified squamous keratinizing epithelium, composed of
proliferating basal and differentiated suprabasal keratinocytee, with an underlying basement
membrane. Keratinocytes are the major cells, constituting 95% of the epidermis, while
Merkel cells, melanocytes, and Langerhans cells are also present.
Keratinocytes in the stratum basale proliferate during mitosis and the daughter cells move
up the strata, changing shape and composition as they undergo multiple stages of cell
differentiation to eventually become anucleated. During thatprocess keratinocytes will
become highly organized, forming cellular junctions (desmosomes) between each other and
secreting keratin proteins that aid in protection, and lipids which contribute to the formation
of an extracellular matrixwhich serves to provide mechanical strength to the skin.
Keratinocytes from the stratum corneum are eventually shed from the surface
(desquamation). This process is called keratinization and takes place within about 30 days.