-
Epidermis (definition and function)
- The most superficial layer of the skin made up of keratinocytes (~90%), melanocytes, and Langerhans cells
- Fx: Barrier of physical and immunological protection
-
Epidermis (layers)
- Basal layer (stratum basale)
- Spinous layer (stratum spinosum)
- Granular layer (stratum granulosum)
- Stratum corneum
-
Keratinocytes
- The main component of the epidermis
- Contain tonofilamints/tonofibrils as the cytoskeleton
- Over about 28 days, undergo proliferation, differentiation, and keratinization before being sloughed off
-
Tonofilaments
These keratin intermediate filaments are produced by keratinocytes and aggregate into tonofibrils to form the cytoskeleton and serve as anchors for intercellular desmosome attachment
-
Keratin composition
- Consist as pairs of an acidic keratin and a basic keratin
- Basal keratinocytes contain types 5 and 14
- Suprabasal keratinocytes contain types 1 and 10
-
Basal layer
- Deepest layer of the epidermis
- Mitotically active, proliferative
- Contains columnar keratinocytes which are attached to the basement membrane by hemidesmosomes
-
Spinous layer
- A layer of the epidermis found between the basal layer and the granular layer
- Contains polygonal keratinocytes filled with keratin filament bundles (tonofibrils)
-
Desmosomes
- Cytoplasmic plaques composed of plakoglobin and desmoplakin which are connected to tonofilaments (intracellularly) and the cadherins desmogleins and desmocollins (intercellularly)
- Connect adjacent keratinocytes
-
Granular layer
- A layer of the epidermis found between the spinous layer and the stratum corneum
- Contains flattened keratinocytes filled with keratohyaline granules (and lysosomal granules)
-
Keratohyaline granules
- Granules found in keratinocytes of the granular layer of epidermis which are not membrane bound and will eventually help form:
- *The interfibrillary matrix of filaggrin which cements keratin filaments together
- *The inner lining of the horny (cornified) cells aka the marginal band
-
Stratum corneum
The uppermost layer of the epidermis containing dead and dying cells without nuclei or desmosomes filled with mature keratin
-
Zones of the basement membrane
- Plasma membrane of the basal keratinocytes
- Lamina lucida
- Lamina densa (made mostly of type IV collagen)
- Sub basal lamina fibrous zone
-
Hemidesmosomes
- Connect keratinocytes of the basal layer of epidermis to the basement membrane via intercellular integrin
- Have a single intracellular attachment plaque made of bullous pemphigoid antigen 1 (BP1 or BP230)
-
Dermis (definition, function, layers)
- Made of mostly fibroblasts (which secrete the ECM made of collagen, elastin, ground substance), vascular, and neural elements
- Fx: Give support and elasticity to skin, support the vascular network, and thermoregulate
- Layers: Papillary dermis and reticular dermis
-
Papillary dermis
- A layer of the dermis which is made up of loose connective tissue (primarily type III collagen)
- Contains nerve endings and superficial and deep vascular networks which are controlled by the sympathetic nervous system
-
Dermal papillae
Fingerlike processes invading the epidermis from the dermis
-
Reticular dermis
- A layer of the dermis which is made up of dense irregular connective tissue (primarily type I collagen) and gives skin its strength and elasticity
- Contains glands and hair follicles
|
|