Human Organ Systems Test 1, Lecture 4

• The most superficial layer of the skin made up of keratinocytes (~90%), melanocytes, and Langerhans cells
• Fx: Barrier of physical and immunological protection

• Basal layer (stratum basale)
• Spinous layer (stratum spinosum)
• Granular layer (stratum granulosum)
• Stratum corneum

• 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

These keratin intermediate filaments are produced by keratinocytes and aggregate into tonofibrils to form the cytoskeleton and serve as anchors for intercellular desmosome attachment

• 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

• Deepest layer of the epidermis
• Mitotically active, proliferative
• Contains columnar keratinocytes which are attached to the basement membrane by hemidesmosomes

• A layer of the epidermis found between the basal layer and the granular layer
• Contains polygonal keratinocytes filled with keratin filament bundles (tonofibrils)

• Cytoplasmic plaques composed of plakoglobin and desmoplakin which are connected to tonofilaments (intracellularly) and the cadherins desmogleins and desmocollins (intercellularly)
• Connect adjacent keratinocytes

• A layer of the epidermis found between the spinous layer and the stratum corneum
• Contains flattened keratinocytes filled with keratohyaline granules (and lysosomal 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

The uppermost layer of the epidermis containing dead and dying cells without nuclei or desmosomes filled with mature keratin

• Plasma membrane of the basal keratinocytes
• Lamina lucida
• Lamina densa (made mostly of type IV collagen)
• Sub basal lamina fibrous zone

• 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)

• 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

• 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

Fingerlike processes invading the epidermis from the 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