Structure and Cells of the Skin

Skin Structure

• The skin consists of two main layers: the epidermis (superficial epithelial layer) and the dermis (deep underlying connective tissue layer)
• The skin rests on the hypodermis, a connective tissue rich in adipose tissue

Cells of Epidermis

• Keratinocytes: most abundant type, found in the epidermis
• Melanocytes: found scattered in the stratum basale, produce melanin pigment
• Langerhans cells: found in the stratum spinosum, have a role in immune response
• Merkels cells: found among keratinocytes in the stratum basale, function as mechanoreceptors

Layers of Epidermis

• Stratum germinativum (basal layer): single layer of cuboidal to columnar cells, rests on basement membrane
• Stratum spinosum (prickle cell layer): several layers of polyhedral cells
• Stratum granulosum: 3-5 layers of cells that become flattened as they are pushed upward, accumulate granules of two types
• Stratum lucidum (clear layer): 3-5 layers of flattened cells
• Stratum corneum (cornified layer): dead, scale-like cells

Melanocytes

• Produce melanin pigment, which is transferred to adjacent keratinocytes
• Melanin synthesis depends on the presence of tyrosinase enzyme located in melanosomes, formed in the RER and packed in Golgi

Langerhans Cells

• Located in the stratum spinosum, contain specific rod-like inclusions called Birbeck granules
• Function as antigen-presenting cells, phagocytose foreign antigens, process and present them on their surface to T-lymphocytes

Merkel Cells

• Originate from the neural crest, located among keratinocytes in the stratum basale
• Function as mechanoreceptors, associated with unmyelinated sensory nerve fibers

Dermis

• Consists of two layers: an outer papillary layer and an inner reticular layer containing thick collagen bundles
• Most of the nerve supply and all the vascular supply is found in the dermis and hypodermis

Sweat Glands

• Eccrine glands: simple coiled tubular glands, found all over the body, most numerous in the palms and soles
• Apocrine glands: simple coiled tubular glands, found in the axilla and pubic regions

Sebum Production

• Sebum is secreted by sebaceous glands, which open into the upper part of the hair follicle
• Sebum has bacteriostatic, fungistatic properties, and softens the stratum corneum