Anatomy Chapter 6

Epidermal dendritic cells

Epidermal dendritic cells are immune cells that help fight infection in the epidermis. These immune cells are often present in the stratum spinosum and stratum granulosum, but they are not identifiable in standard histologic preparations.

Stratum spinosum

Several layers of polygonal keratinocytes form the stratum spinosum, or spiny layer. Each time a keratinocyte stem cell in the stratum basale divides, a daughter cell is pushed toward the external surface from the stratum basale, while the other cell remains as a stem cell in the stratum basale. Once this new cell enters the stratum spinosum, it begins to differentiate into a non-dividing, highly specialized keratinocyte.

Integument layers

a layer of stratified squamous epithelium called the epidermis, and a deeper layer of primarily dense irregular connective tissue called the dermis

Tactile cells

also called Merkel cells, are few in number and found scattered among the cells within the stratum basale. Tactile cells are sensitive to touch and, when compressed, they release chemicals that stimulate sensory nerve endings, providing information about objects touching the skin

Stratum Basale

deepest epidermal layer is the stratum basale, also known as the stratum germinativum, or basal layer. This single layer of cuboidal to low columnar cells is tightly attached to an underlying basement membrane that separates the epidermis from the connective tissue of the adjacent dermis.

Epidermis

epithelium of the integument is called the epidermis. It is a keratinized, stratified squamous epithelium

Keratinocytes

most abundant cell type in the epidermis and are found throughout all epidermal strata. The stratum basale is dominated by large keratinocyte stem cells, which divide to generate new cells that replace dead keratinocytes shed from the surface. Their name is derived from their synthesis of keratin, a protein that strengthens the epidermis considerably. Keratin is a family of fibrous structural proteins that are both tough and insoluble. Fibrous keratin molecules can twist and intertwine around each other to form helical intermediate filaments of the cytoskeleton. The keratins found in epidermal cells of the skin are called cytokeratins. Their structure in these cells gives skin its strength and makes the epidermis almost waterproof.

Melanocytes

ong, branching processes and are scattered among the keratinocytes of the stratum basale. They produce and store the pigment melanin in response to ultraviolet light exposure. Their cytoplasmic processes transfer melanin pigment within melanosomes to the keratinocytes within the basal layer and sometimes in more superficial layers. This pigment (which includes the colors black, brown, tan, or yellow-brown) accumulates around the nucleus of the keratinocyte and shields the nuclear DNA from ultraviolet radiation. The darker tones of the skin result from melanin produced by the melanocytes.