Epidermis Cells Overview

Epidermis Cells

• Composed of five cell types: Stem cells, Keratinocytes, Melanocytes, Tactile cells, and Dendritic cells.

Stem Cells

• Undifferentiated cells that divide to create keratinocytes.
• Located in the deepest epidermal layer, the stratum basale.

Keratinocytes

• The most abundant cells in the epidermis, primarily responsible for keratin synthesis.
• Nearly all visible epidermal cells in histological specimens are keratinocytes.

Melanocytes

• Found in the stratum basale, alongside stem cells and keratinocytes.
• Synthesize melanin, a pigment that provides skin color and protects against UV radiation.
• Melanin granules accumulate on the "sunny side" of keratinocyte nuclei, shielding DNA from UV potential mutations.

Tactile Cells

• Few in number, these cells serve as touch receptors.
• Located in the basal layer of the epidermis and linked to dermal nerve fibers, forming tactile discs.

Dendritic Cells

• Immune cells located in the stratum spinosum and stratum granulosum.
• Originate from bone marrow, migrating to the epidermis and other epithelia to monitor for toxins and pathogens.
• Help alert the immune system upon detection of invaders.

Dermis

• Positioned beneath the epidermis, with thickness ranging from 0.2 mm to 4 mm.
• Composed mainly of collagen, along with elastic and reticular fibers, fibroblasts, and blood vessels.
• Contains nerve endings, cutaneous glands, and embeds hair follicles and nail roots.
• The boundary between dermis and epidermis features dermal papillae (upward extensions) and epidermal ridges (downward extensions) for interlocking stability.
• Divided into two layers: papillary (loose areolar tissue, rich in blood vessels) and reticular (dense irregular connective tissue).

Hair Structure

• Composed of three layers in cross-section: Medulla, Cortex, and Cuticle.

Medulla

• The innermost layer of hair, characterized by loosely arranged cells and air spaces.
• Prominent in thick hairs, such as eyebrows, but narrower or absent in thinner hair types.

Cortex

• The main bulk of a hair, consisting of elongated keratinized cells.
• Appears cuboidal to flattened in cross-sections.

Cuticle

• Composed of multiple thin, scaly cells that overlap, resembling roof shingles with edges pointing upward.

Hair Follicle

• A diagonal tube extending into the dermis and sometimes hypodermis.
• Composed of two primary layers: an epithelial root sheath (an extension of the epidermis) and a connective root sheath.