Epidermis Layers Overview

Study Notes

Stratum Basale: Also known as stratum germinativum; the deepest layer of the epidermis composed of a single layer of keratinocytes, 10-25% melanocytes, and some Merkel cells; known for rapid cell division.
Stratum Spinosum: Referred to as the prickly layer; consists of several layers; contains a web-like system of intermediate filaments with melanocytes and Langerhans' cells contributing to its structure.
Stratum Granulosum: Known as the granular layer; a thin layer, typically 3-5 layers thick; cells flatten and accumulate keratohyalin and lamellar granules; plasma membrane thickens in this layer.
Stratum Lucidum: Called the clear layer; composed of a few rows of flattened dead keratinocytes; found only in thick skin.
Stratum Corneum: Also known as the horny layer; 20-30 cells thick and comprises about 3/4 of the epidermis; consists of keratin and lamellar bodies, providing protection against various assaults.

Keratinocytes: Continuously reproduce, move to the surface, and eventually flake off; cycle through every 25-45 days; found mainly in the top layers of the epidermis.
Melanocytes: Produce melanin in the stratum basale; melanin is responsible for skin color and offers protection against light; use a branching process to distribute melanin.
Langerhans' Cells: Also known as epidermal dendritic cells; derived from bone marrow; located in the stratum spinosum; function as macrophages activating the immune response.
Merkel Cells: Located at the dermal-epidermal junction; associated with sensory nerve endings to help perceive touch.

Common Skin Issues: Skin manifests over 1,000 conditions and ailments, including cancer and burns.
Burn Causes: Result from damage due to intense heat, electricity, radiation, or chemicals.
Immediate Threat of Burns: Loss of body fluids leading to dehydration.
Secondary Threat of Burns: Risk of infection.

First-Degree Burns: Affect only the epidermis causing redness, swelling, and pain; sunburn is an example.
Second-Degree Burns: Damage both the epidermis and upper dermis; characterized by blistering; also called partial-thickness burns.
Third-Degree Burns: Involve full thickness of the skin and are not painful due to nerve destruction; require skin grafting; classified as full-thickness burns.

ABCDE Rule for Skin Lesions:
- Asymmetrical: Sides do not match.
- Border Irregularity: Borders are uneven.
- Color: Various colors present, including black, brown, tan, blue, and red.
- Diameter: Lesions larger than 6mm.
- Evolving: Changes in size, shape, or color over time.

Hair Composition: Formed from keratinized cells produced by hair follicles; melanin provides hair color.
Hair Structure: Divided into root (in the skin) and shaft (protects from external environment).
Hair Follicle Sheath: Composed of inner and outer sheaths; inner sheath promotes hair growth, while the outer sheath offers protection with strong keratin.
Arrector Pili: Smooth muscle bundles that contract and cause hair to stand upright.
Nail Structure: Composed of a free edge, body, proximal root, nail matrix (responsible for growth), and lunula (region covering the root).