Bio 4.1 Structure of Epidermis and Skin factors

Stratum Germinativum (Stratum Basale)

• Deepest layer of the epidermis.
• Contains basal cells, melanocytes, and Merkel cells.
• Produces new keratinocytes through cell division.

Epidermal Ridges

• Finger-like projections of the epidermis into the dermis.
• Help strengthen the connection between the epidermis and dermis.
• Form fingerprints on the hands and feet.

Basal Cells

• Cells found in the stratum basale.
• Continuously divide to produce new keratinocytes.
• New cells are pushed toward the surface as older cells are shed.

Merkel Cells

• Found in the stratum basale.
• Associated with sensory nerve endings.
• Detect light touch.

Stratum Spinosum

• Located above the stratum basale.
• Contains many keratinocytes connected by strong junctions.
• Provides strength and flexibility to the epidermis.
• Contains Langerhans cells.

Langerhans Cells

• Found mainly in the stratum spinosum.
• Help provide immune defense by detecting foreign substances.

Stratum Granulosum

• Located above the stratum spinosum.
• Keratinocytes produce keratin and waterproofing substances.
• Cells begin to die as they move toward the surface.

Stratum Lucidum

• Thin, clear layer found only in thick skin.
• Located between the stratum granulosum and stratum corneum.
• Found in the palms and soles.

Stratum Corneum

• Outermost layer of the epidermis.
• Made mostly of dead, keratin-filled cells.
• Provides protection and helps prevent water loss.
• Cells are continuously shed and replaced.

Deep to Superificial

Stratum basale → Stratum spinosum → Stratum granulosum → Stratum lucidum → Stratum corneum*

Dermis

Layer of connective tissue located below the epidermis. Provides strength, support, and nourishment to the skin.

Papillary Layer

Superficial (upper) layer of the dermis.
• Made mainly of areolar connective tissue.
• Contains small blood vessels, nerves, and sensory receptors.
• Helps nourish the epidermis.

Dermal Papillae

• Finger-like projections of the papillary layer that extend into the epidermis.
• Increase contact between the dermis and epidermis.
• Contain blood vessels and sensory receptors.
• Help form fingerprints.

Reticular Layer

• Deeper and thicker layer of the dermis.
• Made mainly of dense irregular connective tissue.
• Contains collagen and elastic fibers.
• Provides the skin with strength and flexibility.
• Contains structures such as hair follicles, sweat glands, sebaceous glands, blood vessels, and nerves.

Hypodermis

• Structure: The hypodermis, also called the subcutaneous layer or superficial fascia, is located below the dermis. It is mainly made of areolar connective tissue and adipose tissue.

• Function: It anchors the skin to underlying tissues, provides insulation, cushioning/protection, and stores energy as fat.

• Important: The hypodermis is not technically part of the skin, but it lies directly underneath it.