Anatomy of the Dermis and Subcutaneous Layer

Dermis

• Anchors the epidermis to underlying tissues
• Nourishes itself and the epidermis
• Composed of two layers:
  • Papillary Layer: Areolar connective tissue containing dermal papillae
  • Reticular Layer: Dense irregular connective tissue containing collagen and elastic fibers

Epidermal Ridges/Dermal Papillae

• Anchor the epidermis to the dermis.
• Epidermal ridges project toward the dermis.
• Dermal papillae project towards the epidermis.

Dermis Functions

• Highly vascular, nourishing the epidermis and helping regulate body temperature.
• Innervated with sensory receptors, detecting pressure, touch, temperature, and pain.
• Controls gland secretions and blood flow.

Anatomical Cleavage Lines (Langer's Lines)

• Patterns in the skin reflecting the orientation of collagen fibers in the dermis.
• Indicate the direction of skin elasticity and resistance to stretching.

Subcutaneous Layer (Hypodermis)

• Composed of areolar and adipose connective tissues.
• Not part of the integument.
• Serves as an adipose storage site.
• A good injection site.

Subcutaneous Layer Functions

• Stabilizes and joins the skin to underlying tissues.
• Allows for separate movement.
• Provides insulation to conserve heat.
• Acts as a shock absorber.
• Nourishes via blood vessels

Integumentary System Functions

• Protects from injury, toxins, temperature extremes, and UV rays.
• Retards water loss and gain.
• Regulates metabolism through Vitamin D3 synthesis.
• Facilitates secretion and absorption.
• Performs immune functions.
• Aids in body temperature regulation.
• Contributes to sensory reception.

Epidermis

• Keratinized stratified squamous epithelium.
• Avascular.
• Composed of five layers:
  • Stratum Basale: Deepest layer containing cuboidal to columnar cells undergoing mitosis. Includes stem cells, keratinocytes, melanocytes, and tactile cells.
  • Stratum Spinosum: Newest formed layer of cells, primarily keratinocytes and dendritic cells.
  • Stratum Granulosum: Keratinization occurs here, where keratin, a tough and waterproof protein, is produced. Cells die.
  • Stratum Lucidum: Only present in thick skin (palms and soles). Protects from UV damage.
  • Stratum Corneum: Exposed surface, varying in size.
• Takes 7-10 days for a cell to move from the stratum basale to the stratum corneum.

Thin vs. Thick Skin

• Thin Skin: Four epidermal layers, found on most of the body.
• Thick Skin: all five epidermal layers, found on palms, fingertips, and soles of the feet.

Epidermal Layers

• Older cells are pushed towards the surface as new ones are formed.
• Cells die and become hardened and flattened.
• Cells fill with keratin, a water-resistant protein.
• Found on all exposed skin surfaces, except the eye.

Skin Color

• Influenced by carotene, melanin, and hemoglobin.
• Melanocytes produce melanin.
• Melanin production varies genetically.
• All individuals have the same amount of melanocytes, but produce different amounts and colors of melanin.
• UV light stimulates melanin production.
• Melanin protects skin from UV damage.
• Freckles and moles are areas with high concentrations of melanin.

Melanocytes

• Located in the stratum basale.
• Produce and distribute melanin.
• Protect against UV radiation.

Vitamin D

• Epidermis produces Vitamin D3 (cholecalciferol) in response to sunlight.
• Absorbed by blood vessels in the dermis.
• Transformed to calcitriol (active form) in the liver and kidneys.
• Increases calcium and phosphate absorption.
• Essential for healthy bones and teeth.
• Requires 10-15 minutes of sunlight exposure.

The Hypodermis (Subcutaneous Layer)

• Deepest layer beneath the skin, not part of the integument.
• Composed of loose connective tissue and adipose tissue.
• Ideal for slow sustained absorption of medication.
• Contributes to heat production.
• Stabilizes and joins the skin to underlying tissues.

Accessory Structures of the Skin

• Nails: Epidermal modifications of the stratum corneum, providing protection for fingers and toes, composed of keratin.
  • Cuticle: A small extension at the tip of the proximal nail fold.
  • Lunula: The whitish area of the proximal end of the nail.
• Hair: Present on all skin surfaces except palms, soles, lips, nipple, and parts of external genitalia.
  • Functions: Protection, facial expression, insulation, guarding openings, sensitivity to touch, visual identification, and chemical signaling.
• Hair Follicles: Develop from epidermal cells at the base of a dermis depression; responsible for hair growth.
• Exocrine Glands: Two main types:
  • Sweat glands: Transport secretions to the epidermis via a sweat pore.
    • Merocrine (eccrine) glands: Function throughout life, secreting clear sweat (water, salts, and wastes).
    • Apocrine glands: Begin functioning at puberty, secreting viscous secretions (pheromones).
  • Sebaceous glands: Secrete sebum into hair follicles and onto hair.
    • Sebum: An oily substance lubricating and protecting skin and hair, inhibiting bacteria.

Other Integumentary Glands

• Ceruminous glands: Modified sweat glands in the ear canal producing cerumen (earwax).
• Mammary glands: Structurally similar to apocrine sweat glands, responsible for milk production.