Skin

Skin Overview

  • Skin: The outer covering of the body, known as the integument. It plays several critical roles, including protection, sensory reception, and thermoregulation.

  • Layers of Skin: Comprised mainly of two layers: the epidermis and the dermis.

Epidermis

  • Definition: The outermost layer of skin.

  • Structure: Contains stratified squamous keratinized epithelium and is avascular.

  • Keratinocytes: These are the most numerous cells, responsible for producing keratin, a tough waterproof protein.

  • Melanocytes: Spider-shaped cells located in the deepest layer of the epidermis that produce melanin, which protects against UV radiation.

  • Epidermal Dendritic Cells: Also known as Langerhans cells, function in the immune response.

Layers of the Epidermis

  • Stratum Corneum:

    • Most superficial layer, contains 20-30 layers of dead keratinized cells.

    • Protects from mechanical and chemical stress.

  • Stratum Lucidum (thick skin only):

    • Few translucent layers of dead keratinocytes.

  • Stratum Granulosum:

    • Three to five layers where organelles begin to disintegrate and keratinization occurs.

  • Stratum Spinosum:

    • Several layers of keratinocytes linked by desmosomes, also contains dendritic cells.

  • Stratum Basale (deepest layer):

    • Contains actively mitotic stem cells; new cells move to more superficial layers.

Dermis

  • Structure: Located beneath the epidermis, consists of two layers, the papillary and reticular layers.

  • Papillary Layer:

    • Composed of areolar connective tissue with dermal papillae, creating fingerprints and aiding in sensation.

  • Reticular Layer:

    • Dense irregular connective tissue; makes up 80% of the dermis, containing collagen fibers.

    • Forms tension lines significant for surgical incisions.

Hypodermis

  • Also known as the superficial fascia.

  • Composed mainly of adipose tissue, it cushions, insulates, and gives shape to the body.

Skin Color and Appendages

  • Skin Color: Determined by melanin production, genetics, UV exposure, and diet. All races have similar numbers of melanocytes.

  • Appendages: Include eccrine sweat glands, sebaceous glands, and hair follicles.

    • Eccrine Glands: Regulate temperature through sweat secretion.

    • Sebaceous Glands: Produce sebum for hair and skin lubrication, can lead to acne.

Functions of the Integumentary System

  • Protection: Acts as a barrier against pathogens, chemical stress, and dehydration.

  • Thermoregulation: Involves sweating and blood flow adjustments to maintain body temperature.

  • Sensation: Contains sensory receptors for touch and pressure.

  • Metabolic Function: Involves the production of vitamin D.

Skin Pathologies

  • Skin Cancer: Main types include:

    • Basal Cell Carcinoma: Least malignant, most common.

    • Squamous Cell Carcinoma: Arises in keratinocytes, rapid growth.

    • Melanoma: Cancer of the melanocytes, very aggressive.

  • Burns: Classified by severity:

    • First Degree: Epidermis only, e.g., sunburn.

    • Second Degree: Damage to epidermis and dermis, causes blisters.

    • Third Degree: Full thickness burn, potentially life-threatening.