Untitled Quiz

Study Notes

Skin is the largest organ in the body, primarily composed of the epidermis (outer layer) derived from ectoderm.
The epidermis is keratinized stratified squamous epithelium.
The epidermis has five layers:
- Stratum basale (deepest layer), 10-15% of cells are melanocytes.
- Stratum spinosum (thickest layer).
- Stratum granulosum (thin layer, 4-6 cells, cells flatten)
- Stratum lucidum (only in thick skin, 2-3 layers of keratinocytes).
- Stratum corneum (20-30 layers of flattened cells, containing keratinocytes, melanocytes, Merkel cells, and Langerhans cells).

The dermis is derived from mesoderm.
It consists of strong flexible connective tissue (primarily collagen), fibroblasts, macrophages, mast cells, and white blood cells (WBCs). Also contains elastic fibers.
The dermis supplies the epidermis with nutrients and moisture.
Contains blood vessels, lymphatic vessels, and nerve endings.
The dermis has two layers:
- Papillary layer: A thin superficial layer containing elastin and collagen fibers, phagocytes, and adipose tissue. Projections into the epidermis are papillae, forming fingerprints. Contains nerve endings (Meissner corpuscles).
- Reticular layer: 80% of the dermis' thickness, irregular dense connective tissue that contains well-vascularized cutaneous plexus. Gives skin its elasticity and contains sweat glands and hair follicles.

Keratinocytes: Primary skin cells, producing keratin.
Melanocytes: Spider-shaped cells producing melanin for UV protection. Melanin granules accumulate on keratinocyte surfaces.
Dendritic cells (Langerhans cells): Macrophages activating the immune system.
Mechanoreceptors:
- Merkel cells: Slowly adapting light-touch receptors connected to sensory endings.
- Ruffini corpuscles: Slowly adapting receptors located in the dermis.
- Meissner corpuscles: Rapidly adapting light-touch receptors in the superficial dermis.
- Pacinian corpuscles: Detect deep pressure and vibration in the deep dermis.

Hair: Grows in the hair papilla of the dermis, composed of keratinized cells.
- Each hair follicle has a sebaceous gland.
- Terminal hairs (coarse) are found on the scalp, eyebrows, etc..
- Vellus hair (fine) covers newborns.
Nails: Dense keratinized epidermis cells protecting finger/toe tips.
- Nail plate: the actual fingernail, made of keratin.
- Nail bed: below the plate, continuous with the basal and spinosum layers.
- Nail matrix (nail root): deep to the skin, where new nail formation occurs.

Protection: Prevents dehydration, infection, physical injury, and UV light injury.
Thermoregulation: Insulation (hair and adipose tissue) and heat dissipation (sweat evaporation). Increased blood flow helps regulate temperature.
Sensory Function: Free nerve endings respond to pain, touch, heat, and cold.
Metabolic Function: Vitamin D3 synthesis with UV absorption, for calcium metabolism. Excess electrolytes are removed in sweat. Fat storage occurs in subcutaneous tissue.
Aesthetic Function: Contributes to appearance and attractiveness.