Skin

• Skin - the largest organ of the body. It is a physical barrier that protects the underlying tissues and organs from microorganisms, physical trauma, ultraviolet radiation, and dehydration.
• Skin - plays a vital role in temperature maintenance, fluid and electrolyte balance, absorption, excretion, sensation, immunity, and vitamin D synthesis.
• Epidermis - is the outer layer of the skin, is composed of distinct layers, the stratum corneum, stratum lucidum, stratum granulosum, and stratum germinativum
• Dermis - a well-vascularized, connective tissue layer containing collagen, elastic fibers, nerve endings, and lymph vessels. The origin of the sebaceous glands, sweat glands, and the hair follicles
• Dermal papillae - connect the dermis to the epidermis
• Sebaceous glands - are attached to hair follicles, and therefore, present over most of the body, excluding soles of the palm.
• Sebum - sebaceous glands secrete an oily substance that waterproofs the hair and the skin
• Eccrine gland - located over the entire skin that secretes sweat and thermoregulation which functions accomplished by the evaporation of sweat from the skin surface
• Apocrine glands - associated with hair follicles in the axillae, perineum, and areolae of the breasts
• Subcutaneous tissue - beneath the dermis, a loose connective tissue containing fat cells, blood vessels, nerves and the remaining portions of sweat glands and hair follicles
• Subcutaneous tissue - stores fat as an energy, provides insulation to conserve internal body heat, serves as a cushion to protect bones and internal organs, and contains vascular pathways for the supply of nutrients and removal of waste products to and from the skin
• Freckles - flat, small macules of pigment that appear following sun exposure

  
• Vitiligo depigmentation of the skin

  
• Striae (stretch marks)

  
• Seborrheic keratosis - a warty or crusty pigmented lesion

  
• Scar

  
• Mole (nevus) - a flat or raised tan brownish marking up to 6 mm wide

  
• Cutaneous tag - raised papule with a depressed center

  
• Cutaneous horn

  
• Cherry angiomas - small raised spots (1-5 mm wide) typically seen with aging