chapter 5

• Protection

  • Skin provides protection against abrasion and ultraviolet light
  • Prevents microorganisms from entering the body
  • Reduces water loss
• Sensation

  • Has sensory receptors that can detect heat, cold, touch, pressure, and pain
• Vitamin D production


  • Exposed to ultraviolet light, skin produces a molecule that can be transformed into vitamin D
• Temperature regulation

  • Blood flow beneath the skin's surface and activity of sweat gland help regulate the body temperature

  
• Excretion

  • Small amounts of waste products are lost through the skin and in gland secretions
• Epidermis


  One of the two major tissues that make up the skin

  
• Dermis

  One of the two major tissues that make up the skin, 10 to 20 times thicker than the epidermis

  
• Subcutaneous tissue

  Layer of connective tissue that the skin rests on, not part of the skin but connects it to underlying muscle or bone

  
• Epidermis

  • Most superficial layer of skin
  • Stratified squamous epithelium
  • New cells produced by mitosis in deepest layers, push older cells to the surface where they slough off
• Keratinization

  Process where epidermal cells change shape and chemical composition, becoming filled with protein keratin which makes them more rigid and durable
• Stratum basale

  Deepest stratum of the epidermis, consists of cuboidal or columnar cells that undergo mitotic divisions about every 19 days
• Stratum corneum

  Most superficial stratum of the epidermis, consists of 25 or more layers of dead squamous cells filled with keratin and coated/surrounded by lipids
• Callus

  Thickened area of stratum corneum in skin subjected to friction
• Corn


  Thickening of the stratum corneum over a bony prominence, forming a cone-shaped structure
• Dermis

  • Dense collagenous connective tissue containing fibroblasts, adipocytes, and macrophages
  • Nerves, hair follicles, smooth muscles, glands, and lymphatic vessels extend into it

  
• Cleavage lines

  Orientation of collagen fibers in the dermis, making an incision parallel to them lessens the gap and produces less scar tissue

  
• Stretch marks


  Skin is overstretched
• Dermal papillae

  Upper part of the dermis that extend toward the epidermis, contain blood vessels to supply the epidermis
• Intradermal injection

  Drawing the skin taut and inserting a small needle at a shallow angle into the dermis
• Subcutaneous injection


  Pinching the skin to form a "tent" and inserting a short needle into the adipose tissue of the subcutaneous tissue
• Intramuscular injection


  Inserting a long needle at a 90-degree angle to the skin into a muscle deep to the subcutaneous tissue
• Melanin


  Group of pigments primarily responsible for skin, hair, and eye color, provides protection against ultraviolet light
• Melanocytes


  Cells that produce melanin, have many long processes that extend between the epithelial cells of the deep epidermis

  
• Albinism


  Recessive genetic trait that causes a deficiency or absence of melanin, resulting in fair skin, white hair, and unpigmented irises
• Cyanosis

  Decrease in blood O2 content produces a bluish color of the skin

  
• Carotene

  Yellow pigment found in plants like squash and carrots, can cause skin to become yellowish if consumed in large amounts
• Subcutaneous tissue


  • Attaches the skin to underlying bone and muscle
  • Supplies the skin with blood vessels and nerves
  • Loose connective tissue including adipose tissue that contains about half the body's stored lipids

  
• Adipose tissue


  Functions as padding and insulation, responsible for appearance and individual differences in body fat
• Women have higher total body fat (21-30%) compared to men (13-25%)
• Hair follicle

  Invagination of the epidermis that extends deep into the dermis
• Hair shaft

  Part of the hair that protrudes above the skin surface

  
• Hair root


  Part of the hair below the skin surface
• Hair bulb

  Expanded base of the hair root
• Cortex

  Hard outer layer surrounding the softer center (medulla) of a hair
• Cuticle

  Single layer of overlapping cells that covers the cortex and holds the hair in the follicle

  
• Hair papilla


  Extension of the dermis that protrudes into the hair bulb, supplies nourishment for hair production
• Arrector pili


  Smooth muscle cells that contract to cause the hair to become more perpendicular to the skin's surface
• Sebaceous glands


  Simple, branched acinar glands that produce sebum, an oily white substance that lubricates the hair and skin surface
• Eccrine sweat glands

  Simple, coiled, tubular glands that produce a secretion that is mostly water with a few salts, open onto the skin surface through sweat pores
• Apocrine sweat glands

  Simple, coiled, tubular glands that produce a thick secretion rich in organic substances, open into hair follicles in the armpits and genitalia