Chapter 05 - Integumentary System

• Integumentary system


  The skin and accessory structures, such as hair, glands, and nails
• The appearance of the integumentary system can indicate physiological imbalances in the body
• Integumentary system functions


  • Protection
  • Sensation
  • Vitamin D production
  • Temperature regulation
  • Excretion
• Epidermis


  The most superficial layer of skin, a layer of epithelial tissue that rests on the dermis
• Dermis


  A layer of dense connective tissue
• Subcutaneous tissue


  A layer of connective tissue that is not part of the skin
• Epidermis


  • Prevents water loss and resists abrasion
  • Composed of distinct layers called strata
  • Stratum corneum consists of dead squamous cells filled with keratin
  • Cells of the deepest strata perform mitosis
• Excessive sloughing of stratum corneum cells

  • Dandruff
• Thickened areas of stratum corneum

  • Callus
  • Corn
• Dermis


  • Composed of dense collagenous connective tissue
  • Contains fibroblasts, adipocytes, and macrophages
  • Contains nerves, hair follicles, smooth muscles, glands, and lymphatic vessels
  • Collagen and elastic fibers provide structural strength and resistance to stretch
  • Cleavage lines are more resistant to stretch
• If the skin is overstretched, the dermis can be damaged, leaving stretch marks
• Dermal papillae


  Projections toward the epidermis found in the upper part of the dermis, containing many blood vessels
• The dermal papillae in the palms, soles, and digits are arranged in parallel, curving ridges that shape the overlying epidermis into fingerprints and footprints
• Skin color


  • Determined by pigments in the skin, blood circulating through the skin, and the thickness of the stratum corneum
  • Primary pigments are melanin and carotene
  • Melanin provides protection against ultraviolet light
  • Melanin is produced by melanocytes and transferred to epithelial cells
  • Genetic factors, exposure to light, and hormones determine melanin production
• A single mutation can prevent the production of melanin and cause albinism
• Carotene accumulates in the lipids of the stratum corneum and adipocytes, causing yellowish skin if consumed in large amounts
• A decrease in blood flow can make the skin appear pale, and a decrease in blood O2 content can produce cyanosis (bluish skin)
• Subcutaneous tissue


  Loose connective tissue that contains about half the body's stored lipids, functioning as padding and insulation
• The acceptable percentage of body fat varies from 21% to 30% for females and from 13% to 25% for males
• Hair


  • Each hair arises from a hair follicle, an invagination of the epidermis that extends into the dermis
  • Hair has a hard cortex surrounding a softer medulla, covered by a cuticle
  • Hair is produced in cycles, with a growth stage and resting stage
  • Hair color is determined by varying amounts and types of melanin
  • Arrector pili muscles can contract to cause the hair to become perpendicular to the skin's surface
• Sebaceous glands


  Simple, branched acinar glands that produce sebum, an oily, white substance rich in lipids
• Eccrine sweat glands


  Simple, coiled, tubular glands that release sweat by merocrine secretion, for thermal regulation
• Apocrine sweat glands


  Simple, coiled, tubular glands that produce a thick secretion rich in organic substances
• Sebum


  Oily, white substance rich in lipids
• Sebum release


  1. Holocrine secretion

  2. Lubricates hair and skin surface

  3. Prevents drying

  4. Protects against some bacteria
• Sweat glands


  • Eccrine
  • Apocrine
• Eccrine sweat glands


  • Simple, coiled, tubular glands
  • Release sweat by merocrine secretion
  • Located in almost every part of the skin, most numerous in palms and soles
  • Produce secretion that is mostly water with a few salts
• Eccrine sweat release


  1. Ducts open onto skin surface through sweat pores

  2. For thermal regulation

  3. Can also be released due to emotional stress
• Apocrine sweat glands


  • Simple, coiled, tubular glands
  • Produce thick secretion rich in organic substances
  • Open into hair follicles in armpits and genitalia
  • Become active at puberty due to sex hormones
  • Secretion is odorless but breaks down by bacteria giving body odor
• Nail


  Thin plate of dead stratum corneum cells containing hard keratin
• Parts of the nail

  • Nail body
  • Nail root
  • Cuticle (eponychium)
  • Nail matrix
  • Nail bed
• Nail growth


  1. Nail matrix and bed give rise to cells that form the nail

  2. Nail grows continuously
• Protective functions of the integumentary system

  • Reduction in body water loss
  • Barrier against microorganisms and foreign substances
  • Protects underlying structures against abrasion
  • Melanin absorbs UV light
  • Hair protection (insulation, prevent entry of dust/objects)
• Sensory receptors in the skin

  Detect pain, heat, cold, and pressure
• Vitamin D production


  1. UV light causes skin to produce precursor molecule

  2. Precursor converted in liver

  3. Converted again in kidneys to active form

  4. Active vitamin D stimulates intestine to absorb calcium and phosphate
• Increase in body temperature

  Caused by exercise, fever, or environmental temperature increase
• Heat dissipation


  1. Blood vessels in dermis dilate to increase blood flow

  2. Sweat evaporation provides cooling
• Heat conservation


  1. Dermal blood vessels constrict to reduce blood flow and heat transfer to skin

  2. Skin temperature decreases
• Integumentary system plays minor role in excretion
• Cyanosis


  Bluish skin color indicating decreased blood oxygen