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• Integumentary system


  Consists of the skin and accessory structures, such as hair, glands, and nails
• Integument


  Means covering
• Integumentary system functions


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


  Made up of two major tissue layers: the epidermis and the dermis
• Epidermis


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


  A layer of dense connective tissue
• Subcutaneous tissue


  A layer of connective tissue, not part of the skin
• Epidermis cell formation


  1. Basal layer cells undergo mitotic division about every 19 days

  2. One daughter cell becomes a new basal cell and can divide again

  3. The other daughter cell is pushed towards the surface, a journey that takes about 40-56 days
• Stratum corneum


  • Composed of 25 or more layers of dead squamous cells joined by desmosomes
  • As new cells form, they push older cells to the surface, where they slough, or flake off
  • Excessive sloughing of stratum corneum cells from the surface of the scalp is called dandruff
  • In skin subjected to friction, the number of layers in the stratum corneum greatly increases, producing a thickened area called a callus
  • Over a bony prominence, the stratum corneum can thicken to form a cone-shaped structure called a corn
• Dermis


  • Composed of dense collagenous connective tissue containing fibroblasts, adipocytes, and macrophages
  • Nerves, hair follicles, smooth muscles, glands, and lymphatic vessels extend into the dermis
  • Collagen fibers, oriented in many directions, and elastic fibers are responsible for the structural strength of the dermis and resistance to stretch
  • Cleavage lines, or tension lines, in the skin, are more resistant to stretch
  • An incision made parallel with these lines tends to gap less and produce less scar tissue
  • If the skin is overstretched for any reason, the dermis can be damaged, leaving stretch marks
• Factors that determine skin color

  • Pigments in the skin
  • Blood circulating through the skin
  • Thickness of the stratum corneum
• Primary pigments


  Melanin and carotene
• Melanin


  The group of pigments primarily responsible for skin, hair, and eye color
• Carotene


  A lipid-soluble pigment that accumulates in the lipids of the stratum corneum and in the adipocytes of the dermis and subcutaneous tissue
• Carotene


  • If large amounts of carotene are consumed, the skin can become quite yellowish
• Blood in the dermis


  • Contributes to skin color
  • A decrease in blood flow, as occurs in shock, can make the skin appear pale
  • A decrease in the blood O2 content produces a bluish color of the skin, called cyanosis
• Subcutaneous tissue


  • The amount and location of adipose tissue vary with age, sex, and diet
  • Adipose tissue in the subcutaneous tissue functions as padding and insulation
  • The subcutaneous tissue can be used to estimate total body fat
• Hair


  In humans, hair is found everywhere on the skin, except on the palms, soles, lips, nipples, parts of the genitalia, and the distal segments of the fingers and toes<|>Each hair arises from a hair follicle, an invagination of the epidermis
• Subcutaneous tissue


  • It is not part of the skin
  • It attaches the skin to underlying bone and muscles and supplies it with blood vessels and nerves
  • It is loose connective tissue, including adipose tissue that contains about half the body's stored lipids
  • The amount and location of adipose tissue vary with age, sex, and diet. Adipose tissue in the subcutaneous tissue functions as padding and insulation
  • The subcutaneous tissue can be used to estimate total body fat
• Acceptable percentage of body fat

  • 21% to 30% for females
  • 12.5% to 25% for males
• Sweat glands


  • Eccrine
  • Apocrine
• Eccrine sweat glands


  • They are simple, coiled, tubular glands and release sweat by merocrine secretion
  • Eccrine glands are located in almost every part of the skin but most numerous in the palms and soles
  • They produce a secretion that is mostly water with a few salts
  • Eccrine sweat glands have ducts that open onto the surface of the skin through sweat pores and are for thermal regulation
  • Sweat can also be released in the palms, soles, armpits, and other places because of emotional stress
• Nails


  • The visible part of the nail is the nail body, and the part of the nail covered by skin is the nail root
  • The cuticle, or eponychium, is stratum corneum that extends onto the nail body and the nail root extends distally from the nail matrix
  • The nail also attaches to the underlying nail bed, which is located distal to the nail matrix
  • The nail matrix and bed are epithelial tissue with a stratum basale that gives rise to the cells that form the nail
  • A small part of the nail matrix, the lunula, can be seen through the nail body as a whitish, crescent-shaped area at the base of the nail
  • Cell production within the nail matrix causes the nail to grow continuously
• Sensory receptors


  • Many receptors are associated with the skin
  • Receptors in the epidermis and dermis can detect pain, heat, cold, and pressure
  • Although hair does not have a nerve supply, sensory receptors around the hair follicle can detect the movement of a hair
• Vitamin D production


  1. UV light causes the skin to produce a precursor molecule of vitamin D

  2. The precursor molecule is carried by the blood to the kidneys where it is converted again to the active form of vitamin D

  3. The enzymatically converted molecule is carried by the blood to the kidneys where it is converted again to the active form of vitamin D

  4. Vitamin D stimulates the small intestine to absorb calcium and phosphate for many body functions
• As temperature increases


  The rate of chemical reactions within the body can be increased or decreased
• Sensory receptor


  Many receptors are associated with the skin<|>Receptors in the epidermis and dermis can detect pain, heat, cold, and pressure<|>Although hair does not have a nerve supply, sensory receptors around the hair follicle can detect the movement of a hair
• Excretion


  • The integumentary system plays a minor role in excretion, the removal of waste products from the body
  • In addition to water and salts, sweat contains small amounts of waste products, such as urea, uric acid, and ammonia
  • Even though the body can lose large amounts of sweat, the sweat glands do not play a significant role in the excretion of waste products
• Diagnostic aid


  • The integumentary system is useful in diagnosis because it is observed easily
  • Cyanosis, a bluish color to the skin caused by decreased blood O2 content, is an indication of impaired circulatory or respiratory function
  • A yellowish skin color, called jaundice, can occur when the liver is damaged by a disease, such as viral hepatitis
  • Rashes and lesions in the skin can be symptoms of problems elsewhere in the body
• First degree burn


  • A first-degree (superficial) burn involves only the epidermis and is red and painful
  • Slight edema, or swelling, may be present
  • They can be caused by sunburn or brief exposure to very hot or very cold objects, and they heal without scarring in about a week
• Second degree burn


  • Second-degree (partial-thickness) burns damage both the epidermis and the dermis
  • If dermal damage is minimal, symptoms include redness, pain, edema, and blisters
  • Healing takes about 2 weeks, and no scarring results
  • If the burn goes deep into the dermis, the wound appears red, tan, or white; can take several months to heal and might scar
• Third degree burn


  • Third-degree (full-thickness) burns damage the complete epidermis and dermis
  • The region of third-degree burn is usually painless because sensory receptors in the epidermis and dermis have been destroyed
  • Third-degree burns appear white, tan, brown, black, or deep cherry red
• Burn healing


  1. In all second-degree burns, the epidermis, including the stratum basale where the stem cells are found, is damaged

  2. The epidermis regenerates from epithelial tissue in hair follicles and sweat glands, as well as from the edges of the wound

  3. Deep partial-thickness and full-thickness burns take a long time to heal, and they form scar tissue with disfiguring and debilitating wound contractures
• Treatment of burns


  • To prevent complications of deep partial-thickness and full-thickness burns and to speed healing, skin grafts are often performed
  • In a procedure called a split skin graft, the epidermis and part of the dermis are removed from another part of the body and placed over the burn
• Skin cancer


  • Most common cancer
  • Mainly caused by UV light exposure
  • Fair-skinned people more prone
  • Prevented by limiting sun exposure and using sunscreens
  • UVA rays cause tan and is associated with malignant melanomas
  • UVB rays cause sunburns
  • Sunscreens should block UVA and UVB rays
• Types of skin cancer

  • Basal cell carcinomas: Cells in stratum basale affected, removed by surgery
  • Squamous cell carcinomas: Cells above stratum basale affected, can cause death
  • Malignant melanomas: Arises from melanocytes in a mole, rare type, can cause death
• Aging and the integument

  • Blood flow decreases and skin becomes thinner due to decreased amounts of collagen
  • Decreased activity of sebaceous and sweat glands make temperature regulation more difficult
  • Loss of elastic fibers cause skin to sag and wrinkle