Chapter 7: Integumentary System

Skin

  • Also called the cutaneous membrane
  • Organ: two or more tissues grouped together to perform specific tasks
  • Two layers
  • Epidermis
  • Dermis

Epidermis

  • Thin outer layer of the skin
  • Stratified Squamous Epithelium
  • Avascular: no blood supply or its own
  • Oxygen and nutrients diffuse from blood supply in the dermis
  • Can be divided into 5 layers (bottom to top)
  • Stratum germinativum (Stratum basale)
  • Stratum spinosum
  • Stratum granulosum
  • Stratum lucidum
  • Stratum corneum

Stratum Germinativum (Basale)

  • Close to the dermis
  • Well nourished by blood supply in the dermis
  • Constantly dividing (mitosis) and pushing cells toward the surface
  • No longer well nourished
  • Outer cells start to die and keratinize (fill with keratin)

Stratum Corneum

  • Surface layer of epidermis
  • Dead, keratinized cells (about 30 layers)
  • Keratin:
  • Hardens and flattens cells
  • Waterproofs skin
  • Cells constantly sloughed off and replaced from below

Dermis

  • Also called the corium
  • Dense fibrous connective tissue
  • Lots of collagen and elastic fibers make the dermis strong and flexible
  • Accessory structures derived from epidermis but embedded in the dermis
  • Blood vessels, nerves and some muscle also found here
  • Many nerves have sensory receptors for pain, temperature, pressure and touch

Subcutaneous Layer

  • Also called the hypodermis
  • Dermis lies on this layer
  • Not considered part of the skin
  • Composed of loose connective and adipose tissue
  • Functions:
  • Insulation
  • Anchors skin to underlying structures

Skin Color

  • Melanocytes: cells in stratum germinativum that produce melanin
  • Melanin and Carotene gives skin its color
  • Different skin tones due to amount of melanin produced not number of melanocytes
  • All have the same number of melaocytes
  • Production of melanin controlled by pituitary gland hormone: melanocyte-stimulating hormone (MSH)
  • Tanning: increased production of melanin from exposure to UV light
  • Bodies attempt to protect lower layers from harmful effects of UV light
  • Albinism is a complete lack of melanin production
  • Moles and freckles are concentrated spots of melanin
  • Moles may undergo a malignant change and become a malignant melanoma
  • Changes or warning signs to look for
  • Rough or notched edge
  • Asymmetrical
  • Change in color or uneven color
  • Size larger than a pencil eraser
  • Exposure to sunlight increases risk of malignant melanoma
  • High rate of metastasis makes malignant melanoma very hard to treat so need to watch for abnormal moles carefully
  • High melanin production gives a darker skin tone
  • Lower melanin production allows carotene or dermis to show through
  • Carotene gives a yellow skin tone
  • In people without much melanin or carotene the capillaries in the dermis give a pink skin tone
  • Cyanosis: lack of oxygen, blue color
  • Blushing: blood vessels dilate, pink color
  • Blanching: blood vessels constrict, loss of pink color
  • Jaundice: build up of bilirubin due to liver disease, yellow color
  • Ecchymosis: blood escapes and clots under skin, black and blue color

Accessory Structures

  • Hair
  • Nails
  • Glands

Hair

  • Hair covers most of our bodies except palms, soles of feet, lips, nipples, parts of external reproductive organs
  • Eyelashes and eyebrows keep dust and perspiration out of eyes
  • Nose hairs trap dust and keep it out of the lungs

Hair Growth

  • Controlled by sex hormones estrogen and testosterone
  • During puberty hair starts to grow in axillary and pubic areas
  • Males also grow facial and other body hair
  • Excessive hair growth hirsutism

Hair

  • Shaft: above the skin
  • Root: from the dermis to the surface
  • Follicle: downward extension of epithelial cells that surrounds hair root
  • Hair cells die and keratinize as they move out from follicle
  • Color
  • Due to amount of melanin
  • Lots – dark hair
  • Little – blonde hair
  • Modified melanin with iron – red hair
  • Melanocytes less active as we age – gray & white hair
  • Type (straight, wavy, curly)
  • Straight – round shaft
  • Wavy – oval shaft
  • Curly – flat shaft
  • Arrector pili muscles pull hairs into an erect position
  • Arrector pili – smooth muscle (involuntary)
  • Contracts in response to fear or cold
  • Causes goose bumps and shivering

Nails

  • Thin plates of stratified squamous epithelial cells containing very hard keratin
  • Found on the distal ends of fingers and toes
  • Helps protect from injury
  • Growth only occurs at the lunula

Exocrine Glands

  • Two major exocrine glands associated with the skin
  • Sebaceous glands
  • Sudoriferous glands

Sebaceous gland

  • Oil gland
  • Produces sebum (oil)
  • Associated with hair follicles
  • Found in all areas of the body that have hairs
  • Sebum secreted into hair follicle then out onto the surface of the skin
  • Sebum lubricates and helps waterproof the skin and hair
  • Babies born with a covering called the vernix caseosa secreted by the sebaceous glands
  • looks like cream cheese
  • Acne: caused when sebaceous gland blocked or infected with bacteria
  • Blackhead – sebaceous gland blocked with sebum or other debris that turns black when exposed to air
  • Pimple – blocked sebum becomes infected with bacteria

Sudoriferous Glands

  • Sweat glands
  • In the dermis and subcutaneous layer
  • Approximately 3 million on our body
  • Found in all regions of the body, especially palms and soles of feet
  • Two types
  • Apocrine
  • Eccrine

Apocrine Glands

  • Usually associated with hairs
  • Found in axillary and genital areas
  • Respond to emotional stress
  • Activate when frightened, upset, in pain, or sexually excited
  • Sweat not smelly on its own
  • If it lingers on the skin bacteria break it down and get smelly byproducts (BO)

Eccrine Glands

  • Not associated with hair follicles
  • Distributed widely on the body
  • Numerous on the forehead, upper lip, palms and soles
  • Help regulate body temperature
  • Sweat evaporates to cool
  • Sweat mostly water and a few salts

Modified Sweat Glands

  • Mammary Glands
  • Found in breasts and secrete milk
  • Ceruminous Glands
  • Found in the external auditory canal (ear)
  • Secrete cerumen (ear wax)
  • Helps repel insects and traps foreign material

Functions of Skin

  • Keeps bacteria and foreign materials out
  • Keeps water in
  • Excretes water, salt and small amounts of wastes
  • Synthesizes and secretes vitamin D
  • Senses pressure, pain and temperature
  • Helps regulate body temperature

Heat Production

  • All the chemical reactions in the body produce thermal energy as a by product
  • Heat produced by metabolizing cells is the basis for body temperature
  • Greatest amount of heat produced by the muscles and the liver
  • Muscles at rest – 25%
  • Liver – 25%
  • Heat produced dependent on food consumption, hormones, physical activity
  • Heat picked up by the blood and distributed around the body

Heat Loss

  • 80% lost through the skin
  • 20% lost through the respiratory system and excretory products
  • Heat lost through radiation, conduction, convection and evaporation
  • Radiation – heat lost to cooler air
  • Conduction – heat lost to cooler object in contact with the body
  • Convection – heat lost to air currents moving over the surface of the skin
  • Evaporation – heat lost when a liquid becomes a gas

Temperature Regulation

  • Normal body temperature: 98.6 °F
  • Hyperthermia: higher than normal body temperature
  • Hypothermia: lower than normal body temperature
  • Hypothalamus: regulates body temperature
  • Too hot
  • Blood vessels dilate
  • More blood near the surface of the skin
  • Heat lost through radiation, conduction and convection
  • Sweat glands more active
  • Heat lost through evaporation
  • Too cold
  • Blood vessels constrict
  • Less blood near the surface of the skin
  • Sweat glands less active
  • Arrector pili muscles contract causing shivering

Burns

  • Partial-thickness
  • First-degree: epidermis injured
  • Red, painful and slightly edematous
  • Second-degree: epidermis and dermis injured
  • Redness, pain, edema and blister formation
  • Full-thickness
  • Third-degree: epidermis and dermis completely destroyed
  • Often underlying layers also destroyed
  • No pain, sensory structures destroyed
  • May appear white, tan, brown, black or deep cherry red

Disorders of the Integumentary System: From Chart on Page 107

  • Acne
  • Athlete’s foot
  • Cold Sore
  • Eczema
  • Psoriasis
  • Skin Cancer