CHAPTER 6 A&P: INTEGUMENTARY SYSTEM

integumentary system

• aka the cutaneous membrane or integument

• covers the entire surface of the body

• largest organ in the body; 1.8 m²

• comprised of all 4 tissue types

• made up of the skin and several accessory organs

• 2 regions: epidermis and dermis

• hypodermis or subcutaneous tissue attaches the skin to underlying tissue

what are the functions of the skin?

• Protection: protects against harmful substances, UV radiation, microorganisms, and water loss

• Sensation: contains sensory receptors for touch, pressure, temperature changes, and pain

• Excretion: of some wastes

• Production of Vitamin D: starts in skin; when produced and activated, helps with calcium absorption

• Regulation of Body Temperature: helps cool body by sweating and blood flow changes

what are the general characteristics of the epidermis?

• outer, thinner region

• made of stratified squamous epithelium

• 5 layers (strata)- deep to superficial:

  1: stratum basale

  2: stratum spinosum

  3: stratum granulosum

  4: stratum lucidum

  5: stratum corneum

stratum basale

• just superficial to dermis

• constantly dividing; new cells are pushed to the surface, then die and are sloughed off

• Cells:

  • Keratinocytes: most numerous; produce keratin, a water-proofing protein

  • Langerhans Cells: macrophages

  • Melanocytes: produce melanin; skin color and protection from UV radiation

• Sensory nerves:

  • Free Nerve Ending: pain and temperature sensations

  • Tactile Cell (Merkel Cells): touch sensations

stratum spinosum

• composed of eight to ten layers of keratinocytes

• cells can still divide

• spiny appearance due to keratin fibers

• Langerhans Cells: function as a macrophage by engulfing bacteria, foreign particles, and damaged cells that occur in this layer

stratum granulosum

• flattened cells

• contain a lot of keratin and dark-staining keratohyalin pigment granules

stratum lucidum

• just deep to stratum corneum

• smooth, seemingly translucent layer

• found only in thick skin of the palms, soles, and digits

• provides protection from constant friction

• cells are densely packed with eleiden, a clear protein rich in lipids, derived from keratohyalin

  -gives these cells their transparent (or lucid) appearance

  -provides a barrier to water

stratum corneum

• tough, uppermost layer of epidermis

• cells are keratinized (hardened) and dead

• keratin prevents water loss and water gain

• serves as a mechanical barrier against microbes

• the entire layer is replaced over a period of about four weeks

what are the special cells of the epidermis?

dendritic (Langerhans) cells, tactile (Mekel) cells, and Melanocytes

dendritic (Langerhans) cell

• found in the stratum spinosum

• Phagocytes; protect skin and underlying tissues from infection

tactile (Merkel) cells

• found in stratum basale

• along with sensory nerve endings, for Tactile Discs in dermis

• acts as sensory receptor for light touch

melanocytes

• found in stratum basale

• produce the pigment melanin

• absorbs UV light from sunlight and provides skin color

• melanin is distributed to keratinocyte, to protect from UV radiation (DNA damage, fibroblast damage, skin cancer)

what affects skin color ?

• the color of skin is influenced by a number of pigments, including melanin, carotene, and hemoglobin

• Melanin: produced by melanocytes, found in the stratum basale of the epidermis (dark skin= more melanin than pale skin)

• Eumelanin: brownish-black pigment of epidermis

• Pheomelanin: reddish yellow pigment, found in certain areas (the lips)

• exposure to the UV rays of the sun causes melanin to be manufactured and built up in keratinocytes

• the accumulation of melanin in keratinocytes results in the darkening of the skin

• this is increased melanin accumulation protects the DNA of epidermal cells from UV ray damage and the breakdown of folic acid

• too much melanin can interfere with the production of vitamin D

hereditary factors can affect skin color by…

• all people have same number of melanocytes, but vary in amount of melanin produced (this id under genetic control)

• varying distribution and size of melanin granules

• Albinism: inherited mutation in melanin genes; lack melanin so skin is nonpigmented

physiological factors can affect skin color by…

• oxygenation in blood of dermal blood vessels: pinkish, cyanosis

• vasodilation/ vasoconstriction of dermal blood vessels

• accumulation of carotene pigment from diet

• jaundice

environmental factors can affect skin color by…

• sunlight

• UV light from sunlamps

• x-rays

what are characteristics of the dermis?

• thicker than epidermis

• made of 2 layers: papillary layer and reticular layer

• elastic fibers stretch to allow movement of muscles and joints

• contains blood and lymph vessels, nerves, and other structures, such as hair follicles and sweat glands

• vascularization of dermis supplies oxygen and nutrients to cells of dermis and epidermis and causes temporary changes to skin color

papillary layer

• made of loose, areolar connective tissue

• collagen and elastin fibers form a loose mesh

• this superficial layer of the dermis projects into the stratum basale of the epidermis to form finger-like dermal papillae

• within the papillary layer are:

  -fibroblasts

  -small number of fat cells (adipocytes)

  - abundance of small blood vessels

  - phagocytes= help fight bacteria or other infections that have penetrated the outer layers of the skin

  -lymphatic capillaries

  -nerve fibers and touch receptors (Meissner corpuscles)

reticular layer

• underlying the papillary layer

• thicker, composed of dense, irregular connective tissue

• well vascularized, rich sensory and sympathetic nerve supply

• appears reticulated (netlike) due to a tight meshwork of fibers:

• Elastin fibers: skin elasticity, enabling movement

• Collagen Fibers: structure and tensile strength; extends into the papillary layer and the hypodermis and binds water to keep the skin hydrated

hypodermis (aka subcutaneous fat or superficial fascia)

• layer located below the dermis

• connects the sin to fascia of bone and muscle

• composed of areolar and adipose connective tissues

• adipose tissue provides energy storage, insulation, and protective padding

what are the accessory structures of the skin?

hair, nails, and skin glands

hair

• on all body parts except the palms, soles, lips, nipples and portions of the external reproductive organs

• after puberty there is noticeable hair in the axillary and pelvic regions

• hair in different parts of the body has different growing and resting time periods

hair follicles

• formed from epidermal cells

• located in dermis

• cells become keratinized as they are pushed out

• Hair Root: portion of the hair within follicle

• Hair Shaft: portion of hair that continues beyond the skin

• sebaceous (oil) glands

• arrector pili muscle: smooth muscle attached to hair follicle

nails

• formed from specialized epithelial cells

• Nail Root: base of the nail, where growth occurs

• Nail Body: visible portion of the nail

• Cuticle (Eponychium): fold of skin that hides the root

• Nail Bed: rich in blood vessels, pink color

• Lunula (half-moon): thick area of rapidly dividing epithelial cells at base of nail bed

• Epithelial cells become keratinized as they move away from the root

• pink color due to vascular dermis under the nail body (nail itself has no color)

skin glands

• glands: groups of specialized cells that produce and secrete substances into ducts

• sweat glands and sebaceous glands

sweat (sudoriferous) glands

Present in all regions of the skin; some become more active under
stress
b. Apocrine glands
1) Open into hair follicles in genital region and armpits
2) Begin to secrete at puberty
3) Mammary glands are modified apocrine glands
4) Contain compounds that make sweat ‘thicker’
c. Eccrine sweat glands
1) Open onto surface of skin
2) Active when body heats up; helps lower body temperature
3) Sweat (perspiration) is mostly water, but also excretes
wastes
4) Most abundant on palms of hand, soles of feet & forehead
d. Ceruminous glands – modified sweat glands that produce
cerumen (earwax)
e. Mammary glands - produce milk

sebaceous glands

Most are associated with a hair follicle
b. Secrete an oily substance called sebum
1) Lubricates and waterproofs hair and skin
2) Weakens or kills bacteria on skin surface
c. If sebum collects, whiteheads or blackheads form
d. Acne vulgaris – inflammation of the sebaceous glands

heat production and loss

-Important to regulate body temp; slight shift can disrupt rates of metabolic reactions.
-Set point is monitored by hypothalamus in brain.
-Deep body temp stays close to set point of 37 degrees Celsius or 98.6 degrees Fahrenheit
-Skin plays a role in homeostasis mechanisms that regulate body temp
-Heat is product of cellular metabolism; mainly produced by most active cells (liver, skeletal, and cardiac muscle)

heat loss through the skin

Radiation: primary method, infrared heat rays travel from warmer skin to cooler environment

Conduction: heat moves from warmer skin to cooler objects it is in contract with

Convection: Heat loss from skin into circulating air currents

Evaporation: Heat is lost through sweat as it evaporates, and carries heat away from the skin.

When body temperature rises-

Thermoreceptors signal hypothalamus
Vasodilation of dermal blood vessels
Vasoconstriction of deep blood vessels
Sweat glands are activated

When body temperature falls-

Thermoreceptors signal hypothalamus

Vascoconstriction of dermal blood vessels (less blood goes to surface of skin = lose less heat)

Sweat glands are inactive

Muscles contract involuntarily = shivering

Hyperthermia-

-Abnormally high body temp
-Can occur in hot, humid day when sweat can't evaporate.
-When air temp is high, radiation is less effective
-Body may gain heat from hotter air
-Skin becomes dry, person gets weak, dizzy, nauseous, with headache, rapid pulse

Hypothermia-

Abnormally low body temperature

-can result from prolonged exposure to cold or illness
-Shivering is involuntary skeletal muscle contraction, caused by hypothalamus.
-Progresses to confusion, lethargy, loss of reflexes and consciousness
-Without treatment, organs shut down

Inflammation-

-A normal response to injury and stress
-Body's attempt to restrict spread of infection
-Blood vessels in affected tissues dilate and become more permeable, allowing fluids to leak into the damaged tissues

Inflamed skin may become-
Reddened
Swollen
Warm
Painful

First degree burn-

injuries only epidermis, as in sunburn; redness, heat, inflammation.
-Healing only takes days to weeks, no scarring

Second degree burn-

Destroys epidermis and some dermis, as in a burn from hot liquid
-May blister, healing varies with severity of burn
-Stem cells in hair follicles and glands can help regenerate skin
-Usually covers completely, no scarring

Third degree burn-

-Destroys epidermis, dermis, and accessory structures
-Results from prolonged exposure to heat, flames, hot liquids
-Some healing from margins
-Often requires skin graft, skin substitutes

Rule of nines-

-divides body surface into regions of 9% or multiples of 9
-used to estimate extent of injured body surface from a burn for treatment
-from this estimate, plans to replace fluids, electrolytes, and skin can be figured

Life span changes-

-Cell cycle slows, skin becomes scaly, age spots appear
-Epidermis and dermis become thinner
-Loss of fat in subcutaneous layer; person feels cold
-Wrinkling, sagging of skin occur
-Sebaceous glands secrete less oil; skin becomes dry
-Melanin production slows; hair whitens
-Hair thins
-Number of hair follicles decreases
-Nail growth becomes impaired
-Sensory receptors decline
-Body temperature regulation becomes less effective
-Diminished ability to produce Vitamin D

fourth degree burns

involve tissues down to the bone

burns are critical if…

Second-degree burns cover 25% or more of the patient’s
body
b. Third-degree burns cover 10% or more of the patient’s
body
c. Any portion of the body has a fourth-degree burn
d. Third-degree burns occur on the face, hands, or feet
Major concerns associated with severe burns:
a. Fluid loss
b. Heat loss
c. Bacterial infection

what are the steps in wound healing?

a. A blood clot forms
b. White blood cells and fibroblasts move to the injured area
c. Fibroblasts pull the margins of the wound together and
promote tissue regeneration
d. The basal layer of the epidermis produces new cells
e. Proliferating fibroblasts form a scar