The Integumentary System

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The Integumentary System
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Structure of the Skin

• The largest organ of the body
• Consists of two main parts the epidermis and
  the dermis
• The epidermis is the thinner, more superficial
  portion and is composed of epithelial tissue
• The dermis is the thicker, deeper portion and is
  composed of connective tissue

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Structure of the Skin (continued)

• The subcutaneous layer or hypodermis is deep to
  the dermis and is not actually considered a part
  of the skin
• This layer stores fat and contains blood vessels
  that supply the skin it also helps attach the
  skin to the underlying tissues and organs
• Contains Pacinian corpuscles, nerve endings that
  are sensitive to pressure

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Epidermis

• Composed of squamous epithelial cells
• 4 specific types of cells
• Keratinocytesmost epidermal cells (about 90)
  are of this type produce the protein keratin,
  which protects the skin
• Melanocytesproduce the pigment melanin, which is
  a brownish-black pigment that absorbs damaging
  ultraviolet light and contributes to skin color
• Langerhans cellsinvolved with immunity against
  microbes that invade the skin
• Merkel cellslocated in the deepest layer of the
  epidermis help sensory neurons detect touch
  sensations

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Epidermis (continued)

• In most areas of the body, the epidermis consists
  of 4 layers of keratinocytes in various stages of
  development
• In areas exposed to friction (ex. fingertips,
  palms of the hands, soles of the feet), the
  epidermis consists of 5 layers

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Epidermal Layers

• Stratum corneumoutermost layer consists of
  25-30 layers of flattened dead keratinocytes,
  which are continuously shed and replaced
• Stratum lucidumpresent only in the areas with
  significant friction consists of 3-5 layers of
  flattened clear, dead keratinocytes
• Stratum granulosumconsists of 3-5 layers of
  flattened keratinocytes that are in the process
  of dying cells contain protein granules
• Stratum spinosumconsists of 8-10 layers of
  living keratinocytes which appear to have spiny
  processes
• Stratum basaledeepest layer composed of a
  single row of cuboidal or columnar keratinocytes,
  some of which function as stem cells (divide by
  mitosis to produce new keratinocytes)
  melanocytes, Langerhans cells, and Merkel cells
  are also scattered in this layer

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Dermis

• Composed primarily of connective tissue
• Contains blood vessels, nerves, glands, and hair
  follicles embedded in the dermal tissue
• The upper portion of the dermis has many small,
  fingerlike projections called dermal papillae
• This part of the dermis also contains Meissner
  corpuscles, nerve endings that are sensitive to
  touch other nerve endings sense temperature,
  pain, tickling, and itching

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Dermis (continued)

• The deeper part of the dermis contains collagen,
  a protein, and hair follicles, nerves, sebaceous
  (oil) glands, and sudoriferous (sweat) glands
• Collagen gives the skin extensibility and
  elasticity
• The fingers, toes, palms of the hands, and soles
  of the feet have epidermal ridges these increase
  the ability to grip objects by increasing
  friction the epidermal ridge pattern is unique
  for each person when someone touches a smooth
  object, the ridge pattern is transferred as a
  fingerprint

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Skin Color

• 3 pigments are involved in determination of skin
  color
• Melanina brown or black pigment produced within
  the epidermis (by melanocytes)
• Carotenea yellow-orange pigment found in the
  stratum corneum and fatty areas of the dermis and
  subcutaneous layer
• Hemoglobinthe oxygen-carrying pigment inside red
  blood cells which gives them their red color
  makes the skin of whites appear somewhat pink

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Skin Color (continued)

• The number of melanocytes is about the same in
  all people differences in skin color are due
  mainly to the amount of pigment produced
• Exposure to ultraviolet light stimulates the
  production of melanin from the amino acid
  tyrosine
• A tan occurs when melanin accumulates in the
  keratinocytes of the epidermis freckles are
  patches of melanin
• Melanin offers the body some protection against
  ultraviolet radiation

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Skin Color (continued)

• Albinism is the inherited inability to produce
  melanin usually the melanoctyes of affected
  individuals cannot synthesize the enzymes
  necessary for melanin production melanin is
  absent in the skin, eyes, and hair
• Vitiligo is the loss of melanocytes from areas of
  the skin may be caused by an immune system
  malfunction in which antibodies attack the
  melanocytes

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Hair

• An accessory structure of the skin that develops
  from the epidermis
• Present on most skin surfaces except the palms of
  the hands and the soles of the feet
• Composed of columns of dead, keratinized cells
  bonded together
• Hair helps protect the body (from the sun, from
  heat loss, from foreign particles)

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Hair (continued)

• The part of the hair that projects from the
  surface of the skin is called the shaft the root
  is the part that penetrates the skin into the
  dermis
• The shaft and root both consist of 3 concentric
  layers
• Medullainnermost layer contains pigments
• Cortexmiddle layer may contain pigments
• Cuticleoutermost layer very keratinized

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Hair (continued)

• The hair follicle surrounds the root of the hair
  and consists of epidermal tissue the base of the
  follicle is called the bulb blood vessels
  nourish the follicle at the bulb
• The matrix is a layer of cells that arises from
  the stratum basale this layer is the site of
  cell division, and it produces new hair as the
  old is shed

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Hair (continued)

• The arrector pili is a smooth muscle that is
  attached to a hair follicle when it contracts
  (during times of stressex. when frightened or
  cold), the hair is pulled so that goose bumps
  occur
• A sebaceous (oil) gland is generally associated
  with a hair follicle its secretions coat the
  hair and prevents it from drying out

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Hair Growth

• Each hair follicle goes through a cycle
  consisting of a growth stage and a resting stage
• During the growth stage, cells of the matrix
  divide, keratinize, and die new cells are added
  at the root over time, and the hair grows longer
• During the resting stage, the growth of the hair
  stops for awhile

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Hair Growth (continued)

• When a new growth cycle begins, the old hair root
  falls out or is pushed out, and a new hair grows
  in its place
• Normal hair loss (from the scalp) in adults is
  about 100 hairs per day
• At any time, about 85 of hair (in the scalp) is
  in the growth stage
• The growth cycle of hair is affected by many
  factors (ex. illness, age, genetics, gender,
  stress, diet, chemotherapy, and even childbirth)

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Hair Color

• The color of hair is due primarily to the amount
  of melanin in its keratinized cells
• Melanocytes in the matrix produce the melanin
  that passes into the cells of hair
• Dark-colored hair contains mostly true melanin
• Blond hair contains melanin that contains sulfur
• Red hair contains melanin that contains iron
• Gray hair occurs as the enzyme necessary for
  melanin production decreases
• White hair results from air bubbles in the
  medulla area of the shaft

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Sebaceous Glands

• Secrete an oily substance called sebum
• Most are connected to hair follicles
• The secreting portion lies in the dermis and
  usually opens into the neck of a hair follicle
• There are no sebaceous glands in the palms of the
  hands and the soles of the feet
• Sebum coats the skin and hair, preventing them
  from drying out it also inhibits the growth of
  some bacteria

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Sudoriferous Glands

• Secrete perspiration/sweat
• 2 types of sweat glands
• Eccrine
• Apocrine

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Eccrine Sweat Glands

• most common type
• distributed throughout the skin (except for the
  lip margins, nail beds, eardrum, and external
  genitals)
• most numerous in the skin of the forehead, palms
  of the hands, and soles of the feet
• The secretory portion is located mainly in the
  dermis
• The excretory duct ends as a pore at the surface
  of the epidermis
• This type of sweat gland functions to help
  regulate body temperature through evaporation and
  to help eliminate specific wastes from the body
• Eccrine sweat consists of water, ions, wastes
  (urea, uric acid, ammonia), amino acids, glucose,
  and lactic acid

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Apocrine Sweat Glands

• Found mainly in the skin of the armpit, groin,
  breasts, and bearded regions of the face in adult
  males dont begin to function until puberty
• The secretory portion is located mainly in the
  subcutaneous layer
• The excretory duct opens into hair follicles
• This type of sweat gland is stimulated during
  emotional stress and sexual excitement
• Apocrine sweat is thicker than eccrine sweat

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Ceruminous Glands

• Modified sweat glands in the external ear
• The combined secretion of these glands and
  sebaceous glands in the ear canal is called
  cerumen, or ear wax
• Cerumen helps prevent the entrance of foreign
  bodies into the ear

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Nails

• Plates of tightly packed, hard, keratinized
  epidermal cells
• Help individuals grip objects and scratch also
  protect the tips of the digits
• Most of the nail body appears pink because of
  blood in capillaries beneath the nail
• The cuticle consists of stratum corneum and
  adheres to the nail
• The nail matrix is composed of cells that divide
  to produce the nail

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Functions of the Skin

• Regulates body temperaturethrough sweating and
  the dilation/constriction of blood vessels in the
  dermis
• Protects against the external environmentprevents
  water loss, protects against the UV light of the
  sun, and resists invasion by microorganisms
• Provides sensory information about the
  environmentthrough tactile sensations (ex.
  touch, pressure, tickling, temperature, pain)
• Serves as a reservoir for bloodvessels in the
  skin carry 8-10 of the total blood flow in a
  resting adult
• Synthesizes vitamin DUV light activates a
  chemical substance in the skin that the liver and
  kidneys convert to vitamin D this vitamin aids
  in the absorption of calcium in foods from the
  gastrointestinal tract into the blood
• Serves as an organ of excretion and absorption

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Aging and the Integumentary System

• Age-related changes in the skin usually become
  noticeable in the late forties
• Most of these changes occur in the dermis
• Collagen and elastic fibers degenerate, and
  wrinkles form
• The skins immune responsiveness decreases as
  Langerhans cells decrease in number

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Aging (continued)

• Sebaceous glands decrease in size, resulting in
  dryer skin
• Sweat production decreases, so the body cannot
  regulate its temperature effectively
• The number of melanocytes decreases, resulting in
  gray hair and irregular skin pigmentation (ex.
  age spots)
• The skin becomes thinner and does not
  heal/regenerate itself well
• Hair and nail growth slows

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Skin Cancer

• caused by excessive exposure to the sun
• 3 main types
• Basal cell carcinomaaccount for 78 of all skin
  cancers tumors arise from cells in the stratum
  basale and rarely spread (metastasize)
• Squamous cell carcinomaaccount for 20 of all
  skin cancers arise from squamous cells of the
  epidermis vary in the tendency to spread
• Malignant melanomaaccount for about 2 of all
  skin cancers arise from melanocytes may
  metastasize rapidly and cause death

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Burns

• Tissue damage caused by excessive heat,
  electricity, radioactivity, or corrosive
  chemicals that denature the proteins in the skin
  cells
• When damaged by burns, the skin is unable to
  carry out its protective functions there may be
  a large loss of fluids, which causes severe
  dehydration that may lead to shock infection is
  another complication of burns

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Burns (continued)

• First-degree burnsinvolve only the epidermis
  characterized by redness (erythema), mild pain,
  but no blisters healing generally occurs in 3-6
  days and may be accompanied by flaking or
  peeling ex. a mild sunburn
• Second-degree burnsinvolve the epidermis and
  possibly part of the dermis some skin functions
  are lost characterized by redness, pain, blister
  formation, and edema (interstitial fluid
  accumulation) healing generally occurs in 3-4
  weeks, but scarring may occur
• Third-degree burnsdestroy a portion of both the
  epidermis and dermis, including associated
  structures most skin functions are lost often
  little or no pain because the nerve endings have
  been destroyed vary in appearance, but
  accompanied by edema difficult to heal
  generally much scarring