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Page 653
Chapter 16 Goals
Students will be able to:
 Name the layers of the skin & the accessory structures
associated with the skin.
 Build medical words using the combining forms that
are related to the specialty of dermatology
 Identify lesions, signs & symptoms, & pathologic
conditions that relate to the skin
 Describe laboratory tests & clinical procedures that
pertain to the skin, & recognize relevant abbreviations
 Apply your new knowledge to understanding medical
terms in their proper contexts, such as medical reports
& records.
Skin
Chapter 16
Pages 653 – 696
Page 654
Introduction
 The
skin & its accessory structures (hair, nails, &
glands) make up the integumentary system of the
body. Integument means covering, & the skin
(weighing 8 to 10 pounds & extending over an
area of 22 square feet in an average adult) is the
outer covering for the body. It is, however, more
than a simple body covering. This complex
system of specialized tissue contains glands that
secrete several types of fluids, nerves that carry
impulses, & blood vessels that aid in the
regulation of the body temperature.
Page 654
Introduction: Cont.
The skin has many important functions:
1. As a protective membrane over the entire body,
the skin guards the deeper tissues of the body
against excessive loss of water, salts, & heat
against invasion of pathogens & their toxins.
2. The skin contains two types of glands that
produce important secretions. These glands in
the skin are the sebaceous glands & sweat
glands. Sebaceous glands produce sebum, an
oily secretion, & sweat glands produce sweat, a
watery secretion.
Page 654
Introduction: Cont.
3.
4.
Nerve fibers under the skin are receptors for
sensations such as pain, temperature, pressure,
& touch.
Nerve fibers coordinate thermoregulation by
carrying messages to the skin from heat centers
in the brain that are sensitive to increases &
decreases in body temperature. Impulses from
these fibers cause blood vessels to bring blood
to the surface & cause sweat glands to produce
the watery secretion that carries heat away.
Page 654
Anatomy of the Skin
 Epidermis
= a thin, cellular membrane layer;
containing keratin
 Dermis
= dense, fibrous, connective tissue layer;
containing collagen
 Subcutaneous
layer = thick, fat-containing tissue
Page 654
Anatomy of the Skin: Cont.
Epidermis
 The epidermis is the outermost totally cellular
layer of the skin.
 It is composed of squamous epithelium.
 Epithelium is the covering of both the internal &
the external surfaces of the body.
 Squamous epithelial cells are flat & scale-like.
 In the outer layer of the skin, these cells are
arranged in several layers (strata) to form
stratified squamous epithelium.
Page 654
Anatomy of the Skin: Cont.
 The
epidermis lacks blood vessels, lymphatic
vessels, & connective tissue & is therefore
dependent on the deeper dermis layer & its rich
network of capillaries for nourishment.
 In fact, oxygen & nutrients seep out of the
capillaries in the dermis, pass through tissue fluid,
& supply nourishment to the lower layers of the
epidermis
Pages 654 – 655
Anatomy of the Skin: Cont.
 The
deepest layer is called the basal layer. The
cells in the basal layer are constantly growing &
multiplying & are the source of all the other cells
in the epidermis. As the basal layer cells divide,
they are pushed upward & away form the blood
supply of the dermal layer by a steady stream of
younger cells. In their movement toward the most
superficial layer of the epidermis, called the
stratum corneum, the cells flatten, shrink, lose
their nuclei, & die, becoming filled with a hard
protein material called keratin.
Page 655
Anatomy of the Skin: Cont.
 The
cells are then called keratinocytes, reflecting
their composition of keratin.
 Finally, within 3 to 4 weeks after beginning as a
basal cell in the deepest part of the epidermis, the
keratinized cell is sloughed off from the surface of
the skin.
 The epidermis is thus constantly renewing itself,
with cells dying at the same rate at which they are
replaced.
 This process slows with age.
Page 655
Anatomy of the Skin: Cont.
 The
basal layer of the epidermis contains special
cells called melanocytes. Melanocytes contain a
pigment called melanin that is transferred to the
other epidermal cells & gives color to the skin.
The number of melanocytes in all human races is
the same, but the amount of melanin within each
cell accounts for the color differences among the
races. Individuals with darker skin process more
melanin within the melanocytes, not a greater
number of melanocytes. Individuals who are
incapable of forming melanin are called albinos.
Page 656
Anatomy of the Skin: Cont.
 Melanin
production increases with exposure to strong
ultraviolet light, & this creates a suntan, which is a
protective response. When the melanin cannot absorb
all of the ultraviolet rays, the skin becomes sunburned
& inflamed. Over a period of years, excessive
exposure to sun tends to cause wrinkles, permanent
pigmentary changes, & even cancer of the skin.
 Because dark-skinned people have more melanin,
they acquire fewer wrinkles & they are less likely to
develop the types of skin cancer that are associated
with ultraviolet light exposure.
Page 656
Anatomy of the Skin: Cont.
Dermis

Dermis = directly below the epidermis;
composed of blood vessels, lymph & nerve
fibers, as well as the accessory organs of the skin,
which are the hair follicles, sweat glands, &
sebaceous glands.
•
To support the elaborate system of nerves,
vessels, & glands, the dermis contains
connective tissue cells & fibers that account
for the extensibility & elasticity of the skin.
Page 656
Anatomy of the Skin: Cont.

The dermis is composed of interwoven elastin &
collagen fibers.
 Collagen = a fibrous protein material found in
bone, cartilage, tendons, & ligaments, as well
as in the skin. It is tough & resistant but also
flexible. In the infant, collagen is loose &
delicate; it becomes harder as the body ages.
 Collagen fibers support & protect the blood &
nerve networks that pass through the dermis.
Collagen diseases affect connective tissues of the
body.
Page 656
Anatomy of the Skin: Cont.
Subcutaneous Layer
 The subcutaneous layer specializes in the
formation of fat.
 Adipocytes are predominant in the subcutaneous
layer, & they manufacture & store large quantities
of fat. Fat deposition varies in different areas of
the body & among individual people.
 Functionally, this layer of the skin is important in
protection of the deeper tissues of the body, as a
heat insulator, & for energy storage.
Page 656
Accessory Structures of the Skin
Hair
 A hair fiber is composed of a tightly fused meshwork
of cells filled with the hard protein called keratin.
Hair growth is similar to the growth of the epidermal
layer of the skin. Deep-lying cells in the hair root
produce keratinized cells that move upward through
hair follicles. Melanocytes are located at the root of
the hair follicle, & they donate the melanin pigment to
the cells of the hair fiber.
 Of the 5 million hairs on the body, about 100,000 are
on the head. They grow about ½ inch per month.
Cutting the hair has no effect on its rate of growth.
Page 657
Accessory Structures of the Skin: Cont.
Nails
 Nails are hard keratin plates covering the dorsal
surface of the last bone of each toe & finger. They are
composed of karatinocytes that are cemented together
tightly & can extend indefinitely unless cut or broken.
A nail grows in thickness & length as a result of
division of cells in the region of the nail matrix,
which is at the base of the nail plate.
 Fingernails grow about 1 mm per week, which means
that they can regrow in 3 to 5 months. Toenails grow
more slowly than fingernails; it takes approximately
12 months for toenails to be replaced completely.
Page 657
Accessory Structures of the Skin: Cont.
 Lunula
= a semilunar whitish region at the base
of the nail plate. It generally can be seen in the
thumbnail of most people & is evident to varying
degrees in other fingernails. Air mixed in with
keratin & cells rich in nuclei give the lunula its
whitish color.
 Cuticle
= a narrow band or epidermis, is at the
base & sides of the nail plate.
 Paronychium
nail boarder.
= the soft tissue surrounding the
Page 657
Accessory Structures of the Skin: Cont.
 Nail
growth & appearacne commonly alter during
systemic disease.
 For
example, grooves in nails may occur with
high fevers & serious illness, & spoon nails
(flattening of the nails plate) develop in iron
deficiency anemia.
 Onycholysis
is the loosening of the nail plate with
separation for the nail bed. It may occur with
infection of the nail & is often seen in psoriasis.
Page 658
Accessory Structures of the Skin: Cont.
Glands
Sebaceous Glands
 Sebaceous glands are located in the dermal layer
of the skin over the entire body, with the
exception of the palms, sole, & lips. They secrete
an oily substance called sebum. Sebum,
containing lipids, lubricates the skin & minimizes
water loss.
 Sebaceous glands are closely associated with hair
follicles, & their ducts open into the hair follicle
through which the sebum is released.
Page 658
Accessory Structures of the Skin: Cont.
 The
sebaceous glands are influenced by sex
hormones, which cause them to hypertrophy at
puberty & atrophy in old age.
 Increased
production of sebum during puberty
contributes to blackhead formation & acne in
some people.
Page 658
Accessory Structures of the Skin: Cont.
Sweat Glands
 Sweat glands (the most common type are eccrine
sweat glands) are tiny, coiled glands found on
almost all body surfaces (about 2 million in the
body).
 They are most numerous in the palm of the hand
(3,000 glands per square inch) & in the sole of the
foot. The coiled eccrine sweat gland originates
deep in the dermis & straightens out to extend up
through the epidermis. The tiny opening on the
surface is a pore.
Page 658
Accessory Structures of the Skin: Cont.
 Sweat,
or perspiration, is almost pure water, with
dissolved materials such as salt making up less
than 1% of the total composition. It is colorless &
odorless. The odor produced when sweat
accumulates on the skin is caused by the action of
bacteria on the sweat.
 Sweat cools the body as it evaporates into the air.
Perspiration is controlled by the sympathetic
nervous system, whose nerve fibers are activated
by the heart regulatory center in the hypothalamic
region of the brain, which stimulates sweating.
Page 659
Accessory Structures of the Skin: Cont.
 A special
variety of sweat gland, active only from
puberty onward & larger than the ordinary kind, is
concentrated in a few areas of the body near the
reproductive organs & in the armpits. These
glands (apocrine sweat glands) secrete an odorless
sweat, containing substances easily broken down
by bacteria on the skin. The bacterial waste
products produce a characteristic human body
order. The milk-producing mammary gland is
another type of apocrine gland; it secretes milk
after the birth of a child.
Page 664
Pathology
Cutaneous Lesions
crust
Collection of dried serum & cellular debris
cyst
Thick-walled, closed sac or pouch
containing fluid or semisolid material
erosion Wearing away or loss of epidermis
fissure Groove or crack-like sore
Flat, pigmented lesion measuring less than
macule
1 cm in diameter
Page 664
Pathology: Cont.
Cutaneous Lesions: Cont.
Solid, round or oval elevated lesion 1 cm or
nodule
more in diameter
Small (less than 1 cm in diameter), solid
papule
elevation of the skin
Growth extending from the surface of the
polyp
mucous membrane
pustule Papule containing pus
ulcer
Open sore on the skin or mucous membrane
(deeper than an erosion)
Page 664
Pathology: Cont.
Cutaneous Lesions: Cont.
Small collection (papule) of clear fluid
vesicle
(serum); blister
wheal
Smooth, edematous (swollen) papule or
plaque that is centrally redder or paler than
the surrounding skin.
Page 666
Pathology: Cont.
Signs & Symptoms
alopecia
Absence of hair from areas
where it normally grows
ecchymosis (plural: Bluish-purplish mark (bruise)
ecchymoses)
on the skin
petechia (plural:
petechiae)
Small, pinpoint hemorrhage
pruritus
Itching
Page 667
Pathology: Cont.
Abnormal Conditions
Injury to tissue caused by heat contact
First-degree burns = superficial epidermal
lesions, erythema, hyperesthia, & no blisters
Second-degree burns (partial-thickness
burns burness burn injury) = epidermal & dermal
lesions, erythema, blisters, & hyperesthia
Third-degree burns (full-thickness burn
injury) = epidermal & dermal are destroyed
(necrosis of skin), & subcutaneous layer is
damaged, leaving charred, white tissue
Pages 666 – 668
Pathology: Cont.
Abnormal Conditions: Cont.
acne
Chronic papular & pustular eruption of
the skin with increased production of
sebum
cellulitis
Diffuse, acute infection of the skin
marked by local heat, redness, pain, &
swelling
eczema
Inflammatory skin disease with
(atopic
erythematous, papulovesicular, or
dermatitis) papalosquamous lesions.
Pages 668 – 670
Pathology: Cont.
Abnormal Conditions: Cont.
exanthematous Rash (exanthem) of the skin due to
viral diseases a viral infection
Death of tissue associated with loss
gangrene
of blood supply
Bacterial inflammatory skin
impetigo
disease characterized by vesicles,
pustules, & crusted-over lesions
Chronic, recurrent dermatosis
psoriasis
marked by itchy, scaly, red plaques
covered by silvery gray scales
Page 670
Pathology: Cont.
Abnormal Conditions: Cont.
scabies
Contagious, parasitic infection of
the skin with intense pruritus
scleroderma
Chronic progressive disease of the
skin & internal organs with
hardening & shrinking of
connective tissue
systemic lupus Chronic autoimmune inflammatory
erythematosus disease of collagen in skin, joints,
(SLE)
& internal organs
Pages 671 – 672
Pathology: Cont.
Abnormal Conditions: Cont.
tinea
Infection of the skin caused by a fungus
urticaria Acute allergic reaction in which red,
(hives)
round wheals develop on the skin
vitiligo
Loss of pigment (depigmentation) in
area of the skin (milk-white patches).
Page 672
Pathology: Cont.
Skin Neoplasms
Benign Neoplasms
Increased growth of cells in the keratin
callus
layer of the epidermis caused by pressure
or friction
Excess hypertrophied, thickened scar
keloid
developing after trauma or surgical
incision
Thickened & rough lesion of the
keratosis epidermis; associated with aging or skin
damage
Page 673
Pathology: Cont.
Skin Neoplasms
Benign Neoplasms: Cont.
White, thickened patches on mucous
leukoplakia membrane tissue of the tongue or
cheek
nevus
(plural:
Pigmented lesion of the skin
nevi)
verruca
Epidermal growth (wart) caused by a
(plural:
virus
verrucae)
Page 674
Pathology: Cont.
Skin Neoplasms
Cancerous Lesions
basal cell
Malignant tumor of the basal cell
carcinoma
layer of the epidermis
squamous cell Malignant tumor of the squamous
carcinoma
epithelial cells in the epidermis
malignant
Cancerous growth composed of
melanoma
melanocytes
Malignant, vascular, neoplastic
Kaposi
growth characterized by cutaneous
sarcoma
nodules.
Page 675
Laboratory Tests & Clinical Procedures
Laboratory Tests
bacterial
analyses
Samples of skin are examined for
presence of microorganisms
fungal
tests
Scrapings from skin lesions, hair
specimens, or nail clippings are sent to a
laboratory for culture & microscopic
examination
Page 675
Laboratory Tests & Clinical Procedures: Cont.
Clinical Procedures
cryosurgery
Use of subfreezing temperature
achieved with liquid nitrogen
application to destroy tissue
curettage
Use of a sharp dermal curette to
scrape away a skin lesion
Tissue is destroyed by burning
electrodesiccation
with an electric spark
Pages 675 – 676
Laboratory Tests & Clinical Procedures: Cont.
Clinical Procedures
Thin layers of malignant tissue
are removed, & each slice is
Mohs surgery
examined microscopically to
check for adequate extent of the
resection
Suspicious skin lesions are
skin biopsy
removed or sampled & examined
microscopically by a pathologist
Substances are injected
skin test
intradermally or applied to the
skin, & results are observed