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Introduction
The organs of the integumentary system
include the skin and its accessory structures
including hair, nails, and glands, as well as
blood vessels, muscles and nerves
Dermatology is the medical specialty for the
diagnosis and treatment of disorders of the
integumentary system.
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Structure of the Skin
The skin (cutaneous membrane) covers the
body and is the largest organ of the body by
surface area and weight
Its area is about 2 square meters (22 square
feet) and weighs 4.5-5kg (10-11 lb), about
16% of body weight
It is 0.5 – 4 mm thick, thinnest on the eyelids,
thickest on the heels; the average thickness
is 1 – 2 mm
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Structure of the Skin
It consists of two major layers:
outer, thinner layer called the epidermis,
consists of epithelial tissue
inner, thicker layer called the dermis
Beneath the dermis is a subcutaneous
(subQ) layer (also called hypodermis)
which attaches the skin to the underlying
tissues and organs.
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Structure of the Skin
The epidermis has a number of important
characteristics:
the epidermis is composed of keratinized
stratified squamous epithelium
it contains four major types of cells:
Keratinocytes (90% of the cells) produce
keratin which is a tough fibrous protein that
provides protection
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Structure of the Skin
Melanocytes: which produce the pigment
melanin that protects against damage by
ultraviolet radiation
Langerhans cells: involved in immune
responses, arise from red bone marrow
Merkel cells: which function in the
sensation of touch along with the adjacent
tactile discs
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Epidermis
The epidermis contains four major layers (thin
skin) or five major layers (thick skin)
Stratum basale (deepest layer) or stratum
germinativum, where continuous cell division
occurs which produces all the other layers
Stratum spinosum, 8-10 layers of
keratinocytes
Stratum granulosum, which includes
keratohyalin and lamellar granules
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Epidermis
Stratum lucidum is present only in thick skin (the
skin of the fingertips, palms, and soles)
Stratum corneum: composed of many sublayers of
flat, dead keratinocytes called corneocytes or
squames that are continuously shed and replaced by
cells from deeper strata; constant friction can stimulate
formation of a callus.
Keratinization, the accumulation of more and more
protective keratin, occurs as cells move from the
deepest layer to the surface layer
Dandruff - an excess of keratinized cells shed from
the scalp
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Dermis
The dermis has several important
characteristics:
is composed of connective tissue containing
collagen and elastic fibers
contains two layers
the outer papillary region consists of areolar
connective tissue containing thin collagen and
elastic fibers, dermal papillae (including
capillary loops), corpuscles of touch and
free nerve endings
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Dermis
The deeper reticular region consists of
dense irregular connective tissue containing
collagen and elastic fibers adipose cells, hair
follicles, nerves, sebaceous (oil) glands, and
sudoriferous (sweat) glands
Striae or stretch marks can appear if the
skin is stretched too much
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Dermis
Lines of cleavage - “tension lines” in the skin
indicate the predominant direction of
underlying collagen fibers
Epidermal ridges reflect contours of the
underlying dermal papillae and form the basis
for fingerprints (and footprints); their
function is to increase firmness of grip by
increasing friction.
Dermatoglyphics - the study of the pattern
of epidermal ridges
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Structural Basis of Skin Color
Variations in skin color arise from variations in
the amounts of three pigments: melanin,
carotene, and hemoglobin
Melanin - a yellow-red or brown-black pigment
produced by melanocytes (located mostly in the
epidermis, where it absorbs UV radiation)
The amount of melanin causes the skin’s color
to vary from pale yellow to red to tan to black
The number of melanocytes are about the same
in all people; differences in skin color is due to
the amount of pigment produced
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Structural Basis of Skin Color
A benign localized overgrowth of melanocytes is a
nevus or mole
Albinism is an inherited inability to produce melanin
- vitiligo is a condition in which there is a partial or
complete loss of melanocytes from patches of skin
Carotene - yellow-orange pigment (found in the
stratum corneum, dermis, and subcutaneous layer)
Hemoglobin - red color (located in erythrocytes
flowing through dermal capillaries)
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Subcutaneous Layer
Subcutaneous (subQ) layer (also called
hypodermis) is not part of the skin but,
among its functions, it attaches the skin to the
underlying tissues and organs; this layer (and
sometimes the dermis) contains lamellated
(pacinian) corpuscles which detect external
pressure applied to the skin.
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Accessory Structures of the Skin
include hair, skin glands, and nails
Hairs (pili) have a number of important
functions:
protection
reduction of heat loss
sensing light touch
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Accessory Structures of the Skin - Hair
Hair is composed of dead, keratinized
epidermal cells
Hair consists of:
shaft which mostly projects above the
surface of the skin
root which penetrates into the dermis
hair follicle
epithelial root sheath (Internal)
dermal root sheath (External)
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Accessory Structures of the Skin
There are different types of hairs including
lanugo, vellus hairs and terminal hairs
Hair color is determined by the amount and
type of melanin, carotene, and blood
Sebaceous (oil) glands are connected to
hair follicles
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Skin Glands
Sebaceous glands secrete an oily substance
called sebum which prevents dehydration of
hair and skin, and inhibits growth of certain
bacteria
Sudoriferous (sweat) glands-- 2 types:
Eccrine or Merocrine sweat glands
Apocrine sweat glands
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Sudoriferous (Sweat) Glands
Numerous eccrine (or merocrine) sweat glands
helps to cool the body by evaporating, and also
eliminates small amounts of wastes
Apocrine sweat glands, located mainly in the skin of
the axilla, groin, areolae, and bearded facial regions of
adult males.
their excretory ducts open into hair follicles- this sweat is
secreted during emotional stress and sexual excitement.
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Ceruminous Glands
Modified sweat glands located in the ear
canal
Along with nearby sebaceous glands, they
are involved in producing a waxy secretion
called cerumen (earwax) which provides a
sticky barrier that prevents entry of foreign
bodies into the ear canal.
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Nails
Nails are composed of hard, keratinized
epidermal cells located over the dorsal
surfaces of the ends of fingers and toes
Each nail consists of:
free edge
transparent nail body (plate) with a whitish
lunula at its base
nail root embedded in a fold of skin
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Types of Skin
There are two major types of skin:
thin (hairy) skin covers all body regions
except the palms, palmar surfaces of digits,
and soles
thick (hairless) skin covers the palms,
palmar surfaces of digits, and soles
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Functions of the Skin
regulation of body temperature
blood reservoir
protection
cutaneous sensations
excretion and absorption
synthesis of vitamin D
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Development of the Integumentary
System
The epidermis develops from the ectoderm;
nails, hair, and skin glands are epidermal
derivatives - the epidermis of a fetus is
protected by a fatty substance called vernix
caseosa
The dermis develops from the mesoderm
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Aging and the Integumentary System
Effects:
• wrinkling
• decrease of skin’s immune responsiveness
• dehydration and cracking of the skin
• decreased sweat production
• decreased numbers of functional melanocytes resulting in
gray hair and atypical skin pigmentation
• loss of subcutaneous fat
• a general decrease in skin thickness
• an increased susceptibility to pathological conditions
Growth of hair and nails decreases; nails may also
become more brittle with age.
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End of Chapter 5
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