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Chapter 5
Integumentary System
Lecture Outline

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Integumentary System1
The integumentary system consists of the skin
and accessory structures, such as hair, glands,
and nails.
Integument means covering.
The appearance of the integumentary system
can indicate physiological imbalances in the
body.

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Integumentary System2
Figure 5.1

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Integumentary System Functions1
1. Protection. The skin provides protection
against abrasion and ultraviolet light.
2. Sensation. The integumentary system has
sensory receptors that can detect heat, cold,
touch, pressure, and pain.
3. Vitamin D production. When exposed to
ultraviolet light, the skin produces a
molecule that can be transformed into
vitamin D.

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Integumentary System Functions2
4. Temperature regulation. The amount of
blood flow beneath the skin’s surface and the
activity of sweat glands in the skin both help
regulate body temperature.
5. Excretion. Small amounts of waste products
are lost through the skin and in gland
secretions.

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Skin
The skin is made up of two major tissue layers: the
epidermis and the dermis.
The epidermis is the most superficial layer of skin.
It is a layer of epithelial tissue that rests on the
dermis.
The dermis is a layer of dense connective tissue.
The skin rests on the subcutaneous tissue, which is
a layer of connective tissue.
The subcutaneous tissue is not part of the skin.

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Epidermis and Dermis
Figure 5.2
(b) ©Victor Eroschenko

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Epidermis1
The epidermis prevents water loss and resists
abrasion.
The epidermis, known as the cutaneous
membrane, is a keratinized stratified squamous
epithelium.
The epidermis is composed of distinct layers
called strata.

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Epidermis2
The stratum corneum, the most superficial
stratum of the epidermis, consists of dead
squamous cells filled with keratin.
Keratin gives the stratum corneum its structural
strength.
Cells of the deepest strata perform mitosis.
As new cells form, they push older cells to the
surface, where they slough, or flake off.

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Epidermis3
Excessive sloughing of stratum corneum cells
from the surface of the scalp is called dandruff.
In skin subjected to friction, the number of
layers in the stratum corneum greatly increases,
producing a thickened area called a callus.
Over a bony prominence, the stratum corneum
can thicken to form a cone-shaped structure
called a corn.

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Dermis1
The dermis is composed of dense collagenous
connective tissue containing fibroblasts,
adipocytes, and macrophages.
Nerves, hair follicles, smooth muscles, glands,
and lymphatic vessels extend into the dermis.
Collagen fibers, oriented in many directions, and
elastic fibers are responsible for the structural
strength of the dermis and resistance to stretch.

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Dermis2
Some collagen fibers are oriented more
directions than others, forming cleavage lines.
Cleavage lines, or tension lines, in the skin, are
more resistant to stretch.
An incision made parallel with these lines tends
to gap less and produce less scar tissue.
If the skin is overstretched for any reason, the
dermis can be damaged, leaving stretch marks.

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Cleavage Lines
Figure 5.3

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Dermis3
Dermal papillae are projections toward the
epidermis found in the upper part of the dermis.
The dermal papillae contain many blood vessels.
The dermal papillae in the palms of the hands,
the soles of the feet, and the tips of the digits
are arranged in parallel, curving ridges that
shape the overlying epidermis into fingerprints
and footprints.

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Skin Color1
Factors that determine skin color include
pigments in the skin, blood circulating through the
skin, and the thickness of the stratum corneum.
The two primary pigments are melanin and
carotene.
Melanin is the group of pigments primarily
responsible for skin, hair, and eye color.
Carotene is a yellow pigment found in plants such
as squash and carrots.

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Skin Color2
Most melanin molecules are brown to black
pigments, but some are yellowish or reddish.
Melanin provides protection against ultraviolet light
from the sun.
Melanin is produced by melanocytes and the melanin
is packaged into vesicles called melanosomes, which
move into the cell processes of melanocytes.
Epithelial cells phagocytize the tips of the melanocyte
cell processes, thereby acquiring melanosomes.

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Melanin Transfer to Epithelial Cells
Figure 5.4

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Skin Color3
Large amounts of melanin form freckles or moles in
some regions of the skin.
Melanin production is determined by genetic factors,
exposure to light, and hormones.
Genetic factors are responsible for the amounts of
melanin produced in different races.
Since all races have about the same number of
melanocytes, racial variations in skin color are
determined by the amount, kind, and distribution of
melanin.

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Skin Color4
Exposure to ultraviolet light—for example, in
sunlight— stimulates melanocytes to increase
melanin production. The result is a suntan.
Although many genes are responsible for skin
color, a single mutation can prevent the
production of melanin and cause albinism.

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Skin Color5
Carotene is lipid-soluble; when consumed, it
accumulates in the lipids of the stratum corneum
and in the adipocytes of the dermis and
subcutaneous tissue.
If large amounts of carotene are consumed, the
skin can become quite yellowish.

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Skin Color6
The color of blood in the dermis contributes to
skin color.
A decrease in blood flow, as occurs in shock, can
make the skin appear pale.
A decrease in the blood O2 content produces a
bluish color of the skin, called cyanosis.

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Subcutaneous Tissue1
The skin (cutaneous membrane) rests on the
subcutaneous tissue.
The subcutaneous tissue, which is not part of the
skin, is sometimes called hypodermis.
The subcutaneous tissue attaches the skin to
underlying bone and muscle and supplies it with
blood vessels and nerves.
It is loose connective tissue, including adipose tissue
that contains about half the body’s stored lipids.

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Subcutaneous Tissue2
The amount and location of adipose tissue vary
with age, sex, and diet.
Adipose tissue in the subcutaneous tissue
functions as padding and insulation.
The subcutaneous tissue can be used to estimate
total body fat.
The acceptable percentage of body fat varies
from 21% to 30% for females and from 13% to
25% for males.

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Hair1
In humans, hair is found everywhere on the skin,
except on the palms, soles, lips, nipples, parts of
the genitalia, and the distal segments of the
fingers and toes.
Each hair arises from a hair follicle, an
invagination of the epidermis that extends deep
into the dermis.
A hair shaft protrudes above the surface of the
skin; the root is below the surface and the hair
bulb is the expanded base of the root.

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Hair2
A hair has a hard cortex, which surrounds a
softer center, the medulla.
The cortex is covered by the cuticle, a single layer
of overlapping cells that holds the hair in the hair
follicle.
Hair is produced in the hair bulb, which rests on
the hair papilla.
The hair papilla is an extension of the dermis
that protrudes into the hair bulb and contains
blood vessels.

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Hair3
Hair is produced in cycles, with a growth stage
and resting stage.
During the growth stage, hair is formed by
mitosis of epithelial cells within the hair bulb;
these cells divide and undergo keratinization.
During the resting stage, growth stops and the
hair is held in the hair follicle.
When the next growth stage begins, a new hair is
formed and the old hair falls out.

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Hair4
The duration of each stage depends on the
individual hair.
Eyelashes grow for about 30 days and rest for
105 days, whereas scalp hairs grow for 3 years
and rest for 1 to 2 years.
The loss of hair normally means that the hair is
being replaced because the old hair falls out of
the hair follicle when the new hair begins to
grow.

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Hair5
Hair color is determined by varying amounts and
types of melanin.
With age, the amount of melanin in hair can
decrease, causing the hair color to become
faded, or the hair can contain no melanin and be
white.
Each hair follicle is attached to smooth muscle
cells called the arrector pili muscle, which can
contract and cause the hair to become
perpendicular to the skin’s surface.

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Hair Follicle
Figure 5.5

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Glands1
The major glands of the skin are the sebaceous
glands and the sweat glands.
Sebaceous glands are simple, branched acinar
glands, with most being connected by a duct to the
superficial part of a hair follicle.
They produce sebum, an oily, white substance rich in
lipids.
The sebum is released by holocrine secretion and
lubricates the hair and the surface of the skin, which
prevents drying and protects against some bacteria.

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Glands2
There are two kinds of sweat glands: eccrine and
apocrine.
Eccrine sweat glands are simple, coiled, tubular
glands and release sweat by merocrine secretion.
Eccrine glands are located in almost every part of
the skin but most numerous in the palms and
soles.
They produce a secretion that is mostly water
with a few salts.

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Glands3
Eccrine sweat glands have ducts that open onto
the surface of the skin through sweat pores and
are for thermal regulation.
Sweat can also be released in the palms, soles,
armpits, and other places because of emotional
stress.

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Glands4
Apocrine sweat glands are simple, coiled, tubular
glands that produce a thick secretion rich in organic
substances.
The glands open into hair follicles in the armpits and
genitalia.
Apocrine sweat glands become active at puberty
because of the influence of sex hormones.
The secretion generally is odorless, but when
released quickly breaks down by bacterial action
giving body odor.

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Glands of the Skin
Figure 5.6

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Nails1
The nail is a thin plate, consisting of layers of
dead stratum corneum cells that contain a very
hard type of keratin.
The visible part of the nail is the nail body, and
the part of the nail covered by skin is the nail
root.
The cuticle, or eponychium, is stratum corneum
that extends onto the nail body and the nail root
extends distally from the nail matrix.

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Nails2
The nail also attaches to the underlying nail bed,
which is located distal to the nail matrix.
The nail matrix and bed are epithelial tissue with a
stratum basale that gives rise to the cells that form
the nail.
A small part of the nail matrix, the lunula, can be
seen through the nail body as a whitish, crescent-
shaped area at the base of the nail.
Cell production within the nail matrix causes the nail
to grow continuously.

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Nail
Figure 5.7

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Integumentary System Protection1
The integumentary system performs many
protective functions:
1. Reduction in body water loss
2. Acts as a barrier that prevents microorganisms
and other foreign substances from entering the
body
3. Protects underlying structures against abrasion
4. Melanin absorbs ultraviolet light and protects
underlying structures from its damaging effects

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Integumentary System Protection2
5. Hair protection: The hair on the head acts as
a heat insulator, eyebrows keep sweat out of
the eyes, eyelashes protect the eyes from
foreign objects, and hair in the nose and ears
prevents the entry of dust and other
materials.
6. The nails protect the ends of the fingers and
toes from damage and can be used in
defense.

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Sensory Receptor
Many sensory receptors are associated with the
skin.
Receptors in the epidermis and dermis can
detect pain, heat, cold, and pressure.
Although hair does not have a nerve supply,
sensory receptors around the hair follicle can
detect the movement of a hair.

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Vitamin D Production
1. UV light causes the skin to produce a precursor
molecule of vitamin D.
2. The precursor molecule is carried by the blood
to the liver where it is enzymatically converted.
3. The enzymatically converted molecule is carried
by the blood to the kidneys where it is converted
again to the active form of vitamin D.
4. Vitamin D stimulates the small intestine to
absorb calcium and phosphate for many body
functions.

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Temperature Regulation1
Regulation of body temperature is important
because the rate of chemical reactions within
the body can be increased or decreased by
changes in body temperature.
Even slight changes in temperature can make
enzymes operate less efficiently and disrupt the
normal rates of chemical changes in the body.
Exercise, fever, and an increase in environmental
temperature tend to raise body temperature.

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Temperature Regulation2
In order to maintain homeostasis, the body
must rid itself of excess heat.
Blood vessels in the dermis dilate and enable
more blood to flow within the skin, thus causing
heat to dissipate from the body.
Sweat also assists in loss of heat through
evaporative cooling.

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Temperature Regulation3
If body temperature begins to drop below
normal, heat can be conserved by the
constriction of dermal blood vessels, which
reduces blood flow to the skin.
Less heat is transferred from deeper structures
to the skin, and heat loss is reduced.
With smaller amounts of warm blood flowing
through the skin, the skin temperature
decreases.

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Heat Exchange in the Skin
Figure 5.8

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Excretion
The integumentary system plays a minor role in
excretion, the removal of waste products from
the body.
In addition to water and salts, sweat contains
small amounts of waste products, such as urea,
uric acid, and ammonia.
Even though the body can lose large amounts of
sweat, the sweat glands do not play a significant
role in the excretion of waste products.

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Diagnostic Aid
The integumentary system is useful in diagnosis
because it is observed easily.
Cyanosis, a bluish color to the skin caused by
decreased blood O2 content, is an indication of
impaired circulatory or respiratory function.
A yellowish skin color, called jaundice, can occur
when the liver is damaged by a disease, such as
viral hepatitis.
Rashes and lesions in the skin can be symptoms of
problems elsewhere in the body.

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Burns1
A burn is injury to a tissue caused by heat, cold,
friction, chemicals, electricity, or radiation.
Burns are classified according to their depth.
Partial-thickness burns are classified as first-
degree and second-degree.
A full-thickness burn is a third-degree burn.

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First-Degree Burn
A first-degree (superficial) burn involves only
the epidermis and is red and painful.
Slight edema, or swelling, may be present.
They can be caused by sunburn or brief
exposure to very hot or very cold objects, and
they heal without scarring in about a week.

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Second-Degree Burn
Second-degree (partial-thickness) burns damage
both the epidermis and the dermis.
If dermal damage is minimal, symptoms include
redness, pain, edema, and blisters.
Healing takes about 2 weeks, and no scarring
results.
If the burn goes deep into the dermis, the
wound appears red, tan, or white; can take
several months to heal and might scar.

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Third-Degree Burn
Third-degree (full-thickness) burns damage the
complete epidermis and dermis.
The region of third-degree burn is usually
painless because sensory receptors in the
epidermis and dermis have been destroyed.
Third-degree burns appear white, tan, brown,
black, or deep cherry red.

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Burn Healing
In all second-degree burns, the epidermis,
including the stratum basale where the stem
cells are found, is damaged.
The epidermis regenerates from epithelial tissue
in hair follicles and sweat glands, as well as from
the edges of the wound.
Deep partial-thickness and full-thickness burns
take a long time to heal, and they form scar
tissue with disfiguring and debilitating wound
contractures.

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Treatment of Burns
To prevent complications of deep partial-thickness
and full-thickness burns and to speed healing, skin
grafts are often performed.
In a procedure called a split skin graft, the
epidermis and part of the dermis are removed from
another part of the body and placed over the burn
When it is not possible or practical to move skin
from one part of the body to a burn site, physicians
sometimes use artificial skin or grafts from human
cadavers.

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Burns2
Figure 5.9

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Skin Cancer
Most common cancer
Mainly caused by UV light exposure
Fair-skinned people more prone
Prevented by limiting sun exposure and using
sunscreens
UVA rays cause tan and is associated with malignant
melanomas
UVB rays cause sunburns
Sunscreens should block UVA and UVB rays

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Types of Skin Cancer
Basal cell carcinoma:
• cells in stratum basale affected
• cancer removed by surgery
Squamous cell carcinoma:
• cells above stratum basale affected
• can cause death
Malignant melanoma:
• arises from melanocytes in a mole
• rare type
• can cause death

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Cancer of the Skin
Figure 5.13
(a) ©Dr. P. Marazzi/Science Source RF; (b) ©Dr. P. Marazzi/Science Source; (c) Source: National Cancer Institute

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Aging and the Integument
Blood flow decreases and skin becomes thinner
due to decreased amounts of collagen
Decreased activity of sebaceous and sweat
glands make temperature regulation more
difficult
Loss of elastic fibers cause skin to sag and
wrinkle