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Art & science
If you would like to contribute to the Art & science
section, email [email protected]
The synthesis of art and science is lived by the nurse in the nursing act
Josephine G Paterson
The integumentary system: anatomy,
physiology and function of skin
McLafferty E et al (2012) The integumentary system: anatomy, physiology and function of skin.
Nursing Standard. 27, 3, 35-42. Date of acceptance: April 13 2010.
Abstract
This article, which forms part of the life sciences series, examines
the anatomy and physiology of skin, also termed the integumentary
system. Skin is composed of two main layers, the epidermis and
dermis. The structure of the epidermis and dermis are described
and their functions are discussed. Accessory structures, such as
nails and hair are also considered. Although many diseases of the
skin exist, two common conditions – psoriasis and decubitus ulcers –
are described in this article.
Authors
Ella McLafferty
Retired, was senior lecturer, School of Nursing and Midwifery,
University of Dundee.
Charles Hendry
Retired, was senior lecturer, School of Nursing and Midwifery,
University of Dundee.
Alistair Farley
Lecturer in nursing, School of Nursing and Midwifery,
University of Dundee.
Correspondence to: [email protected]
Keywords
Anatomy and physiology, body systems, integumentary system,
skin and skin disorders
Review
All articles are subject to external double-blind peer review and
checked for plagiarism using automated software.
Online
Guidelines on writing for publication are available at
www.nursing-standard.co.uk. For related articles visit the archive
and search using the keywords above.
© NURSING STANDARD / RCN PUBLISHING
p35-42w3.indd 35
The skin is a complex arrangement of
structures with a range of different, but important,
functions. The skin is composed of two main
layers, the epidermis and dermis (Waugh and
Grant 2010, Tortora and Derrickson 2009a).
The subcutaneous layer is found beneath the
dermis and is not considered part of the skin
(Tortora and Derrickson 2009a).
Nurses need to be knowledgeable about what
is considered to be healthy skin (Pringle and Penzer
2002). This is important, as the condition of the
skin may often be a sign of underlying disease
(Casey 2002). Changes in the skin may be one
of the first indicators of an underlying health
problem. Many nurses will be familiar with
cyanosis where, because of poor delivery of oxygen
to the tissues, the patient’s skin appears blue.
Structure of the skin
The skin is the largest organ in the body,
accounting for approximately 16% of the total
body weight of an adult (Tortora and Derrickson
2009a). The skin weighs twice as much as the
brain, approximately 3-5kg (Turkington and
Dover 2007). Skin varies in thickness according
to function and area of the body. On the eyelids,
the skin is only 0.5mm thick, whereas it can be
as much as 3-4mm thick on the soles of the feet
(Brooker 1998). Skin is generally 1-2mm thick
(Tortora and Derrickson 2009a).
The skin consists of thick outer layers, a
widespread system of sweat glands sensitive
to temperature changes and an extensive layer
of fatty tissue under the surface of the skin. The
skin also contains many cells that are sensitive
to touch, pain, pressure, itching and temperature
(Turkington and Dover 2007).
september 19 :: vol 27 no 3 :: 2012 35
14/09/2012 13:02
Art & science life sciences: 6
Epidermis
The epidermis is composed of stratified
keratinised squamous epithelium (Tortora
and Derrickson 2009a) and is made up of
many layers near the surface of the skin
(Turkington and Dover 2007). The epidermis
contains four main types of cells, most of which
are keratinocytes, which make up 90% of the
cells found in this layer. Melanocytes make up
8% of epidermal cells and are responsible for
producing the pigment, melanin. Langerhans
cells and Merkel cells are also found within
the epidermis. Langerhans cells are involved
in the immune response and Merkel cells
function in the sensation of touch (Tortora
and Derrickson 2009a). The epidermis is
avascular (without blood vessels) and is
dependent on blood vessels of the dermis for
oxygenation, metabolite provision and removal
of metabolic waste products.
The epidermis is made up of a number
of layers, including (Figure 1):
Stratum

basale, the deepest layer (also
called the stratum germinativum).
Stratum

spinosum or prickle cell layer.
Stratum

granulosum or granular layer.
Stratum

lucidum (finger tips, palms
and soles).
Stratum

corneum, which is the top layer.
These layers represent the different stages
of maturation of the cells and their movement
from the stratum basale up to the stratum
corneum, where they are shed. The epidermis
renews itself through cell division in its deepest
layer (Burr and Penzer 2005).
Stratum basale
The stratum basale is made up of a single row
of columnar keratinocytes. Other types of cells
found within this layer include melanocytes
and Merkel cells (Tortora and Derrickson 2009a).
The stratum basale is the only layer within
the epidermis that consists of cells capable of
division. Keratinocytes in the stratum basale
undergo mitosis and two daughter cells are
produced; one remains in the stratum basale,
while the other migrates up through the other
layers to the surface of the epidermis. This
process takes approximately 28 days in an
average epidermis of 0.1mm thickness (Tortora
and Derrickson 2009a).
The stratum basale is the nearest layer to the
dermis and is located under the epidermis. The
dermis contains a blood supply and provides
nourishment to the stratum basale. However,
as the daughter cells move further away from
the stratum basale, they receive less nutrition. As
a result the cells die. In addition, the cells become
more keratinised – they accumulate more keratin,
which is a fibrous protein involved in protecting
the skin from heat, chemicals and microorganisms.
In healthy skin, a balance between the formation
of new keratinocytes in the stratum basale and the
shedding of dead keratinocytes from the stratum
corneum is maintained.
The stratum basale also contains melanocytes,
which produce melanin. Melanocytes account
for one in every six cells in the stratum basale
(Turkington and Dover 2007). Melanin is a
pigment that protects the skin from the harmful
effects of ultraviolet (UV) light. Melanocytes have
FIGURE 1
The skin showing the layers of the epidermis and main structures of the dermis
Hair shaft
Stratum
corneum
Opening
of sweat
ducts
Epidermis
Germinative
layer
Sebaceous
gland
Sweat gland
Dermis
Stratum
corneum
Stratum
lucidum
Stratum
granulosum
Epidermis
Germinative
layer
Hair root
36 september 19 :: vol 27 no 3 :: 2012
p35-42w3.indd 36
Dermis
Subcutaneous
tissue
peter lamb
Hair follicle
© NURSING STANDARD / RCN PUBLISHING
14/09/2012 13:02
long, slender projections that contain melanin
granules. The projections extend between the
keratinocytes and transfer the granules to them.
Once inside the keratinocytes, the granules gather
to form a protective covering around the nucleus,
protecting the keratinocytes from damage caused
by UV light.
The colour of the skin is genetically determined
and environmentally modified by UV light
exposure. Skin colour is related to the amount
of melanin in epidermal cells. The more melanin
produced, the darker the skin. Nurses should
be able to advise patients of the importance
of avoiding too much UV light, whether from
natural sunlight or sunbeds. They should also
inform patients of the need to cover their skin
when outdoors and to use appropriate UV filter
creams, commonly known as sun blocks. Tortora
and Derrickson (2009a) recommended a sun
protection factor of no less than 15 to protect
against UV light.
Merkel cells are also found in the stratum
basale scattered among the keratinocytes. Merkel
cells make contact with the flattened process of
a sensory neuron called a Merkel disc. Merkel
cells and their discs detect the sensation of touch.
Stratum spinosum
As the daughter cells of the keratinocytes move
into the next layer, the stratum spinosum, they
lose their ability to divide. They also become
rounder and ‘spikier’ in shape (hence this layer’s
name). The stratum spinosum is five to 12 cells
thick. While in this layer, the single daughter
cells join together via intracellular bridges called
desmosomes. As the cells move through this layer,
the daughter cells continuously break and reform
desmosomes. These intracellular bridges have
thorn-like projections that draw adjacent cells
close together (Thibodeau and Patton 2007).
This arrangement contributes to the tensile
strength and flexibility of the skin.
Langerhans cells, developed from specialised
dendritic cells of the immune system, are found
in the stratum spinosum. They are also found in
the dermis, lymph nodes and thymus (Turkington
and Dover 2007). These cells are produced in the
red bone marrow and then migrate to the stratum
spinosum, where they participate in immune
responses against microorganisms. They function
by attracting and phagocytosing microbes and
presenting their antigens to T lymphocytes,
thereby activating the lymphocytes to destroy
the appropriate cells (Pringle and Penzer 2002).
Langerhans cells are crucial in helping other
cells of the immune system to recognise invading
microorganisms and destroy them.
© NURSING STANDARD / RCN PUBLISHING
p35-42w3.indd 37
Stratum granulosum
As the cells move through the epidermal layers
towards the surface of the skin they become
longer and flatten horizontally to form the
stratum granulosum. The stratum granulosum
is composed of three to five layers of flattened
keratinocytes. In this layer, the cells go through
a process known as apoptosis, which is an
orderly, genetically programmed cell death
during which the nucleus breaks up and
the cell dies. The cells are no longer able to
perform any metabolic functions (Tortora
and Derrickson 2009a).
By this stage, the cells lose their nucleus and
become keratinised and are comprised entirely
of a tough pliable protein called keratin (Pringle
and Penzer 2002). Keratohyalin is also present
in this layer. It consists of darkly staining
proteins that convert tonofilaments to keratin.
Odland’s bodies may also be seen. These are
membrane-coating, lamellar granules that produce
lipid, which extrudes into the spaces between the
cells and helps them stick together.
Stratum lucidum
The stratum lucidum is only found in areas where
the skin is thick, such as the palms of the hands
and soles of the feet (Tortora and Derrickson
2009a). This layer contains three to five layers
of clear, dead keratinocytes that are flattened
and made up of large amounts of keratin and
thickened plasma membranes. The stratum
lucidum lies between the stratum granulosum
and the stratum corneum and provides some
degree of waterproofing to the skin.
Stratum corneum
The stratum corneum is the uppermost layer.
It consists of 25-30 layers of flattened, dead
keratinocytes (Tortora and Derrickson 2009a).
The cells are arranged in orderly, vertical stacks
and appear to be composed of cell membranes that
are firmly attached to each other. The cells contain
the protein keratin, which helps protect the skin
and underlying tissues from heat, microorganisms
and chemicals. The intracellular lipid from the
lamellar granules in the stratum granulosum
cements the cells together and is vital in preventing
the cells from drying out.
As cells move through the stratum corneum
they lose their stickiness and are shed singly or
in clumps, known as squamae. Most people who
have ever seen or had a plaster cast removed will
recognise the accumulation of dead skin cells on
the surface of the skin. Dandruff and the majority
of house dust are dead, shed skin cells – the
favoured food of house dust mites that trigger
september 19 :: vol 27 no 3 :: 2012 37
14/09/2012 13:02
Art & science life sciences: 6
asthma in susceptible individuals (Kumar and
Clark 2009).
Each of the layers represents a stage in the life
of an epidermal cell. Since the stratum corneum
is the final layer between the body and the external
environment, it is at risk of considerable wear and
tear. Cells are lost from this layer on a continous
basis. If a part of the skin is exposed to constant
friction a hard callus can form, which is an
abnormal thickening of the stratum corneum
(Tortora and Derrickson 2009a).
Dermis
The dermis lies below the epidermis and above
the subcutaneous layer, and is responsible for
providing nutrients and physical support to the
epidermis (Burr and Penzer 2005). The dermis
contains lymph vessels, nerve endings, hair follicles
and glands (Figure 1) (Pringle and Penzer 2002). It
is anchored to the epidermis by rete ridges, which
are furrows. These furrows stabilise and allow
the exchange of nutrients between the dermis and
epidermis (Turkington and Dover 2007). However,
the two layers may become separated as a result of
shearing forces or friction, allowing fluid to collect
between the epidermis and dermis, forming what
is commonly known as a blister.
The dermis is composed of two layers: the
reticular and papillary layers. The papillary layer
contains the nerves and capillaries that nourish the
epidermis, whereas the reticular layer is made up
of strong connective tissue containing collagen and
elastic fibres (Pringle and Penzer 2002).
Collagen and elastin
Collagen and elastin in the dermis are arranged in a
woven network of fibres that have significant tensile
strength, providing the dermis with the ability
to stretch and contract (Tortora and Derrickson
2009a). Collagen is a protein that contributes
to approximately 70% of the dry weight of the
dermis. When the skin is stretched the collagen
fibres prevent tearing as a result of their high tensile
strength (Pringle and Penzer 2002).
Elastin fibres are synthesised by fibroblasts.
These fibres are finer than collagen and are found,
interwoven, among the collagen bundles. Elastin
also has elastic properties that allow the skin to
return to its normal position after stretching. With
increasing age, there is a reduction in the number
of collagen fibres, which stiffen and break up. This
results in the collagen fibres losing their shape and
becoming tangled. Meanwhile, the elastic fibres
lose some of their elasticity, thicken into bundles
and fray. These changes result in the appearance
of wrinkled skin (Tortora and Derrickson 2009a).
38 september 19 :: vol 27 no 3 :: 2012
p35-42w3.indd 38
Glands in the dermis
The skin contains three to four million sweat
glands. The function of these glands is to release
sweat into hair follicles or on to the skin surface
through pores. There are two types of sweat glands
– eccrine glands and apocrine glands – based on
their structure, location and type of secretion
(Tortora and Derrickson 2009a).
Eccrine glands Eccrine glands are simple, coiled
glands that are distributed in many areas
of the skin, but especially in the skin of the
forehead, palms of the hands and soles of the
feet. The eccrine glands produce sweat, which
is predominantly composed of water, but
includes sodium and chlorine ions, urea,
uric acid, ammonia, amino acids, glucose and
lactic acid. A total of 600ml of sweat is produced
daily. Sweat glands have an important role in
thermoregulation through evaporation (Tortora
and Derrickson 2009a).
Apocrine glands Apocrine glands are not active
during childhood, but are activated by sex
hormones during puberty (Pringle and Penzer
2002). The apocrine glands are also simple coiled
tubular glands and are mainly found in the
axillae, groin, areolae of the breasts and bearded
regions of the face in adult males (Tortora and
Derrickson 2009a). Unlike the eccrine glands,
the sweat produced by the apocrine glands is
slightly viscous and has a milky or yellowish
appearance. This sweat has no smell when it
leaves the gland. However, when it meets bacteria
on the surface of the skin, the bacteria metabolise
sweat components to produce a musky odour,
commonly described as body odour (Tortora and
Derrickson 2009a).
Sebaceous glands Sebaceous glands are simple,
branched acinar glands. An acinar gland is
a gland that has a sac-like secretory unit and
an obvious lumen. Most sebaceous glands, but
not all, are connected to hair follicles. They are
most commonly found on the face, neck and
back (Pringle and Penzer 2002). Sebaceous
glands secrete sebum, which is an oily substance
composed of a combination of triglycerides,
cholesterol, proteins and organic salts. Sebum
covers the surface of the hairs and protects them
from drying and becoming brittle. Sebum also
inhibits excessive evaporation of water from the
skin so that the skin remains soft and supple
(Tortora and Derrickson 2009a).
As well as acting as a lubricant, sebum also has
antifungal and antibacterial properties (Pringle
and Penzer 2002). Hormonal activity during
puberty may cause overactivity of sebaceous
glands leading to overproduction of sebum,
which can sometimes lead to the presence of open
© NURSING STANDARD / RCN PUBLISHING
14/09/2012 13:02
comedones (blackheads) and closed comedones
(whiteheads).
Ceruminous glands Ceruminous glands, which
are found in the external ear, are modified sweat
glands. These glands produce a waxy lubricating
secretion, which combines with secretions from
the sebaceous glands to produce a yellowish
substance called cerumen. The function of
cerumen is to provide a sticky barrier, which
together with the hairs in the external auditory
canal inhibits the entrance of foreign bodies
and insects into the ear. Cerumen also prevents
bacteria and fungi from entering the cells
because of its waterproofing ability (Tortora and
Derrickson 2009a).
Blood vessels
There are two main networks of cutaneous
arteries. The deep plexus (a network of blood
vessels) is found where the dermis and the
subcutaneous fat layer join. This network supplies
the dermis and subcutaneous layers of tissue with
blood. Small tributaries run from this plexus,
supplying hair follicles, sweat glands and other
structures within the dermis. At the uppermost
level of the dermis, the superficial plexus branches
off and carries blood vessels to the epidermis and
dermis boundary (Pringle and Penzer 2002).
Hair
Each hair is made up of columns of dead,
keratinised epidermal cells connected together
with extracellular proteins. The shaft of hair is the
segment that projects above the surface of the skin.
The root of the hair is the segment of hair that lies
deep in the shaft and is anchored in the dermis or
subcutaneous layer.
The root of the hair is surrounded by a hair
follicle. This follicle is made up of an external
and internal root sheath, which together make
up the epithelial root sheath. The dermis that
encircles the hair follicle is called the dermal
root sheath. The base of each hair follicle and
the surrounding dermal root sheath is called
the bulb and has a similar shape to an onion.
The bulb contains the layer of cells called the
hair matrix. The hair matrix cells arise from
the stratum basale, which is the layer where cell
division occurs. Therefore the hair matrix cells
are responsible for the growth of existing hairs.
They also produce new hairs when old hairs are
shed (Tortora and Derrickson 2009a).
The growth cycle for each hair follicle has
three stages:
Growth.

Regression.

Resting.

© NURSING STANDARD / RCN PUBLISHING
p35-42w3.indd 39
The cells of the hair matrix divide during the
growth stage. New cells are added at the base
of the hair so that existing cells are pushed up
through the shaft and the hair grows longer.
During this process the hair becomes keratinised
and dies. The hair stops dividing during the
regression stage and the hair follicle atrophies
and the hair no longer grows. Finally, the hair
follicle enters a resting stage. Scalp hair remains
in the growth stage for two to six years, while
the reg …
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