Download Layers of the Skin

The Skin: Layers, Structures, Functions
Layers of the Skin
Layers of the Skin
•
The skin is composed of 3 layers:1,2
•
•
A thin outer layer called the
epidermis
•
A thicker middle layer called the
dermis
•
The hypodermis or subcutaneous
tissue, which sits below the dermis,
and is abundant in fat (adipose
tissue)
The skin also contains blood vessels (arteries, veins, and capillaries),
sensory nerve fibres, and accessory structures such as hair, nails,
sebaceous glands, and sweat glands.
References
1.Weller R, Hunter J, Savin J, et al. The function and structure of the skin. In: Sugden M, Blundell R, eds. Clinical Dermatology. 4th ed. Malden, MA: Blackwell Publishing, Inc.;
2008:10-33.
2.VenesD, BidermanA, Fenton B, et al, eds. Taber's Cyclopedic Medical Dictionary. 21st ed. Philadelphia, PA: F.A. Davis Company; 2009.
Epidermis
•
The epidermis is the topmost layer of the skin.
•
It is between 0.1 and 1.0 mm thick, and is made up of many layers of closely
packed cells.
•
It can also become a portal through which foreign substances may enter the
body, and thus houses cells that participate in the immune response to
protect the body from these invaders.1,2
References
1.Weller R, Hunter J, Savin J, et al. The function and structure of the skin. In: Sugden M, Blundell R, eds. Clinical Dermatology. 4th ed. Malden, MA: Blackwell Publishing,
Inc.; 2008:10-33.
2.Norris DA. Structure and function of the skin. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2012:2498-2503
Cells of the Epidermis
Cells of the Epidermis
Cells of the Epidermis
•
•
The epidermis is primarily made up
of keratinocytes, which produce a
protein called keratin that gives the
skin its strength.
Keratinocytes account for
approximately 85% of all epidermal
cells are also an important
component of hair and nails.1,2
References
1.Weller R, Hunter J, Savin J, et al. The function and structure of the skin. In: Sugden M, Blundell R, eds. Clinical Dermatology. 4th ed. Malden, MA: Blackwell Publishing, Inc.; 2008:10-33.
2.Norris DA. Structure and function of the skin. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2012:2498-2503
Cells of the Epidermis
Cells of the Epidermis
Langerhans cells can be thought of as highly
specialised dendritic cells.
• They are produced in the bone marrow,
then migrate to their target tissue: the middle
of the epidermis.
• They are an important subset of antigenpresenting cells (APC) that process antigens
and present them to T cells in the skin or
lymph nodes.
• They become more abundant at sites of
inflammatory skin disorders.1,2
References
1.Weller R, Hunter J, Savin J, et al. The function and structure of the skin. In: Sugden M, Blundell R, eds. Clinical Dermatology. 4th ed. Malden, MA: Blackwell Publishing, Inc.; 2008:10-33.
2.Norris DA. Structure and function of the skin. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2012:2498-2503
Cells of the Epidermis
Cells of the Epidermis
Melanocytes are the only cells
that can synthesise melanin, a
pigment that helps protect the
skin from damaging ultraviolet
radiation1,2
References
1.Weller R, Hunter J, Savin J, et al. The function and structure of the skin. In: Sugden M, Blundell R, eds. Clinical Dermatology. 4th ed. Malden, MA: Blackwell Publishing, Inc.; 2008:10-33.
2.Norris DA. Structure and function of the skin. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2012:2498-2503
Cells of the Epidermis
Cells of the Epidermis
Merkel cells are
concentrated near hair
follicles and enable the
sensation of fine touch.1
References
1.Weller R, Hunter J, Savin J, et al. The function and structure of the skin. In: Sugden M, Blundell R, eds. Clinical Dermatology. 4th ed. Malden, MA: Blackwell Publishing, Inc.;
2008:10-33.
Epidermal Layers
In normal skin, the
thickness of the
epidermis is kept
constant by the
balance between
shedding of the
superficial layer of
cells and cell
division at the
deepest layer.1
References
1.Weller R, Hunter J, Savin J, et al. The function and structure of the skin. In: Sugden M, Blundell R, eds. Clinical Dermatology. 4th ed. Malden, MA: Blackwell Publishing, Inc.;
2008:10-33.
Epidermis Layers
Epidermis Layers
The horny layer is the
outermost layer of the
epidermis. It is
comprised of dead,
flattened keratinocytes
that provide a barrier
for water loss,
infectious agents, and
toxic chemicals 1
References
1.Weller R, Hunter J, Savin J, et al. The function and structure of the skin. In: Sugden M, Blundell R, eds. Clinical Dermatology. 4th ed. Malden, MA: Blackwell Publishing, Inc.; 2008:10-33.
Epidermis Layers
Epidermis Layers
The granular layer is
composed of 2 to 3
layers of keratinocytes
undergoing
differentiation and
programmed cellular
death (apoptosis).1,3
Keratinocytes in this
layer secrete the lipids
needed to prevent the
loss of water from the
body.1
References
1.Weller R, Hunter J, Savin J, et al. The function and structure of the skin. In: Sugden M, Blundell R, eds. Clinical Dermatology. 4th ed. Malden, MA: Blackwell Publishing, Inc.; 2008:1033.
Epidermis Layers
Epidermis Layers
The spiny layer is
composed of keratinocytes
undergoing differentiation.
They are attached to each
other by projections that
resemble prickles or
spines.1
References
1.Weller R, Hunter J, Savin J, et al. The function and structure of the skin. In: Sugden M, Blundell R, eds. Clinical Dermatology. 4th ed. Malden, MA: Blackwell Publishing, Inc.; 2008:10-33.
Epidermis Layers
Epidermis Layers
The basal layer is the
deepest layer of the
epidermis.
It is composed of a
single layer of
columnar cells and is
responsible for skin
cell proliferation.1
References
1.Weller R, Hunter J, Savin J, et al. The function and structure of the skin. In: Sugden M, Blundell R, eds. Clinical Dermatology. 4th ed. Malden, MA: Blackwell Publishing, Inc.;
2008:10-33.
Dermis
The dermis provides structural and nutritional support to the epidermis
Dermis
Similar to the
epidermis, the dermis
also contains
Langerhans cells. In
addition, the dermis
contains dermal
dendritic cells that play
a role in immune
response together with
Langerhans cells.1
References
1.Weller R, Hunter J, Savin J, et al. The function and structure of the skin. In: Sugden M, Blundell R, eds. Clinical Dermatology. 4th ed. Malden, MA: Blackwell Publishing, Inc.; 2008:10-33.
Dermis
Fibroblasts are the
primary cell of the dermis
and the connective
tissues they produce give
the skin its elasticity,
tensile strength, and
resilience to tears.1
References
1.Weller R, Hunter J, Savin J, et al. The function and structure of the skin. In: Sugden M, Blundell R, eds. Clinical Dermatology. 4th ed. Malden, MA: Blackwell Publishing, Inc.; 2008:10-33.
Dermis
Downward growths of the epidermis and upward projections
of the dermis create ridges that increase the bonding area
between the epidermis and dermis. These ridges are most
readily observed on the fingertips as fingerprints.1
References
1.Weller R, Hunter J, Savin J, et al. The function and structure of the skin. In: Sugden M, Blundell R, eds. Clinical Dermatology. 4th ed. Malden, MA: Blackwell Publishing, Inc.; 2008:10-33.
Cells of the Dermis
Cells of the Dermis
Mast cells can trigger a local
inflammatory response to antigen by
releasing substances that act on blood
vessels. They are particularly
important in allergic responses.1
References
1. Murphy K. Basic concepts in immunology. In: Janeway'sImmunobiology. 8th ed. New York, NY: Garland Science; 2012:1-36
Cells of the Dermis
Langerhans cells are highly specialised dendritic cells.
They are an important subset of antigen-presenting cells
(APC) that process antigens and present them to T cells in
the skin or lymph nodes. Langerhans cells become more
abundant at sites of inflammatory skin disorders.1,2
References
1.Weller R, Hunter J, Savin J, et al. The function and structure of the skin. In: Sugden M, Blundell R, eds. Clinical Dermatology. 4th ed. Malden, MA: Blackwell Publishing, Inc.; 2008:10-33.
2.Norris DA. Structure and function of the skin. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2012:2498-2503.
Cells of the Dermis
Lymphocytes possess a powerful ability to recognize
and mount a targeted attack against pathogenic
microorganisms. However, they require the
participation of the innate immune system to initiate
this attack.1
References
1. Murphy K. Basic concepts in immunology. In: Janeway'sImmunobiology. 8th ed. New York, NY: Garland Science; 2012:1-36.
Cells of the Dermis
Fibroblasts are the primary cell type of the dermis.
They are capable of producing collagen, elastin, and
reticular protein fibres, from which the connective
tissues develop.1,2
References
1. Weller R, Hunter J, Savin J, et al. The function and structure of the skin. In: Sugden M, Blundell R, eds. Clinical Dermatology. 4th ed. Malden, MA: Blackwell Publishing, Inc.; 2008:10-33.
2. VenesD, BidermanA, Fenton B, et al, eds. Taber's Cyclopedic Medical Dictionary. 21st ed. Philadelphia, PA: F.A. Davis Company; 2009.
Cells of the Dermis
Macrophages are always present in the dermis. They are
considered to be a front-line component of the dermal innate
immune response.1
References:
1.Murphy K. Basic concepts in immunology. In: Janeway'sImmunobiology. 8th ed. New York, NY: Garland Science; 2012:1-36.
Components of the Dermis
The dermis is a fibrous and
elastic matrix of connective
tissue that provides a structural
scaffold for various cells,
vessels, nerves, and epidermal
appendages, such as hair, sweat
glands, and sebaceous
glands.1,2
Although the skin consumes little
oxygen, it has an abundant
blood supply that is found in
the dermis. In addition to playing
an important role in temperature
regulation, the blood vessels in
the dermis supply the sweat
glands and hair follicles.1,2
References
1. Weller R, Hunter J, Savin J, et al. The function and structure of the skin. In: Sugden M, Blundell R, eds. Clinical Dermatology. 4th ed. Malden, MA: Blackwell Publishing, Inc.; 2008:10-33.
2. Norris DA. Structure and function of the skin. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2012:2498-2503.
Types of Fibres in the Dermis
Collagen fibre:1
•
Constitutes 70% to 80% of the dermis
•
Prevents skin from tearing
Reticular fibre:1
•
Fine collagen fibres that surround blood vessels and accessory structures
Elastic fibre:1
•
Accounts for approximately 2% of the dermis
•
Returns skin to its unstretched state
References
Weller R, Hunter J, Savin J, et al. The function and structure of the skin. In: Sugden M, Blundell R, eds. Clinical Dermatology. 4th ed. Malden, MA: Blackwell Publishing, Inc.; 2008:10-33.
Hypodermis
The hypodermis serves to
insulate the body from
temperature irregularities,
absorb shock, and provide a
calorie reserve.1
Consisting primarily of
adipose tissue, the
hypodermis or subcutaneous
tissue lies beneath the
dermis, separating it from
underlying muscles.2
References
1. Weller R, Hunter J, Savin J, et al. The function and structure of the skin. In: Sugden M, Blundell R, eds. Clinical Dermatology. 4th ed. Malden, MA: Blackwell Publishing, Inc.; 2008:10-33.
2. Norris DA. Structure and function of the skin. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2012:2498-2503
Structures of the Skin
Structures of the Skin
•
Other key structures in
the skin include:
•
hair,
•
nails,
•
sweat glands, and
•
sebaceous glands.1
References
1. Weller R, Hunter J, Savin J, et al. The function and structure of the skin. In: Sugden M, Blundell R, eds. Clinical Dermatology. 4th ed. Malden, MA: Blackwell Publishing, Inc.; 2008:10-33.
Hair Follicles
•
Each hair develops from a group of
epidermal cells found at the base of
the follicle in the region of cell division.
This process is nourished by blood
circulation through the hair papilla, a
projection of connective tissues in the
deep end of the follicle.1
•
As epidermal cells are pushed toward
the surface, they become keratinized
and die, forming hair shafts composed
of fused plates of keratin that project
from the surface of the epidermis.1
•
The hair shaft can act as a channel for
discharge of products from apocrine
sweat glands and sebaceous glands.1
References
1. Norris DA. Structure and function of the skin. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2012:2498-2503.
Hair Follicles
•
•
Hairs do not grow continuously, but
pass through a life cycle:1
1.
Growth: about 3 years
2.
Cessation
3.
Rest: about 3 months
After this, a new hair develops from the
hair follicle and the existing hair falls
out.1
References
1. Norris DA. Structure and function of the skin. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2012:2498-2503.
Types of Hair Follicles
There are 3 types of hair follicles:1
References
1. Norris DA. Structure and function of the skin. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2012:2498-2503.
Types of Hair Follicles
There are 3 types of hair follicles:1
• Vellus: located over most of the
body
References
1. Norris DA. Structure and function of the skin. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2012:2498-2503.
Types of Hair Follicles
There are 3 types of hair follicles:1
• Vellus: located over most of the
body
• Terminal: located on the scalp,
beard area, axilla, groin, and
other hairy areas
References
1. Norris DA. Structure and function of the skin. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2012:2498-2503.
Types of Hair Follicles
There are 3 types of hair follicles:1
• Vellus: located over most of the body
• Terminal: located on the scalp,
beard area, axilla, groin, and other
hairy areas
• Sebaceous: located on the scalp,
face, beard, chest, back, axilla, and
groin; have a minimal hair shaft but
hypertrophied sebaceous glands
References
1. Norris DA. Structure and function of the skin. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2012:2498-2503.
Sweat Glands
There are 2 types of sweat glands:1
1.
2. Apocrine
• Scent glands that secrete products
into hair follicles
• Develop following onset of puberty
• Secretion increased by heightened
tension, such as fear or sexual
excitement
• Present in axilla, external genitalia,
areolar skin around nipples, and
perianal area
Eccrine
• Secrete sweat directly onto
skin’s surface in response to
heat
• Found throughout the skin,
but concentrated in the
palms, soles, and head
References
1. Norris DA. Structure and function of the skin. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2012:2498-2503.
Sebaceous Sweat Glands
Sebaceous glands produce a type of oil called
sebum. These glands:1
• Are located throughout dermis,
except for palms of hands and soles
of feet
• Become activated by onset of
puberty
• Secrete fatty acids, triglycerides,
and other lipids into hair follicles
References
1. Norris DA. Structure and function of the skin. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2012:2498-2503.
Apocrine Sweat Glands
Apocrine sweat glands are anchored in the dermis,
and the composition of their discharge is not
completely understood.1
They secrete strong-smelling
substances and are responsible for
body odour and pheromones.1,2
Locations:1
1. Axilla
2. External genitalia
3. Skin around nipples
4. Perianal area
Development:1
• Following onset of puberty
References
1. Norris DA. Structure and function of the skin. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2012:2498-2503.
2. Weller R, Hunter J, Savin J, et al. The function and structure of the skin. In: Sugden M, Blundell R, eds. Clinical Dermatology. 4th ed. Malden, MA: Blackwell Publishing, Inc.;
2008:10-33.
Apocrine Sweat Glands
Apocrine sweat glands are anchored in the dermis,
and the composition of their discharge is not
completely understood.1
They secrete strong-smelling
substances and are responsible for
1,2 localisation of apocrine sweat glands
• Since
the anatomical
body odour
and pheromones.
closely corresponds to the typical distribution of HS lesions,
Locations:1apocrine sweat glands were historically thought to be
1. Axilla implicated in the pathogenesis of the disease.
• However,
2. External
genitalia this theory has since been discarded in favour of a
primary role for follicular occlusion in the development of
3. Skin around
nipples 3,4
the disease.
4. Perianal area
Development:1
• Following onset of puberty
References
1. Norris DA. Structure and function of the skin. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2012:2498-2503.
2. Weller R, Hunter J, Savin J, et al. The function and structure of the skin. In: Sugden M, Blundell R, eds. Clinical Dermatology. 4th ed. Malden, MA: Blackwell Publishing, Inc.;
2008:10-33.
3. Layton A. Pathology of HidradenitisSuppurativa. In: JemecGBE, RevuzJ, Leyden JL, eds. HidradenitisSuppurativa. Germany: Springer; 2006:25-33.
4. PoliF, JemecGBE, RevuzJ. Clinical Presentation. In: JemecGBE, RevuzJ, Leyden JL, eds. HidradenitisSuppurativa. Germany: Springer; 2006:11-24.
Functions of the Skin
Functions of the Skin
The skin performs multiple protective and regulatory
functions.1
1. Protection
2. Immunologic Response
3. Regulation of Body Temperature
4. Sensory Input
5. Metabolic Functions
6. Barrier to Water
References
1. Weller R, Hunter J, Savin J, et al. The function and structure of the skin. In: Sugden M, Blundell R, eds. Clinical Dermatology. 4th ed. Malden, MA: Blackwell Publishing, Inc.;
2008:10-33.
Functions of the Skin
The skin performs multiple protective and regulatory
functions.1
1. Protection
•
The epidermis resists friction and
tangential stress. Melanin pigment
and antioxidant enzymes in the
epidermis protect the skin against
radiation.
•
The horny layer of the epidermis
acts as a barrier to external
substances; it is thickened on the
palms of the hand and soles of the
feet to provide extra padding and
protection.
•
The reticular dermis is a barrier to
injury and trauma as well as a
cushion for underlying structures.2
References
1. Weller R, Hunter J, Savin J, et al. The function and structure of the skin. In: Sugden M, Blundell R, eds. Clinical Dermatology. 4th ed. Malden, MA:
Blackwell Publishing, Inc.; 2008:10-33.
2. Norris DA. Structure and function of the skin. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders;
2012:2498-2503.
Functions of the Skin
The skin performs multiple protective and regulatory
functions.1
2. Immunologic Response
•
The skin is the outermost arm of the
immune response and is designed to
defend against infection, abnormal
cells, and toxins through innate and
adaptive immune responses.2,3
References
1. Weller R, Hunter J, Savin J, et al. The function and structure of the skin. In: Sugden M, Blundell R, eds. Clinical Dermatology. 4th ed. Malden, MA:
Blackwell Publishing, Inc.; 2008:10-33.
2. Norris DA. Structure and function of the skin. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders;
2012:2498-2503.
3. Murphy K. Basic concepts in immunology. In: Janeway'sImmunobiology. 8th ed. New York, NY: Garland Science; 2012:1-36.
Functions of the Skin
The skin performs multiple protective and regulatory
functions.1
3. Regulation of Body Temperature
•
Sweat and blood vessels play an
important role in body temperature
regulation2
•
Evaporation from eccrine sweat glands
is critical for thermoregulation.
•
Dilation or constriction of blood vessels
regulates heat exchange in the skin.
•
Up to 4% to 5% of total blood volume in
the body may be stored in skin vessels
References
1. Weller R, Hunter J, Savin J, et al. The function and structure of the skin. In: Sugden M, Blundell R, eds. Clinical Dermatology. 4th ed. Malden, MA:
Blackwell Publishing, Inc.; 2008:10-33.
2. Norris DA. Structure and function of the skin. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders;
2012:2498-2503.
Functions of the Skin
The skin performs multiple protective and regulatory
functions.1
4. Sensory Input
•
The skin is the largest sensory organ of
the body.1,2
•
The skin and mucous membranes are
the principal sites of both pleasant and
unpleasant sensations.1,2
•
Specialised sensory structures register
pressure applied to the skin, and free
nerve endings detect heat and pain.1,2
References
1. Weller R, Hunter J, Savin J, et al. The function and structure of the skin. In: Sugden M, Blundell R, eds. Clinical Dermatology. 4th ed. Malden, MA:
Blackwell Publishing, Inc.; 2008:10-33.
2. Norris DA. Structure and function of the skin. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders;
2012:2498-2503.
Functions of the Skin
The skin performs multiple protective and regulatory
functions.1
5. Metabolic Functions
•
One of the metabolic functions of the
skin is the synthesis of vitamin D by
keratinocytes. 1,2
•
Sunlight converts molecules in the
epidermis to a precursor of vitamin
D, which is transported to the
kidneys to be converted into active
vitamin D.1,2
•
Active vitamin D facilitates
gastrointestinal absorption of
calcium.1,2
References
1. Weller R, Hunter J, Savin J, et al. The function and structure of the skin. In: Sugden M, Blundell R, eds. Clinical Dermatology. 4th ed. Malden, MA: Blackwell Publishing, Inc.;
2008:10-33.
2. Horst RL, Reinhardt TA, Reddy GS. Vitamin D metabolism. In: Feldman D, Pike JW, GlorieuxFH, eds. Vitamin D. 2nd ed. Burlington, MA: Elsevier Inc.; 2005:15-36.
Functions of the Skin
The skin performs multiple protective and regulatory
functions.1
5. Barrier to Water
•
Sebum is secreted into hair follicles and
helps keep the hairs and the skin soft
and relatively waterproof.1
•
The horny layer of the epidermis
prevents water loss by evaporation.1,2
References
1. Weller R, Hunter J, Savin J, et al. The function and structure of the skin. In: Sugden M, Blundell R, eds. Clinical Dermatology. 4th ed. Malden, MA: Blackwell Publishing, Inc.;
2008:10-33.
2. Norris DA. Structure and function of the skin. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Elsevier Saunders; 2012:2498-2503.