CHAPTER 5: THE INTEGUMENTARY SYSTEM
FUNCTIONS OF THE INTEGUMENTARY SYSTEM
Protection: The ability of skin to protect underlying tissues from mechanical stress, pathogens, heat, chemicals, UV
radiation, and decreases water loss/gain and inhibits bacterial growth from the skin’s surface.
Chemical barriers: Protection is provided by the chemical barriers of the skin, which include “protective”
secretions and melanin. The acid mantle refers to the acidic secretions of the skin, which inhibit bacterial growth
on the skin’s surface. Bacterial growth is, also, inhibited and controlled by natural antibiotics called defensins
produced by skin cells, dermcidin in sweat, and sebum produced by sebaceous glands . In addition, melanin is a
pigment that absorbs UV radiation to protect skin cells from damage caused by this type of electromagnetic
radiation.
Physical/Mechanical barriers: Protection is provided by the physical/mechanical barriers of the keratinized
epithelial cells that compose the epidermis. In addition, the epidermal surface is covered with sebum and
glycolipids, which inhibits osmosis and the diffusion of water-soluble substances across its surface. However,
lipid-soluble substances, like oxygen, carbon dioxide, lipid-soluble vitamins (i.e. vitamin A, D, E, and K), plant
chemicals (i.e. oleoresins), and organic solvents (i.e. acetone and paint thinners) can penetrate the skin.
Biological barriers: Protection is provided by biological barriers, which include Langerhans cells in the epidermis,
macrophages in the dermis, and DNA. Langerhans cells respond to antigens (i.e. pathogens) that present
themselves in the epidermis, and macrophages phagocytize pathogens (i.e. bacteria and viruses) that penetrate
the epidermis and dermis. Like melanin, DNA protects the skin against UV radiation as the electrons in DNA
absorb the radiation and transfer it to the atomic nuclei, which release it as heat.
Thermoregulation: The ability of skin to regulate body temperature via evaporative cooling by releasing sweat onto the
skin’s surface and via vasodilation in the dermis to adjust blood flow in the skin.
Cutaneous sensation: The ability of skin to detect tactile sensations (touch, pressure, vibration, itch, and tickle) and
thermal sensations due to the sensory receptors and nerve endings located in the dermal layer of the skin.
Metabolic functions: The skin is capable of synthesizing various molecules for biochemical processes.
Vitamin D synthesis: The ability of skin to synthesize vitamin D precursors from modified cholesterol molecules
by absorbing UV radiation from sunlight. These molecules enter the blood supply and circulate to all areas of the
body, where they will be converted into vitamin D.
Epidermal metabolism: Epidermal cells are, also, capable of performing various metabolic functions. For
example, keratinocyte enzymes can inhibit some cancer-causing chemicals that penetrate the skin and can
metabolize steroid hormones, like transforming cortisone into hydrocortisone. Some skin cells can synthesize
important proteins, like collagenase, which is an enzyme involved in the catabolism of collagen and helps deter
the production of wrinkles.
Blood reservoir: The dermis contains an extensive blood supply (5-10% of the total blood volume in the body) due to an
abundance of blood vessels located in this layer.
Excretion: The ability of skin to eliminate substances from the body, such as metabolic wastes (i.e. urea, uric acid,
ammonia, and bilirubin) and drug metabolites.
STRUCTURE OF THE SKIN
Cutaneous membrane (skin): The skin is the largest organ of the body based on weight and surface area. To watch a
brief video about interesting facts of the skin, please view: What is Skin?
Epidermis: The epidermis is the thin layer of the skin, located superficial to the dermis, composed of keratinized
stratified squamous epithelium.
Dermis: The dermis is the thick layer of the skin, located deep to the epidermis, composed of areolar connective
tissue (papillary region) and dense irregular connective tissue (reticular region).
Hypodermis (subcutaneous (subQ) layer; superficial fascia): The hypodermis is located deep to the dermis, and it’s
composed of adipose and areolar connective tissues. Proteins fibers from the dermis extend into the hypodermis, which
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, CHAPTER 5: THE INTEGUMENTARY SYSTEM
anchor the dermis to this layer. The hypodermis stores fat, acts as an energy reserve, contains large blood vessels to
provide the dermis with nutrients and remove waste products, and contains Pacinian corpuscles to detect deep pressure.
EPIDERMIS The epidermis is composed of four basic cell types.
Keratinocytes: Approximately 90% of all epidermal cells are keratinocytes. These cells form 4 or 5 distinct layers
in the epidermis, and they function to produce keratin. Keratin is a tough, fibrous protein that functions to protect
tissues from heat, chemicals, and microbes. It, also, provides a water-repellant barrier that decreases water loss
and gain from the body, and it inhibits the entry of microbes and foreign substances.
Melanocytes: Melanocytes are cells that function to produce melanin, a pigment that provides yellow-red to
brown-black coloring of the skin. In addition to providing color, melanin absorbs ultraviolet (UV) radiation from the
sun, which helps protect epidermal cells from the damaging effects of UV light.
Langerhans cells (epidermal dendritic cells): Langerhans cells are specialized macrophages that originate in the
red bone marrow and migrate to the epidermis (stratum spinosum). They function to initiate immune responses
against microbes that invade the skin and are easily damaged by UV radiation.
Merkel cells: Merkel cells are the least numerous of the epidermal cells and are located in the stratum basale,
where they make contact with neurons. They function to detect different aspects of touch.
Thin skin: Thin skin of the epidermis includes the stratum basale, stratum spinosum, stratum granulosum, and stratum
corneum.
Thick skin: Thick skin of the epidermis includes all of the epidermal layers (stratum basale, stratum spinosum, stratum
granulosum, stratum lucidum, and stratum corneum), and it’s located in the skin of the fingertips, palms, and soles of the
feet, where friction is the greatest.
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FUNCTIONS OF THE INTEGUMENTARY SYSTEM
Protection: The ability of skin to protect underlying tissues from mechanical stress, pathogens, heat, chemicals, UV
radiation, and decreases water loss/gain and inhibits bacterial growth from the skin’s surface.
Chemical barriers: Protection is provided by the chemical barriers of the skin, which include “protective”
secretions and melanin. The acid mantle refers to the acidic secretions of the skin, which inhibit bacterial growth
on the skin’s surface. Bacterial growth is, also, inhibited and controlled by natural antibiotics called defensins
produced by skin cells, dermcidin in sweat, and sebum produced by sebaceous glands . In addition, melanin is a
pigment that absorbs UV radiation to protect skin cells from damage caused by this type of electromagnetic
radiation.
Physical/Mechanical barriers: Protection is provided by the physical/mechanical barriers of the keratinized
epithelial cells that compose the epidermis. In addition, the epidermal surface is covered with sebum and
glycolipids, which inhibits osmosis and the diffusion of water-soluble substances across its surface. However,
lipid-soluble substances, like oxygen, carbon dioxide, lipid-soluble vitamins (i.e. vitamin A, D, E, and K), plant
chemicals (i.e. oleoresins), and organic solvents (i.e. acetone and paint thinners) can penetrate the skin.
Biological barriers: Protection is provided by biological barriers, which include Langerhans cells in the epidermis,
macrophages in the dermis, and DNA. Langerhans cells respond to antigens (i.e. pathogens) that present
themselves in the epidermis, and macrophages phagocytize pathogens (i.e. bacteria and viruses) that penetrate
the epidermis and dermis. Like melanin, DNA protects the skin against UV radiation as the electrons in DNA
absorb the radiation and transfer it to the atomic nuclei, which release it as heat.
Thermoregulation: The ability of skin to regulate body temperature via evaporative cooling by releasing sweat onto the
skin’s surface and via vasodilation in the dermis to adjust blood flow in the skin.
Cutaneous sensation: The ability of skin to detect tactile sensations (touch, pressure, vibration, itch, and tickle) and
thermal sensations due to the sensory receptors and nerve endings located in the dermal layer of the skin.
Metabolic functions: The skin is capable of synthesizing various molecules for biochemical processes.
Vitamin D synthesis: The ability of skin to synthesize vitamin D precursors from modified cholesterol molecules
by absorbing UV radiation from sunlight. These molecules enter the blood supply and circulate to all areas of the
body, where they will be converted into vitamin D.
Epidermal metabolism: Epidermal cells are, also, capable of performing various metabolic functions. For
example, keratinocyte enzymes can inhibit some cancer-causing chemicals that penetrate the skin and can
metabolize steroid hormones, like transforming cortisone into hydrocortisone. Some skin cells can synthesize
important proteins, like collagenase, which is an enzyme involved in the catabolism of collagen and helps deter
the production of wrinkles.
Blood reservoir: The dermis contains an extensive blood supply (5-10% of the total blood volume in the body) due to an
abundance of blood vessels located in this layer.
Excretion: The ability of skin to eliminate substances from the body, such as metabolic wastes (i.e. urea, uric acid,
ammonia, and bilirubin) and drug metabolites.
STRUCTURE OF THE SKIN
Cutaneous membrane (skin): The skin is the largest organ of the body based on weight and surface area. To watch a
brief video about interesting facts of the skin, please view: What is Skin?
Epidermis: The epidermis is the thin layer of the skin, located superficial to the dermis, composed of keratinized
stratified squamous epithelium.
Dermis: The dermis is the thick layer of the skin, located deep to the epidermis, composed of areolar connective
tissue (papillary region) and dense irregular connective tissue (reticular region).
Hypodermis (subcutaneous (subQ) layer; superficial fascia): The hypodermis is located deep to the dermis, and it’s
composed of adipose and areolar connective tissues. Proteins fibers from the dermis extend into the hypodermis, which
Page 1
, CHAPTER 5: THE INTEGUMENTARY SYSTEM
anchor the dermis to this layer. The hypodermis stores fat, acts as an energy reserve, contains large blood vessels to
provide the dermis with nutrients and remove waste products, and contains Pacinian corpuscles to detect deep pressure.
EPIDERMIS The epidermis is composed of four basic cell types.
Keratinocytes: Approximately 90% of all epidermal cells are keratinocytes. These cells form 4 or 5 distinct layers
in the epidermis, and they function to produce keratin. Keratin is a tough, fibrous protein that functions to protect
tissues from heat, chemicals, and microbes. It, also, provides a water-repellant barrier that decreases water loss
and gain from the body, and it inhibits the entry of microbes and foreign substances.
Melanocytes: Melanocytes are cells that function to produce melanin, a pigment that provides yellow-red to
brown-black coloring of the skin. In addition to providing color, melanin absorbs ultraviolet (UV) radiation from the
sun, which helps protect epidermal cells from the damaging effects of UV light.
Langerhans cells (epidermal dendritic cells): Langerhans cells are specialized macrophages that originate in the
red bone marrow and migrate to the epidermis (stratum spinosum). They function to initiate immune responses
against microbes that invade the skin and are easily damaged by UV radiation.
Merkel cells: Merkel cells are the least numerous of the epidermal cells and are located in the stratum basale,
where they make contact with neurons. They function to detect different aspects of touch.
Thin skin: Thin skin of the epidermis includes the stratum basale, stratum spinosum, stratum granulosum, and stratum
corneum.
Thick skin: Thick skin of the epidermis includes all of the epidermal layers (stratum basale, stratum spinosum, stratum
granulosum, stratum lucidum, and stratum corneum), and it’s located in the skin of the fingertips, palms, and soles of the
feet, where friction is the greatest.
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