Anatomy and Physiology Notes
Unit 2: Protection, Support and Movement
Chapter 5: The Integumentary System
CLE3251.2.1:
CLE3251.2.2:
IDY structures of the integumentary system and show the relationship between these
structures and their function
Investigate the physiological mechanisms that allow the integumentary system to function
An Introduction the Integumentary System
Objectives:
Describe the main structural features of the epidermis, and explain the functional significance
of each.
The Integumentary system is the largest, most accessible, and underappreciated organ system. It is often
referred to simply as the integument, and accounts for around 16% of your total body weight. It is your body’s
first line of defense against an often hostile environment because it is where your body and the outside world
meet.
Two major components of the integumentary system:
1. Cutaneous membrane – skin
a. Epidermis – (epi – above) superficial epithelium
b. Dermis – underlying area of connective tissues
c. Hypodermis – AKA subcutaneous layer –loose connective tissue that separates the dermis from
the deep fascia around other organs such as muscles or bones
i. Not technically part of the integument, but it is important in stabilizing the position of
the skin in relation to underlying tissues while permitting independent movement
ii. Fascia: connective tissue fibers, primarily collagenous, that form sheets or bands
beneath the skin to attach, stabilize, enclose, and separate muscles and other internal
organs
iii. Collagenous: made of strong, insoluble protein fibers that are common in connective
tissues
2. Accessory structures – hair, nails, and multicellular exocrine glands
a. Located primarily in the dermis and protrude through the epidermis to the skin surface
Functions of the skin and hypodermis:
1. Protection of underlying tissues and organs against impact, abrasion, fluid loss, and chemical attack
2. Excretion of salts, water, and organic wastes by integumentary glands
3. Maintenance of normal body temp through either insulation or evaporative cooling, as needed
4. Production of melanin, which protects underlying tissue from UV radiation
5. Production of keratin, which protects against abrasion and serves as a water repellent
a. Keratin: forms hair and nails in humans
6. Synthesis of vitamin D₃, a steroid that is subsequently converted to calcitriol, a hormone important to
normal calcium metabolism
7. Storage of lipids in adipocytes in the dermis and in adipose tissue in the subcutaneous layer
a. Adipocytes: fat cells
b. Adipose tissue: loose connective tissue dominated by fat cells
8. Detection of touch, pressure, pain, and temp stimuli, and the relaying of that information to the nervous
system
Section 5.1: The epidermis is composed of strata (layers) with various functions
The epidermis:
1. Is made of a stratified squamous epithelium: a type of tissue composed of several layers of flattened
and plate-like cells that form a superficial covering or internal lining of a body cavity or vessel.
2. Provides the body with protection against microorganisms entering the body.
3. Is avascular: contains no local blood vessels, but relies on capillaries in the dermis that carry nutrients
and oxygen to and from the epidermis
4. Is dominated by keratinocytes: cells formed in several layers that contain large amounts of the protein
keratin, which protects against abrasion and serves as a water repellent
Strata of the epidermis: (Stratum: Latin word for “layer”; paired with Latin name for the function of the layer); In
order from deep to superficial
1. Basal lamina: a layer of filaments and fibers that attach an epithelium to the underlying connective
tissue
2. Stratum Germinativum: the innermost epidermal layer that forms epidermal ridges, which extend into
the dermis and are adjacent to the dermal papillae (nipple shaped mounds) that project into the
epidermis.
a. These ridges help strengthen the bond between the Stratum Germinativum and the underlying
dermis. They also increase the surface area of the skin and increase friction, allowing for better
grip. The ridge shapes and patterns are determined by genetic information, and the pattern is
unique to you and will not change during your lifetime.
b. Basal cells (AKA germinative cells): stem cells whose divisions replace the more superficial
keratinocytes that are lost or shed at the epithelial surface
c. Merkel cells: receptor cells that are found on skin surfaces that lack hair and are sensitive to
touch, releasing chemicals that stimulate sensory nerve endings
d. Melanocytes: pigment cells found in the stratum Germinativum that cause brown skin tones
e. Associate the word Germinativum with germinate, which means to sprout or grow. Just as
blades of grass sprout upward and extend beyond the soil, the daughter cells of stem cells
dividing in this stratum are pushed toward the skin surface; on the way, they elongate, acquire
organelles, and mature.
3. Stratum Spinosum: literally means “spiny layer” because the cells look like miniature pincushions in
standard tissue sections
a. Consists of 8-10 layers of keratinocytes bound together by desmosomes: small, circular, dense
areas within the intercellular bridge that forms the site of adhesion between certain epithelial
cells, especially the stratified epithelium of the epidermis
b. Also contains dentritic cells (AKA Langerhans cells), that participate in the immune response by
stimulating a defense against microorganisms that manage to penetrate the superficial layers of
the epidermis and superficial skin cancers.
4. Stratum Granulosum: “grainy layer”
a. Consists of 3-5 layers of keratinocytes from stratum Spinosum, that have started making large
amounts of keratin and keratohyalin: forms dense cytoplasmic granules that promote
dehydration (and eventual death) of the cell as well as aggravation and cross-linking of keratin
fibers
5. Stratum Lucidum: “clear layer” located in the thick skin of the palms and soles that covers the stratum
granulosum
6. Stratum Corneum: the exposed surface of skin where evaporation (AKA perspiration) occurs.
a. Insensible perspiration: water from between skin cells slowly penetrates the skin surface (about
1 pint per day) and evaporates without being able to see or feel the water loss
b. Sensible perspiration: water produced by active sweat glands that you can see or feel.
Section 5.2: Factors influencing skin color are epidermal pigmentation and dermal circulation
Objectives:
Explain what accounts for individual differences in skin color, and discuss the response of
melanocytes to sunlight exposure.
Epidermal pigmentation: effects the color of skin tone and caused by two pigments
1. Carotene: an orange-yellow pigment that normally accumulates in epidermal cells.
a. Most apparent in light-skinned individuals and in fatty tissues in the deep dermis and
subcutaneous layer.
b. Can be converted into vitamin A, which is required for normal maintenance of epithelia and the
synthesis of photoreceptor pigments in the eyes
2. Melanin: a brown, yellow-brown, or black pigment produced by Melanocytes
a. Light-skinned people produce less melanin, or melanin that lasts temporarily. Dark-skinned
people have larger melanosomes, causing skin pigmentation to be darker and more permanent.
b. Protects skin layers from harmful effects of sunlight with high amounts of UV radiation,
including DNA damage (mutations and promoting development of cancer cells), burns, and
premature wrinkling. However, small amounts of UV radiation are beneficial, because it
stimulates production of a compound required for calcium ion homeostasis.
Dermal Circulation: effects the color of capillaries in the skin
1. Hemoglobin: pigment contained in red blood cells that binds and transports oxygen in the bloodstream,
causing blood to become bright red
a. When the body temp rises, the blood vessels / capillaries dilate so the skin can act as a radiator
and lose this heat, which causes the skin to become flushed and red.
b. On the other hand, when the blood supply is temporarily reduced, as occurs when you are
frightened, the skin becomes relatively pale (turns “white” with fear) as a result of a sudden
drop of blood supply to the skin
c. When you are extremely cold, the oxygen levels in the tissues decline and hemoglobin releases
oxygen and turns a much darker red, causing the skin to look a “bluish” color called cyanosis.
Changes in skin appearance can be useful in diagnosing diseases that primarily affect other body systems.
1. Jaundice: the liver is unable to excrete bile, so a yellowish pigment accumulates in body fluids, and in
advanced stages, the skin and whites of the eyes turn yellow
2. Some tumors affecting the pituitary gland result in secretion of large amounts of melanocyte-stimulating
hormone (MSH), causing a darkening of the skin, as it the individual has an extremely dark bronze tan.
3. Addison disease: the pituitary gland secretes large quantities of adrenocorticotropic hormone (ACTH),
which is similar to MSH
4. Vitiligo: Melanocytes are lost due to immune defense malfunctions, where antibodies attack normal
melanocytes, causing light spots on primarily dark-skinned individuals
5. Skin cancers and melanomas
Section 5.5: The dermis is the tissue layer that supports the epidermis
Objectives:
Describe the structure and functions of the dermis
Two major components of the dermis:
1. A superficial papillary layer: consists of areolar tissue (loose connective tissue with open spacious
framework) , capillaries, lymphatics, and sensory neurons that supply the surface of the skin
2. Deeper reticular layer: consists of an interwoven meshwork of dense irregular connective tissue
containing both collagen and elastic fibers
Dermatitis: an inflammation of the skin that primarily involves the papillary layer and typically begins in a part of
the skin exposed to infection or irritated by chemicals, radiation or mechanical stimuli (poison ivy, battery acid,
mild sunburn, etc)
Dermal Strength and Elasticity:
1. Supported by two types of fibers located within the dermis
a. Collagen fibers: very strong fibers that resist stretching but are easily bent or twisted, limiting
flexibility to prevent tissue damage
b. Elastic fibers: permit stretching and then recoil to original length, providing flexibility
2. Skin turgor: the flexibility and resilience of the skin
a. Water also plays an important role in strength and elasticity of the skin. Dehydration, aging,
hormones, and UV radiation can alter the amount of elastin in the dermis (sometimes
permanently) resulting in wrinkles and sagging skin.
b. Stretch marks: Wrinkles and creases that occur when the skin is stretched beyond its elastic
limits and results in damage to the dermis, which prevents it from recoiling to its original size.
c. Tretinoin (Retin-A) is a vitamin A derivative that can be applied to the skin that was originally
used to treat acne, but also increases blood flow to the dermis and stimulates dermal repair
causing a decrease in wrinkle formation and size
Lines of cleavage: pattern of fiber bundles that are arranged to resist forces applied to the skin during normal
movement. Whether a cut scars or heals without scarring depends upon the location of the cut in reference to
the lines of cleavage
Dermal blood supply:
1. Cutaneous plexus: a network of arteries and tributaries within the subcutaneous layer that supplies the
skin, hair follicles, sweat glands, and other structures in the dermis with blood, nutrients, and oxygen
2. Papillary plexus: a network of small arteries that provides blood to capillary loops that follow the
contours of the epidermis-dermis boundary
a. Trauma to the skin often results in a contusion (bruise), because as dermal blood vessels
rupture, blood leaks into the dermis, and the area develops a “black and blue” coloring.
Innervation of the skin: Nerve fibers in the skin control blood flow, adjust gland secretion rates, and monitor
sensory receptors in the dermis and deeper layers of the epidermis
Section 5.6: The hypodermis is tissue beneath the dermis that connects it to underlying tissues
Objectives:
Describe the structure and functions of the hypodermis
The hypodermis consists of areolar and adipose tissues and is quite elastic. Its superficial regions contain large
arteries and veins, providing the skin with a substantial amount of blood as the veins constrict. For this reason,
the skin is often described as a blood reservoir. The deeper portion contains smaller and fewer capillaries and
more fatty cells, making subcutaneous injection a useful method for administering drugs that should not be
injected directly into the bloodstream.
This fatty layer provides extra insulation and helps reduce heat loss, and also serves as an energy reserve and a
shock absorber for rough activities.
As we mature to puberty, hormones change the distribution of subcutaneous fat: men begin storing fat in the
neck, on the arms, along the lower back and over the buttocks; women begin storing fat at the breasts,
buttocks, hips and thighs.
Section 5.10: Several steps are involved in repairing the integument following an injury
Objectives:
Explain how the skin responds to injury and repairs itself
Four stages in the regeneration of skin after injury:
1. Bleeding occurs when damage extends through the epidermis into the dermis.
2. Blood clot (scab) forms at the surface, temporarily restoring the integrity of the epidermis and
restricting entry of additional microorganisms into the damaged area.
3. Over time, deeper portions of the clot dissolve, and the number of capillaries decline. Fibroblast activity
leads to the appearance of collagen fibers and typical ground substance.
4. Formation of an inflexible, fibrous, noncellular scar tissue completes the repair process, but does not
restore the tissue to its original condition.
Taboo? Tattoos, piercings, keloids, ‘branding” and other scar patterns are all used to “enhance” the appearance
of the integument; some aboriginal cultures intentionally produce keloids as a form of body decoration.
 Keloids: a thick, raised area of scar tissue covered by a shiny, smooth epidermal surface that most
commonly develop on the upper back, shoulders, anterior chest, or earlobes, usually on people with
dark skin.
Section 5-7: Hair is composed of keratinized dead cells that have been pushed to the surface.
Hairs are nonliving structures produced in organs called hair follicles.
Arrector pili muscles: hair erector muscles
Functions of hair and hair follicles:
 Protect scalp from UV radiation
 Cushion light impacts to the head
 Insulate the skull
 In nostril: Prevent entry of foreign particles and insects into the nose
 Eyelashes: Prevent entry of foreign particles and insects into the eye
 Eyebrows: keep sweat out of the eyes
Section 5-8: Sebaceous glands and sweat glands are exocrine glands found in the skin.
Sebaceous glands: oil glands that discharge an oily lipid secretion (sebum) into hair follicles
Functions of sebum:
 Inhibit the growth of bacteria
 Lubricate and protect the keratin of the hair shaft
 Conditions surrounding skin of the hair shaft
Two types of Sweat glands: aka sudoriferous glands
1. Apocrine sweat glands: begin secreting sweat from hair follicles at puberty as a nutrient source for
bacteria, which intensifies an odor; located in the armpits (axillae), around the nipples, and in the pubic
region
2. Eccrine / Merocrine sweat glands: causes sensible perspiration that secretes directly onto the surface of
the skin
Functions of merocrine sweat gland activity:
 Cool skin surface to reduce body temperature
 Excrete water and electrolytes
 Provide protection from environmental hazards by diluting harmful chemicals and discouraging
microorganism growth
Two other Integumentary glands:
1. Mammary glands: anatomically related to Apocrine sweat glands, controlled by sex hormones and
pituitary hormones
2. Ceruminous glands: modified sweat glands in the ear; produce earwax that traps foreign particles,
preventing them from reaching the ear drum
Section 5-9: Nails are keratinized epidermal cells that protect the tips of fingers and toes
Cells of the nails can be affected by conditions that alter body metabolism, so changes in the shape, structure, or
appearance of the nails can be useful in diagnosing individuals with chronic respiratory disorders, thyroid gland
disorders, or AIDS, psoriasis or blood disorders.
Section 5.11: Effects of aging include dermal thinning, wrinkling, and reduced melanocyte activity
Objectives:
Summarize the effects of aging on the skin
Effects of aging on integument:
 Epidermal thinning causes the connections between the dermis and epidermis to weaken, making older
people more prone to injury, skin tears, and skin infections.
 Decrease of dentritic cells reduces the sensitivity of the immune system and encourages skin damage
and infection.
 Decline in vitamin D₃ production results in reduced calcium and phosphate absorption, which leads to
muscle weakness and reduction in bone strength and density.
 Decline in melanocyte activity causes more sensitivity to sunlight exposure and sunburn.
 Decline in glandular activity causing skin to become dry and scaly, and impaired perspiration increases
the risk of overheating in warm environments because the sweat glands cannot help regulate body
temperature as effectively as in young people.
 Reduced blood supply to the dermis makes the skin become cool, which stimulates thermoreceptors
causing the elderly to feel cold, even in a warm room. However, because of reduced circulation and
sweat gland function lessening their ability to lose body heat, exposure to high temps can cause their
body temp to soar dangerously high.
 The cessation or slowing of hair follicle functions produces thinner, finer hair, and because melanocyte
activity decreases, these hairs are gray or white.
 Thinning of the dermis and elastic fiber network leads to a weaker, less resilient integument, causing
wrinkles and sagging skin, most likely occurring in areas that have been exposed to the sun.
 Reduction in sex hormone levels causes secondary sexual characteristics between males and females to
become more similar and less distinctive.
 Healing of the integument occurs more slowly, usually resulting in recurring skin infections.
Section 5.12: The integumentary system provides protection for all other body systems
Objectives:
systems.
Give examples of interactions between the integumentary system and each of the other organ
Interactions Between Integumentary System and other Organ Systems
 Provides structural support
 Synthesizes vitamin D₃ essential for calcium and phosphorous absorption (for
Integumentary
bone maintenance and growth)
Muscular
 Contractions of skeletal muscles pull against skin of face, producing facial
expressions important in communication
 Synthesizes vitamin D₃ essential for normal calcium absorption (that plays an
Integumentary
essential role in muscle contraction)
Nervous
 Controls blood flow and sweat gland activity for thermoregulation;
stimulates contraction of arrector pill muscles to elevate hairs
 Receptors in dermis and deep epidermis provide sensations of touch,
Integumentary
pressure, vibration, temperature, and pain
Endocrine
 Sex hormones stimulate sebaceous gland activity; male and female sex
hormones influence growth, distribution of subcutaneous fat, and apocrine
sweat gland activity; suprarenal hormones alter dermal blood flow and help
mobilize lipids from adipocytes
Integumentary
 Synthesizes vitamin D₃, precursor of calcitrol
Cardiovascular
 Provides oxygen and nutrients; delivers hormones and cells of immune
system; carries away carbon dioxide, waste products, and toxins; provides
heat to maintain normal skin temp
 Stimulation of mast cells produces localized changes in blood flow and
Integumentary
capillary permeability
Lymphoid
 Assists in defending the integument by providing additional macrophages
and mobilizing lymphocytes
 Provides physical barriers that prevent entry of pathogens; dendritic cells
and macrophages resist infection; mast cells trigger inflammation and initiate
Integumentary
the immune response
Respiratory
 Provides oxygen and eliminates carbon dioxide
Integumentary
 Hairs guard entrance to nasal cavity
Digestive
 Provides nutrients for all cells and lipids for storage by adipocytes
Integumentary
 Synthesizes vitamin D₃ needed for absorption of calcium and phosphorous
Urinary
 Excretes waste products; maintains normal pH and ion composition of body
fluids
 Assists in excretion of water and solutes; keratinized epidermis limits fluid
Integumentary
loss through skin
Reproductive
 Sex hormones affect hair distribution, adipose tissue distribution in
subcutaneous layer, and mammary gland development
 Covers external genitalia; provides sensations that stimulate sexual
behaviors; mammary gland secretions provide nourishment for newborn
Integumentary
infant
Skeletal