SOMAPL15 — The Integumentary System

Martini, Ober, Bartholomew · Chapter 5 · EAP Objectives 2600–2609

12 Exam Questions 10 Learning Objectives SOMAPE1A

Medical Vocabulary — Root Words & Terms OBJ 2600 — Define the medical vocabulary components related to the integumentary system.

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Every integumentary term is built from Latin or Greek roots. Knowing the roots lets you decode unfamiliar words on the exam without having memorized each one. These roots appear directly in answer choices.

Root / Prefix	Meaning	Example Term
cornu	horn	stratum corneum, cornified
cutis	skin	cutaneous membrane
derma	skin	dermis, dermatitis
epi-	above / over	epidermis (sits above the dermis)
facere	to make	cornified (cornu + facere = horn-made)
germinare	to start growing	stratum germinativum
keros	horn	keratin
kyanos	blue	cyanosis
luna	moon	lunula (pale crescent of the nail)
melas	black	melanin, melanocyte
onyx	nail	eponychium (epi- + onyx = over the nail)
papilla	nipple-shaped mound	dermal papillae

EXAM PATTERN These roots appear embedded in answer choices. If you see "kyanos" linked to a skin condition, that condition involves blue skin. If you see "epi-," it means above or over. Use the root to narrow answers you haven't seen before.

General Functions of the Integumentary System OBJ 2601 — Communicate the general functions of the integumentary system.

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The integumentary system consists of the cutaneous membrane (epidermis + dermis) and accessory structures (hair, nails, exocrine glands). The hypodermis lies below the dermis and connects the integument to deeper tissues, but is not officially part of the integumentary system.

The Five Functions

1. Protection Covers and protects underlying tissues from impacts, chemicals, and infections. Prevents loss of body fluids.

2. Temperature Maintenance Regulates heat exchange with the environment by controlling blood vessel dilation and sweat gland activity.

3. Synthesis & Storage of Nutrients The epidermis synthesizes vitamin D₃. The dermis stores lipids in adipose tissue.

4. Sensory Reception Receptors in the integument detect touch, pressure, pain, and temperature and relay information to the nervous system.

5. Excretion & Secretion Integumentary glands excrete salts, water, and organic wastes. Mammary glands (specialized integumentary glands) secrete milk.

EXAM TRAP Vitamin D₃ synthesis occurs in the epidermis, not the dermis. Lipid storage occurs in the dermis (adipose tissue). These two are frequently swapped in answer choices.

Main Structural Features of the Epidermis OBJ 2602 — Identify the main structural features of the epidermis and their functional significance.

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The epidermis is a stratified squamous epithelium. Thick skin (palms and soles) has five strata. Thin skin (the rest of the body) has four — it lacks the stratum lucidum. Thin skin is ~0.08 mm thick (like a plastic sandwich bag). Thick skin is ~0.5 mm (like a paper towel). The terms refer only to the epidermis thickness, not the entire integument.

The Five Strata — Deepest to Most Superficial

Layer	What It Is	Key Feature
Stratum Basale (deepest)	Single layer of large stem cells (basal/germinative cells). Attached to basement membrane by hemidesmosomes. Contains melanocytes and touch-sensitive cells.	Only layer that actively divides to replace shed cells. Melanocytes synthesize melanin here.
Stratum Spinosum	Spiny layer — cells displaced from the basale, may still divide.	Adds thickness. Cells continue to move upward.
Stratum Granulosum	Grainy layer — cells stop dividing and begin producing large amounts of keratin.	Keratin is extremely durable and water-resistant. In humans it forms skin surface, hair, calluses, and nails.
Stratum Lucidum (thick skin only)	Clear, glassy layer. Cells are flattened, densely packed, and filled with keratin.	Present ONLY in thick skin of palms and soles. Absent in thin skin.
Stratum Corneum (most superficial)	15–30 layers of dead, flattened, keratinized (cornified) cells. Connected by desmosomes. Shed in large groups or sheets.	Physical and chemical barrier. Relatively dry — resists growth of many microorganisms.

Cell Transit Time A cell takes 7–10 days to move from the stratum basale to the stratum corneum. During transit it loses oxygen and nutrient access, fills with keratin, and dies. Dead cells then remain in the corneum for about 2 more weeks before being shed. Total time from birth to shedding: roughly 3–4 weeks.

Epidermal Ridges & Dermal Papillae The stratum basale forms epidermal ridges that extend downward into the dermis. Dermal projections called dermal papillae extend upward between the ridges. This interlocking arrangement increases the surface area for diffusion of nutrients from dermal blood vessels into the epidermis (the epidermis has no blood vessels of its own). On palms and soles, this ridge pattern creates friction ridges — fingerprints — which are genetically determined, unique to each person, and do not change over a lifetime.

EXAM TRAP The epidermis has no blood vessels. All nutrients diffuse from dermal capillaries through the basement membrane. Questions that ask about the blood supply to the epidermis are really asking about dermal capillaries in the papillary layer.

CLINICAL — Transdermal Drug Administration Fat-soluble drugs dissolved in lipid solvents can diffuse across epidermal cell membranes. Movement is slow through the stratum corneum. Transdermal patches (e.g., scopolamine for motion sickness, nicotine for smoking cessation) require very high drug concentrations to overcome this slow rate. A brief electrical pulse can temporarily open channels in the stratum corneum to allow drug penetration. Fat-soluble drugs work better transdermally than water-soluble drugs because they can cross plasma membranes.

Individual Differences in Skin Color OBJ 2603 — Communicate what accounts for individual differences in skin, such as skin color.

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Skin color results from two interacting factors: epidermal pigments and dermal blood flow.

The Two Epidermal Pigments

Carotene Orange-yellow pigment that accumulates in epidermal cells. Found in orange vegetables (carrots, squash). Excess carotene turns light skin orange. Can be converted to vitamin A, required for maintenance of epithelial tissues and synthesis of photoreceptor pigments in the eye.

Melanin Brown, yellow-brown, or black pigment produced by melanocytes in the stratum basale. Stored in intracellular vesicles called melanosomes and transferred to epithelial cells. Colors the entire epidermis. Protects nuclear DNA from UV damage by concentrating around the nuclear envelope.

Dermal Circulation and Skin Color Blood vessels in the dermis normally give skin a reddish tint (most visible in lightly pigmented individuals). When vessels dilate (exercise, heat), skin flushes red. When vessels constrict (fear), skin becomes pale.

Cyanosis When blood loses oxygen to surrounding tissues during sustained reduction in circulation, it turns darker red. Seen from the skin surface, this darker blood appears blue — called cyanosis (kyanos = blue). Most visible in thin-skinned areas: lips, ears, under the fingernails. Causes include extreme cold, heart failure, and severe asthma.

Freckles Small pigmented spots on pale-skinned individuals. Represent areas of greater-than-average melanin production. Most abundant on sun-exposed surfaces such as the face.

Albinism An inherited condition in which melanin is not produced by melanocytes, even though those cells are present in normal numbers and distribution. Individuals with albinism have light-colored skin and hair. The melanocytes exist — they just cannot produce pigment.

EXAM TRAP Differences in skin color between individuals reflect the level of melanin production, NOT the number of melanocytes. Everyone has roughly the same number of melanocytes. Do not confuse melanocyte count with melanin output.

UV Radiation — Effects on Skin & Role of Melanocytes OBJ 2604 — Communicate the effects of ultraviolet radiation on the skin and the role played by melanocytes.

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Sunlight contains significant amounts of ultraviolet (UV) radiation. Small amounts are beneficial. Large or repeated amounts are damaging.

Beneficial Effects of UV — Vitamin D₃ Pathway Epidermal cells in the stratum spinosum and stratum basale convert a cholesterol-related steroid into vitamin D₃ when exposed to UV radiation. The liver absorbs, modifies, and releases this product. The kidneys then convert it into the hormone calcitriol. Calcitriol is essential for the absorption of calcium and phosphorus by the small intestine. Inadequate vitamin D₃ leads to abnormally weak and flexible bones.

Melanocyte Response to Sunlight Melanocyte activity slowly increases in response to UV exposure, peaking around 10 days after initial exposure (this is why a tan develops gradually). Within epidermal cells, melanin concentrates around the nuclear envelope to absorb UV before it can damage nuclear DNA. The melanocyte-to-basal-cell ratio ranges from 1:4 to 1:20, varying by body region.

Harmful Effects of UV Immediate: mild to severe burns. Long-term: premature wrinkling (connective tissue damage) and chromosomal damage to stem cells in the stratum basale or melanocytes — leading to skin cancer. Ozone layer depletion globally increases skin cancer rates.

The Three Skin Cancers

Cancer	Origin	Danger
Basal Cell Carcinoma	Stratum basale. Most common skin cancer. Appears as a waxy bump. ~Two-thirds of cases involve chronically UV-exposed areas.	Low. Metastasis seldom occurs. Surgical removal is standard treatment.
Squamous Cell Carcinoma	More superficial epidermal layers. Less common than basal cell. Almost entirely restricted to sun-exposed skin.	Low-moderate. Metastasis seldom occurs. Surgical removal.
Malignant Melanoma	Melanocytes. Usually begins in a mole but can appear anywhere. Cancerous melanocytes grow rapidly.	HIGH. Metastasizes through the lymphatic system. Prognosis depends entirely on early detection and treatment.

EXAM TRAP — Most Common vs. Most Dangerous Basal cell carcinoma = most common skin cancer. Malignant melanoma = most dangerous. These two are frequently swapped. Melanoma metastasizes through the lymphatic system, not just local spread.

CLINICAL NOTE SPF of at least 15 is recommended for outdoor activities. Fair-skinned individuals: SPF 20–30. To prevent melanoma: avoid UV exposure during midday hours; use sunblock, not tanning oil.

Dermis & Hypodermis — Structure & Function OBJ 2605 — Communicate the main structural features of the dermis and subcutaneous layers and their functional significance.

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The dermis lies beneath the epidermis. It has two major components: the superficial papillary layer and the deeper reticular layer. It provides mechanical strength, flexibility, and protection. It is highly vascular and contains sensory receptors.

Papillary Layer Areolar connective tissue. Named after the dermal papillae. Contains capillaries and nerves supplying the surface of the skin. Supports and nourishes the overlying epidermis. This is where the capillaries that feed the epidermis are located.

Reticular Layer Dense, irregular connective tissue — an interwoven meshwork. Contains elastic fibers (provide flexibility) and collagen fibers (limit flexibility to prevent tissue damage). Collagen fiber bundles blend upward into the papillary layer and extend downward into the hypodermis.

What Else Is in the Dermis Both dermal layers contain blood vessels (cardiovascular system), lymphatic vessels (lymphatic system), and nerve fibers (nervous system). Hair follicles and sweat glands, though derived from the epidermis, extend into the dermis. Nerve fibers control blood flow, adjust gland secretion rates, and monitor sensory receptors in the dermis and deeper epidermis.

Cutaneous Plexus Blood supply to the skin arises from a network of blood vessels in the hypodermis at the border with the reticular layer of the dermis. This network is called the cutaneous plexus. Its branches within the dermis provide nutrients and oxygen and remove carbon dioxide and waste products.

Hypodermis (Subcutaneous Layer) Lies beneath the dermis. NOT part of the integumentary system. Connects the skin to deeper tissues (skeletal muscles, organs) while permitting their independent movement. Composed of areolar tissue with many fat cells. Functions: insulation (baby fat reduces infant heat loss), energy reserve, and shock absorber. Contains the large blood vessels of the cutaneous plexus in its superficial region, but has few capillaries and no vital organs in its deeper region — making it a safe site for subcutaneous injection with a hypodermic needle.

Subcutaneous Fat Distribution at Puberty Men accumulate fat at: neck, upper arms, lower back, buttocks. Women at: breasts, buttocks, hips, thighs. Both sexes can accumulate abdominal fat.

EXAM TRAP The hypodermis is NOT part of the integumentary system. It connects the integument to underlying structures. Do not confuse the hypodermis with the reticular layer of the dermis.

Accessory Structures — Hair, Glands & Nails OBJ 2606 — Identify the skin's accessory structures and communicate their functions.

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Accessory structures of the integument are: hair follicles, sebaceous glands, sweat glands, and nails. All are derived from the epidermis. Hair projects above the skin surface everywhere except the palms, soles, sides of fingers and toes, lips, and portions of the external genitalia.

Hair Structure — Three Layers of a Hair Shaft

Cuticle (outermost) Overlapping shingle-like cells. Hard keratin. Outermost protective layer.

Cortex (middle) Hard keratin. Gives the hair its stiffness.

Medulla (core) Soft, flexible keratin. Central core of the hair.

Hair Root vs. Hair Shaft Root = portion anchored in the skin below the surface. Shaft = visible portion above the surface.

Hair Follicle & Hair Formation Hair follicles project deep into the dermis and usually into the hypodermis. The follicle walls contain all epidermal cell layers. At the base of each follicle is the hair papilla — a peg of connective tissue containing capillaries and nerves. Epithelial stem cells in the hair matrix surround the papilla and divide to produce the hair. As daughter cells are pushed upward, they keratinize and die — the hair root becomes the hair shaft at about the midpoint to the skin surface.

Hair Growth Cycle A scalp hair grows for 2–5 years at about 0.3 mm per day. The follicle then becomes inactive for a comparable period, then starts a new growth cycle — the old hair is pushed out. Straight hairs are round in cross section; curly hairs are flattened.

Hair Color Melanocytes at the hair papilla produce melanin. Different forms of melanin produce colors from black to red. With aging, melanin production decreases and hair lightens. White hair results from both lack of pigment AND air bubbles in the shaft. Hair cannot "turn white overnight" because each hair is dead and inert — color change is gradual.

Hair Functions Head hair: UV protection, cushioning against light blows, insulation for the skull. Nasal and ear canal hairs: filter foreign particles. Eyelashes: protect the eye surface. A sensory nerve fiber at the base of each follicle detects hair movement — provides an early-warning system for skin surface threats.

Arrector Pili Muscle Bundle of smooth muscle extending from the papillary dermis to the connective tissue sheath of each hair follicle. When stimulated by cold or emotional states (fear, rage), it contracts — the hair stands upright and the attached sebaceous gland is squeezed, releasing sebum. The result is "goose bumps."

Sebaceous (Oil) Glands Discharge oily sebum into hair follicles (or directly onto skin via sebaceous follicles on the face, back, chest, nipples, and external genitalia). Sebum lubricates hair and skin and inhibits bacterial growth. Secretion type: holocrine — the gland cell ruptures and dies to release its lipid content. Sensitive to sex hormones — secretion accelerates at puberty. Blocked ducts → inflammation → acne.

Sweat Glands (Sudoriferous Glands) — Two Types

Apocrine Sweat Glands Secrete into hair follicles. Located in armpits, around nipples, pubic region. Active at puberty. Produce sticky, cloudy, potentially odorous secretion. The sweat itself is a food source for bacteria — bacteria intensify the odor. Despite the name "apocrine," these glands actually use merocrine secretion (name is a historical misnomer). Deodorants mask odor; antiperspirants contract gland openings to reduce secretion volume from both gland types.

Merocrine (Eccrine) Sweat Glands Secrete directly onto the skin surface. Far more numerous — 2–5 million in an adult. Palm of hand: ~500 glands/cm² (3,000/in²). Sweat is 99% water + electrolytes (mainly sodium chloride), organic nutrients, and waste products including urea. Primary function: cool the skin and lower body temperature. Also contain dermicidin — an antibiotic peptide that protects against microorganisms.

Specialized Sweat Glands Mammary glands are structurally related to apocrine sweat glands and secrete milk. Ceruminous glands in the external ear combine their secretions with sebum to form earwax.

Nail Anatomy Nails protect the dorsal tips of the fingers and toes and limit distortion when digits are under mechanical stress. The nail body is the visible part — dense, dead, keratinized cells, recessed below surrounding epithelium. The nail bed is the epidermis beneath the nail body. The nail root is where nail production occurs — an epithelial fold not visible from the surface. The cuticle (eponychium) is a portion of the stratum corneum that extends over the exposed nail near the root (epi- + onyx = over the nail). The lunula is the pale crescent near the root where underlying blood vessels are obscured (luna = moon).

EXAM TRAP — Apocrine vs. Merocrine Destination Apocrine glands secrete INTO hair follicles. Merocrine (eccrine) glands secrete DIRECTLY onto the skin surface. Despite the name "apocrine," both types actually use merocrine secretion — the name is historical. Do not confuse where the secretion goes with how it is secreted.

EXAM TRAP — Nail Growth Location Nail growth occurs at the nail root. Not the nail body. Not the nail bed. The nail bed is what the nail sits on. The root is where new cells are produced.

Skin Injury & Repair OBJ 2607 — Communicate how the skin responds to injury and repairs itself.

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Skin can regenerate effectively after considerable damage because stem cells are present in both its epithelial and connective tissue components. A clean incision heals faster than a broad abrasion. When large surface areas are involved, infection and fluid loss complicate repair.

Four Stages of Skin Repair (Figure 5-9)

Inflammatory Response: Damage extends through the epidermis into the dermis — bleeding occurs. Mast cells in the dermis trigger an inflammatory response, causing enhanced blood flow to the area and attracting phagocytes.
Scab Formation: A blood clot (scab) forms at the surface, temporarily restoring epidermal integrity and blocking additional microorganisms. Most of the clot is an insoluble network of fibrin — a fibrous protein that forms from blood proteins during the clotting response. Cells of the stratum basale rapidly divide and begin migrating along the wound edges to replace missing epidermal cells. Macrophages and phagocytes clear debris and pathogens. Granulation tissue forms: the combination of blood clot, fibroblasts, and an extensive capillary network.
Fibroblast Activity (~1 week): The scab is undermined by epidermal cells migrating over the fibroblast meshwork. Phagocytic activity near the wound nearly ends. The fibrin clot breaks up. Fibroblasts have formed an extensive collagen fiber meshwork in the dermis.
Scar Tissue (weeks later): Scab shed. Epidermis complete. Fibroblasts in the dermis continue building scar tissue that gradually elevates the overlying epidermis. The repaired dermis contains abnormally high numbers of collagen fibers and relatively few blood vessels. Severely damaged hair follicles, sebaceous and sweat glands, and nerves are not repaired — they are replaced by fibrous tissue.

Keloids In some adults (more often those with dark skin), scar tissue formation continues beyond the requirements of repair. A keloid is a flattened mass of scar tissue that grows outward from the injury site into surrounding dermis, covered by a shiny, smooth epidermal surface. Keloids are harmless. Most common on upper back, shoulders, anterior chest, and earlobes. Note: surgical procedures on fetuses do not leave scars.

Burns — Classification by Depth (Table 5-1)

Classification	Layers Affected	Appearance & Sensation
First-Degree Burn partial-thickness	Killed: superficial epidermal cells Injured: deeper epidermis, papillary dermis	Inflamed; tender
Second-Degree Burn partial-thickness	Killed: superficial and deeper epidermal cells; dermis may be affected Injured: may extend into reticular layer; most hair follicles and glands unaffected	Blisters; very painful
Third-Degree Burn full-thickness	Killed: all epidermal and dermal cells Injured: hypodermis and deeper tissues	Charred; no sensation — sensory nerves destroyed. Sepsis is the leading cause of death in burn patients.

EXAM TRAP — Burns and Sensation A third-degree burn has no pain at the burn site because the sensory nerves are destroyed. Second-degree burns are the most painful of the three. Sepsis (dangerous, widespread bacterial infection) is the leading cause of death in burn patients — not fluid loss or the burn itself.

Effects of Aging on the Integumentary System OBJ 2608 — Communicate the effects of the aging process on the skin.

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Aging affects all components of the integumentary system. Multiple changes interact to worsen outcomes for elderly patients.

More Skin Injuries & Infections Stem cell activity declines → epidermis thins. Connections between epidermis and dermis weaken. Result: skin is damaged and infected more easily.

Reduced Immune Response Macrophages and immune cells in the skin decrease to about half the levels at maturity (roughly age 21). Further increases susceptibility to skin damage and infection.

Weaker Bones Vitamin D₃ production declines by approximately 75%. Reduced calcitriol → reduced calcium and phosphate absorption → weaker bones.

Increased Sun Sensitivity Melanocyte activity declines → less melanin → less UV protection. Light-skinned individuals become very pale.

Dry, Scaly Skin Glandular activity declines → reduced sebum production and reduced perspiration.

Hair Thinning & Color Change Follicles stop functioning or produce finer hairs. Decreased melanocyte activity → gray or white hair.

Sagging & Wrinkling Dermis becomes thinner. Elastic fiber network decreases. Integument becomes weaker and less resilient. Most noticeable in sun-exposed areas.

Impaired Heat Loss Blood supply to the dermis decreases AND sweat glands become less active simultaneously. Combined effect: the elderly lose body heat much less efficiently. Overexertion or high temperatures (sauna, hot tub) can cause dangerously high body temperature.

Slower Skin Repair Uninfected blister in a young adult: repairs in 3–4 weeks. Same repair at ages 65–75: 6–8 weeks. Slow repairs increase the risk of recurrent infections.

CLINICAL CONNECTION Reduced dermis blood flow combined with less active sweat glands is why elderly patients are at high risk for heat stroke. They cannot dissipate body heat normally. This combination is a commonly tested clinical application.

Functional Relationships — Integumentary & Other Systems OBJ 2609 — Identify the functional relationships between the integumentary system and other body systems.

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The integumentary system does not operate in isolation. Its dermis is the interface through which multiple organ systems connect to and support the skin's functions.

Cardiovascular System Blood vessels in both dermal layers regulate skin temperature. The cutaneous plexus delivers nutrients and oxygen and removes waste. Vessel dilation and constriction change skin color and regulate heat loss.

Lymphatic System Lymphatic vessels in the dermis help tissues defend and repair themselves after injury or infection.

Nervous System Nerve fibers in the dermis control blood flow, adjust gland secretion rates, and monitor sensory receptors. Receptors detect touch, pressure, pain, and temperature.

Skeletal System Skin synthesizes vitamin D₃ → liver and kidneys convert it to calcitriol → calcitriol drives calcium and phosphate absorption in the small intestine → essential for bone strength.

Endocrine System Sebaceous glands are sensitive to sex hormones. At puberty, increased hormone levels accelerate sebum production. Calcitriol (derived from vitamin D₃) acts as a hormone on the intestine to drive mineral absorption.

Immune System Macrophages and immune cells reside in the skin. Dermicidin in merocrine sweat provides antibiotic protection. Lymphatic vessels clear pathogens. Aging reduces skin immune cell populations by ~50%.

Digestive System Calcitriol (derived from skin-produced vitamin D₃) is required for calcium and phosphate absorption in the small intestine. Skin indirectly drives digestive mineral uptake.

Reproductive System Mammary glands (structurally related to apocrine sweat glands) secrete milk. Sex hormone changes at puberty affect sebaceous gland activity and subcutaneous fat distribution by sex.

BIG PICTURE — From the Textbook The epidermis is a multilayered, flexible, self-repairing barrier that prevents fluid loss, provides protection from UV radiation, produces vitamin D₃, and resists damage from abrasion, chemicals, and pathogens. The dermis provides mechanical strength, flexibility, and protection for underlying tissues. It is highly vascular and contains a variety of sensory receptors that provide information about the external environment.

2600 — Medical Vocabulary

2601 — General Functions

2602 — Structural Features of the Epidermis

2603 — Individual Differences in Skin Color

2604 — UV Radiation & Melanocytes

2605 — Dermis & Hypodermis

2606 — Accessory Structures

2607 — Skin Injury & Repair

2608 — Effects of Aging

2609 — System Relationships

SOMAPL15 Practice Test — Complete

SOMAPL15 — The Integumentary System