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Dermatology

Study and treatment of integumentary system: the skin (integument), hair, nails, and cutaneous glands.

Skin is body’s largest organ.

Two layers within skin plus a nearby layer.

Epidermis: epithelium of skin.
Dermis: connective tissue of skin.
Hypodermis: connective tissue just underneath skin.

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Fig. 5.1

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Epidermis

Keratinized stratified squamous epithelium

Superficial cells are dead

Avascular

Nutrients must diffuse from deeper connective tissue

Sparse nerve endings

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Cells of the Epidermis 1

Keratinocytes.

Synthesize keratin.
Vast majority of epidermal cells (found in many layers).

Stem cells.

Divide and produce keratinocytes.
Only in stratum basale (deepest layer of epidermis).

Melanocytes.

Make melanin – a brown to black pigment.

Melanin is taken up by keratinocytes and used to protect their DNA from ultraviolet radiation.

Found in stratum basale.

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Cells of the Epidermis 2

Tactile (Merkel) cells.

Touch receptors that join with nerves.
Only found in stratum basale.

Dendritic (Langerhans) cells.

Immune surveillance.
Found in stratum spinosum, stratum granulosum (two middle layers of epidermis).

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Strata and Cell Types of the Epidermis

Figure 5.3

(a) ©Biophoto Associates/Science Source

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Cells and Layers of the Epidermis

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Figure 5.3

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Figure 5.2b

Melanocyte

Melanin granule

Tactile

(Merkel) cell

Sensory

nerve ending

Epidermal

dendritic cell

Dermis

Keratinocytes

Stratum corneum

Most superficial layer; 20–30 layers of dead

cells represented only by flat membranous

sacs filled with keratin. Glycolipids in

extracellular space.

Stratum granulosum

Three to five layers of flattened cells,

organelles deteriorating; cytoplasm full of

lamellated granules (release lipids) and

keratohyaline granules.

Stratum spinosum

Several layers of keratinocytes unified by

desmosomes. Cells contain thick bundles of

intermediate filaments made of pre-keratin.

Stratum basale

Deepest epidermal layer; one row of actively

mitotic stem cells; some newly formed cells

become part of the more superficial layers. See

occasional melanocytes and epidermal

dendritic cells.

Desmosomes

(b)

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Layers of Epidermis

Superficial to deep

Stratum corneum

Several layers of dead, scaly cells

Stratum lucidum

Only in thick skin
Cells lack organelles

Stratum granulosum

Cells have dark granules

Stratum spinosum

Several layers of cells

Stratum basale

Only one cell thick
Varied cell types

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Layers of the Epidermis

Listed from deepest to most superficial:

Stratum basale.

Only one cell thick.
Varied cell types.

Stratum spinosum.

Several layers of cells; often thickest layer of epidermis.

Stratum granulosum.

Cells have dark granules.

Stratum lucidum.

Only in thick skin.
Cells lack organelles.

Stratum corneum.

Several layers of dead, scaly cells.

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Thick versus Thin Skin

Thick skin

Palms of hands, front of fingers, soles of feet, bottom of toes
Hairless, no sebaceous oil glands, but does sweat
Adaptive for high friction

Thin skin

Covers most of body
Hairy, has both sebaceous oil glands and sweat glands

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Figure 5.2a

Dermis

Stratum corneum

Most superficial layer; 20–30 layers of dead

cells represented only by flat membranous

sacs filled with keratin. Glycolipids in

extracellular space.

Stratum granulosum

Three to five layers of flattened cells,

organelles deteriorating; cytoplasm full of

lamellated granules (release lipids) and

keratohyaline granules.

Stratum spinosum

Several layers of keratinocytes unified by

desmosomes. Cells contain thick bundles of

intermediate filaments made of pre-keratin.

Stratum basale

Deepest epidermal layer; one row of actively

mitotic stem cells; some newly formed cells

become part of the more superficial layers.

See occasional melanocytes and epidermal

dendritic cells.

(a)

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Stratification of the Skin and Hypodermis 1

TABLE 5.1 Stratification of the Skin and Hypodermis.

Layer	Description
Epidermis	Keratinized stratified squamous epithelium
Stratum corneum	Dead, keratinized cells of the skin surface
Stratum lucidum	Clear, featureless, narrow zone seen only in thick skin
Stratum granulosum	Two to five layers of cells with dark-staining keratohyalin granules; scanty in thin skin
Stratum spinosum	Many layers of keratinocytes, typically shrunken in fixed tissues but attached to each other by desmosomes, which give them a spiny look; progressively flattened the farther they are from the dermis. Dendritic cells are abundant here but are not distinguishable in routinely stained preparations.
Stratum basale	Single layer of cuboidal to columnar cells resting on basement membrane; site of most mitosis; consists of stem cells, keratinocytes, melanocytes, and tactile cells, but these are not all distinguishable with routine stains. Melanin is conspicuous in keratinocytes of this layer in black to brown skin.

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Stratification of the Skin and Hypodermis 2

TABLE 5.1 Stratification of the Skin and Hypodermis, Continued

Layer	Description
Dermis	Fibrous connective tissue, richly endowed with blood vessels and nerve endings. Sweat glands and hair follicles originate here and in hypodermis.
Papillary layer	Superficial one-fifth of dermis; composed of areolar tissue; often extends upward as dermal papillae
Reticular layer	Deeper four-fifths of dermis; dense irregular connective tissue
Hypodermis	Areolar or adipose tissue between skin and muscle

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Table 5.1

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The Dermis

Rich in collagen fibers
Large blood supply
Contains cutaneous glands, hair follicles, piloerector muscles, and nail roots

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Figure 5.4

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Two Layers of Dermis

Papillary layer

Superficial, thin layer
Areolar tissue
Rich in blood vessels

Reticular layer

Deep, thick layer
Dense, irregular connective tissue
Striae (stretch marks): stretching of the dermal collagen

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Figure 5.1

Epidermis

Hair shaft

Dermis

Reticular

layer

Papillary

layer

Hypodermis

(superficial fascia)

Dermal papillae

Pore

Subpapillary

vascular plexus

Appendages

of skin

• Eccrine sweat

gland

• Arrector pili

muscle

• Sebaceous

(oil) gland

• Hair follicle

• Hair root

Nervous structures

• Sensory nerve fiber

• Pacinian corpuscle

• Hair follicle receptor

(root hair plexus)

Cutaneous vascular

plexus

Adipose tissue

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Figure 5.1

Epidermis

Hair shaft

Dermis

Reticular

layer

Papillary

layer

Hypodermis

(superficial fascia)

Dermal papillae

Pore

Subpapillary

vascular plexus

Appendages

of skin

• Eccrine sweat

gland

• Arrector pili

muscle

• Sebaceous

(oil) gland

• Hair follicle

• Hair root

Nervous structures

• Sensory nerve fiber

• Pacinian corpuscle

• Hair follicle receptor

(root hair plexus)

Cutaneous vascular

plexus

Adipose tissue

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Hypodermis

Not a true layer of the skin
Located below the dermis
Contains adipose (subcutaneous fat) and areolar tissue
Functions

Energy storage
Thermal insulation
Connection to deeper tissue

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Skin Color

Melanin: produced by melanocytes

Eumelanin: brownish black
Pheomelanin: reddish yellow
Across individuals, skin tones vary due to type and distribution of melanin (not number of melanocytes)

Hemoglobin: red pigment of blood
Carotene

Yellow orange
Concentrates in stratum corneum

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Variation in Skin Pigmentation

Figure 5.5 a, b

(a bottom) ©Dennis Strete/McGraw-Hill Education, (a top) ©Lopolo/Shutterstock, (b bottom) ©Dennis Strete/McGraw-Hill Education, (b top) ©Arthur Tilley/Getty Images

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Diagnostic Skin Colors

Cyanosis

Blueness
Lack of oxygen

Erythema

Redness
Increased blood flow

Pallor

Pale or ashen
Reduced blood flow

Albinism

White
Genetic lack of melanin

Jaundice

Yellow
Liver and bilirubin

Hematoma

Bruise

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Skin Markings

Friction ridges of fingertips.

Aid in sensitivity to texture and ability to grasp.
Cause fingerprint pattern.

Flexion lines (creases).

Where skin near joint attaches to deeper tissue.

Freckles.

Flat, melanized patches.
Vary with heredity and UV exposure.

Mole (nevus).

Elevated patch of melanized skin.
“Beauty marks.”

Hemangiomas (birthmarks).

Discolored skin.
Caused by benign tumors of capillaries.

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Hair

Also known as a pilus (singular) or pili (plural)
Hair is an accessory organ of the skin (as are nails, skin glands)
Filament of keratinized cells
Grows from a tube called a hair follicle
Grows on most thin skin

Exceptions include: lips, nipples, parts of genitals, and distal segments of fingers

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Functions of Hair

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Table 5.2

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Structure of Hair and Follicle

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Figure 5.6

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Lengthwise Structure of a Hair

Three zones along length of hair

Bulb

Swelling at base where hair originates in dermis
Dermal papilla – provides nutrition
Hair matrix – hair’s growth center (mitosis)

Root

Remainder of hair within follicle
Dead tissue

Shaft

Portion above the skin’s surface
Dead tissue

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Cross Sectional Structure of a Hair

Three layers:

Medulla

Internal layer
Loosely arranged cells and air spaces

Cortex

Bulk of hair
Several layers of long cells

Cuticle

Outer layer
Overlapping scaly cells

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Figure 5.7

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The Basis of Hair Color and Texture

Straight hair is round in cross section, curly hair is flatter.

Color depends on pigment within cells of cortex.

Figure 5.7 a, b, c, d

©Joe DeGrandis/McGraw-Hill Education

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Hair Follicle

Diagonal tube extending in dermis or as deep as hypodermis
Two layers

Epithelial root sheath (inner layer)
Connective tissue root sheath (derived from dermis)

Hair receptors

Nerve fibers that respond to hair’s movement

Piloerector muscle (arrector pili)

Smooth muscle that causes “goose bumps”

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Figure 5.6a

Hair shaft

Arrector

pili

Sebaceous

gland

Hair root

Hair bulb

(a) Diagram of a cross section of

a hair within its follicle

• Connective tissue

root sheath

• Glassy membrane

• External epithelial

root sheath

• Internal epithelial

root sheath

Follicle wall

• Cuticle

• Cortex

• Medulla

Hair

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Figure 5.6c

Hair shaft

Arrector

pili

Sebaceous

gland

Hair root

Hair bulb

(c)

Diagram of a longitudinal view of the expanded hair

bulb of the follicle, which encloses the matrix

• Internal epithelial root sheath

• External epithelial root sheath

• Connective tissue root sheath

Follicle wall

Hair matrix

Melanocyte

Hair papilla

Subcutaneous adipose tissue

• Medulla

• Cortex

• Cuticle

• Glassy membrane

Hair root

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(d) Photomicrograph of longitudinal view

of the hair bulb in the follicle (160x)

Follicle wall

Hair matrix

Hair papilla

Subcutaneous

adipose tissue

Hair root

• Connective

tissue root sheath

• Glassy membrane

• External epithelial

root sheath

• Internal epithelial

root sheath

• Cuticle

• Cortex

• Medulla

Hair shaft

Arrector

pili

Sebaceous

gland

Hair root

Hair bulb

Figure 5.6d

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Nails

Derivatives of stratum corneum
Composed of very thin, dead, scaly cells with parallel rows of keratin
Primates have flat nails, as opposed to claws, for easier manipulation

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Nails, continued

Nail plate

Free edge
Nail body
Nail root

Nail fold

Nail groove

Nail bed

Hyponychium
Nail matrix
Lunule
Eponychium (cuticle)

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Figure 5.9

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Fig. 5.9

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Figure 5.7

Lateral

nail fold

Lunule

Nail

matrix

Root of nail

Proximal

nail fold

Hyponychium

Nail bed

Phalanx (bone of fingertip)

Eponychium

(cuticle)

Body

of nail

Free edge

of nail

(a)

(b)

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Cutaneous Glands

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Figure 5.10

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Figure 5.5b

(b) Photomicrograph of a

sectioned eccrine gland (220x)

Secretory cells

Dermal connective

tissue

Duct

Sebaceous

gland

Sweat pore

Eccrine

gland

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Figure 5.5a

(a) Photomicrograph of a sectioned

sebaceous gland (220x)

Sebaceous

gland duct

Hair in

hair follicle

Secretory cells

Dermal

connective

tissue

Sebaceous

gland

Sweat

pore

Eccrine

gland

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Sweat (Sudoriferous) Glands

Merocrine (eccrine) glands

Numerous, widespread, and especially abundant on palms, soles, and forehead
Simple ducts lead to pores at skin surface
Produce watery perspiration to cool body

Also contains some wastes found in urine

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Sweat (Sudoriferous) Glands

Apocrine glands

Found in groin, anal region, axilla, areola,

and beard

Ducts open into hair follicle
Produce sweat with many fatty acids

Bacterial metabolism of those fats causes odor

Respond to stress and sexual stimulation
Develop in puberty
Believed to secrete pheromones

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Ceruminous Glands

Found in auditory canal
Cerumen

Earwax
Combination of sebum and dead skin cells

Keeps eardrum pliable, waterproofs canal, kills bacteria, and coats guard hairs

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Mammary Glands

Produce milk
Not synonymous with breasts

Glands develop during pregnancy and lactation, otherwise scant

Modified apocrine gland

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Sebaceous Glands

Produce oily secretion called sebum
Usually open into hair follicle
Holocrine secretion
Keep skin and hair from becoming brittle

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Cutaneous Glands 2

TABLE 5.3 Cutaneous Glands.

Gland Type	Definition
Sudoriferous glands	Sweat glands.
Apocrine	Sweat glands that function as scent glands; found in the regions covered by the pubic, axillary, and male facial hair; open by ducts into hair follicles.
Eccrine (Merocrine)	Sweat glands that function in evaporative cooling; widely distributed over the body surface; open by ducts onto the skin surface.
Sebaceous glands	Oil-producing glands associated with hair follicles.
Ceruminous glands	Glands of the ear canal that produce cerumen (earwax).
Mammary glands	Milk-producing glands located in the breasts.

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Cutaneous Glands 2

TABLE 5.3 Cutaneous Glands.

Gland Type	Definition
Sudoriferous glands	Sweat glands.
Apocrine	Sweat glands that function as scent glands; found in the regions covered by the pubic, axillary, and male facial hair; open by ducts into hair follicles.
Eccrine (Merocrine)	Sweat glands that function in evaporative cooling; widely distributed over the body surface; open by ducts onto the skin surface.
Sebaceous glands	Oil-producing glands associated with hair follicles.
Ceruminous glands	Glands of the ear canal that produce cerumen (earwax).
Mammary glands	Milk-producing glands located in the breasts.

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Functions of the Skin

Resistance to trauma and infection
Water retention
Synthesis of vitamin D
Sensation
Thermoregulation
Nonverbal communication

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Table 5.4

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Skin Cancer

Induced by UV rays (both natural and tanning beds).

Elderly and fair-skinned most common.

3 types:

Basal cell carcinoma.
Squamous cell carcinoma.
Malignant melanoma.