Chapter 1
4 Lecture
HUMAN ANATOMY
Chapter 4
The Integumentary
System
Skin (Integument)
• Epidermis—superficial region
• Epithelial tissue
• Non-vascularize
• Dermis—underlies epidermis
•
•
•
•
Mostly fibrous connective tissue
Tough leathery layer composed of fibrous connective tissue
Dense Irregular CT
Good supply of blood
• Hypodermis (superficial fascia)
–
–
–
–
Subcutaneous layer deep to skin
Not part of skin but shares some functions
Mostly adipose tissue that absorbs shock & insulates
Anchors skin to underlying structures – mostly
muscles
Figure 5.1 Skin structure.
Hair shaft
Dermal papillae
Epidermis
Subpapillary
plexus
Papillary
layer
Sweat pore
Appendages of
skin
Eccrine sweat gland
Arrector pili muscle
Sebaceous (oil)
gland
Hair follicle
Hair root
Dermis Reticular
layer
Hypodermis
(subcutaneous
tissue; not part
of skin)
Nervous structures
Sensory nerve fiber
with free nerve endings
Lamellar corpuscle
Hair follicle receptor
(root hair plexus)
Cutaneous plexus
Adipose tissue
Introduction
•
The integumentary system, or
integument, is composed of skin,
hair, nails, sweat, oil, and
mammary glands.
• Functions of the skin:
–
–
–
–
–
Protection
Thermoregulation
Sense organ
Vitamin D production
Excretion
What are the major characteristics of the skin?
• Waterproof, stretchable, washable, and
permanent-press, that automatically
repairs small cuts, rips and burns and is
guaranteed to last a lifetime.
• Surface area of up to 2.2 square meters
• 11 pounds
• 7% of total body weight
• Pliable yet tough
Epidermis
• Keratinized stratified squamous epithelium
• Four or five distinct layers
–
–
–
–
–
Stratum basale
Stratum spinosum
Stratum granulosum
Stratum lucidum (only in thick skin)
Stratum corneum
• Four cell types
–
–
–
–
Keratinocytes
Melanocytes
Dendritic (langerhans) cells
Tactile (merkel) cells
Figure 5.2a The main structural features of the skin epidermis.
Stratum corneum
Most superficial layer; 20–30 layers of dead cells, essentially
flat membranous sacs filled with keratin. Glycolipids in
extracellular space.
Stratum granulosum
Typically five layers of flattened cells, organelles deteriorating;
cytoplasm full of lamellar granules (release lipids) and
keratohyaline granules.
Dermis
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 dendritic
cells.
Epidermis
Dermis
Basement membrane
Epidermis
Dermis
Hypodermis
The Epidermis
• Keratinocytes are the most abundant
cells in the epidermis.
– At least four different cell layers can be found
on most areas of the body.
• Melanocytes are pigment cells found
deep in the epidermis.
• Merkel cells are sensory cells.
• Langerhans cells are fixed macrophages.
What are the different types of cells in
the epidermis?
• Keratinocytes
– Produce a fibrous protein
called keratin
– Are formed in the lowest
levels of the epidermis.
– Pushed upward by the
production of new cells
beneath them.
– Become dead and scalelike
– Millions rub off everyday
Layers of the Epidermis
Strata of epidermis and the process of keratinization
Table 4.1 Epidermal Layers
Figure 4.3 Structure of the Epidermis
What are the different types of cells in the epidermis?
• Melanocytes
– Synthesizes the pigment
melanin
– Melan-black
– Can transfer melanin to
keratinocytes
– Protects skin from
ultraviolet light.
– Responsible for skin
color.
– Melanoma.
melanocyte
Melanin in
keratinocytes
What are the different types of cells in the epidermis?
• Langerhans’ cells
– Formed in bone
marrow.
– Move to the skin
– Macrophages
Langerhans’
cell
What are the different types of cells in the epidermis?
• Merkel Cells
– Has a spiked
appearance
– Connected to nerve
cells from dermis
– Function as sensory
receptors for touch.
– Towards the dermis
Layers of Skin
• Two types of skin: Thick & Thin
• Thick skin has five layers
• Thin skin has four layers
Thick and Thin Skin
Strata granulosum and lucidum
Keratohyalin and eleidin
precursors to keratin in S.
corneum
Figure 4.4 Thin and Thick Skin
What are the Layers of the EPIDERMIS?
Five layers (superficial to deep):
Stratum corneum
Stratum lucidum**
Stratum granulosum
Stratum spinosum
Stratum basale
(germinativum)
**Thick skin only
Layers of the Epidermis: Stratum Corneum (Horny Layer)
• Outer most layer of epidermis.
• 20–30 rows of dead, flat, anucleate
keratinized membranous sacs
• Three-quarters of epidermal thickness
• Though dead, its cells have functions
– Protect deeper cells from environment and
water loss
– Protect from abrasion and penetration
– Barrier against biological, chemical, and
physical assaults
– Sloughs off
Cell Differentiation in Epidermis
• Cells change from stratum basale to
stratum corneum
• Accomplished by specialized form of
apoptosis
– Controlled cellular suicide
– Nucleus and organelles break down
– Plasma membrane thickens
– Allows cells to slough off as dandruff and
dander
– Shed ~ 50,000 cells every minute
Figure 5.2b The main structural features of the skin epidermis.
Keratinocytes
Stratum corneum
Most superficial layer; 20–30 layers of dead cells,
essentially flat membranous sacs filled with keratin.
Glycolipids in extracellular space.
Stratum granulosum
Typically five layers of flattened cells, organelles
deteriorating; cytoplasm full of lamellar granules
(release lipids) and keratohyaline granules.
Stratum spinosum
Dendritic
Several layers of keratinocytes unified by desmosomes.
cell
Cells contain thick bundles of intermediate filaments
made of pre-keratin.
Sensory
Stratum basale
nerve
Dermis
Deepest epidermal layer; one row of actively
ending
mitotic stem cells; some newly formed cells
Melanin
Tactile
become part of the more superficial layers.
granule
(Merkel) cell
See occasional melanocytes and dendritic
Melanocyte
Desmosomes
cells.
Layers of the Epidermis: Stratum Lucidum (Clear Layer)
• Only in thick skin
• Thin, translucent band superficial to the
stratum granulosum
• A few rows of flat, dead keratinocytes
Layers of the Epidermis: Stratum Granulosum (Granular Layer)
• Thin - four to six cell layers
• Cell appearance changes
– Cells flatten
– Nuclei and organelles disintegrate
– Keratinization begins
• Cells accumulate keratohyaline granules
– Help form keratin in upper layers
– Cell accumulate lamellar granules
• Their water-resistant glycolipid slows water loss
• Cells above this layer die
– Too far from dermal capillaries
Layers of the Epidermis: Stratum Spinosum (Prickly Layer)
• Several layers thick
– 8-10 cells
• Cells contain web-like system of
intermediate pre-keratin filaments attached
to desmosomes
• Abundant melanosomes and dendritic
cells
Stratum Spinosum
Layers of the Epidermis: Stratum Basale (Basal Layer)
•
•
•
•
Deepest epidermal layer
Also called stratum germinativum
Firmly attached to dermis
Single row of stem cells
– Actively mitotic
– Produces two daughter cells
• One cell journeys from basal layer to surface
– Takes 25–45 days
– Dies as moves toward surface
• One cell remains in stratum basale as stem cell
• Melanocytes compose 10 – 25% of this layer
Stratum Basale
•
•
•
•
•
Lowest epidermal layer, near dermis
Good nutrient supply
Reproduces by mitosis
Cuboidal, columnar in shape
Moves to upper epidermis in 27 days.
Stratum Basale
DERMIS
Irregular Dense Connective Tissue
Collagenous fibers
Dermis
• Strong, flexible connective tissue
• Cells
– Fibroblasts, macrophages, and occasionally mast
cells and white blood cells
• Fibers in matrix bind body together
– "Hide" used to make leather
• Contains nerve fibers; blood and lymphatic vessels
• Contains epidermal hair follicles; oil and sweat
glands
• Two layers
– Papillary – areolar connective tissue; includes dermal
papillae
– Reticular - “reticulum” (network) of collagen and
reticular fibers
Figure 5.1 Skin structure.
Hair shaft
Dermal papillae
Epidermis
Subpapillary
plexus
Papillary
layer
Sweat pore
Appendages of
skin
Eccrine sweat gland
Arrector pili muscle
Sebaceous (oil)
gland
Hair follicle
Hair root
Dermis Reticular
layer
Hypodermis
(subcutaneous
tissue; not part
of skin)
Nervous structures
Sensory nerve fiber
with free nerve endings
Lamellar corpuscle
Hair follicle receptor
(root hair plexus)
Cutaneous plexus
Adipose tissue
Dermal Organization and the
Subcutaneous Layer
Figure 4.7 The Structure of the Dermis and the Subcutaneous Layer
Papillary Layer
• Areolar connective tissue with collagen
and elastic fibers
• Its superior surface contains peglike
projections called dermal papillae
• Dermal papillae contain capillary loops,
Meissner’s corpuscles, and free nerve
endings
• Dermal papillae make up epidermal
ridges, which give rise to fingerprints
Dermal Papillae
• Most contain capillary loops
• Some contain meissner's corpuscles (touch
receptors)
• Some contain free nerve endings (pain
receptors)
• In thick skin lie atop dermal ridges that cause
epidermal ridges
– Collectively ridges called friction ridges
• Enhance gripping ability
• Contribute to sense of touch
• Pattern is fingerprints
Figure 5.4a Dermal modifications result in characteristic skin markings.
Openings of
Friction
sweat gland ducts ridges
Friction ridges of
fingertip (SEM 12x)
Layers of the Dermis: Reticular Layer
•
•
•
•
~80% of dermal thickness
Dense fibrous connective tissue
Elastic fibers provide stretch-recoil properties
Collagen fibers
– Provide strength and resiliency
– Bind water
– Cleavage lines because most collagen fibers parallel
to skin surface
• Externally invisible
• Important to surgeons
• Incisions parallel to cleavage lines gap less and heal more
readily
Figure 5.4b Dermal modifications result in characteristic skin markings.
Cleavage lines in the
reticular dermis
Skin Markings
• Flexure lines
– Dermal folds at or near joints
– Dermis tightly secured to deeper structures
– Skin cannot slide easily for joint movement
causing deep creases
– Visible on hands, wrists, fingers, soles, toes
Figure 5.4c Dermal modifications result in characteristic skin markings.
Flexure lines
on digit
Flexure lines
on the palm
Flexure lines of the
hand
Other Skin Markings
• Striae
– Silvery-white scars
– "Stretch marks"
– Extreme stretching causes dermal tears
• Blister
– From acute, short-term trauma
– Fluid-filled pocket that separates epidermal
and dermal layers
Sensory Structures of Dermis
•
•
•
•
•
Deep touch/pressure: Pacinian corpuscles
Light touch/pressure: Meisner’s corpuscles
Warm temperature: Free nerve endings
Cold temperature: Free nerve endings
Pain: Free nerve endings
Meisner’s Corpuscles
• Meissner's corpuscles (or tactile
corpuscles) are a type of nerve ending,
responsible for sensitivity to light touch.
• They are distributed throughout the skin,
but concentrated in areas especially
sensitive to light touch, such as the
fingertips, palms, soles, lips, tongue, face
and the skin of the male and female
genitals.
• They are primarily located just beneath the
• epidermis within the dermal papillae.
Skin Color
• Three pigments contribute to skin color
– Melanin
• Only pigment made in skin
– Carotene
– Hemoglobin
Melanin
• Two forms
– Reddish-yellow to brownish-black
• Color differences due to amount and form
• Produced in melanocytes
– Same relative number in all people
• Migrates to keratinocytes to form "pigment
shields" for nuclei
• Freckles and pigmented moles
– Local accumulations of melanin
• Sun exposure stimulates melanin production
• Sunspots (tinea versicolor) are fungal infection;
not related to melanin
Carotene and Hemoglobin
• Carotene
– Yellow to orange pigment
• Most obvious in palms and soles
– Accumulates in stratum corneum and
hypodermis
– Can be converted to vitamin a for vision and
epidermal health
• Yellowish-tinge of some asians – carotene
and melanin variations
• Hemoglobin
– Pinkish hue of fair skin
Skin Color in Diagnosis
• Cyanosis
– Blue skin color - low oxygenation of hemoglobin
• Erythema (redness)
– Fever, hypertension, inflammation, allergy
• Pallor (blanching)
– Anemia, low blood pressure, fear, anger
• Jaundice (yellow cast)
– Liver disorder
• Bronzing
– Inadequate steroid hormones in addison's disease
• Bruises
– Clotted blood beneath skin
Appendages of the Skin
• Derivatives of the epidermis
– Hairs and hair follicles
– Nails
– Sweat glands
– Sebaceous (oil) glands
Why is hair useful?
• Senses insects that land on the skin.
• Hair on the head protects the head from a
blow, sunlight and heat loss.
• Eyelashes shield the eye
• Nose hairs filter the air
What are hairs?
• Made from hair follicles
• Made of dead keratinized skin cells
– Not in palms, soles, lips, nipples, portions of
external genitalia
• Two parts shaft and root
• Hair pigments
– Melanins (yellow, rust, brown, black); trichosiderin in
red hair
– Gray/white hair: decreased melanin production,
increased air bubbles in shaft
Hair Anatomy
• Shaft has 3 layers
of cells
– Medulla(central
core)
– Cortex (bulky layer)
– Cuticle (heavily
keratinized;
protects hair)
Accessory Structures
• Hair follicles and hair:
– Hair is a nonliving
keratinized structure that
extends beyond the
surface of the skin in
most areas of the body.
– 98% of the 5 million hairs
on the body are not on
the head.
– Hair follicles are the
organs that form the
hairs.
Figure 4.9a Accessory Structures of the Skin
Hair Follicles
• Extend from epidermal surface to dermis
• Two-layered wall - part dermis, part epidermis
• Hair bulb
–
–
–
–
Expanded deep end
Hair follicle receptor (root hair plexus)
Sensory nerve endings - touch receptors
Hair matrix
• Actively dividing area
• Arrector pili
– Smooth muscle attached to follicle
– Responsible for "goose bumps"
• Hair papilla
– Dermal tissue - blood supply
Figure 5.5a Skin appendages: Structure of a hair and hair follicle.
Follicle wall
• Peripheral
connective tissue
(fibrous) sheath
• Glassy membrane
• Epithelial root sheath
• External root sheath
• Internal root sheath
Hair shaft
Hair
• Cuticle
• Cortex
• Medulla
Diagram of a cross section of a hair within its follicle
Arrector
pili
Sebaceous
gland
Hair root
Hair bulb
Figure 5.5b Skin appendages: Structure of a hair and hair follicle.
Follicle wall
• Peripheral
connective tissue
(fibrous) sheath
• Glassy membrane
• Epithelial root sheath
• External root sheath
• Internal root sheath
Hair
• Cuticle
• Cortex
•Medulla
Photomicrograph of a cross section of a
hair and hair follicle (100x)
Hair and hair follicles: complex
Derived from epidermis and dermis
Everywhere but palms, soles, nipples, parts of
genitalia
*“arrector pili” is smooth muscle
*
Hair bulb:
epithelial cells
surrounding
papilla
Hair papilla
is connective
tissue________________
Hair Follicle
Hair Thinning and Baldness
• Alopecia
– Hair thinning in both sexes after a age 40
• True (frank) baldness
– Genetically determined and sex-influenced
condition
– Male pattern baldness caused by follicular
response to DHT (dihydrotestosterone)
– Treatments
• Minoxidil (rogaine) and finasteride (propecia)
What are the parts of nails?
• A nail is a scalelike modification of the
epidermis
• Made of tightly compressed keratinized
cells
• Useful tools to pick up small objects or
scratch an itch.
• Nail matrix is the region responsible for
nail growth.
Figure 5.6 Skin appendages: Structure of a nail.
Lunule
Lateral
nail fold
Free edge Body Eponychium
Root of nail
of nail
of nail (cuticle)
Proximal
Nail
nail fold
matrix
Hyponychium
Nail bed Phalanx (bone of fingertip)
Sweat Glands
• Also called sudoriferous glands
• All skin surfaces except nipples and parts of
external genitalia
• ~3 million per person
• Two main types
– Eccrine (merocrine) sweat glands
– Apocrine sweat glands
Eccrine Sweat Glands
•
•
•
•
Most numerous
Abundant on palms, soles, and forehead
Ducts connect to pores
Function in thermoregulation
– Regulated by sympathetic nervous system
• Their secretion is sweat
– 99% water, salts, vitamin c, antibodies,
dermcidin (microbe-killing peptide), metabolic
wastes
Figure 5.7b Photomicrograph of a sectioned eccrine gland (140x).
Sebaceous
gland
Sweat
pore
Eccrine
gland
Duct
Dermal connective
tissue
Secretory cells
Photomicrograph of a
sectioned eccrine
gland (140x)
Eccrine Gland
Sweat Gland
Sweat Gland Exiting the Skin
Apocrine Sweat Glands
• Confined to axillary and anogenital areas
• Sweat + fatty substances + proteins
– Viscous; milky or yellowish
– Odorless until bacterial interaction  body odor
• Larger than eccrine sweat glands
• Ducts empty into hair follicles
• Begin functioning at puberty
– Function unknown but may act as sexual scent gland
• Modified apocrine glands
– Ceruminous glands—lining of external ear canal;
secrete cerumen (earwax)
– Mammary glands – secrete milk
Sebaceous (Oil) Glands
• Widely distributed
– Not in thick skin of palms and soles
• Most develop from hair follicles and secrete into
hair follicles
• Relatively inactive until puberty
– Stimulated by hormones, especially androgens
• Secrete sebum
– Oily holocrine secretion
– Bactericidal
– Softens hair and skin
Glands in the Skin
Figure 4.12 A Classification of Exocrine Glands in the Skin
Sebaceous (Oil) Glands
• Widely distributed
– Not in thick skin of palms and soles
• Most develop from hair follicles and secrete into
hair follicles
• Relatively inactive until puberty
– Stimulated by hormones, especially androgens
• Secrete sebum
– Oily holocrine secretion
– Bactericidal
– Softens hair and skin
Figure 5.7a Photomicrograph of a sectioned sebaceous gland (90x).
Sebaceous
gland
Dermal
connective
Hair in
hair follicle
tissue
Sebaceous
gland duct
Sweat
pore
Eccrine
gland
Secretory cells
Photomicrograph of a
sectioned sebaceous
gland (90x)
Sebaceous Gland
Hypodermis
• “Hypodermis” (Gk) = below the skin
• “Subcutaneous” (Latin) = below the skin
• Also called “superficial fascia”
“fascia” (Latin) =band; in anatomy: sheet of connective
tissue
• Fatty tissue which stores fat and anchors
skin (areolar tissue and adipose cells)
• Different patterns of accumulation
(male/female)
What are the primary functions of
the Integumentary System?
• Protection
– Chemical barrier: low pH of skin secretions
slows bacterial growth.
• Human defensin is an antibiotic that destroys
bacteria (produced by human skin)
Physical barriers
– Physical barrier: very few substance are able
to enter the skin. Substances able to pass.
• Lipid-soluble substances: oxygen, carbon dioxide,
some vitamins
• Oleoresins- poisons (poison ivy)
• Organic solvents- dry-cleaning fluid, paint thinner
• Salts of heavy metals- lead, mercury, nickel
• Penetration enhancers- drug agents that help
substances into the body.
Functions cont.
• Thermoregulation- skin contains sweat glands
that secrete watery fluid, that when evaporated,
cools the body.
• Sensation- Skin contains sensory receptors that
detect cold, touch, and pain.
• Vitamin D synthesis- cholesterol in the skin is
bombarded by sunlight and converted to vitamin
D (calcium cannot be absorbed from digestive
tract)
Functions cont.
• Blood reservoir- blood will be moved
from skin to muscles during strenuous
activity.
• Excretion- Sweating is an important outlet
for wastes such as salt and nitrogen
containing compounds. (urine)
Skin Cancer
• Most skin tumors are benign (not cancerous)
and do not metastasize (spread)
• Risk factors
– Overexposure to UV radiation
– Frequent irritation of skin
• Some skin lotions contain enzymes that can
repair damaged DNA
• Three major types of skin cancer
– Basal cell carcinoma
– Squamous cell carcinoma
– Melanoma
Basal Cell Carcinoma
• Least malignant; most common
• Stratum basale cells proliferate and slowly
invade dermis and hypodermis
• Cured by surgical excision in 99% of
cases
Skin Cancer
Sqaumous cell carcinoma
Basal cell carcinoma
Melanoma
Squamous Cell Carcinoma
• Second most common type
• Involves keratinocytes of stratum
spinosum
• Usually scaly reddened papule on scalp,
ears, lower lip, and hands
• Does metastasize
• Good prognosis if treated by radiation
therapy or removed surgically
Melanoma
• Cancer of melanocytes
• Most dangerous
– Highly metastatic and resistant to chemotherapy
• Treated by wide surgical excision accompanied
by immunotherapy
• Key to survival is early detection – ABCD rule
– A: asymmetry; the two sides of the pigmented area do
not match
– B: border irregularity; exhibits indentations
– C: color; contains several (black, brown, tan,
sometimes red or blue)
– D: diameter; larger than 6 mm (size of pencil eraser)
Skin Cancer: Malignant Melanoma
• Signs and Symptoms
– From melanocytes
– Appear on trunk, head,
neck of men
– Appear on arms and
legs of women
– Itches or bleeds
24-84
• Treatment
– Surgery and biopsy
– Removal of lymph
nodes
– Chemotherapy and
radiation therapy
– Immunotherapy
Skin Cancer: Stages of Melanoma
Stage 0
Only found in epidermis
Stage I
Stage II
Spread to epidermis and dermis (1 to 2 mm
thick)
2 to 4 mm thick plus ulceration
Stage III
Spread to one or more lymph nodes
Stage IV Spread to other body organs or lymph nodes
far from original melanoma
Melanoma
Melanomas can develop anywhere on your body, but they most often
develop in areas that have had exposure to the sun, such as your
back, legs, arms and face.
A-B-C-D-E guide developed by the American
Academy of Dermatology:
A is for asymmetrical shape. Look for moles with irregular
shapes, such as two very different-looking halves
B is for irregular border. Look for moles with irregular,
notched or scalloped borders — characteristics of
melanomas.
C is for changes in color. Look for growths that have many
colors or an uneven distribution of color.
D is for diameter. Look for new growth in a mole larger than
about 1/4 inch (6 millimeters).
E is for evolving. Look for changes over time, such as a
mole that grows in size or that changes color or shape.
Moles may also evolve to develop new signs and symptoms,
such as new itchiness or bleeding.
Kaposi's Sarcoma (KS)
Rare, cancer of the cells that line blood vessels (endothelial cells)
• Clinically: brownish-red to blue colored skin lesions found most
frequently on legs and feet
• Caused by Human Herpes Virus 8 (HHV-8) which causes the cells
that line blood vessels (endothelial cells) to become cancerous in
the setting of profound and prolonged immunosuppression.
PSORIASIS
Developmental Aspects
• Fetal
– Ectoderm  epidermis; Mesoderm  dermis and
hypodermis
– Lanugo coat: delicate hairs in 5th and 6th month
– Vernix caseosa: sebaceous gland secretion; protects
skin of fetus
• Infancy to adulthood
– Skin thickens; accumulates more subcutaneous fat
– Sweat and sebaceous gland activity increases
– Effects of cumulative environmental assaults show
after age 30
– Scaling and dermatitis become more common
Developmental Aspects
• Aging skin
– Epidermal replacement slows, skin becomes thin, dry
and itchy (decreased sebaceous gland activity)
– Subcutaneous fat and elasticity decrease, leading to
cold intolerance and wrinkles
– Increased risk of cancer due to decreased numbers of
melanocytes and dendritic cells
– Hair thinning
• To delay
– UV protection, good nutrition, lots of fluids, good
hygiene