Chapter 5 (Skin) Flashcards
Integumentary system consists of:
– Skin
– Hair
– Nails
– Sweat glands
– Sebaceous (oil) glands
Skin consists of two distinct regions:
Epidermis and Dermis
Epidermis
superficial region
Consists of epithelial tissue and is avascular
Dermis
underlies epidermis
Mostly fibrous connective tissue, vascular
Hypodermis (superficial fascia)
Subcutaneous layer deep to skin
Not part of skin but shares some functions
Mostly adipose tissue that absorbs shock and insulates
Anchors skin to underlying structures: mostly muscles
Epidermis consists mostly of what epithelium
keratinized stratified squamous epithelium
Keratinocytes
Produce fibrous keratin (protein that gives skin its protective
properties)
Major cells of epidermis
Tightly connected by desmosomes
Millions slough off every day
Melanocytes
Spider-shaped cells located in deepest epidermis
Produce pigment melanin, which is packaged into melanosomes
– Melanosomes are transferred to keratinocytes, where they protect
nucleus from UV damage
Dendritic (Langerhans) cells
Star-shaped macrophages that patrol deep epidermis
– Are key activators of immune system
Tactile (Merkel) cells
Sensory receptors that sense touch
Five layers of skin
- Stratum basale
- Stratum spinosum
- Stratum granulosum
- Stratum lucidum (only in thick skin)
- Stratum corneum
Stratum basale (basal layer)
– Deepest of all epidermal layers (base layer)
– Layer that is firmly attached to dermis
– Consists of a single row of stem cells that actively divide (mitotic),
producing two daughter cells each time
One daughter cell journeys from basal layer to surface, taking 25–45
days to reach surface
– Cell dies as it moves toward surface
Other daughter cell remains in stratum basale as stem cell
– Layer also known as stratum germinativum because of active mitosis
– 10–25% of layer also composed of melanocyte
Stratum spinosum (prickly layer)
– Several cell layers thick
– Cells contain weblike system of intermediate prekeratin filaments attached
to desmosomes
Allows them to resist tension and pulling
– Keratinocytes in this layer appear spikey, so they are called prickle cells
– Scattered among keratinocytes are abundant melanosomes and dendritic cells
Stratum granulosum (granular layer)
– Four to six cells thick, but cells are flattened, so layer is thin
– Cell appearance changes
Cells flatten, nuclei and organelles disintegrate
Keratinization begins
– Cells accumulate keratohyaline granules that help form keratin
fibers in upper layers
Cells also accumulate lamellar granules, a water-resistant glycolipid
that slows water loss
– Cells above this layer die
Too far from dermal capillaries to survive
Stratum lucidum (clear layer)
– Found only in thick skin
– Consists of thin, translucent band of two to three rows of clear, flat, dead
keratinocytes
– Lies superficial to the stratum granulosum
Stratum corneum (horny layer)
– 20–30 rows of flat, anucleated, keratinized dead cells
– Accounts for three-quarters of epidermal thickness
– Though dead, cells still function to:
Protect deeper cells from the environment
Prevent water loss
Protect from abrasion and penetration
Act as a barrier against biological, chemical, and physical assaults
Dermis
Strong, flexible connective tissue
Cells include fibroblasts, macrophages, and occasionally mast cells and white
blood cells
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Fibers in matrix bind body together
– Makes up the “hide” that is used to make leather
Contains nerves, blood vessels, and lymphatic vessels
Contains epidermal hair follicles, oil glands, and sweat glands
2 layers of dermis
– Papillary
– Reticular
Papillary Layer
Superficial layer of areolar connective tissue consisting of loose, interlacing
collagen and elastic fibers and blood vessels
Loose fibers allow phagocytes to patrol for microorganisms
Dermal papillae: superficial region of dermis that sends fingerlike projections
up into epidermis
– Projections contains capillary loops, free nerve endings, and touch
receptors (tactile corpuscles, also called Meissner’s corpuscles)
In thick skin, dermal papillae lie on top of dermal ridges, which give rise to
epidermal ridges
– Collectively ridges are called friction ridges
Enhance gripping ability
Contribute to sense of touch
Sweat pores in ridges leave unique fingerprint pattern
Reticular Layer
Makes up ~80% of dermal thickness
Consists of coarse, dense fibrous connective tissue
– Many elastic fibers provide stretch-recoil properties
– Collagen fibers provide strength and resiliency
Bind water, keeping skin hydrated
Cutaneous plexus: network of blood vessels between reticular layer and
hypodermis
Extracellular matrix contains pockets of adipose cells
Cleavage (tension) lines in reticular layer are caused by many collagen
fibers running parallel to skin surface
– Externally invisible
– Important to surgeons because incisions parallel to cleavage lines heal
more readily
Flexure lines of reticular layer are dermal folds at or near joints
– Dermis is tightly secured to deeper structures
– Skin’s inability to slide easily for joint movement causes deep creases
– Visible on hands, wrists, fingers, soles, toes
Striae
Extreme stretching of skin can cause dermal tears, leaving silvery white scars (stretch marks)
Blisters
fluid-filled pockets that
separate epidermal and dermal layers
Three pigments contribute to skin color
Melanin, Carotene, and Hemoglobin
Melanin
Only pigment made in skin; made by melanocytes
– Packaged into melanosomes that are sent to keratinocytes to shield
DNA from sunlight
– Sun exposure stimulates melanin production
Two forms: reddish yellow to brownish black
All humans have same number of keratinocytes, so color differences
are due to amount and form of melanin
Freckles and pigmented moles are local accumulations of melanin
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
Hemoglobin
Pinkish hue of fair skin is due to lower levels of melanin
– Skin of Caucasians is more transparent, so color of hemoglobin
shows through
Hair
Consists of dead keratinized cells
None located on palms, soles, lips, nipples, and portions of external genitalia
Functions:
– Warn of insects on skin
– Hair on head guards against physical trauma
– Protect from heat loss
– Shield skin from sunlight
Structure of a Hair
Hairs (also called pili): flexible strands of dead, keratinized cells
Produced by hair follicles
Contains hard keratin, not like soft keratin found in skin
– Hard keratin is tougher and more durable, and cells do not flake off
Regions of a Hair
– Shaft: area that extends above scalp, where keratinization is complete
– Root: area within scalp, where keratinization is still going on
Three parts of hair shaft:
– Medulla: central core of large cells and air spaces
– Cortex: several layers of flattened cells surrounding medulla
– Cuticle: outer layer consisting of overlapping layers of single cells
Structure of a Hair Follicle
Extends from epidermal surface to dermis
Hair bulb: expanded area at deep end of follicle
Hair follicle receptor (or root hair plexus): sensory nerve endings that wrap
around bulb
– Hair is considered a sensory touch receptor
Wall of follicle composed of:
– Peripheral connective tissue sheath
Derived from dermis
Also called fibrous sheath
– Glassy membrane: thickened basal lamina
– Epithelial root sheath
Derived from epidermis
Hair matrix: actively dividing area of bulb that produces hair cells
– As matrix makes new cells, it pushes older ones upward
Arrector pili: small band of smooth muscle attached to follicle
– Responsible for “goose bumps”
Hair papilla
– Dermal tissue containing a knot of capillaries that supplies nutrients to
growing hair
Nails
Scale-like modifications of epidermis that contain hard keratin
Act as a protective cover for distal, dorsal surface of fingers and toes
Consist of free edge, nail plate, and root
Nail bed is epidermis underneath keratinized nail plate
Nail matrix: thickened portion of bed responsible for nail growth
Nail folds: skin folds that overlap border of nail
Eponychium: nail fold that projects onto surface of nail body
Also called cuticle
Hyponychium: area under free edge of plate that accumulates dirt
Nails normally appear pink because of underlying capillaries
– Lunule: thickened nail matrix, appears white
Abnormal color or shape can be an indicator of disease
Sweat Glands
Also called sudoriferous glands
All skin surfaces except nipples and parts of external genitalia contain sweat
glands
– About 3 million per person
Two main types
– Eccrine (merocrine) sweat glands
– Apocrine sweat glands
Contain myoepithelial cells
– Contract upon nervous system stimulation to force sweat into ducts
Eccrine (Merocrine) Sweat Glands
Most numerous type
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
Apocrine Sweat Glands
Confined to axillary and anogenital areas
Secrete viscous milky or yellowish sweat that contains fatty substances and
proteins
– Bacteria break down sweat, leading to body odor
Larger than eccrine sweat glands with ducts emptying into hair follicles
Begin functioning at puberty
– Function unknown but may act as sexual scent gland
– Ceruminous glands: lining of external ear canal; secrete cerumen
(earwax)
– Mammary glands: secrete milk
Sebaceous (Oil) Gland
Widely distributed, except for 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 (bacteria-killing) properties
– Softens hair and skin
Functions of Skin
– Protection
– Body temperature regulation
– Cutaneous sensations
– Metabolic functions
– Blood reservoir
– Excretion of wastes
Three major types of skin cancer
– Basal cell carcinoma
– Squamous cell carcinoma
– Melanoma
Basal cell carcinoma
– Least malignant and most common
– Stratum basale cells proliferate and slowly invade dermis and hypodermis
– Cured by surgical excision in 99% of cases
Squamous cell carcinoma
– Second most common type; can metastasize
– Involves keratinocytes of stratum spinosum
– Usually is a scaly reddened papule on scalp, ears, lower lip, or hands
– Good prognosis if treated by radiation therapy or removed surgically
Melanoma
– Cancer of melanocytes; is most dangerous type because it is 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 colors (black, brown, tan, sometimes red or
blue)
D: diameter; larger than 6 mm (size of pencil eraser)
To evaluate burns, the Rule of Nines is used
– Body is broken into 11 sections, with each section representing 9% of
body surface (except genitals, which account for 1%)
– Used to estimate volume of fluid loss
First-degree burn
Epidermal damage only
– Localized redness, edema (swelling), and pain
Second-degree burn
Epidermal and upper dermal damage
– Blisters appear
– First- and second-degree burns are referred to as partial-thickness
burns because only the epidermis and upper dermis are involved
Third-degree burn
Entire thickness of skin involved (referred to as full-thickness burns)
Skin color turns gray-white, cherry red, or blackened
No edema is seen and area is not painful because nerve endings are
destroyed
Skin grafting usually necessary
Cyanosis
Blue skin color – low oxygenation of hemoglobin
Erythema (redness)
Fever, hypertension, inflammation, allergy
Pallor (blanching or pale color)
Anemia, low blood pressure, fear, anger
Jaundice (yellow cast)
Liver disorders
Bronzing
Inadequate steroid hormones (example: Addison’s disease)
Bruises (black-and-blue marks)
Clotted blood beneath skin
Appendages of skin
- Eccrine sweat gland
- Arrector pili muscle
- Sebaceous (oil) gland
- Hair follicle
- Hair root
Dermis
Papillary and 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)
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 one to five layers of flattened
cells, organelles deteriorating; cytoplasm
full of lamellar 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 dendritic
cells
Severity of burns
Anterior and posterior
head and neck, 9%
Anterior and posterior
upper limbs, 18%
Anterior and posterior
trunk, 36%
Perineum, 1%
Anterior and posterior
lower limbs, 36%
