Ch. 5: The Integumentary System

Skin Consists of 2 layers

Epidermis: outermost protective shield of body

Dermis: underlies epidermis and makes up bulk of skin

Keratinocyte

produce fibrous keratin (protein that gives skin its protective properties)

Major cells of epidermis

Melanocytes

Produce pigment melanin, which is packaged into melanosomes

Melanosomes are transferred to keratinocytes

Dendritic cells/Langerhans cells

Ingest foregin substances and are key activators of immune system

Tactile epithelial cells/Merkel cells

Sensory receptors for touch located at epidermal-dermal junction

Thick skin

contains all five layers (including stratum lucidum)

Located on palms, fingertips, and soles

Thin skin

conatins only four layers (no stratum lucidum)

Stratum Basale (basal layer)/ Stratum germinativum

Deepest of all epidermal layers

Layer that is firmly attached to dermis

consist of a single row of stem cells that actively divide (mitotic), producing two daughter cells each time

Stratum spinosum (prickly layer)

Several cell layers thick

cells contain weblike system of intermediate pre-keratin filaments attached to desmosomes

Keratinocytes in this layer appear spikey, so they are called prickle cells

Stratum Granulosum (granular layer)

Four to six cells thick, but cells are flattened, so layer is thin

Cell appearance changes

Cells above this layer die

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

Papillary dermis

is the thin, superficial layer of areolar connective tissue consisting of loose, interlacing collagen and elastic fibers and blood vessels

Dermal Papillae

superficial region of dermis that sends fingerlike projections up into epidermis

-Contain capillary loops, free nerve endings, and touch receptors

Friction ridges

occur in thick skin

function:

• enhances gripping ability

• contribute to sense of touch by enhancing vibrations detected by receptors (lamellar corpuscles)

Reticular dermis

makes up of dermal thickness

consists of coarse, dense irregular connective tissue

Dermal vascular plexus

network of blood vessels b/t reticular layer and subcutaneous tissue

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

Melanin

• Only pigment made in skin; made by melanocytes

• Made from amino acid tyrosine by tyrosinase

• packaged into melanosomes that are sent to shield DNA of keratinocytes from damaging UV sunlight

• Two forms: reddish yellow to brownish black

Carotene

yellow to orange pigment

accumulated in stratum corneum and subcutaneous tissue

can be converted to vitamin A for vision and epidermal health

Hemoglobin

pinkish hue of fair skin is due to lower levels of melanin

Hair/pili

consists of dead, keratinized cells

Functions:

• sense insects on skin before bite or sting

• hair on head guards against pysical trauma

• protect from heat loss

• shield skin from sunlight

• eyelashes shield eyes

• nose hairs filter particles from inhaled air

Root

portion w/n scalp, where keratinization is still going on

Shaft

portion that extends above scalp, where keratinzation is complete

Three part 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

Hair follicle

extends from epidermal surface to dermis

Hair bulb

expanded area at deep end of follice

hair follicle receptor/root hair plexus

sensory nerve endings that wrap around bulb

Hair matrix

actively dividing area of bulb that produces hair cells

Arrector pili

small band of smooth muscle attached to follicle

Vellus hair

pale, fine body hair of childern and adult females

Terminal hair

coarse long hair

-found on scapl and eyebrows

Nails

are scale-like modifications of epidermis that contain hard keratin

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

Cuticle/eponychium

nail fold that projects onto surface of nail body

Hyponychium

area under free edge of plate that accumulates dirt

Lunule

thickened nail matrix, appears white

Sweat glands/ sudoriferous glands

help control body temperature

two main types:

-Eccrine sweat glands/merocrine sweat glands

-Apocrine sweat glands

Modified Apocrine sweat glands

Ceruminous glands: located in lining of external ear canal; secrete cerumen (earwax)

Mammary glands: secrete milk

Skin protection

Chemical barriers

• Sweat, which contains antimicrobial proteins

• Sebum and defensins, which kill bacteria

• cells also secrete antimicrobial defensin

  • Acid mantle: low pH of skin retards bacterial multiplication

Physical barriers

• Flat dead, keratinized cells of stratum corneum, surrounded by glycolipds, block most water and water-soluble substances

Biolgical barriers

-Dendritic cells

• Located in the epidermis

• Engulf foreign antigens (invaders) and present to white blood cells, activating the immune response

-Macrophages

• Located in the dermis

• Also activate immune system by presenting foreign antigens to white blood cells

Cutaneous sensory receptors

are part of the nervous system

Exteroreceptors

respond to stimuli outside body

-Touch: tactile (Meissner’s) corpuscle in dermal papillae and tactile epithelial cells with associated sensory nerve

-Deep pressure: lamellar (Pacinian) corpuscles in deeper dermis or subcutaneous tissue

Hair movement: hair follicle receptors

Painful stimuli of the skin: free nerve endings

Recognizing Skin Cancer

ABCD rule

-A:asymmetry; the two sides of the pigmented area do not match

-B: border irregularity; exhibits indentation

-C: color; contains several colors (black, brown, tan, sometimes red or blue)

-D: diameter; larger than 6mm

-E: evolution or evolving; changes over time