Dermatology- study of integumentary system
Integumentary system- skin, hair, glands, & nails
Main job: maintain homeostasis between body & its external environment by regulating body
functions & protecting body structures; temperature regulation, metabolic regulation,
sensory reception, excretion; uses ultraviolet light to make vitamin D; keeps water loss
to a minimum; protects from invading pathogens
Skin = cutaneous membrane = integument
Largest organ of body so is made of several kinds of tissue (epithelial, connective, smooth
muscle & nervous)
7% of body mass (~9 lb)
1.5-2 m2
1.5-4mm thick (thickest on soles of feet &
palms of hands, thinnest on eyelids & eardrum)
Made of 2 main layers: epidermis & dermis
Epidermis
Superficial protective layer made of stratified squamous epithelial tissue
Top layers are dead cells & deepest layers are living
New cells every 28 days & it takes 14 days for cells to move from bottom to top; takes a cell 1
month to go from stratum basale to being shed
No blood vessels, nerves or sensory receptors; must be nourished by diffusion from below
Layers from bottom to top (deepest to most superficial)
Stratum basale (basal layer)- single layer of cells touching dermis; cells cuboidal to
columnar in appearance; only layer where mitosis occurs; responsible for cell
division & replacement
4 types of cells
Keratinocytes- most abundant type; make keratin to toughen &
waterproof skin
Melanocytes- make melanin to protect from UV light; have branches
of cytoplasm that transfer pigment
Tactile cells- sparse sensory receptor cells that are sensitive to touch
Nonpigmented granular dendrocytes- protective cells that eat bacteria
& epidermal cancer cells
Stratum spinosum (spiny layer)- contains several layers of cells; spiny appearance due to
spine-like extensions arising from keratinocytes; this layer plus basal layer
sometimes called stratum germinativum
Stratum granulosum- 3 or 4 flattened layers of cells that contain granules of
keratohyalin that will become keratin; cells contain fibers of keratin & shriveled
nuclei; keratinization begins here as cells fill up with keratin
Stratum lucidum- layers appear clear because no cell parts are visible; only found in
lips & thickened skin of soles & palms; 2-3 cell layers
Stratum corneum- 25-30 layers of flattened scale-like cells; thousands shed daily &
replaced with cells from below; these cells are cornified; cornification is the
drying/flattening of cells caused by keratinization; keratin filled cells prevent
water loss
Dermis
Deeper thicker layer of skin made of dense irregular connective tissue
0.5-3 mm thick so is thickest layer of skin
Contains all 3 types of connective tissue fibers (collagen, elastin & reticular) but mostly collagen
Skin tone originates in this layer with the elastin & collagen fibers forming a structural
foundation
Young people have more elastic fibers than elderly so their skin is less baggy & with
fewer wrinkles
This layer provides nourishment to epidermis since epidermis lacks blood vessels
Contains sweat glands, oil secreting glands, nerve endings, hair follicles, blood vessels, nail
roots, smooth muscle tissue
Contains many nerve endings- effectors that cause muscles/glands to respond, also sensory
receptors that respond to a variety of stimuli (touch, pressure, temperature, pain,etc)
Some areas have more receptors than other
Dermal blood vessels supply nutrients to basal layer of epidermis & structures within dermis;
also help regulate body temperature & blood pressure; vasoconstriction keeps heat in
body by keeping blood vessels away from surface; vasodilation allows heat to escape
by allowing blood to flow freely & closer to surface
Layers of dermis (top to bottom)
Stratum papillarosum- upper part of dermis in contact with epidermis; made of loose
connective tissue; for nourishment of epidermis; papillae projections extend
into dermis & form base for friction ridges; projections also increase contact
between epidermis & dermis
Stratum reticularosum- deeper thicker layer of dermis; collagen fibers more dense here
& form flexible network; if stretched too far can leave tear which will be
repaired with a stretch mark
Hypodermis
Subcutaneous tissue that binds dermis to underlying organs
Mostly loose connective tissue & adipose cells interlaced with blood vessels, reinforced with
collagenous & elastin fibers
Usually 8% thicker in females since they have more adipose tissue
Stores lipids, insulates, cushions, regulates body temperature
Drugs injected here are absorbed quickly
This layer not considered part of integumentary system
Normal skin color attributed to pigments
Melanin
Brown-black pigment made by melanocytes
Number of melanocytes the same for all but the amount of melanin each cell makes
determines racial variations
Protects basal layer from sunlight’s UV rays
Gradual exposure of skin to sun increases production of melanin (tanning)
Lack of melanin results in albinism; freckles are an aggregation of melanin; vitiligo is
the lack of melanocytes in localized area causing white spots; liver spots or
serrheic hyperferatoses are benign growths of melanocytes due to age
Carotene
Yellowish pigment from vegetables that can accumulate in cells of stratum corneum
& fatty parts of dermis
Orientals have an abundance of this pigment
Hemoglobin
Oxygenated blood flowing through dermis gives pinkish tones
Fingerprints = friction ridges
Congenital patterns of exposed skin surfaces such as finger & toe pads, palms & soles
Formed by 4th month of fetal development
Formed by the pull of elastic fibers in dermis
Function to prevent slippage when grasping
4 basic patterns with no 2 individuals having identical fingerprints (not even identical twins)
On palms you also have flexion creases & joints will have flexion lines
Acquired due to usage of hands & joints
Aging skin
Skin repair takes longer due to a reduced number & activity of stem cells in basal layer
Decrease in number & efficiency of epidermal dendritic cells
Thinner, drier scalier appearance
Cells not in nice neat columns but are in disarray
Collage fibers decrease in number, organization & density (wrinkling)
Elastin fibers because coarser, denser & less resilient (wrinkling)
Tiny blood vessels in dermis become thick walled & leaky which leads to impaired
thermoregulation
General loss of hair, nerve cells, sweat ducts, oil glands
Less vitamin D production
Connective tissue stiffens or breaks down beneath skin (wrinkling)
Supporting fat disappears (wrinkling)
Aging is caused by
Intrinsic processes- genetically programmed aging
Extrinsic processes- accumulated environmental damage such as photoaging (resulting from
chemical reactions triggered by exposure to sunlight)
Hair, nails & glands are derivatives of the skin
Hair
Makes us mammals but presence is greatly reduced; some regions are hairless such as lips,
palms, soles, nipples & genitalia
Main job: protection, heat retention, facial expression, sensory reception, visual identification,
chemical signal dispersion
Parts of hair
Shaft- visible but dead part of hair above surface of skin
Bulb- enlarged base of root inside hair follicle
Root- base of hair where it develops from stratum basale cells & receives nutrients from
dermal blood supply
In healthy person, hair grows 1mm/3 days but as it becomes longer this slows
Hair’s lifespan varies (3-4 months for eyelash, 3-4 years for scalp hair)
You lose 10-100 hairs daily & baldness results when hair is lost but not replaced
In cross section, hair has 3 layers
Medulla- inside layer made of loosely arranged cells separated by air
Cortex- thick outer layer consisting of hardened tightly packed cells
Cuticle- tough outer covering; cells have serrated edges that give hair a scaly
appearance under microscope
Texture is determined by a hair’s cross sectional shape
Color is determined by type & amount of pigment produced in stratum basale; more melanin
means darker color & gray/white results from lack of pigment, air spaces in shaft also
contribute to color
Attached to each hair follicle is oil gland & arrector pili muscle (muscle involuntarily responds to
stimuli & makes goose bumps so hair stand up)
Types of hair
Lanugo- fine, silky unpigmented fetal hair that appears during last trimester
Angora- grows continuously on scalp & male faces
Definitive- grows to certain length & then stops, most common type; ex. Eyelashes,
eyebrow, pubic, axillary
Nails
Formed from compressed stratum corneum of epidermis so are considered modifications of
epidermis
Main job: protect distal tips
Hardness due to dense keratin fibrils between cells
Grow by changing superficial cells of nail matrix into nail cells that are harder & transparent;
grow at rate of 1mm/week (fingernails grow faster than toenails, longer fingers grow
faster, heat accelerates growth); growth needs good nutrition but gelatin & vitamin
supplements won’t help nails grow more rapidly in a healthy person
Polish enamels harden nails but polish removers dry them out & cause brittleness
Poor circulation slows growth of nails & can produce thicker, rougher, yellow tinted nails
Parts of nail
Body- plate-like “nail” that rests on nail bed (actually stratum spinosum); appears
pinkish due to underlying vascular tissue; sides protected by nail fold & nail
groove is between sides & body
Free border- extends over thickened region of hyponychium (quick)
Hidden border- covered by eponychium (cuticle); contains growth area or nail matrix;
can see the lunula or moon shaped area; keeps dirt, irritants & microorganisms
from base of nail
Glands
Located in dermis where they are supported & receive nutrients
Exocrine glands since they release secretions directly or through ducts
Types of skin glands
Sebaceous glands- oil glands associated with hair follicles; secrete sebum onto shaft of
hair to lubricate & waterproof stratum corneum & prevents hair from becoming
brittle; blocked ducts can become infected & result in acne; sex hormones
regulate production/secretion of sebum; sebum has some bacteria killing
properties; these glands most plentiful on face, scalp, chest & upper back
Sudoriferous glands- sweat glands excrete perspiration onto skin’s surface; perspiration
contains water, salts, urea & uric acid; used for evaporative cooling & excretion
of wastes; most numerous on palms, soles, axillary & pubic areas, on forehead
Eccrine (merocrine)- sweat glands found all over the body; about 3 million on
body; used for evaporative cooling
Apocrine- larger glands found in axillary & pubic regions; secrete into hair
follicles; not functional until puberty; produced substances do not smell
until bacteria begin to break them down
Mammary glands- modified apocrine glands that secrete milk
Ceruminous glands- specialized glands in external auditory canal; modified sweat
glands; secrete cerumen (ear wax); wax acts as water/insect repellant & keeps
tympanic membrane pliable