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INTEGUMENTMs. Hughes
Bio II
Integumentary System (Skin)
the skin has a surface area of 1.5 to 2 square meters, weighs 9 to 11 pounds (7% of total body weight in the average adult), and varies in thickness from 1.5 mm – 4 mm
every square centimeter (cm) of the skin contains: 70 cm of blood vessels, 55 cm of nerves, 100 sweat
glands, 15 oil glands, 230 sensory receptors, and about 500,000 cells that are constantly dying/being replaced
pliable, tough, waterproof, insulates, cushions without our skin, we would quickly fall prey to
bacteria and perish from water and heat loss
Skin Cell
protects the body from mechanical damage (bumps and cuts) chemical damage (acids, bases, poisons) thermal damage (heat and cold) UV radiation (sunlight) invasion (bacterial)
capillary network and sweat glands regulate heat loss mini-excretory system (skin loses urea, salts, and
water during sweating) manufactures several proteins important in immunity synthesizes vitamin D from sunlight and cholesterol contains sensory receptors for touch, pressure,
temperature, and pain two distinct regions
epidermis and dermis usually firmly connected but friction/burns may cause them
to separate and form a blister
Epidermis
avascular thick to prevent water loss different types of cells
keratinocytes
produce keratin protective properties arise in the deepest part of the epidermis undergo almost continuous mitosis reach free surface of skin, they are dead,
scalelike structures (keratin-filled plasma membranes) millions of these dead cells rub off every day (we have a totally new epidermis every 35 to
45 days)
Melanocytes
specialized epithelial cells that synthesize the pigment melanin
touch all the keratinocytes melanin granules accumulate on superficial, or
"sunny," side of keratinocyte nucleus forms a pigment shield to protect the nucleus from
the damaging effects of UV radiation same relative number of melanocytes skin color due to differences in melanocyte activity freckles/moles are where melanin is concentrated
in one spot
five distinct layers (deep to superficial):
Basal layer aka stratum germinativum (“growing layer”)
deepest attached to the underlying dermis and
receive nourishment single row of cells representing the
youngest keratinocytes rapid division of these cells push daughter
cells upward alternate name, stratum basale (“bottom
layer”) 10% to 25% melanocytes
stratum spinosum (“prickly layer”)
weblike system of intermediate filaments tension-resisting bundles of
keratin filaments keratinocytes in this layer are somewhat
flattened and irregular in shape
stratum granulosum (“granular layer”)
three to five cell layers nuclei/organelles begin to disintegrate
which makes keratinocytes flat granules of keratin accumulate which helps in slowing water loss
superficial to this layer epidermal cells are too far from dermal capillaries
adequate nourishment is not received and they die
stratum lucidum (“clear layer”)
appears as a thin translucent band just above the stratum granulosum
clear, flattened, dead keratinocytes present only in thick skin
stratum corneum (“horny layer”)
20 to 30 cell layers thick accounts for up to three-quarters of the
epidermal thickness keratin and thickened plasma membranes
protect the skin against abrasion and penetration
glycolipids between cells waterproofs this layer cornified/horny cells shed from the scalp and
flakes slough off dry skin average person sheds 40 pounds of these skin
flakes in a lifetime
Dermis
vascularized, contains a rich nerve supply, is a shock absorber, and anchors the skin
nutrients reach the epidermis by diffusion
two major layers – papillary and reticular
Papillary Layer
fibers form a loosely woven mat heavily invested with blood vessels
superior surface has nipple-like projections called dermal papillae
contain capillary loops, nerve endings (pain receptors), and touch receptors
larger mounds called dermal ridges produce looped/whorled ridges on the epidermal surface
epidermal ridges increase friction and enhance the gripping ability of the fingers and feet
lots of sweat pores on ridges that leave unique patterns (fingerprints)
Reticular Layer
deeper layer containing sweat glands, oil glands, and blood vessels (80% of the dermis)
has deep pressure receptors and lots of phagocytes
has collagen fibers (toughness and attracts water to help the skin stay hydrated) and elastin fibers
(provides elasticity) - both are lost with age
Subcutaneous Tissue
deep to the dermis known as the hypodermis or superficial
fascia anchors the skin to underlying organs shock absorber and insulator for the
deeper tissues
Skin Color
3 pigments contribute to skin color: melanin, carotene, and hemoglobin
Pigments
melanin
only melanin is made in the skin ranges in color from yellow to reddish-
brown to black stimulated to greater activity when we
expose our skin to sunlight prolonged sun exposure causes a
substantial melanin buildup
carotene yellow to orange accumulate in the stratum corneum and
fatty tissue of the hypodermis color is most obvious in the palms and
soles, where the stratum corneum is thickest
hemoglobin pinkish hue of fair skin reflects the red color
of oxygenated hemoglobin
Appendages of the Skin
made in the epidermis - sweat glands, sebaceous (oil) glands, hair follicles/hair, and nails
1. sweat (sudoriferous) glands formed by stratum germinativum and
pushed deep into the dermis entire skin surface except the nipples
and parts of the external genitalia 2.5 million per person
2. eccrine glands more numerous abundant on the palms, soles of the feet, and
forehead duct extends to open in a funnel-shaped pore secretion is commonly called sweat
99% water, with some salts, vitamin C, antibodies, traces of metabolic wastes, lactic acid, and small amounts of ingested drugs
pH between 4 and 6 major role is to prevent overheating of the
body heat-induced sweating begins on the
forehead and then spreads over the rest of the body
emotionally induced sweating (cold sweat brought on by fright, embarrassment, or nervousness) begins on the palms, soles, and armpits and then spreads to other body areas
3. apocrine glands confined to the axillary and genital areas larger than eccrine glands ducts empty into hair follicles same basic components as true sweat, plus some
fatty substances and proteins viscous with a milky or yellowish color secretion is odorless bacteria on skin use fat/proteins for nutrients and
cause it to develop the musky body odor begin to function at puberty little role to play in thermoregulation
2 other specialized apocrine glands ceruminous glands
found in the lining of the external ear canal secrete a rather sticky substance called
cerumen, or earwax thought to deter insects and block entry of
foreign material mammary glands
specialized sweat glands secrete milk
3. sebaceous (oil) glands
formed by stratum germinativum and pushed deep into the dermis
found all over the body except palms and soles small on the body trunk and limbs, but large
on the face, neck, and upper chest oily secretion called sebum secreted into a hair
follicle or to a pore on the skin surface softens/lubricates hair and skin, prevents
hair from becoming brittle, and slows water loss from skin
important bactericide
3. sebaceous (oil) glands
central cells of the gland accumulate lipids until they burst
stimulated by hormones - inactive during childhood
if blocked by accumulated sebum, a whitehead forms
a whitehead dries/darkens to form a blackhead acne is an active inflammation of the
sebaceous glands accompanied by pimples caused by bacterial infection
4. hair follicles/hair
follicles extend from the epidermal surface into the dermis (hypodermis in the scalp)
deep end of the follicle is expanded, forming a hair bulb with sensory nerve endings (root hair plexus)
papilla (nipple-like bit of tissue) containing a knot of capillaries, protrudes into the hair bulb
wall thins as it approaches the hair bulb so that only a single layer of stratum germinativum cells covers
the papilla to supply nutrients to the growing hair
the growth zone (matrix) in the hair bulb includes cells that actively divide to produce hair
(often triggered by chemical signals)
4. hair follicles/hair
associated with each hair follicle is a bundle of smooth muscle cells called an arrector pili
contraction pulls the hair follicle into an upright position & dimples the skin surface (goose bumps)
bending the hair can also stimulate nerves (sensing an insect crawling over your skin)
millions of hairs are scattered over nearly all of the body about 100,000 of them in the scalp (lose an average of 90
scalp hairs daily) life span of hairs varies but follicles remain active for years
(average is four) eyebrow follicles remain active for 3-4 months why eyebrows are never as long as the hairs on your head
rate of hair growth about 2 mm per week
4. hair follicles/hair
hair pigment is made by melanocytes at the base of the hair follicle
gray or white hair results from decreased melanin production lips, nipples, parts of the external genitalia, and thick-
skin areas (palms/soles) totally lack hair hair on the scalp guards the head against physical trauma,
heat loss, and sunlight eyelashes shield the eyes nose hairs filter large particles like lint and insects from
inhaled air hairs consist largely of flexible cells produced by hair follicles as it grows, the older part of the hair is pushed upward, and
its fused cells become increasingly keratinized and die
4. hair follicles/hair
hard keratin is tougher, more durable, and individual cells do not flake off
chief regions of a hair are the shaft (projects from skin), and the root (embedded in the skin)
cross sectional shape of the shaft determines straight or curly hair type:
flat/ribbonlike shaft - hair is kinky oval shaft - hair is smooth and silky (maybe
wavy) round shaft - hair is straight and tends to be
coarse
4. hair follicles/hair
classified as vellus or terminal vellus
body hair of children and adult females pale, fine
terminal coarser, often longer hair of the eyebrows and scalp body hair of adult males appear in the axillary and pubic regions at puberty
of both sexes influenced by nutrition, hormones, and conditions
that increase local dermal blood flow
4. hair follicles/hair
hair grows fastest from the teen years to the 40s - then growth slows (age-related atrophy)
leads to hair thinning and some degree of baldness much less dramatic in women coarse terminal hairs are replaced by vellus hairs true (frank) baldness is male-pattern baldness and
is genetically determined delayed-action gene switches on in adulthood and
changes the response to testosterone follicular growth cycles become short (many hairs
never emerge from follicles before shedding)
5. Nails
scalelike modification of the epidermis that contains hard keratin forms a clear protective covering on the dorsal surface of the
distal part of a finger or toe each nail has a free edge, a body (visible attached portion), and
a proximal root (embedded in the skin) lateral/proximal borders are overlapped by skin folds called nail
folds (proximal nail fold is the cuticle) deeper layers of the epidermis (stratum germinativum) extend
beneath the nail as the nail bed thickened proximal portion of the nail bed, called the nail matrix,
is responsible for nail growth pink color due to underlying capillaries some melanin can be seen thru the nail if the skin color is dark white crescent over matrix is lunula
Homeostatic Imbalances of the Skin
the skin can have more than 1000 different disorders (allergies, bacterial, viral, fungal, burns, cancers)
athlete’s foot (tinea pedis) red, peeling skin between or underneath the toes (usually but not always
itchy) cold sores
herpes virus that localizes in a mucosal cutaneous nerve as a small blister that itches and stings
remains dormant until activated by emotional upset, fever, or UV radiation contact dermatitis
itching, redness, and swelling of the skin due to chemical irritants burns
tissue damage and cell death caused by heat, electricity, UV radiation, or chemicals
body loses fluids through seepage from wound leading to dehydration dehydration leads to renal failure and circulatory shock volume of fluid loss can be estimated by the “rule of nines”
Athletes foot
Cold sore
Contact dermatitis
Burns
the body is divided into 11 areas each representing 9% plus 1% for the perineum
burned skin is sterile for 24 hours before bacteria/fungi begin invading thru damaged areas
1st degree burns – only the epidermis is damaged, redness/swelling occur, regeneration
2nd degree burns – epidermis/upper dermis is damaged, blisters develop, regeneration
3rd degree burns – destroys entire thickness of skin, burned areas appear white/black, no regeneration
Skin Cancer
single most common type of cancer cause of most are unknown but the most
important risk factor is UV exposure most are benign and do not spread
(warts) some are malignant
basal cell carcinoma least malignant, most common, slow growing stratum germinativum does not form keratin
and spread into the dermis easily removed with high recovery rate
squamous cell carcinoma appears red and scaly, rapid growth starts in stratum spinosum on scalp, ears,
dorsal hand chance for complete recovery if caught early
malignant melanoma cancer of the melanocytes begins as spontaneous cancer in
pigmented areas (often from pigmented moles)
metastasizes rapidly into surrounding lymph/blood vessels
often fatal
Skin Cancer
ABCD rule for recognizing melanoma A – asymmetry (sides do not have the same
shape) B – border irregularity (edges are not
smooth) C – color (more than one color) D – diameter (larger than 6mm)