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)