chapter 6: the integumentary system

skin is the body’s

largest organ (~20 lbs)

dermatology

the study of the integument (skin)

the integumentary system is made up of

• integument (skin)

• accessory organs (hair, nails, cutaneous glands)

this system is the most

noticeable organ system and it can also show symptoms from various diseases of other organ systems

skin

• largest/heaviest organ

• made up of two parts:

  ------epidermis (epithelium) & dermis (L areolar CT; D irregular CT)

the hypodermis is not part of the skin but it is made of

• areolar CT and adipose tissue

• regions of predominately adipose tissue which are subcutaneous fat

skin is classified as thick or thin based on the

thickness of the epidermis alone

thick skin

• found on palms, soles, and corresponding surfaces on fingers and toes

• lacks hair follicles and sebaceous glands but has sweat glands

thin skin

• covers everything of the body that the thick skin doesn’t cover

• contains hair follicles, sweat, and sebaceous glands

functions of the skin

• contains the body

• resists trauma and infection

• serves as a barrier to water loss/gain, UV radiation, and certain chemicals

• vitamin D synthesis

• sensation

• thermoregulation

• nonverbal communication

resist trauma and infection

• keratin, abundant desmosomes, and a dry slightly acid mantle surface (pH 4-6)

• also certain defensive molecules are present (dermicidin and defensins)

sensation

nerves not uniform in distribution

• more abundant in face, palms, fingers, soles, nipples, and genitalia

multiple sensations originate from receptors in the skin

• hot, cold, touch, texture, pressure, vibration, pain

thermoregulation

via cutaneous vasoconstriction and vasodilation

keratinized epithelium

found in epidermis and covered with a layer of dead compressed cells (keratinocytes)

nonkeratinized epithelium

lacks the dead layer of cells (keratinocytes)

a closer look at epidermis

• lacks blood vessels and relies on diffusion of nutrients from underlying CT (dermis)

• some nerve endings for touch and pain

• many cell types present

1. stem cells - unipotent

2. keratinocytes

3. melanocytes

4. tactile cells

5. dendritic cells

stratum basale (deepest layer)

simple cuboidal/columnar stem cells, melanocytes, keratinocytes

stratum spinosum

layers of keratinocytes; deep cells make more keratinocytes through mitosis---superficial cells make keratin

stratum granulosum

3-5 layers of keratinocytes, flat layers, and organelles are deteriorating

stratum lucidum

only in thick skin; keratinocytes have no organelles; cells are packed together with eleidin (protein)

stratum corneum

made of dead cells (up to 30 layers) that are highly keratinized

resists abrasion, penetration, and water loss

stem cells - epidermis

undifferentiated cells that give rise to keratinocytes in the stratum basal

keratinocytes - epidermis

major cell; responsible for making keratin

melanocytes - epidermis

make melanin; cells remain in the stratum basale

• packages of melanin (melanosomes) are exocytosed and absorbed by nearby keratinocytes

• melanin protects the nucleus of the keratinocyte from UV radiation

tactile cells - epidermis

involved in sensation of touch; tactile discs include the cell and associated nerve endings

dendritic cells - epidermis

immune cells that have migrated to the stratum spinosum or stratum granulosum

life history of keratinocytes in stratum basal

• begins with differentiation from stem cells

(process can be sped up/intensified by constant abrasion leading to a production of a thicker epidermis- callus or corn)

• pushed towards the surface and the cells of the stratum spinosum rarely divide; rather accumulate as pre-keratin molecules

life history of keratinocyte in stratum granulosum

• keratinocytes flatten and increase keratin (protection) and lipid production

• cell surface is waterproofed by releasing lipid mixture

• cells die

• in conjunction with tight junctions, an epidermal water barrier is created

life history of keratinocyte in stratum corneum

• sloughed off as dander through exfoliation

• dandruff is clumps of dander held together by sebum

dermis

• made primarily of collagen but has elastic and reticular fibers along with cells typical of CT

• HIGHLY vascular

• contains many cutaneous glands and nerve endings

• LOCATION NOT ORIGIN of hair follicles and nail roots

papillary region of the dermis

superficial; areolar CT

• conspicuous dermal papilla and epidermal ridges

• produces friction ridges that lead to finger prints

• exceptionally tall dermal papillae in highly sensitive areas to allow nerve endings to reach closer to the surface

reticular layer of dermis

deep; dense irregular CT

• striae (stretch marks) occur because of fibrosis occurring in this region

three pigments contribute to skin color

• melanin (melanocytes)-----only pigment made in skin

• carotene (stratum corneum)---------------------from plant products, accumulates in corneum and fatty deposits of the hypothermis, converts to vitamin A; good for epidermal health

• hemoglobin (blood vessels)------ pinkish color; more evident in lighter skin

pheomelanin

reddish yellow

eumelanin

brownish black

melanin

• produced in melanocytes

• color difference of skin is due to the amount and form of melanin ------lighter skin = larger clumps & dark skin = smaller clumps

• melanin migrates to keratinocytes to form “pigment shields” for nuclei (UV protection)

• freckles and pigmented moles are accumulations of melanin

cyanosis

blue skin color- low oxygenation of hemoglobin

erythema (redness)

fever, hypertension, inflammation, allergy

pallor (blanching)

anemia, low blood pressure, fear, anger

jaundice (yellow cast)

liver disorder

hematoma (bruises)

clotted blood beneath the skin

albinism

• genetic mutation disorder

• melanocytes don’t make melanin

• skin is pink, hair white, irises unpigmented

friction ridges

• fingertips, soles of feet

• enhance sense of touch and grip

flexion lines (flexion creases)

• dermal folds at/near joints

• dermis tightly secured to deeper structures

hemangiomas (birthmarks)

• benign tumors of the capillaries

• capillary hemangiomas or cavernous hemangiomas-- present at or soon after birth, often disappear with age

• port-wine stain-- flat, pinkish to dark color in color; remain for life

accessory organs of the integumentary system

hair, nails, and cutaneous glands

hair and nails- made primarily of dead, keratinized epidermal cells (hard keratin)

hair (pili)

all over the body except palms, soles, nipples, and parts of the external genitalia

functions of hair (pili)

• sensation of insects and parasites on the skin

• head hair helps retain heat, protect the scalp from UV radiation

• beard and axillary and pubic hair signify sexual maturity and may aid in transmission of sexual scents

• guard hairs (vibrissae) protect the eyes, nasal cavity, and ears from debris

• eyebrows may protect eyes from sweat and is also important in facial expressions

lanugo (no pigment)

fine hairs on the fetus during last trimester

vellus (some pigment)

replaces lanugo hair; remains dominant on women and makes up 2/3 of their body hair, 1/10 on men, and all the hair on children except for the terminal hair

terminal hair (heavily pigmented)

makes up the hair on the scalp, eyebrows, and eyelashes; after puberty it makes up the hair of the axilla, pubic region, male facial hair, some of the hair on trunk and limbs

hair shaft

sticks out from skin

hair root

part of the hair in the follicle

layer of keratinized cell- cuticle

heavily keratinized; arranged like overlapping shingles

layer of keratinized cell-cortex

hard keratin with injected melanin, flattened

layer of keratinized cell-medulla

large cells and air spaces

what is the follicle?

a tube of epidermial (epithelial) in the dermis

hair bulge

contains stem cells for follicle growth and capillaries for blood supply

hair receptors

nerve fibers that detect hair movement

pilorector muscles

AKA arrector pili or pilomotor muscles

-smooth muscle to raise hairs. (goosebumps)

-hair matrix---- mitotically active cells- hair growth

cross sectional hair shapes

straight = round

wavy = oval

curled = flat

hair color due to pigment

brown/black = rich in eumelanin

red= rich in pheomelanin, some eumelanin

blond= little eumelanin and some phemomelanin

gray= little melanin; airspace in the medulla

alopecia

-thinning of the hair

influenced by nutritional and other health factors

pattern baldness

-genetic and hormonal

in males = dominant trait influenced by testosterone

in females = recessive trait influenced by testosterone

hirsutism

-undesireable hair growth (especially in women and children)

influenced by abnormal testosterone levels and genetics

nails

• hardened derivative of the stratum corneum

• made of thin, dead keratinocytes with parallel-arranged hard keratin fibers

• changes in nail appearance can indicate

  1. yellowing nails---respiratory or thyroid gland disorders

  2. concavity of nail (spoon nail)---- iron deficiency

  3. horizontal lines (beau’s lines)----malnutrition

free edge

extends beyond distal edge of fingertip

nail body

visible attached portion

nail root

proximal edge of nail embedded in skin

nail bed

epidermal layers deep to nail body

nail matrix

thickened proximal portion of nail bed --- makes the nail cells which become keratinized as the nail body grows distally

sudoriferous (sweat) glands

apocrine sweat glands (also merocrine)

merocrine (eccrine) sweat glands

sebaceous glands

oil glands; secrete sebum; utilize holocrine secretion method; important for normal hair and skin health

ceruminous glands

only in external ear; secretions combine with sebum to make ear wax (cerumen); important to keep eardrum pliable; waterproof canal; kill bacteria; block foreign particles

mammary glands

secrete breast milk

apocrine sweat glands

• confined to axillary (armpit), areolar (nipple), and genital areas: beards of adult males

• secretions (INTO hair follicle) contain fatty acids and proteins

• secretion is odorless

• begin functioning during puberty (androgen influenced)

• activated by nerve fibers during pain, stress, and sexual activity

merocrine sweat glands

• secrete to skin surface

• acidic secretion --- primarily made of water (99%), some NaCl, vitamin C, some waste products (ammonia, urea, uric acid) , lactic acid

• creates acid mantle (pH 4-6) = inhibits bacteria

• widely distributed on body--- palms, soles, forehead

• primarily responsible for cooling the body

• evaporative cooling (water has high specific heat- hydrogen bonds)

myoepithelial cells

push perspiration up the duct

insensible perspiration

occurs constantly ~500 mL day

diaphoresis

sweat that is noticeable caused by heat and exercise

acne

Inflammation of sebaceous glands, follicle blocked with keratinocytes and Sebum, develops ​into a whitehead composed of these and bacteria; more inflammation results in pus (pimple)

dermatitis

Any inflammation of the skin, usually with itching and redness; (e.g. poison ivy/oak)

eczema

Itchy, red, “weeping” skin lesions caused by an allergy, may progress to thickened, leathery, dark patches

psoriasis

Recurring, reddened plaques covered with silvery scale; possibly caused by an autoimmune response; hereditary

rosacea

A rashlike formation, often around nose and cheeks, marked by fine networks of dilated blood vessels; worsened by hot drinks, alcohol, and spicy food.

seborrheic dermatitis

Patches of scaly white or yellowish inflammation often on head, face, chest, back; called crɑdle cɑp​

(a yellow, crusty scalp lesion) in infants. Cause unknown, but related to genetic and climatic factors.

tinea

Any fungal infection of the skin; common in moist areas such as the axilla, groin, and foot (ɑthlete’s foot). E.g. ringworm

skin cancer

uncontrolled division of skin cells, most are benign, others are malignant

most important risk factors are exposure to UV radiation and genetics

mole

uniform color, even contour, relatively small

cancer

various color, scalloped border, large and spreading

basal cell carcinoma

least malignant; most common;  cells of stratum basale proliferate and invade dermis and subcutaneous layers

squamous cell carcinoma

Cells of stratum spinosum; believed to be sun-induced (head and hands). Not so bad unless – metastasizes to nearby lymph nodes

malignant melanoma

cancer of the melanocytes; accounts for only 5% of skin cancers but is often deadly​

• Does not respond to chemotherapy ​

• Average lifespan- 6 months ​

• Greatest risk factor is family history

first degree burn

partial thickness burn

• epidermis damaged only

second degree

partial thickness burn

• blistering occurs (fibrosis possible = scar tissue)

• upper regions of dermis damaged

third degree

full thickness burn

• epidermis, dermis, hypodermis, and underlying tissue (muscle/bone)

• requires skin grafts

• no regeneration of skin