INTEGUMENTARY SYSTEM

Epidermis

Function:

protection

excretion

temp regulation

synthesis of VD

cutaneous sensation

nonverbal communication

Components:

cutaneous membrane (skin)

accessory structure/appendages (hair, nails, exocrine gland)

Structure:

avascular

nourished by diffusion from capillaries of dermis

stratified squamous cells

arranged into strata

Cells:

keratinocytes (most abundant) -produce keratin for strength -form in lowest layer -dead & scale like

dendritic (Langerhans) -immune cell

tactile (Merkel) -detect light, touch, superficial pressure

melanocytes -produce pigment for skin color -大家都有一样的量

Desquamation: deeper layer cells mitosis -move toward surface -older cells slough off

Keratinization: cell move toward -fill with keratin, die & serve as layer resist abrasion -forms permeability layer

Thick skin: 

5 strata

6x thicker 

area subject to pressure/friction

palm, sole, fingertip

Thin skin:

4 strata

more flexible

0.08mm thick 

cover rest body

Stratum

Germinativum:

dominated by large basal cells 

divided to replace more superficial keratinocytes (lost/shed at surface)

Merkel

sensitive to touch & release chemicals stimulate sensory nerve endings when compressed

Spinosum: spiny

8-10 layers

stem cell divide 

one of daughter cells pushed above the germinativum into spinosum

Langerhans stimulate defense against microbe that manage to penetrate superficial layers & superrficial skin cancers

Granulosum: grainy

3-5 layers

stop dividing

manufacture large qty of keratohyalin & keratin (fibrous protein=dead cells)

Lucidum: glassy/clear

thick skin

covers granulosum

flat, densely packed cells filled with keratin

Corneum: horn

surface of thick & thin skin

15-30 layers keratinized cells

keratinization on all exposed surfaces 

water resistant not waterproof

relatively dry not suitable for growth of microbe

maintenance involve coating surface with lipid secretions from sebaceous & sweat glands

insensible perspiration: water evaporate w/o visible (sweat)

loss 500ml water each day

damage to epidermis increase rate of fluid movement 

Osmotic force 

hypotonic

water into epidermis

epithelial cells swell 4x normal values

hypertonic

water leave body, cross epidermis from underlying tissues

slow process long term exposure to seawater accelerate dehydration

Hyperkeratosis 

Callus茧: thickened patches appear on thick skin in response to chronic abrasion & distortion

Corn鸡眼: more localized areas of excessive keratin production form in thin skin on/between toes -hard & soft

Psoriasis: active germinativum 

specific area: scalp, elbow, palm, sole, groin, nail

skin cells replace every 3-4 w

psoriasis process takes only 3-7 d

affected area cover with small silvery scales continuously flake off

developed in 20-30% individuals

inherited

painless and treatable 

Skin color

Carotene: corneum, light skin individuals/food

Bilirubin: RBC breakdown -jaundice 

some bilirubin reabsorb by blood & produce more Hb

80% conjugated in spleen & release in intestine -yellowish face, sclera 

Pigment composition & concentration

Melanin: germinativum 

squeeze between/deep to epithelial cells 

protect from UV 

damage DNA, mutate, cancer

1:4 1:20

>2000/mm2 -cheeks, forehead, nipples, genital region 

concentration increase

-when cheeks & forehead expose to UV

-on nipples during pregnancy/birth -melanocyte-active hormones released to bloodstream from pituitary gland

same melanocyte number, different level of synthetic activity

albinism: inherited lack of tyrosinase, incapable of producing melanin -normal distribution melanocyte

freckles or liver spots: melanocytes in a patch

vitiligo: autoimmune loss of melanocytes -produce white patches 

Dermal circulation/blood supply

Hb: RBC gives pinkish to fair skin

Oxy Hb: bright red color -gives vessel in dermis a reddish tint -most apparent in lightly pigmented individuals

dilated blood vessel, red skin -mosquito bites, blush, in pain, inflammation

less O2, less Hb, dull skin/pale/bluish color =cyanosis -extreme cold, heart ds/failure, severe asthma 

Dermis lies beneath epidermis

gives structural strength

collagen & elastic fibers, fibroblasts, macrophages, adipocytes

nerves, blood vessels, hair follicles, smooth muscles, glands, lymphatic vessels

sensory functions: pain, itch, tickle, temp, touch, pressure, 2-point discrimination

cleavage lines: elastin & collagen fibers oriented in some directions more than in others

important in surgery: incision parallel to lines, less gap, faster heal, less scar tissue

if skin overstretch, striae occurs

Nerve fibers

control blood flow

adjust gland secretion rates

monitor sensory receptors in dermis & deeper layers of epidermis

Merkel discs monitor Merkel cells

Meissner's corpuscles (papillae): light touch

Pacinian corpuscles (reticular): deep pressure & vibration

Accessory structure

epidermal derivatives

Hairs 

5 mil 98% general body surface

not on sides & sole, palm, sides of finger & toes, lips, external genitalia

originate in hair follicles

Function:

protection UV

cushion a blow to head

insulate skull

guard entrance 

help prevent entry of foreign particles & insects (eyelash, nostril, external ear canal)

sensory nerves surround base of follicles -sensitivity for early-warning system -prevent injury

insulating coat

response to cold/emotional state (fear/rage), arrector pili muscle contract, force hair stand erect, goose bump 

Sebaceous gland (oil)

sebum

lubrication, keeps hair moist, prevent drying, inhibits growth of bacteria

numerous on scalp & face

very sensitive to changes in concentrations of sex hormones 

secretory activities accelerate at puberty

excessive secretion plugs gland & follicle produce acne

Sweat glands 

Sudoriferous (apocrine)

in armpit (axillae), around nipples, in groin

communicate with hair follicles

produce pheromones =sticky, milky white, odorous, enable olfactory communication with other members of species -sexual arousal

respond to stress & sexual activity 

begin secrete at puberty

Merocrine

more numerous, smaller, widely distributed

2-5 mil in adult

palm & sole

sensible perspiration

99% water + electrolytes (NaCl), organic nutrients, waste 

pH 4-6.8

Function:

reduce body temp -degree of secretory activity regulated by neural & hormonal mechanisms 

excrete water & electrolytes +ingested drugs 

protection -dilutes harmful chemicals, discourages growth of microbe

Mammary glands

complex interaction between sex hormones & pituitary hormones

Ceruminous glands

modified sweat gland in external auditory canal

cerumen (ear wax)+tiny hairs along canal traps foreign particles/small insects -keep them from reaching eardrum

Aging 

Epidermis thin:

germinative cell activity declines

more prone to injury & infections

Langerhans decrease by 50% level at maturity:

reduce sensitivity of immune system 

encourage skin damage & infection

VD3 decrease by 75%:

low Ca & P absorption

muscle weakness & decrease bone strength

Melanocyte activity declines:

pale skin

more sensitive to sun exposure 

more likely to experience sunburn

Glandular activity declines:

dry skin, often scaly

sebum reduce

merocrine less active

impaired perspiration

cannot lose heat fast

Reduced blood supply:

sweat glands less active

Dermis thin:

elastic fibers network decrease in size

integument weaker & less elastic

sagging & wrinkling

Hair follicles stop functioning/produce thinner, finer hairs:

decreased melanocyte activity

grey/white hair 

Burns 

Causes: 

heat

radiation

electricity

chemicals

Seriousness measurement:

layers affected

surface area affected

1st degree

only epidermis

sunburn

redden skin, slight-moderate pain

no blisters, swelling

burns heal w/o scar

2nd

partial thickness

entire epidermis & top dermis

skin redness, pain, blisters

heal within 10-14 d with minimal scar

if burn goes deep into dermis, healing 1-4 months -scar

3rd

full thickness

entire epidermis & dermis

destroy blood vessels, glands, hair follicles, pain receptors

white-tan, brown-black, plain red wound

very slow healing

infection 

dehydration

difficult in body temp regulation

4th

burns all down to bone

little chance of survival 

Rule of Nines 

determine amount of burn affected body surface 

infection may delay healing