Chapter 6

Integumentary System

I. IntroductionIntroduction

A. Organs are composed of two or more kinds of tissues

B. Largest organ of the body is the skin (“Integumentary System” includes skin, hair, nails & glands)

II. Functions of the Integumentary SystemII. Functions of the Integumentary System

A. Protection = skin protects against abrasion, UV light, microorganisms, dehydration

B. Sensation = sensory receptors detect heat, cold, touch, pressure, & pain

C. Vitamin D production = skin produces a molecule that can be transformed into vitamin D when exposed to UV light

D. Regulates body temperature = body temperature controlled by blood flow through skin and sweat gland activity

E. Excretion = small amounts of waste lost through skin/gland secretions

III. Layers of the IntegumentIII. Layers of the Integument A. Hypodermis (“under + skin”) or Subcutaneous (“below + skin”)

1. Attaches skin to underlying bone and muscle2. Supplies skin with blood vessels & nerves3. Not part of the skin4. Composed of loose connective & adipose

tissuea. Padding & insulationb. Sex differencesc. Total body fat estimates made from

pinching hypodermis5. Site of subcutaneous injections

B. Skin = Dermis + epidermis Dermis = layer of dense connective tissue Epidermis = (upon the dermis) layer of epithelial tissue

resting on dermisa. Hypodermis = foundation of house

b. Dermis = house

c. Epidermis = roof

1. Dermis

a. Connects epidermis to underlying connective tissue

b. Composed of collagen, elastic fibers, fibroblasts, fat cells, & macrophages (fewer fat cells & blood vessels than hypodermis)i. Collagen fiber orientation can either resists or

be susceptible to stretching (cleavage/tension lines) – Figure 5.2

c. Nerve endings, hair follicles, smooth muscle, glands, lymphatic vessels extend into dermis (Figure 5.1)

d. Dermal papillae = projections into upper dermis extending toward epidermis; contain many blood vessels (Fig. 5.3a)i. Supply epidermis with nutrientsii. Remove wasteiii. Regulate body temperatureiv. Found in hands & feet – fingerprints/ridges

for friction and grip• Dermis is part of animal hide used in

making leather• Site of injections like TB test

2. Epidermis (“upon + skin”)a. Prevents water loss, injury, entrance of harmful chemicalsb. Composed of stratified squamous epithelium

i. Mitosis in deepest layers, pushing older cells to surface where they slough off

ii. Outermost cells protect those underneathiii. Deeper replicating cells replace cells lost from the

surfacec. During migration from “deep” to “superficial” cells

change in shape and chemical compositioni. Keratinization = cells fill with keratin

• Cells die and form protective layer resisting abrasion & forming permeability layer

d. Epidermis is stratified (strata = layer) (Fig. 5b)i. Stratum basale = base layer

• Cuboidal or columnar cells – mitosis every 19 daysii. Intermediate strataiii. Stratum corneum = horny layer

• Mos superficial• Dead, squamous cells filled with keratin• Coated/surrounded by lipids, prevent fluid loss• 25+ layers of dead cells joined by desmosomes• Calluses (hard skin) = increase in number of layers in

stratum corneum due to friction• Corn = similar reaction as callus, just over a bony

prominence

3. Skin color (Pigments in the Epidermis)a. Determined by pigments in skin, blood

circulating in skin, thickness of stratum corneumb. Melanin (black) = group of pigments

determining color of skin, hair, and eyesi. Usually brown to black, sometimes yellowish

or reddishii. Melanocytes (black cell)

• Golgi bodies in melanocytes package melanin into melanosomes, then phagocytized by epithelial cells (Fig. 5.4)

Large amounts of melanin in freckles, moles, genitalia, nipples, areolas

Less melanin in lips, palms, soles Racial variations – due to amount, kind, and

distribution of melanin All races have ~same number of melanocytes Melanin production determined by genetic

factors, light exposure, hormones1. Albinism = recessive gene for deficiency/absence of

melanin

2. UV exposure stimulates melanin production = suntan

3. Pregnancy – darker nipples and areolas, genitalia, cheekbones, forehead, chest, midline

c. Cyanosis (dark blue color) = decrease in blood oxygen

d. Birthmarks = congenital disorders of capillaries in the dermis

e. Carotene = yellow pigment in carrots and squash, lipid soluble – Vitamin A

1. Accumulates in lipids of stratum corneum & fat in dermis and hypodermis = yellow tinted skin

IV. Accessory Skin StructuresA. Hair

1. Characteristic of all mammalsa. Thick hair = fur

2. Hair anatomy:a. Hair shaft = portion of hair above skin surfaceb. Hair root = portion of hair below skin surfacec. Hair bulb = base of hair rootd. Medulla= center of haire. Cortex (bark) = surrounds the medullaf. Cuticle (skin) = single layer of overlapping cells

holding hair follicleg. Hair follicle = extension of epidermis deep into

dermisi. Plays role in tissue repair

3. Hair growth:a. Cyclic: growth stage + resting stage

i. Hair bulb produces hair; nourished by blood vessels

ii. Epithelial cells undergo keratinization in hair bulb; cells are added to base of hair – hair “growth”

iii. Growth stops during resting stage

iv. Next growth stage causes hair to fall out

i. Pattern baldness – permanent loss of hair

4. Hair color determined by varying amounts & types of melanin

a. Melanin production decreases with age = gray/white

Hair Type Growth Stage Resting Stage

Eyelash 30 days 105 days

Scalp 3 years 1-2 years

B. Muscles1. Arrector pili (that which raises,

hair) = contraction of these muscles cause hair to “stand on end”… goosebumps

a. Composed of smooth muscle

b. Evolutionary advantage in mammals – traps air (heat) for insulation, also look larger - intimidation

C. Glands1. Sebaceous glands

a. Simple, branched acinar/alveolarb. Produce sebum – oily substance lubricating hair & skin

surface, preventing drying out & bacterial infection

C. Glands, continued…2. Sweat glands (two types):

a. Merocrine sweat glandsi. Simple, coiled tubular w/ ducts opening

to skin surfaceii. Every part of skin, most abundant in

palms/solesiii. Produce sweat: slightly salty water-based

secretion• Evaporative cooling• Emotional stress produces sweat in palms,

soles, axillae (used in lie detector tests!)

b. Apocrine sweat glandsi. Simple, coiled tubular with ducts opening

into hair follicles of axillae & genitalia• Become active at puberty due to sex

hormone influence

ii. Secretes thick organic substances• Broken down by bacteria = body odor

D. Nails1. distal ends of digits of primates2. Nail = thin, horny plate at end of fingers and toes,

consisting of several layers of dead epithelial cells (stratum corneum) containing a hard keratin

3. Nail anatomy:a. Nail body = visible part of nailb. Nail root = part of nail covered by skinc. Eponychium or cuticle (upon + nail) = stratum

corneum extending onto nail bodyd. Nail bed = nail root and nail body attach to thise. Nail matrix = proximal portion of nail bed w/o

nail root attachedi. Produces cells that result in nail growthii. Nails grow continuously

f. Lunula = whitish, crescent-shape at base of nail

V. Physiology of the Integumentary System

A. Protection1. Prevents water loss (lipids)2. Prevents entry of microorganisms/foreign substances

(secretions & skin)3. Protects against abrasion (stratified squamous epithelium)4. Protects against UV light damage (melanin)5. Hair: insulation (head), keeps foreign

objects/microorganisms/sweat out (eyelashes, eyebrows, nose & ear hairs)

6. Damage protection/defense (nails)

V. Physiology of the Integumentary System, cont.

B. Sensation1. Nervous receptors in dermis & epidermis (pain, heat, cold, pressure)

C. Vitamin D Production1. Vitamin D precursor made in skin, modified by liver, sent to kidney

were becomes vitamin D2. Required for calcium & phosphate absorption in intestines

D. Temperature Regulation1. Necessary for enzyme function2. Blood vessels (arterioles) in dermis dilate to lose heat, constrict to keep it in

E. Excretion1. Removal of waste products from the body – small role2. Sweat: water, salts, urea, uric acid, ammonia

VI. Integumentary System as a Diagnostic Aid

Cyanosis = skin appears bluish, low oxygen in blood (indicates impaired circulatory or respiratory function)

Jaundice = skin appears yellowish, liver damage causes bile pigment buildup

Rashes, lesions, vitamin deficiencies, iron deficiencies

A. Burns1. Partial-thickness burns – part of stratum basale viable

a. First-degree burns – involves epidermis, red, painful, edemai. Sunburn, quick exposure to hot/cold

ii. No scarring, heal quickly

b. Second-degree burns – destruction of epidermis an dermis, recovery happens from edge of burn

c. Full-thickness or third-degree burnsi. Painless b/c nervous tissue destroyed

ii. Whit, tan, brown, black, or deep cherry red

iii. Scarring with disfiguration, extended healing time

iv. Skin grafts (self, cadavers, pigs, lab-grown?)

B. Skin Cancer1. Most common type of cancer (UV

radiation, chemicals, radiation)2. Basal cell carcinoma – stratum basale

to dermis forming an open ulcera. Treatment: surgery or radiation

3. Squamous cell carcinoma – cells immediately superficial to stratum basale

a. Produce tumors – continue dividing, can be fatal

4. Malignant melanoma – arise from melanocytes (moles)

a. Can be fatal (will metastasize)

VII. Effects of Aging on Integumentary Systema) Diminishing skin function due to compositional and

functional changes in its layers

b) Age spot = increase in number of melanocytes in some areas vs. freckles = increase in melanin production