INTEGUMENTARY SYSTEM

OBJECTIVES1. Describe the general functions of the

integumentary system2. Describe the main structural features of the

epidermis and explain their functional significance

3. Explain what accounts for individual differences in skin, such as skin color

4. Describe how the integumentary system helps to regulate body temperature

5. Discuss the effects of ultraviolet radiation on the skin and the role played by melanocytes

6. Discuss the functions of skin’s accessory structures

7. Describe the mechanisms that produce hair and that determine hair color and texture

8. Explain how the skin responds to injury and repairs itself

9. Summarize the effects of aging on the skin

INTRODUCTION

Integumentary system (or integument) = skin, hair, nails, various glands

- skin is largest organ in the body!

STRUCTURE AND FUNCTION

The integument has 2 major components:

1. CUTANEOUS MEMBRANE

- Epidermis/Superficial epithelium

- Dermis

2. ACCESSORY STRUCTURES

- hair, nails, exocrine glands

**Subcutaneous layer

FUNCTIONS

1. Protection- impacts, chemicals, infections, loss of body fluids

2. Temperature maintenance

3. Making and storing of nutrients- vitamin D3 (calcium uptake); adipose tissue

4. Sensory reception- touch, pressure, pain, temp. stimuli

5. Excretion and secretion- salts, water, milk

EPIDERMIS

Stratified squamous epithelium

- STRATIFIED???

- Thick skin- palms, soles > 5 layers

- Thin skin- all body > 4 layers

STRATA OF EPIDERMISSTRATA = LAYERSIn order from the

basement membrane toward the surface are:

1. Stratum germinativum2. Intermediate strata-

Stratum spinosum, Stratum granulosum,

Stratum lucidum3. Stratum corneum

STRATUM GERMINATIVUM- Deepest epidermal layer!

- Attached to basement membrane

- EPIDERMAL RIDGES- Purpose?

* Fingerprints!

- DERMAL PAPILLAE

BOTH INCREASE SURFACE AREA

STRATUM GERMINATIVUM- Germinative cells- Stem cells

- Melanocytes- info. About objects touching the skin

* make MELANIN- yellow-brown pigment

that colors skin

INTERMEDIATE STRATA

- 3 layers- become more specialized toward surface

- Stem cells enter stratum spinosum, continue to divide

- Stratum granulosum has cells displaced from stratum spinosum

- find the protein KERATIN here

INTERMEDIATE STRATA

- Stratum lucidum- clear, covers stratum granulosum in thick skin of palms and soles

STRATUM CORNEUM

- outermost layer, KERATINIZED CELLS

- dead cells tightly connected by desmosomes

TIMELINE- 2-4 weeks to go from s. germinativum to s.

corneum

- cell is removed from its oxygen and nutrient supply, is filled with keratin, and finally dies

- dead cells usually remain in the s. corneum for about 2 weeks before they are shed

- as these layers are lost, they are replaced from below

SKIN COLORCaused by interaction between:

1. epidermal pigments

2. dermal blood supply

1. PIGMENTATION

The epidermis has pigments CAROTENE and MELANIN

CAROTENE- orange-yellow

- Orange skin???

- can be converted to vitamin A- required for normal maintenance of epithelial tissue, eyes

MELANIN- brown, yellow-brown, or black pigment produced by melanocytes

- Injected into s. germinativum and intermediate strata

- Melanocyte activity increases after sunlight exposure

FRECKLES- areas of larger-than-average melanin production

ULTRAVIOLET (UV) RADIATION

- Why a little is good- Vitamin D3

- too much is bad

- melanin to the rescue!

- long-term exposure can still cause damage

UV RADIATIONEFFECTS:

- Premature wrinkling

- skin cancers

- Ozone layer

- SPF is essential! How much?

DIFFERENCES IN SKIN COLOR

Skin color differences are due to HOW MUCH melanin is produced

- albinism (albino)- no melanin

2. DERMAL CIRCULATION

- Lots of O2 = bright red blood

- More pronounced tones when blood vessels are dilated- inflammation

- when vessels are constricted (frightened), skin becomes pale

- during a prolonged reduction in circulation, blood loses oxygen and becomes dark red, then blue CYANOSIS

VITAMIN D3Limited exposure to the sun is beneficial:- epidermal cells in stratum germinativum and

intermediate strata convert a steroid into VITAMIN D3

- this is modified and converted into a hormone called CALCITRIOL which is essential for the absorption of calcium and phosphorus by the small intestine

- deficiency of vitamin D3 causes abnormal bone growth

SKIN CANCER

BASAL CELL CARCINOMA- malignant cancer that originates in the stratum germinativum

- most common typeSQUAMOUS CELL CARCINOMAS- less

common- metastasis seldom occurs in either;

survival is good

MELANOMAS- seldom-occurring and life-threatening

- usually begin from moles, but may appear anywhere in the body

- can grow rapidly and metastasize through the lymphatic system

- survival depends on when condition is detected and treated

- AVOIDING UV RADIATION CAN PREVENT ALL 3 TYPES OF CANCER

The Dermis

The Dermis

The dermis lies below the epidermis and has 2 main components:

Papillary layer

Reticular layer

PAPILLARY LAYER

- consists of loose connective tissue that supports and nourishes the epidermis

- contains capillaries and nerves supplying the surface of the skin

RETICULAR LAYER

- deeper layer- consists of interwoven meshwork of dense,

irregular connective tissue- boundary between reticular and papillary

layers is indistinct- collagen fibers of reticular layer extend into the

subcutaneous layer- reticular layer provides support and

attachment for dermis while allowing flexibility

OTHER DERMAL COMPONENTS

The dermis contains all of the cells found in connective tissue proper (macrophages, fibroblasts, etc)

- accessory organs such as hair follicles and sweat glands extend into the dermis

- other systems communicate with the skin through the dermisEx: reticular and papillary layers contain blood vessels, lymph vessels, and nerve fibers

- blood vessels provide nutrients and oxygen, and remove CO2 and wastes

- blood and lymph vessels help local tissues defend and repair themselves after injury or infection

- nerve fibers control blood flow, adjust gland secretion rates, and monitor nerve receptors

The Subcutaneous Layer

Subcutaneous Fat

The dermis is connected to the subcutaneous layer by an extensive network of connective tissue fibers

- the subcutaneous layer is not actually part of the integument, but is important in stabilizing position of the skin in relation to underlying tissue

- this layer contains many fat cells (adipose)

- these adipose cells provide infants and small children with a layer of “baby fat” which reduces heat loss, and acts as a shock absorber to prevent injury

- as we age, we accumulate this fat in different places:

* Men- around neck, upper arms, lower back, buttocks

* Women- breasts, buttocks, hips, thighs

* Both accumulate in abdominal area

- the subcutaneous layer is very elastic, has large blood vessels, and contains no vital organs

Accessory Structures

HAIR FOLLICLES

Hair covers the body almost everywhere EXCEPT:

Sides and soles of feetPalms

Sides of fingers and toesLips

STRUCTURE OF HAIR- hair follicles project into the dermis and often

into the subcutaneous layer

- walls of each follicle contain all the cell layers found in epidermis

- the epithelium at the base of a follicle surrounds the HAIR PAPILLA- a peg of connective tissue containing capillaries and nerves

- hair is formed by the repeated divisions of epithelial stem cells surrounding the papilla

- as daughter cells are pushed to the surface, the hair lengthens and the cells become keratinized and die

- the point at which this occurs marks the boundary of the HAIR ROOT and HAIR SHAFT

- hairs grow and are shed according to a HAIR GROWTH CYCLE based on the activity of hair follicles

- generally, a hair in the scalp grows from 2 to 5 years at a rate of about 0.3 mm per day, and then its follicle may become inactive for some time

- when another growth cycle begins, the old hair is pushed toward the surface to be shed

- differences in hair length between individuals depends on variations in growth rate and in the length of the hair growth cycle

- other differences in hair appearance result from size of follicles and shape of hairs

FUNCTIONS OF HAIR- there are approximately 5 million hairs on the

human body- the 100,000 hairs on the head protect the

scalp from UV light, cushion a light blow to the head, and insulate the skull

- hairs guarding the entrance to the nostrils and ears, as well as the eyelashes, defend against entry of foreign particles and insects

- each hair follicle as a sensory nerve associated with it you can feel a single hair move : early warning system

- smooth muscles called ARRECTOR PILI MUSCLES are connected to the hair follicle

- when stimulated, they pull on follicle and cause hair to stand up- “goose bumps”

HAIR COLOR- hair color depends on differences in type and

amount of pigment produced by melanocytes in the papilla

- color is genetically determined- color may also be influenced by hormonal or

environmental changesEx: pigment production decreases with age, and color of hair lightens

- white hair results from lack of pigment, and the presence of air bubbles in the hair shaft

- as number of white hairs increases, individual’s color is described as GRAY

- on average, about 50 hairs are lost from the head per day

SEBACEOUS GLANDS

Sebaceous glands are a type of exocrine gland that discharge a waxy secretion into hair follicles and onto the skin

- contraction of arrector pili muscles squeezes the sebaceous glands, forcing the secretions into the hair follicles and onto the surrounding skin

- the secretion is called SEBUM- it lubricates the hair and inhibits growth of bacteria

Sebaceous glands are very sensitive to changes in concentrations of sex hormones

- secretions increase at puberty

- an individual with large sebaceous glands may be prone to ACNE

- in acne, sebaceous glands become blocked and secretions accumulate causing pimples to form

SWEAT GLANDSThe skin contains 2 types of sweat glands:

Apocrine sweat glands

Merocrine sweat glands

APOCRINE GLANDS

- secrete their products into hair follicles in the armpits, around the nipples, and in the groin

- at puberty, these glands begin discharging a sticky, cloudy secretion that becomes odorous when broken down by bacteria

- antiperspirant works by contracting the sweat gland openings and decreasing the quantity of secretions

MEROCRINE GLANDS

- far more numerous than apocrine glands

- the skin of an adult contains 2-5 million merocrine glands

- palms and soles have the highest number

- merocrine glands are coiled tubular glands that discharge their secretions directly onto the surface of the skin

- secretions are called PERSPIRATION- cool the surface of the skin and reduce body temperature

When a person sweats in the hot sun, all merocrine glands are working together:

- blood vessels beneath the epidermis are flushed with blood- skin becomes red

- skin surface is warm and wet, and as the moisture evaporates, the skin cools

- if body temperature falls too low, perspiration stops, blood flow to the skin decreases, and the cool, dry surfaces release little heat to the environment

SWEAT IS 99% WATER- but also contains salts, organic nutrients, and

waste products such as urea

- is what gives sweat a salty taste- when all merocrine glands are working

together, perspiration can exceed 1 gallon per hour

- you must drink fluids to replenish this lossOTHER TYPES OF SWEAT GLANDS:- mammary glands produce milk- ceruminous glands in the ear produce ear

wax

NAILS

Nails form on dorsal surface of fingers and toes, and protect the exposed tips and help limit their distortion when they are subjected to mechanical stress

STRUCTURE- visible NAIL BODY made up of a mass of

dead, keratinized cells- it extends below the surrounding epithelium

- nail body covers an area of epidermis called the NAIL BED

- nail production occurs at the NAIL ROOT- an epithelial fold that you cannot see from the surface

- a portion of the stratum corneum extends over the exposed nail nearest the root, forming the CUTICLE

- underlying blood vessels give nails their pink color

- vessels may be obscured near the root, leaving a pale crescent known as the LUNULA

- nail structure

CONTROL OF HOMEOSTASIS

The integumentary system can respond directly and indirectly to many local influences or stimuli

Ex: when skin is subjected to mechanical stresses, stem cells in the stratum germinativum divide more rapidly to increase the thickness of the epithelium CALLUSES FORM

INJURY AND REPAIR

Skin can regenerate because stem cells are present in epithelial and connective tissue components

- speed and effectiveness of skin repair depends on the type of wound* an INCISION (slender, straight cut) may heal quickly * an ABRASION (scrape) may take longer to heal because it involves a greater area

4 STAGES OF SKIN REGENERATION

1. When damage extends though epidermis and into the dermis, bleeding occurs

2. Blood clot or SCAB that forms temporarily restricts the entry of additional microorganisms

- clot is made up of protein called FIBRIN- cells of stratum germinativum rapidly divide

and migrate along sides of the wound to replace missing epidermal cells

- phagocytes patrol damaged area and clear away debris and pathogens

3. Dermal repairs must occur before epithelial cells can cover the surface

- fibroblasts and connective tissue stem cells divide to produce mobile cells that invade deeper areas of injury

- capillaries follow the fibroblasts, providing a circulatory supply

- combination of blood clots, fibroblasts, and capillary network is called GRANULATION TISSUE

- over time, the clot dissolves and number of capillaries decreases

- fibroblast activity leads to formation of collagen fibers and ground substance

4. Scar tissue is formed

- dermis will contain many collagen fibers and few blood vessels

- damaged hair follicles, glands, muscle cells, and nerves are seldom repaired

BURNSBurns result from exposure of skin to heat,

radiation, electrical shock, or strong chemical agents

- severity reflects depth of penetration and total area affected

FIRST-DEGREE BURN- superficial cells of epithelium are killed- deeper areas of the epidermis and papillary

dermis are injured- area appears inflamed and is tender

SECOND-DEGREE BURN

- superficial and deeper cells of epidermis are killed; dermis may be affected

- reticular layer of epidermis may be injured, but most accessory structures are unaffected

- blisters are present; very painful

THIRD-DEGREE BURN

- all epidermal and dermal cells are killed

- subcutaneous layer and deeper tissues and organs are injured

- skin is charred; individual has no sensation at all

AGING

SOME CHANGES THAT OCCUR WITH AGING:

1. Skin injuries and infections become more common- epidermis thins

2. Sensitivity of immune system reduced- immune cells are decreasing in number

3. Muscles become weaker, bone strength decreases- decline in vitamin D3 production

4. Sensitivity to sun exposure increases- less melanin produced

5. Skin becomes dry and scaly- sebum and perspiration production decreases

6. Hair thins and color changes- follicles stop functioning; again decreased melanin production

7. Sagging and wrinkling of skin- dermis becomes thinner and elastic fiber network decreases

8. Ability to lose heat decreases- blood supply to dermis is reduced; sweat glands become less active

- more prone to overheating

9. Skin repairs slowly