5_ integument

8/12/2019 5_ Integument

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The Integumentary System

Guaranteed to Last a Lifetime

Chapter 5


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Integumentary SystemIntegument (skin) and Accessory Organs Cutaneous Membrane (Skin) largest organ

- epidermis- dermis

Accessory Organs derive from epithelial cells of theepidermis but all extend into the dermis- sweat glands and sebaceous (oil) glands

- hair follicles- nails

Hypodermis has similar functions as skin

- fatty layer deep to the skin

- connects skin to underlying organs


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Figure 5.1

Skin Structure


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Functions of The Skin

Helps the body to maintain homeostasis Protection against environmental hazards

Thermoregulation

Synthesis and storage of lipid reserves Synthesis of vitamin D

Excretion (urea, salts, water) Sensory information

Coordination of immune response


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LE 4-1

Produce hairs thatprotect skull Assist inthermoregulation Excrete wastes Lubricate

epidermis

Produces hairs thatprovide delicatetouch sensations ongeneral body surface

Protect andsupport tipsof fingersand toes

Nourishes andsupports epidermis

Restricts spread of pathogens penetratingepidermis

Stores lipid reserves

Attaches skin todeeper tissues Sensory receptors

detect touch, pressure,pain, vibration, andtemperature

Vessels assist inthermoregulation

Controls skinpermeability,prevents water loss

Prevents entry of pathogens

Synthesizesvitamin D 3

Sensory receptors

detect touch,pressure, pain,and temperature

Coordinates immuneresponse topathogens andskin cancers

PAPILLARY LAYER RETICULAR LAYER

Physical protection fromenvironmental hazards

Synthesis and storage of lipid reserves

Thermoregulation

Excretion Synthesis of vitamin D 3

Sensory information Coordination of immune response

to pathogens and cancers in skin

Protects dermis fromtrauma, chemicals


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Epidermis

Consists of keratinized stratified squamous epithelium

4 distinct cell types:keratinocytes, melanocytes , Merkel cells, andLangerhans cells

Layers of the Epidermis (from superficial to deep):- Stratum corneum- Stratum lucidum (only in thick skin)

- Stratum granulosum- Stratum spinosum- Stratum basale


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Figure 5.3

Layers of the Epidermis


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Fig 5.4

Thick vs Thin Skin

5 layers vs 4 layers or strata (bed sheets)

- covers palms and soles - covers rest of the body


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Epidermal Cells Keratinocytes produce keratin , a tough fibrous protein- provides physical and mechanical protection

- produces antibiotics and enzymes that detoxify harmful chemicals- undergoes almost continuous mitosis

Melanocytes produce the skin pigment melanin (black)- made in granules and transferred to nearby keratinocytes- cluster on the superficial side of keratinocytes (between incoming

radiation and cell nuclei) shielding the cells DNA from UV rays- digested by lysosomes in light-skinned people- secretes signaling moleules in response to UV radiation that act tomodulate the skins immune and inflammatory responses

Merkel cells hemisphere-shaped cells sensitive to touch- when compressed release chemicals that stimulate disclike sensorynerve endings (touch receptor)

Langerhans cells star-shaped dendritic type cells- take up pathogens by receptor-mediated endocytosis- travel to a nearby lymph node to initiate an antigenic immune response


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Stratum Basale (Basal Layer)

Aka the stratum germinativum (germinating layer) - the deepestepidermal layer firmly attached to the underlying dermis

Consists of a single row of cells mostly young keratinocytes(stem cells)- as these cells are pushed up by production of new cells beneath them

they make the keratin that eventually fills their cytoplasm- when they reach the skin surface they are dead, flat sacs of keratin

Merkel cells are distributed sparsely among the keratinocytes

- associate with disclike sensory nerve ending 10-25% of the cells are spider-shaped m elanocytes (melanin

cells)


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Stratum Spinosum (Spiny Layer)

Name is derived from spinelike extensions of its keratinocytes(artifact created during tissue preparation)

Several cell layers thick

Lower rate of mitosis than in the basal layer

Contain thick bundles of intermediate filaments- tonofilaments (tension filaments) that contain pre-keratin (tension-resisting protein)

Langerhans cells - scattered among the keratinocytes- initiate an immune response to all foreign cells that carry a foreignantigen (lymphocyte activation)


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Stratum Granulosum (Granular Layer)

Thin layer with many granules

Composed of 1 to 5 layers of flattened keratinocytes

Contain abundant tonofilaments

Contain granules - keratohyalin and lamellated (plated)- keratohyalin granules help form keratin in the more superficial layers- lamellated granules contain a waterproof glycolipid that is secretedinto the extracellular space (slows water loss across the epidermis)

PM of the cells thicken to become more resistant

*Epidermal cells in the layers above the stratum granulosum,are too far from the dermal (underlying CT) capillaries to

receive nourishment


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Stratum Lucidum (Clear Layer)

Aka the transition zone Occurs only in thick skin

In light microscopy appears as a thin translucent band

Consists of a few rows of flat, dead keratinocytes- electron microscopy reveals these cells are identical to the next layer


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Stratum Corneum (Horny Layer)

Most external (superficial) layer of the epidermis Many cells thick and much thicker than in thin skin

Dead keratinocytes are completely filled with keratin- upon death their nuclei and organelles disintegrated

Keratin consists of tonofilaments embedded in a gluefrom the keratohyalin granules- both the keratin and the cells thickened PMs protect skin againstabrasion and penetration

Waterproof layer due to the glycolipid between the cells Cells are referred to as cornified or horny (cornu = horn)

- they are the dandruff shed from the scalp and flakes from dry skin

- an average person sheds ~18 kg (40 lbs) in a lifetime


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(b)(a)


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The Dermis

The 2 nd major layer of the skin is a strong flexible CT that bindsthe entire body together

Consists of 2 layers: the papillary and reticular layers

Cell types: fibroblast, macrophages, mast cells, and

scattered WBCs Fiber types: collagen, elastic, and reticular

Richly supplied with nerve fibers and BVs


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Dermal BVs

2 vascular plexuses -network of converging & diverging vessels

Deeper cutaneous plexus (between hypodermis and dermis)

- nourishes the hypodermis and the structures within the deeper portionsof the dermis

More superficial subpapillary plexus (below dermal papillae)

- supplies more superficial dermal structures, the dermal papillae and theepidermis

Dermal BVs play a critical role in thermoregulation

- BVs are extensive and can hold 5% of all blood in the body- if internal organs need more blood or heat, nerves stimulate dermalvessels to constrict shunting more blood into the general circulation- on hot days dermal vessels engorge with warm blood, cooling the bodyby radiating heat away from it


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Papillary Dermal Layer

Papillary layer superficial 20% of the dermis Composed of areolar CT with thin collagen & elastic fibers

Papillae (nipples), fingerlike projections that extend into theoverlying epidermis- increases surface area for exchange of gases, nutrients, and wasteproducts between the dermal layers- avascular epidermis depends on the diffusion of these materials- interdigitation strengthens the dermal-epidermal junction reducingblister formation

Contains dermal ridges papillae lie atop of these mounds- elevates overlying epidermis into epidermal ridges (friction ridges)create fingerprints, palmprints, and footprints- increases friction, enhances gripping ability of the hands and feet- patterns are unique and genetically determined

- sweat pores, open along crests of epidermal ridges leave distinctfingerprints


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Reticular Dermal Layer

Deeper reticulum (network) layer accounts for ~80% of thedermis thickness Consists of dense irregular CT ECM has thick bundles of interlaced collagen & elastic fibers

- named for its networks of collagen fibers

Lines of cleavage or tension lines- separation formed by less dense regions between collagen bundles- invisible lines occur over the entire body important that surgeons makeincisions parallel to these lines

Collagen fibers give skin its strenth and resilience Elastic fibers provide stretch-recoil properties

- extreme stretching results in striae (streaks)

Flexure lines, markings from the deep part of the dermis


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Figure 5.5

Flexure lines form as a result of a continual folding of theskin, often over joints, where the dermis attaches tightly to

underlying structures (palm, wrist, soles, fingers, and toes)


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Hypodermis (below the skin)

Fatty hypodermis deep to the skin aka the superficialfascia = subcutaneous (below the skin) layer

Consists of both areolar and adipose CT Stores fat

Anchors skin to underlying structures (mostly muscle)- but allows skin to slide relatively freely

Insulator fat a poor conductor of heat prevents heatloss from the body

Thickens with weight gain- accumulates 1 st in the thighs and breasts of s- in s accumulates in the anterior abdomen (beer belly)

Ski C l


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Skin Color

3 pigments melanin, carotene, hemoglobin

Melanin, most important - tyrosine (tyrosinase)- ranges from yellow to reddish to brown to black

Carotene , yellow-orange pigment - vegetables- accumulates in the epidermis stratum corneum and in the fat of thehypodermis

Pink hue - oxygenated hemoglobin- from capillaries of the dermis- Caucasian skin contains little melanin allows color of blood to show- bruising reflects sites where blood escaped from the circulation andclotted below the skin

Hematoma (blood swelling), clotted mass of escaped blood


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Abnormal Skin Colors

Cyanosis bluish color

Erythremia abnormal redness Jaundice yellowish color

Pallor pale or ashen color Albinism pale skin, white hair, pink eyes

Hematoma black & blue bruise

N il


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(on the nail)

(little moon)

Superficial keratinizedlayers of the epidermis

Has a distal free edge,a body, and a root;rests on a epidermalnail bed

Pink color due to richnetwork of capillaries inthe underlying dermis

Figure 5.6

Nails


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Hair Distributed all over the skin surface, except on palms, soles,nipples, and parts of external genitalia

Main function - to sense touch Thermoregulation

- scalp hair protects the head against direct sunlight on hot days and heat

loss on cold days

Consists of a flexible strand of dead, keratinized cells- hard keratin predominates in hair and nails:1) tougher and more durable 2) cells do not flake off

Chief parts the root (embedded in the skin) and the shaft

(projects above the skin surface)

H i St t


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Figure 5.7

Hair Structure

A hair shaft consists of 3 concentric layers:Medulla (middle) central core of large cells and air sacsCortex consists of several layers of flattened cellsCuticle a single layer of overlapping cells

- most heavily keratinized provides strength and binding

H i F lli l


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Hair Follicles

Extend from the epidermal surface into the dermis Hair bulb expanded end of the follicle

Hair follicle receptor or root hair plexus knot of sensorynerve endings

CT papilla (hair papilla) dermal bit that protudes into thehair bulb contains a knot of capillaries

Hair matrix epithelial cells in the hair bulb- proliferating cells that form the hair shaft

Wall of a hair follicle is composed of:- an outer CT root sheath (derived from the dermis)- inner epithelial root sheath (derived from the epidermis)

Glassy membrane basement membrane of the follicleepithelium

A t ili ( i f th h i ) l


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Figure 5.7

Arrector pili (raiser of the hair) muscle

Bundle of smooth muscle cells associated with each follicle


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Figure 5.8

Scanning electron micrograph of a hair shaftemerging from a follicle at the epidermal surface

T d G h f H i


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Figure 5.9

Types and Growth of Hair

Vellus (vell=wool,fleece): body hair, fine and short

Terminal : longer coarser scalp hair and hair that appears at puberty

Androgens ( testosterone ): male sex hormone that influences terminalhair (face, chest, arms, and legs)

Active follicle

Resting follicle

S b ( ) Gl d


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Sebaceous (greasy) GlandsThe skins oil glands Occur over entire body except palms and soles

Simple alveolar glands with several alveoli openings into asingle duct- alveoli filled with cells (no lumen) that produce sebum (animal fat)

Holocrine secretion (holos = whole)- central cells fill with oily lipids until they burst- empty sebum into the upper 1/3 of hair follicles- spread superficially to cover the skin

- secretion stimulated by hormones, especially androgens Makes skin and hair oily and in addition:

- collects dirt, softens and lubricates hair and skin, prevents hair frombecoming brittle, keeps epidermis from cracking- helps to slow water loss across the skin and kills bacteria

Sebaceous Glands


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Figure 5.10

Sebaceous Glands

S ( d if ) Gl d


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Sweat (sudoriferous) GlandsOnly mammals have sweat glands

humans have > 2.5 million over entire skin surface

- produce about 500 ml of sweat per day (up to 12L)

Sweat - 1 a blood filtrate released by exocytosis- 99% water + some salts (NaCl) and traces of metabolic wastes (urea,

ammonia, uric acid)- acidic property retards growth of bacteria

2 types of sweat glands eccrine (secreting) & aprocrine- both secrete in response to heat or stress- eccrine glands are more numerous and produce true sweat- aprocrine glands are mainly confined to the axillary, anal, and genital

areas and produce viscous and sometimes a milky or yellow color secretion

Sweat Glands


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Figure 5.10b

Sweat Glands

Eccrine glands - most abundanton palms, soles, and forehead

- coiled, secretory base in the deepdermis and hypodermis- duct opens at skin surface ( pore )

Note: facial pores are openings of hair

follicles

Apocrine glands - function at

puberty due to androgens- ducts open into hair follicles- involved in sexual signaling(pheromones)

Burns


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Burns

Tissue damage inflicted by heat, electricity, radiation,extreme friction, or chemical

Immediate threat from serious burns loss of body fluids- severe inflammatory edema- dehydration leads to circulatory shock

Followed by infection loss of skin barrier

Classified by severity (depth): partial and full-thickness- 1 st degree = only epidermis is damaged (sunburn)- 2 nd degree = epidermis and upper part of the dermis (blisters)

- 3 rd degree = epidermis, dermis, hypodermis

Rule of Nines - divides the body into 11 regions- Critical burns: 1) over 10% of the body has 3 rd degree burns; 2) 25%

of the body has 2nd

degree burns; 3) 3rd

degree burns on the face,hands, or feet

Burns Rule of Nines


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Figure 5.11

Burns Rule of Nines

Skin Cancer


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Skin Cancer

Most common type of cancer, ~million new cases in US / year

Highest risk factor overexposure to UV rays in sunlight

Increased risk with use of indoor tanning

3 types of skin cancer:

- Basal Cell Carcinoma- Squamous Cell Carcinoma- Melanoma

Squamous Cell CarcinomaBasal Cell Carcinoma


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Figure 5.12

Arises from the keratinocytesof the stratum spinosum

Scaly, irregular, reddenedpapule that grows rapidly

Metastasis - if not removed Overall cure rate 99% Treatment - radiation, surgery,

skin creams with anticancerdrugs

Least malignant; most common(>30% of all Caucasians)

Cells of stratum basale proliferate,invading the dermis & hypodermis

Most common lesions are dome-shaped, shiny nodules on the face

Nodules develop an ulcer

Grows slowly, metastasis is rare 99% full cure by removal

O l 1 f 20 ki


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Only 1 of every 20 skin cancers Increasing by 3-8% / yr in US Often arises from existing moles Melanoma cells metastasize

- into surrounding circulatory vessels Key to survival early detection

- low survival chance mole >4mm thick

Resistant to chemotherapy andimmunotherapy ABCD(E) rule

Asymmetry 2 halves dont matchBorder irregularity indents / notchesColor pigment spot, several colorsDiameter - >6mm

Elevation above the skin surface

Most DangerousMelanoma

Cancer of Melanocytes

The Skin Throughout Life


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The Skin Throughout Life

Epidermis develops from embryonic ectoderm Dermis and hypodermis develop from mesoderm Melanocytes develop from neural crest cells (3 months) In 5 th and 6 th months fetus covered with lanugo (wool/down) Shed by the 7 th month when vellus hairs appear Birth skin covered with vernix caseosa (varnish of cheese) Adolescence, acne may appear, subsides in early adulthood Optimal appearance in 20s 30s

- after skin shows harmful effects of continued environmental assaults

- dermatitis become more common Photoaging

- pigment spots liver spots

- large amounts of melanin protect skin from photoaging

Clinical Terms


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Clinical Terms

Alopecia

Athletes Foot

Boils and Carbuncles

Cold Sores (Fever Blisters)

Impetigo (an attack)

Psoriasis (an itching)

Vitiligo (blemish)

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