c h a p t e r two distinct layers epidermis the dermis...

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PowerPoint® Lecture Slides prepared by Leslie Hendon University of Alabama, Birmingham

C H A P T E R

Copyright © 2011 Pearson Education, Inc.

5 The Integumentary System


The Skin and the Hypodermis

•  Skin—our largest organ •  Accounts for 7% of body weight •  Varies in thickness from 1.5–4.4mm •  Divided into two distinct layers • Epidermis • Dermis

•  Hypodermis—lies deep to the dermis • Composed of areolar and adipose tissues • Not part of the integumentary system, but

shares some of skin’s properties


Skin Structure

Figure 5.1

Epidermis

Hair shaft

Dermis Reticular layer

Papillary layer

Hypodermis (superficial fascia)

Dermal papillae

Pore

Subpapillary vascular plexus

Appendages of skin Eccrine sweat gland Arrector pili muscle Sebaceous (oil) gland Hair follicle Hair root

Nervous structures Sensory nerve fiber Lamellar (Pacinian) corpuscle Hair follicle receptor (root hair plexus)

Dermal vascular plexus

Adipose tissue


The Skin and Hypodermis

•  Functions 1.  Protection—cushions organs and protects from

bumps, chemicals, water loss, UV radiation 2.  Regulation of body temperature---Capillary

network and sweat glands regulate heat loss 3.  Excretion—urea, salts, and water lost through

sweat 4.  Production of vitamin D---Epidermal cells use

UV radiation to synthesize vitamin D 5. Sensory reception—Contains sense organs

associated with nerve endings


Figure 5.2 Gross structure of skin and underlying tissues.

Deep fascia

Muscle

Hypodermis

Dermis

Epidermis


Epidermis •  Is composed of keratinized stratified squamous

epithelium •  Contains four main cell types

•  Keratinocytes •  Location—stratum spinosum; produce keratin a fibrous

protein •  Melanocytes

•  Location—basal layer; manufacture and secrete the pigment melanin

•  Tactile epithelial cells (Merkel cells) •  Location—basal layer; attached to sensory nerve endings

•  Dendritic cells (Langerhans cells) •  Location—stratum spinosum; part of immune system;

macrophage-like

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Epidermis

•  Keratinocytes—most abundant cell type in epidermis •  Arise from deepest layer of epidermis •  Produce keratin, a tough fibrous protein •  Produce antibodies and enzymes •  Keratinocytes are dead at skin's surface


Layers of the Epidermis

•  Stratum basale (stratum geminativum) •  Stratum spinosum •  Stratum granulosum •  Stratum lucidum (only in thick skin) •  Stratum corneum


Epidermal Cells and Layers of the Epidermis

Figure 5.3a Dermis (a)

Stratum corneum Most superficial layer; 20–30 layers of dead cells represented only by flat membranous sacs filled with keratin. Glycolipids in extracellular space.

Stratum granulosum Three to five layers of flattened cells, organelles deteriorating; cytoplasm full of lamellated granules (release lipids) and keratohyaline granules.

Stratum spinosum Several layers of keratinocytes unified by desmosomes. Cells contain thick bundles of intermediate filaments made of pre-keratin. Stratum basale Deepest epidermal layer; one row of actively mitotic stem cells; some newly formed cells become part of the more superficial layers. See occasional melanocytes and dendritic cells.


Figure 5.3a Epidermal cells and layers of the epidermis.

Stratum corneum

Stratum granulosum

Stratum spinosum

Stratum basale

Dermis

Desmosomes

Most superficial layer; 20–30 layers of dead cells represented only by flat membranous sacs filled with keratin. Glycolipids in extracellular space.

One to five layers of flattened cells, organelles deteriorating; cytoplasm full of lamellar granules (release lipids) and keratohyaline granules.

Several layers of keratinocytes unified by desmosomes. Cells contain thick bundles of intermediate filaments made of pre-keratin.

Deepest epidermal layer; one row of actively mitotic stem cells; some newly formed cells become part of the more superficial layers. See occasional melanocytes and dendritic cells.


Epidermal Cells and Layers of the Epidermis

Figure 5.3b

Melanocyte Melanin granule

Tactile epithelial cell

Sensory nerve ending

Dendritic cell Dermis

Keratinocytes

Desmosomes (b)

Stratum corneum Most superficial layer; 20–30 layers of dead cells represented only by flat membranous sacs filled with keratin. Glycolipids in extracellular space.

Stratum granulosum Three to five layers of flattened cells, organelles deteriorating; cytoplasm full of lamellated granules (release lipids) and keratohyaline granules.

Stratum spinosum Several layers of keratinocytes unified by desmosomes. Cells contain thick bundles of intermediate filaments made of pre-keratin. Stratum basale Deepest epidermal layer; one row of actively mitotic stem cells; some newly formed cells become part of the more superficial layers. See occasional melanocytes and dendritic cells.


Figure 5.3b Epidermal cells and layers of the epidermis. Stratum corneum

Stratum granulosum

Stratum spinosum

Stratum basale

Desmosomes

Most superficial layer; 20–30 layers of dead cells represented only by flat membranous sacs filled with keratin. Glycolipids in extracellular space.

One to five layers of flattened cells, organelles deteriorating; cytoplasm full of lamellar granules (release lipids) and keratohyaline granules.

Several layers of keratinocytes unified by desmosomes. Cells contain thick bundles of intermediate filaments made of pre-keratin.

Deepest epidermal layer; one row of actively mitotic stem cells; some newly formed cells become part of the more superficial layers. See occasional melanocytes and dendritic cells.

Keratinocytes

Dermis

Dendritic cell Sensory nerve ending

Melanocyte

Tactile epithelial cell

Melanin granule

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Layers of the Epidermis •  Stratum basale

•  Deepest layer of epidermis •  Attached to underlying dermis •  Cells actively divide •  Stratum basale contains

•  Tactile epith. Cells/Merkel cells—associated with sensory nerve ending

•  Melanocytes—secrete the pigment melanin •  Stratum spinosum (spiny layer)

•  “Spiny” appearance caused by: •  Artifacts of histological preparation

•  Contains thick bundles of intermediate filaments (tonofilaments) •  Resist tension •  Contain protein prekeratin

•  Contains star-shaped dendritic cells •  A type of macrophage •  Function in immune system


Layers of the Epidermis •  Stratum granulosum

•  Consists of keratinocytes and tonofilaments •  Tonofilaments contain:

•  Keratohyaline granules—help form keratin •  Lamellated granules—contain a waterproofing glycolipid

•  Stratum lucidum (clear layer) •  Occurs only in thick skin

•  Locations of thick skin—palms and soles •  Composed of a few rows of flat, dead keratinocytes

•  Stratum corneum (horny layer) •  Thick layer of dead keratinocytes and thickened plasma

membranes •  Protects skin against abrasion and penetration


Figure 5.4 Thick skin.

Stratum corneum

Epidermis

Dermis

Stratum lucidum Stratum granulosum

Stratum spinosum

Stratum basale

Dermal papilla

Collagen fibers

Papillary dermis

Reticular dermis


Dermis

•  Second major layer of the skin •  Strong, flexible connective tissue •  Richly supplied with blood vessels (important role in

temperature control) and nerves •  Has two layers

•  Papillary layer—includes dermal papillae •  Reticular layer

•  Deeper layer—80% of thickness of dermis •  Flexure lines

•  Creases on palms


The Two Regions of the Dermis

Figure 5.5

Dermis

(a) Light micrograph of thick skin identifying the extent of the dermis, (100×)

(b) Papillary layer of dermis, SEM (570×)

(c) Reticular layer of dermis, SEM (430×) Copyright © 2011 Pearson Education, Inc.

Friction ridges

(a) Friction ridges of finger tip (SEM 20×)

(b) Cleavage lines in the reticular dermis

(c) Flexure lines of the hand

Openings of sweat gland ducts

Flexion creases on digit Flexion creases on the palm

Dermal Modifications

Figure 5.6

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Hypodermis

•  Deep to the skin—also called superficial fascia or subcutaneous layer

•  Contains areolar and adipose CT •  Anchors skin to underlying structures •  Helps insulate the body •  Has different distribution in males and

females


Skin Color

•  Three pigments contribute to skin color •  Melanin • Most important pigment—made from

tyrosine •  Carotene • Yellowish pigment from carrots and

tomatoes •  Hemoglobin • Caucasian skin contains little melanin • Allows crimson color of blood to show

through


Nails

•  Nails—scalelike modification of epidermis •  Made of hard keratin •  Parts of the nail • Free edge • Body • Root • Nail folds • Eponychium—cuticle


Lateral nail fold

Lunule

(a)

Nail matrix

Root of nail Proximal nail fold

Nail bed Phalanx (bone of fingertip)

Eponychium (cuticle)

Body of nail

Free edge of nail

(b)

Structure of a Nail

Figure 5.7


Appendages of the Skin

•  Hair •  Flexible strand of dead, keratinized cells •  Hard keratin—tough and durable •  Chief parts of a hair • Root—imbedded in the skin • Shaft—projects above skin's surface



•  Hair has three concentric layers of keratinized cells •  Medulla—central core •  Cortex—surrounds medulla •  Cuticle—outermost layer

•  Hair follicles •  Extend from epidermis into dermis

•  Hair bulb •  Deep, expanded end of the hair follicle

•  Root plexus •  Knot of sensory nerves around hair bulb

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Cross Section of a Hair

Figure 5.8a, b

Hair shaft

Arrector pili Sebaceous gland

Hair root

Hair bulb

(a) Diagram of a cross section of a hair within its follicle

Connective tissue root sheath

Follicle wall

Cuticle

Glassy membrane

Cortex Medulla

Internal epithelial root sheath

External epithelial root sheath

Hair

Hair shaft


Hair root

Hair bulb (b) Photomicrograph of a cross section

of a hair and hair follicle (185×)


Follicle wall

Cuticle

Glassy membrane

Cortex Medulla



Hair


Hair shaft


Hair root

Hair bulb

(c) Diagram of a longitudinal view of the expanded hair bulb of the follicle, which encloses the matrix




Follicle wall

Hair matrix

Melanocyte

Hair papilla

Subcutaneous adipose tissue

Medulla Cortex Cuticle

Glassy membrane

Hair root

Longitudinal Section of Base of Follicle

Figure 5.8c, d

Hair shaft


Hair root

Hair bulb

(d) Photomicrograph of longitudinal view of the hair bulb in the follicle (130×)




Follicle wall

Hair matrix

Hair papilla

Subcutaneous adipose tissue

Medulla Cortex Cuticle

Glassy membrane

Hair root



•  Arrector pili muscle •  Bundle of smooth muscle •  Hair stands erect when arrector pili contracts

•  Vellus hairs •  Body hairs of women and children

•  Terminal hairs •  Hair of scalp •  Axillary and pubic area (at puberty)

•  Hair thinning and baldness •  Due to aging •  Male pattern baldness


Sebaceous Glands

•  Occur over entire body •  Except palms and soles

•  Secrete sebum—an oily substance •  Simple alveolar glands •  Holocrine secretion—entire cell breaks up to

form secretion •  Most are associated with a hair follicle

•  Functions of sebum •  Collects dirt; softens and lubricates hair and

skin


(a) Photomicrograph of a sectioned sebaceous gland (140×)

Sebaceous gland duct

Hair in hair follicle

Secretory cells

Dermal connective tissue

Sebaceous gland

Sweat pore

Eccrine gland

Sebaceous Glands

Figure 5.9a Copyright © 2011 Pearson Education, Inc.

Figure 5.8a Skin glands.

Photomicrograph of a sectioned sebaceous gland (90×)


Sebaceous gland duct

Hair in hair follicle

Secretory cells

Sebaceous gland

Eccrine gland

Sweat pore

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Sweat Glands

•  Sweat glands (sudoriferous glands) widely distributed on body

•  Sweat—is a blood filtrate •  99% water with some salts •  Contains traces of metabolic wastes • About 2% urea


(b) Photomicrograph of a sectioned eccrine gland (140×)

Secretory cells


Duct

Sebaceous gland

Sweat pore

Eccrine gland

Sweat Glands

Figure 5.9b


Sweat Glands

•  Two types of sweat gland •  Eccrine gland (merocrine)

•  Most numerous—these produce true sweat •  Apocrine gland

•  Confined to axillary, anal, and genital areas •  Produce a special kind of sweat

•  Musky odor—attracts a mate •  Signal information about a person’s immune

system, MHC •  Ceruminous glands and mammary glands

•  Modified apocrine glands


Burns •  Classified by severity •  First-degree burn—only upper epidermis is

damaged •  Second-degree burn—upper part of dermis is

also damaged • Blisters appear • Skin heals with little scarring

•  Third-degree burn • Consumes thickness of skin • Burned area appears white, red, or blackened

loss of body fluids, infection, loss of temperature control


(b) Skin bearing full thickness burn (third-degree burn)

3rd degree burn

Estimating Burns Using the Rule of Nines

Figure 5.10

(a) Skin bearing partial thickness burn (first- and second-degree burns)

1st degree burn

2nd degree burn

Anterior and posterior head and neck, 9%

41⁄2% 41⁄2%

Anterior and posterior upper limbs, 18%

Anterior and posterior lower limbs, 36%

100%

(c) Rule of nines; used to estimate extent of burns

Totals Anterior values

Anterior and posterior trunk, 36% Anterior

trunk, 18%

9% 9% (Perineum, 1%)

41⁄2%


Skin Cancer  The most common type of cancer

•  Basal cell carcinoma •  Least malignant and most common

•  Squamous cell carcinoma •  Arises from keratinocytes of stratum spinosum

•  Melanoma •  A cancer of melanocytes •  The most dangerous type of skin cancer

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Skin Cancer

Figure 5.11 Copyright © 2011 Pearson Education, Inc.

The Skin Throughout Life

•  Middle to old age •  Skin thins and becomes less elastic •  Shows harmful effects of environmental

damage •  Skin inflammations become more common

c h a p t e r two distinct layers epidermis the dermis...

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