Integumentary Integumentary SystemSystem

Skin and It’s Accessory Skin and It’s Accessory OrgansOrgans

Skin (Integument)Skin (Integument)

Consists of three major regionsConsists of three major regions Epidermis – outermost superficial Epidermis – outermost superficial

regionregion Dermis – middle regionDermis – middle region Hypodermis (superficial fascia) – Hypodermis (superficial fascia) –

deepest regiondeepest region

Skin (Integument)Skin (Integument)

Figure 5.1

EpidermisEpidermis

Composed of keratinized stratified Composed of keratinized stratified squamous epithelium, consisting of four squamous epithelium, consisting of four distinct cell types and four or five layersdistinct cell types and four or five layers

Cell types include keratinocytes, Cell types include keratinocytes, melanocytes, Merkel cells, and melanocytes, Merkel cells, and Langerhans’ cellsLangerhans’ cells

Outer portion of the skin is exposed to the Outer portion of the skin is exposed to the external environment and functions in external environment and functions in protectionprotection

Cells of the EpidermisCells of the Epidermis

Keratinocytes – produce the fibrous Keratinocytes – produce the fibrous protein keratinprotein keratin

Melanocytes – produce the brown pigment Melanocytes – produce the brown pigment melaninmelanin

Langerhans’ cells – epidermal Langerhans’ cells – epidermal macrophages that help activate the macrophages that help activate the immune systemimmune system

Merkel cells – function as touch receptors Merkel cells – function as touch receptors in association with sensory nerve endingsin association with sensory nerve endings

Layers of the Epidermis:Layers of the Epidermis:

Figure 5.2b

Deepest epidermal layer firmly Deepest epidermal layer firmly attached to the dermisattached to the dermis

Consists of a single row of the Consists of a single row of the youngest keratinocytesyoungest keratinocytes

Cells undergo rapid division, hence Cells undergo rapid division, hence its alternate name, stratum its alternate name, stratum germinativumgerminativum

Layers of the Epidermis: Layers of the Epidermis: Stratum Basale Stratum Basale

(Basal Layer)(Basal Layer)

Cells contain a weblike system of Cells contain a weblike system of intermediate filaments attached to intermediate filaments attached to desmosomesdesmosomes

Melanin granules and Langerhans’ Melanin granules and Langerhans’ cells are abundant in this layercells are abundant in this layer

Layers of the Epidermis: Layers of the Epidermis: Stratum Spinosum Stratum Spinosum

(Prickly Layer)(Prickly Layer)

Layers of the Epidermis:Layers of the Epidermis:

Figure 5.2b

Thin; three to five cell layers in which Thin; three to five cell layers in which drastic changes in keratinocyte drastic changes in keratinocyte appearance occurs appearance occurs

Keratohyaline and lamellated Keratohyaline and lamellated granules accumulate in the cells of granules accumulate in the cells of this layerthis layer

Layers of the Epidermis: Layers of the Epidermis: Stratum Granulosum Stratum Granulosum

(Granular Layer)(Granular Layer)

Thin, transparent band superficial to Thin, transparent band superficial to the stratum granulosumthe stratum granulosum

Consists of a few rows of flat, dead Consists of a few rows of flat, dead keratinocyteskeratinocytes

Present only in thick skinPresent only in thick skin

Layers of the Epidermis: Layers of the Epidermis: Stratum Lucidum Stratum Lucidum

(Clear Layer)(Clear Layer)

Layers of the Epidermis:Layers of the Epidermis:

Figure 5.2b

Outermost layer of keratinized cellsOutermost layer of keratinized cells Accounts for three quarters of the Accounts for three quarters of the

epidermal thicknessepidermal thickness Functions include:Functions include:

WaterproofingWaterproofing Protection from abrasion and penetrationProtection from abrasion and penetration Rendering the body relatively insensitive Rendering the body relatively insensitive

to biological, chemical, and physical to biological, chemical, and physical assaultsassaults

Layers of the Epidermis: Layers of the Epidermis: Stratum Corneum Stratum Corneum

(Horny Layer)(Horny Layer)

Skin (Integument)Skin (Integument)

Figure 5.1

DermisDermis

Second major skin region containing Second major skin region containing strong, flexible connective tissuestrong, flexible connective tissue

Cell types include fibroblasts, Cell types include fibroblasts, macrophages, and occasionally mast macrophages, and occasionally mast cells and white blood cellscells and white blood cells

Composed of two layers – papillary Composed of two layers – papillary and reticularand reticular

Layers of the Dermis: Layers of the Dermis: Papillary LayerPapillary Layer

Papillary layerPapillary layer Areolar connective tissue with collagen Areolar connective tissue with collagen

and elastic fibersand elastic fibers Its superior surface contains peglike Its superior surface contains peglike

projections called dermal papillaeprojections called dermal papillae Dermal papillae contain capillary loops, Dermal papillae contain capillary loops,

Meissner’s corpuscles, and free nerve Meissner’s corpuscles, and free nerve endingsendings

Layers of the Dermis: Layers of the Dermis: Reticular LayerReticular Layer

Reticular layerReticular layer Accounts for approximately 80% of the Accounts for approximately 80% of the

thickness of the skinthickness of the skin Collagen fibers in this layer add strength Collagen fibers in this layer add strength

and resiliency to the skinand resiliency to the skin Elastin fibers provide stretch-recoil Elastin fibers provide stretch-recoil

propertiesproperties

Skin ColorSkin Color

Three pigments contribute to skin colorThree pigments contribute to skin color Melanin – yellow to reddish-brown to black Melanin – yellow to reddish-brown to black

pigment, responsible for dark skin colorspigment, responsible for dark skin colors Freckles and pigmented moles – result from local Freckles and pigmented moles – result from local

accumulations of melaninaccumulations of melanin Carotene – yellow to orange pigment, most Carotene – yellow to orange pigment, most

obvious in the palms and soles of the feetobvious in the palms and soles of the feet Hemoglobin – reddish pigment responsible for Hemoglobin – reddish pigment responsible for

the pinkish hue of the skinthe pinkish hue of the skin

Skin (Integument)Skin (Integument)

Figure 5.1

Sweat GlandsSweat Glands

Different types prevent overheating of the Different types prevent overheating of the body; secrete cerumen and milkbody; secrete cerumen and milk Eccrine sweat glands – found in palms, soles of Eccrine sweat glands – found in palms, soles of

the feet, and foreheadthe feet, and forehead Apocrine sweat glands – found in axillary and Apocrine sweat glands – found in axillary and

anogenital areasanogenital areas Ceruminous glands – modified apocrine glands Ceruminous glands – modified apocrine glands

in external ear canal that secrete cerumenin external ear canal that secrete cerumen Mammary glands – specialized sweat glands Mammary glands – specialized sweat glands

that secrete milkthat secrete milk

Sebaceous GlandsSebaceous Glands

Simple alveolar glands found all over Simple alveolar glands found all over the bodythe body

Soften skin when stimulated by Soften skin when stimulated by hormoneshormones

Secrete an oily secretion called Secrete an oily secretion called sebumsebum

Structure of a NailStructure of a Nail

Scalelike modification of the epidermis on Scalelike modification of the epidermis on the distal, dorsal surface of fingers and toesthe distal, dorsal surface of fingers and toes

Figure 5.4

HairHair Filamentous strands of dead keratinized Filamentous strands of dead keratinized

cells produced by hair folliclescells produced by hair follicles Contains hard keratin which is tougher and Contains hard keratin which is tougher and

more durable than soft keratin of the skinmore durable than soft keratin of the skin Made up of the shaft projecting from the Made up of the shaft projecting from the

skin, and the root embedded in the skinskin, and the root embedded in the skin Consists of a core called the medulla, a Consists of a core called the medulla, a

cortex, and an outermost cuticlecortex, and an outermost cuticle Pigmented by melanocytes at the base of Pigmented by melanocytes at the base of

the hairthe hair

Hair Function and Hair Function and DistributionDistribution

Functions of hair include:Functions of hair include: Helping to maintain warmthHelping to maintain warmth Alerting the body to presence of insects on the Alerting the body to presence of insects on the

skin skin Guarding the scalp against physical trauma, Guarding the scalp against physical trauma,

heat loss, and sunlightheat loss, and sunlight Hair is distributed over the entire skin Hair is distributed over the entire skin

surface exceptsurface except Palms, soles, and lipsPalms, soles, and lips Nipples and portions of the external genitaliaNipples and portions of the external genitalia

Hair FollicleHair Follicle

Figure 5.6a

Hair FollicleHair Follicle

Figure 5.6c