Chapter 5

*Lecture Outline

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

*See separate FlexArt PowerPoint slides for all figures and tables pre-inserted into PowerPoint

without notes.

Chapter 5 Outline

• Structure and Function of the Integument

• Epidermis

• Dermis

• Hypodermis

• Accessory Organs

• Repair and Regeneration

• Aging and Development

Intro to the Integument

• Integument = skin– largest organ (7% to 8% of body weight)– two layers

• epidermis: superficial layer of stratified squamous epithelium

• dermis: deeper layer of areolar and dense irregular connective tissues– hypodermis (not part of the skin) lies

under dermis, mostly adipose connective tissue

The Integument

Figure 5.1

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Hair shaft

Sweat pore

Epidermal ridge

Dermal papilla

Arrector pili muscle

Sebaceous (oil) gland

Sweat gland duct

Merocrine sweat gland

Sensory nerve fiber

Apocrine sweat gland

VeinArtery

Adipose connective tissue

Areolarconnective tissue

Subcutaneouslayer

Sensoryreceptors

Hair follicle

Epidermis

Dermis

Papillarylayer

Reticularlayer

Integument Functions

• Protection

• Prevention of H2O loss

• Temperature regulation

• Metabolic regulation

• Immune defense

• Sensory reception

• Excretion/Secretion

The Epidermis

• Most superficial layer

• Avascular

• Keratinized stratified squamous epithelium– keratin is a water-insoluble protein– 4 to 5 layers (strata) of distinct cell types

Epidermal Strata

• From deep to superficial (as they grow):– stratum basale– stratum spinosum– stratum granulosum– stratum lucidum (found only in thick skin)– stratum corneum

Stratum Basale

• Only layer that undergoes mitosis

• One layer of cells adjacent to the dermis– keratinocytes: most abundant; produce

keratin to waterproof the skin

– melanocytes: cells with long, branched cytoplasmic processes; produce a pigment (black, brown, or yellow) that absorbs UV light to prevent DNA damage, reducing some forms of skin cancer

– tactile cells: sense touch

Cells of the Stratum Basale

Figure 5.2

Melanocytes

Figure 5.4

Stratum Spinosum

• Several layers thick

• Daughter cells from the stratum basale– differentiate into nondividing (may see a rare

mitotic cell), highly specialized keratinocyte

• Epidermal dendritic cells– phagocytes that engulf invading pathogens

Cells of the Stratum Spinosum

Figure 5.2

Stratum Granulosum

• Three to five layers of keratinocytes– cytoplasm fills with keratin filaments– organelles begin to degrade– fully keratinized cells are dead but strong and

water-insoluble

Stratum Granulosum Cells

Figure 5.2

Stratum Lucidum

• Thin, translucent region, two to three layers thick

• Present only in thick skin such as sole of feet and palms of hands

• Cells lack organelles, filled with eleidin– transparent, intermediate product of keratin

maturation

Cells of the Stratum Lucidum

Figure 5.2

Stratum Corneum

• Most superficial layer of epidermis

• Thickness varies from a few to 30 layers thick depending on location on the body

• Comprised solely of dead keratinocytes– sloughed off by abrasion = dust

Cells of the Stratum Corneum

Figure 5.3

Epidermal Variation: Skin Color

Skin color is determined by three pigments:

• hemoglobin: blood pigment; causes light complexions to look pink (or blue)

• melanin: pigment produced by melanocytes; increases in people exposed to more UV light

• carotene: yellow-orange pigment from food that builds up in the skin

Abnormal Skin Colors

Epidermal Variation: Skin Markings

• Nevus: localized overgrowth of melanocytes– a.k.a. mole

• Hemangioma: proliferation of blood vessels– may disappear (strawberry) in childhood or

may persist (port-wine) through adulthood• Friction ridges: folds of epidermis/dermis on

fingers, palms, soles, and toes for grasping– cause us to leave fingerprints

Fingerprints

Figure 5.5

The Dermis

• Lies deep to the epidermis• Two layers of connective tissues:

– Papillary: superficial– Reticular: deeper

• mainly collagen fibers• contains blood vessels, glands, hair

follicles, nail roots, sensory nerve endings, and smooth muscle

The Dermis

Figure 5.6

The Papillary Layer

• Directly below stratum basale cells of epidermis– dermal papillae and epidermal ridges

interlock, increasing the surface area between epidermis and dermis

– dermal papillae contain capillaries that supply nutrients to the avascular epidermal cells

The Reticular Layer

• Forms majority of the dermis

• Comprised mainly of dense irregular connective tissue with large bundles of collagen fibers, blood vessels, glands, hair follicles, and nerves

– collagen bundles help connect dermis to underlying hypodermis

Lines of Cleavage

• Lines in the deep dermis formed by the orientation of collagen bundles– importance to surgeons: incisions across

these lines heal more slowly than incisions along the lines

Lines of Cleavage

Figure 5.7

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

An incision parallelto cleavage lines is morelikely to heal quickly andnot gape open.

An incisionperpendicular to

cleavage lines maygape and delay healing.

Innervation

• Nerve fibers are present in dermis

– Functions:

• tactile (touch) receptors

• control blood flow

• control glandular secretion

Blood Supply

• Epidermis: avascular

• Dermis: contains blood vessels– important in controlling body temperature

• vasoconstriction: narrowing blood vessels preserves core body heat

• vasodilation: widening blood vessels releases body heat, lowering body temperature

The Hypodermis

• A.K.A. subcutaneous layer– deep to, not really part of, the integument– areolar and adipose connective tissues

• Functions:– protects underlying structures– stores energy– thermal insulation

Hypodermis (Subcutaneous Layer)

Figure 5.6

Epidermal Derivatives

• Structures that grow from the epidermis:

– Nails

– Hairs

– Glands

Nails

• Derived from the stratum corneum• Cells densely packed together filled with

parallel fibers of hard keratin• The nail plate has a whitish free edge, a

pinkish nail body, and a nail root• The nail body covers a layer of epidermis

called the nail bed• The nail bed appears pink because of the

underlying capillaries

Nails

• Protective structures on digits• Parts

– nail body: flat keratinized cells protecting digit

– nail bed: live epidermal cells under nail body– nail root: region hidden by cuticle

• nail matrix: thickened growing part of the nail bed• lunula: white semilunar proximal area of nail body

caused by thickened underlying stratum basale obscuring capillaries in dermis

Fingernail

Figure 5.8

Hair

• Columns of keratinocytes growing from follicles deep in dermis or hypodermis

• Regions of a hair from deep to surface:– Hair bulb– Hair root– Hair shaft

Structure of a Hair

Figure 5.9

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

(a)

Root

Shaft(beyond epidermis)

Sebaceous(oil) gland

Hair follicle

Arrectorpili muscle

Matrix

Hair bulbMelanocyte

Hair papilla

Hair Structure

• From deep to superficial– hair papilla: connective tissue, nerves, and blood

vessels below follicle that support the keratinocytes

– hair bulb: a swelling at bottom of follicle filled with dividing keratinocytes; increase in hair matrix causes hair growth

– arrector pili: involuntary smooth muscle attached to hair shaft; responds to emotional states (fear or rage) and cold temperatures by contracting, standing hair up, and producing “goose bumps”

Structure of a Hair

Figure 5.9

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Hair papilla

Internal rootsheath

Matrix

External rootsheath

Cuticle

Cortex

Connectivetissue rootsheath

Hairbulb

(b)

LM 100x

© Biophoto Associates/Photo Researchers, Inc.

Functions of Hair

• Protection

• Heat retention

• Facial expression

• Sensory reception

• Visual identification

• Chemical signal dispersal

Skin Exocrine Glands

• Two most common types:– sweat glands: produce watery solution

• merocrine and apocrine– sebaceous glands: produce oily

secretions

• Two rarer types:– ceruminous glands: produce ear wax– mammary glands: produce milk

Sweat Glands

Figure 5.10

Merocrine Sweat Glands

• Simple coiled tubular glands that secrete into a duct with a pore on skin’s surface

– secretion is 99% H2O, clear, and controlled by nervous system

– numerous on forehead, palms, and soles• Functions:

– Thermoregulation– Secretion– Protection

Apocrine Sweat Glands

• Simple coiled tubular glands that secrete into hair follicles around nipples (areolae), armpits (axillae), groin (pubic), and anus (anal)– secretion is thick, cloudy, proteins and lipids

• leads to bacterial growth, causing body odor in the above regions

Sebaceous Glands

• Secrete oily sebum into hair follicles– lubricates hair and skin– relatively inactive during childhood; sex

hormones at puberty cause secretions to increase significantly