Chapter 5 *Lecture Outline *See separate FlexArt PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Chapter 5 Outline Structure and Function of the Integument Epidermis 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 Hair shaft Sweat pore Epidermis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hair shaft Sweat pore Epidermis Epidermal ridge Dermal papilla Papillary layer Arrector pili muscle Sebaceous (oil) gland Dermis Sweat gland duct Reticular layer Merocrine sweat gland Sensory nerve fiber Apocrine sweat gland Vein Artery Subcutaneous layer Adipose connective tissue Hair follicle Sensory receptors Areolar connective tissue Figure 5.1

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 An incision perpendicular to Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. An incision perpendicular to cleavage lines may gape and delay healing. An incision parallel to cleavage lines is more likely to heal quickly and not gape open. Figure 5.7

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 Functions: 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 Shaft (beyond epidermis) Root Sebaceous Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Shaft (beyond epidermis) Root Sebaceous (oil) gland Hair follicle Arrector pili muscle Matrix Hair bulb Melanocyte Figure 5.9 Hair papilla (a)

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”

© Biophoto Associates/Photo Researchers, Inc. Structure of a Hair Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Connective tissue root sheath Cortex Cuticle External root sheath Internal root sheath Hair bulb Matrix Hair papilla LM 100x Figure 5.9 (b) © 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: Two rarer 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