The Integumentary System, but Shares Some of Skin’S Properties

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PowerPoint® Lecture Slides The Skin and the Hypodermis prepared by Leslie Hendon University of Alabama, Birmingham • Skin—our largest organ • Accounts for 7% of body weight • Varies in thickness from 1.5–4.4mm C H A P T E R 5 • Divided into two distinct layers • Epidermis The • Dermis Integumentary • Hypodermis—lies deep to the dermis • Composed of areolar and adipose tissues System • Not part of the integumentary system, but shares some of skin’s properties

Skin Structure The Skin and Hypodermis

• Functions 1. Protection—cushions organs and protects from Hair shaft bumps, chemicals, water loss, UV radiation Dermal papillae Epidermis Subpapillary vascular 2. Regulation of body temperature---Capillary Papillary plexus layer network and sweat glands regulate heat loss Pore Appendages of skin 3. Excretion—urea, salts, and water lost through Dermis Reticular Eccrine sweat gland sweat layer Arrector pili muscle Sebaceous (oil) gland Hair follicle 4. Production of vitamin D---Epidermal cells use Hair root UV radiation to synthesize vitamin D Hypodermis (superficial fascia) 5. Sensory reception—Contains sense organs Nervous structures Sensory nerve fiber Dermal vascular plexus associated with nerve endings Lamellar (Pacinian) corpuscle Adipose tissue Hair follicle receptor (root hair plexus)

Figure 5.2 Gross structure of skin and underlying tissues. Epidermis • Is composed of keratinized stratified squamous epithelium • Contains four main cell types • Keratinocytes • Location—stratum spinosum; produce keratin a fibrous protein Epidermis • Melanocytes • Location—basal layer; manufacture and secrete the pigment melanin Dermis • Tactile epithelial cells (Merkel cells) Hypodermis • Location—basal layer; attached to sensory nerve endings Deep fascia • Dendritic cells (Langerhans cells) • Location—stratum spinosum; part of immune system; Muscle macrophage-like

1 Epidermis Layers of the Epidermis

• Keratinocytes—most abundant cell type in • Stratum basale (stratum geminativum) epidermis • Stratum spinosum • Arise from deepest layer of epidermis • Stratum granulosum • Produce keratin, a tough fibrous protein • Stratum lucidum (only in thick skin) Produce antibodies and enzymes • • Stratum corneum • Keratinocytes are dead at skin's surface

Figure 5.3a Epidermal cells and layers of the epidermis.

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

Stratum granulosum One to five layers of flattened cells, organelles deteriorating; cytoplasm full of lamellar granules (release lipids) and keratohyaline granules. Stratum corneum Most superficial layer; 20–30 layers of dead cells represented only by flat membranous sacs filled Stratum spinosum with keratin. Glycolipids in extracellular space. Several layers of keratinocytes unified by desmosomes. Cells contain thick bundles of intermediate filaments made of pre-keratin.

Desmosomes Stratum granulosum Three to five layers of flattened cells, organelles deteriorating; cytoplasm full of lamellated granules (release lipids) and keratohyaline granules. Stratum basale Stratum spinosum Deepest epidermal layer; one row Several layers of keratinocytes unified by of actively mitotic stem cells; desmosomes. Cells contain thick bundles of some newly formed cells become intermediate filaments made of pre-keratin. part of the more superficial Stratum basale layers. See occasional Deepest epidermal layer; one row of actively mitotic melanocytes and dendritic cells. stem cells; some newly formed cells become part of the more superficial layers. See occasional melanocytes and dendritic cells. Dermis

(a) Dermis

Figure 5.3b Epidermal cells and layers of the epidermis. Stratum corneum Most superficial layer; 20–30 Keratinocytes Epidermal Cells and Layers of the layers of dead cells represented only by flat membranous sacs filled with keratin. Glycolipids in Epidermis extracellular space.

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

Stratum corneum Most superficial layer; 20–30 layers of dead cells Stratum spinosum represented only by flat membranous sacs filled with keratin. Glycolipids in extracellular space. Several layers of keratinocytes unified by desmosomes. Cells contain thick bundles of intermediate filaments made of pre-keratin.

Desmosomes Stratum granulosum Three to five layers of flattened cells, organelles deteriorating; cytoplasm full of lamellated granules (release lipids) and keratohyaline granules. Stratum basale Stratum spinosum Deepest epidermal layer; one row Several layers of keratinocytes unified by of actively mitotic stem cells; desmosomes. Cells contain thick bundles of Dermis intermediate filaments made of pre-keratin. some newly formed cells become Stratum basale part of the more superficial Deepest epidermal layer; one row of actively mitotic stem cells; some newly formed cells Dendritic cell layers. See occasional become part of the more superficial layers. See Dermis melanocytes and dendritic cells. occasional melanocytes and dendritic cells. Tactile epithelial cell Dendritic cell Melanin Sensory Sensory Melanocyte granule Melanocyte nerve nerve Melanin ending (b) Desmosomes ending Tactile granule epithelial cell Copyright © 2011 Pearson Education, Inc. Figure 5.3b Copyright © 2011 Pearson Education, Inc.

2 Layers of the Epidermis Layers of the Epidermis

• Stratum basale • Stratum granulosum • Deepest layer of epidermis • Consists of keratinocytes and tonofilaments • Attached to underlying dermis • Tonofilaments contain: Cells actively divide • • Keratohyaline granules—help form keratin • Stratum basale contains • Tactile epith. Cells/Merkel cells—associated with sensory nerve • Lamellated granules—contain a waterproofing glycolipid ending • Stratum lucidum (clear layer) • Melanocytes—secrete the pigment melanin • Occurs only in thick skin • Stratum spinosum (spiny layer) • Locations of thick skin—palms and soles • “Spiny” appearance caused by: • Composed of a few rows of flat, dead keratinocytes • Artifacts of histological preparation • Stratum corneum (horny layer) • Contains thick bundles of intermediate filaments (tonofilaments) • Thick layer of dead keratinocytes and thickened plasma • Resist tension membranes • Contain protein prekeratin • Contains star-shaped dendritic cells • Protects skin against abrasion and penetration • A type of macrophage • Function in immune system

Figure 5.4 Thick skin. Epidermis Dermis

Stratum corneum • Second major layer of the skin

Stratum lucidum • Strong, flexible connective tissue Stratum granulosum • Richly supplied with blood vessels (important role in temperature control) and nerves Stratum spinosum Stratum basale Dermis • Has two layers • Papillary layer—includes dermal papillae Papillary dermis • Reticular layer Dermal • Deeper layer—80% of thickness of dermis papilla • Flexure lines Reticular • Creases on palms Collagen dermis fibers

The Two Regions of the Dermis Dermal Modifications Friction ridges Openings of sweat gland ducts

Dermis

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

(a) Light micrograph of thick skin identifying the extent of the Flexion dermis, (100×) creases (a) Friction ridges of finger on digit tip (SEM 20×) Flexion creases on the palm

(b) Cleavage lines in the (c) Flexure lines of (c) Reticular layer of dermis, SEM (430×) reticular dermis the hand Copyright © 2011 Pearson Education, Inc. Figure 5.5 Copyright © 2011 Pearson Education, Inc. Figure 5.6

3 Hypodermis Skin Color

• Deep to the skin—also called superficial • Three pigments contribute to skin color fascia or subcutaneous layer • Melanin • Contains areolar and adipose CT • Most important pigment—made from tyrosine • Anchors skin to underlying structures • Carotene • Helps insulate the body • Yellowish pigment from carrots and • Has different distribution in males and tomatoes females • Hemoglobin • Caucasian skin contains little melanin • Allows crimson color of blood to show through

Nails Structure of a Nail Lunule Lateral nail fold • Nails—scalelike modification of epidermis • Made of hard keratin • Parts of the nail • Free edge (a) Body Free edge Body Eponychium • of nail of nail (cuticle) Root of nail Proximal Nail • Root nail fold matrix • Nail folds • Eponychium—cuticle

Appendages of the Skin Appendages of the Skin

• Hair • Hair has three concentric layers of keratinized cells • Medulla—central core • Flexible strand of dead, keratinized cells • Cortex—surrounds medulla • Hard keratin—tough and durable • Cuticle—outermost layer Hair follicles • Chief parts of a hair • • Extend from epidermis into dermis • Root—imbedded in the skin • Hair bulb • Shaft—projects above skin's surface • Deep, expanded end of the hair follicle • Root plexus • Knot of sensory nerves around hair bulb

4 Cross Section of a Hair Longitudinal Section of Base of Follicle

Hair shaft Follicle wall Follicle wall Connective Connective tissue tissue root sheath root sheath Glassy membrane External epithelial Glassy membrane root sheath External epithelial Arrector Internal epithelial pili root sheath root sheath Sebaceous Hair root Internal epithelial gland Cuticle root sheath Hair root Hair shaft Cortex Medulla Hair bulb Hair Hair matrix Cuticle Hair papilla Cortex

Medulla Melanocyte Arrector Follicle wall pili Connective (a) Diagram of a cross section of a hair within its follicle tissue root sheath Sebaceous Subcutaneous Glassy membrane gland adipose tissue External epithelial Follicle wall root sheath (c) Diagram of a longitudinal view of the expanded hair Hair shaft Hair root Hair shaft bulb of the follicle, which encloses the matrix Internal epithelial Connective tissue root sheath root sheath Hair bulb Hair root Glassy membrane Cuticle External epithelial Cortex root sheath Arrector Medulla pili Internal epithelial Sebaceous Hair matrix Arrector root sheath gland pili Hair papilla Sebaceous Hair root gland Hair Hair bulb Cuticle Hair root Cortex Subcutaneous adipose tissue Hair bulb Medulla (b) Photomicrograph of a cross section (d) Photomicrograph of longitudinal view of a hair and hair follicle (185×) of the hair bulb in the follicle (130×)

Appendages of the Skin Sebaceous Glands

• Arrector pili muscle • Occur over entire body • Bundle of smooth muscle Except palms and soles • Hair stands erect when arrector pili contracts • • Vellus hairs • Secrete sebum—an oily substance • Body hairs of women and children • Simple alveolar glands • Terminal hairs • Holocrine secretion—entire cell breaks up to • Hair of scalp form secretion • Axillary and pubic area (at puberty) • Most are associated with a hair follicle • Hair thinning and baldness • Functions of sebum • Due to aging • Collects dirt; softens and lubricates hair and • Male pattern baldness skin

Figure 5.8a Skin glands. Sebaceous Sweat Sebaceous Glands Sebaceous gland pore Sweat gland duct pore Dermal connective Hair in Sebaceous tissue hair follicle Dermal gland connective tissue Sebaceous Hair in gland duct hair follicle

Eccrine Eccrine gland gland

Secretory cells Secretory cells

Photomicrograph of a (a) Photomicrograph of a sectioned sectioned sebaceous sebaceous gland (140×) gland (90×)

5 Sweat Glands Sweat Glands Sweat pore • Sweat glands (sudoriferous glands) widely distributed on body • Sweat—is a blood filtrate • 99% water with some salts • Contains traces of metabolic wastes Eccrine Sebaceous gland • About 2% urea gland Duct Dermal connective tissue Secretory cells

Sweat Glands Burns • Classified by severity • Two types of sweat gland • First-degree burn—only upper epidermis is • Eccrine gland (merocrine) damaged • Most numerous—these produce true sweat • Second-degree burn—upper part of dermis is • Apocrine gland also damaged • Confined to axillary, anal, and genital areas • Blisters appear • Produce a special kind of sweat • Skin heals with little scarring • Musky odor—attracts a mate • Third-degree burn • Signal information about a person’s immune • Consumes thickness of skin system, MHC • Burned area appears white, red, or blackened • Ceruminous glands and mammary glands  loss of body fluids, infection, loss of temperature • Modified apocrine glands control

Estimating Burns Using the Rule of Nines Skin Cancer

Anterior values Totals 1st degree burn  The most common type of cancer 1 4 ⁄2% Anterior and posterior head and neck, 9%

Anterior and posterior upper limbs, 18% • Basal cell carcinoma 2nd degree burn

1 1 Anterior and posterior Least malignant and most common 4 ⁄2% Anterior 4 ⁄2% • trunk, 36% (a) Skin bearing partial thickness burn trunk, 18% (first- and second-degree burns) • Squamous cell carcinoma • Arises from keratinocytes of stratum spinosum

3rd degree burn 9% 9% (Perineum, 1%) • Melanoma • A cancer of melanocytes

Anterior and posterior lower limbs, 36% • The most dangerous type of skin cancer

100% (c) Rule of nines; used to estimate (b) Skin bearing full thickness burn extent of burns (third-degree burn) Copyright © 2011 Pearson Education, Inc. Figure 5.10 Copyright © 2011 Pearson Education, Inc.

6 Skin Cancer 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