Lecture 4 Chapter 5: The Integumentary System Anatomy & Physiology I Lecture 4 Chapter 5: The Integumentary System

The Integumentary System The skin and its derivatives that function in protection for the rest of the body

The Skin Consists of two distinct regions: Epidermis—superficial region Epithelial tissue Dermis—underlies epidermis Mostly fibrous connective tissue vascularized

Let’s go deeper Hypodermis (superficial fascia) Subcutaneous layer deep to skin Not part of skin but is also protective Mostly adipose tissue that absorbs shock & insulates Anchors skin to underlying structures – mostly muscles fascia

Hair shaft Dermal papillae Figure 5.1 Skin structure. Hair shaft Dermal papillae Epidermis Subpapillary plexus Papillary layer Sweat pore Appendages of skin Dermis Reticular layer Eccrine sweat gland Arrector pili muscle Sebaceous (oil) gland Hair follicle Hair root Hypodermis (subcutaneous tissue; not part of skin) Cutaneous plexus Nervous structures Sensory nerve fiber with free nerve endings Adipose tissue Lamellar corpuscle Hair follicle receptor (root hair plexus) © 2013 Pearson Education, Inc.

The Epidermis Keratinized stratified squamous epithelium Four or five distinct layers Stratum basale Stratum spinosum Stratum granulosum Stratum lucidum (only in thick skin) Stratum corneum

Cells of Epidermis Four cell types Keratinocytes Melanocytes Dendritic (Langerhans) cells Tactile (Merkel) cells

Cells of Epidermis Keratinocytes Melanocytes Produce fibrous protein keratin Most cells of epidermis Tightly connected by desmosomes Melanocytes 10–25% of cells in deepest epidermis Produce pigment melanin Protect apical surface of keratinocyte nucleus from UV damage

Cells of the Epidermis Dendritic (Langerhans) cells Macrophages – key activators of immune system Tactile (Merkel) cells Sensory touch receptors

Figure 5.2a The main structural features of the skin epidermis. Stratum corneum Most superficial layer; 20–30 layers of dead cells Flat membranous sacs filled with keratin. Stratum granulosum Typically five layers of flattened cells, organelles deteriorating; Stratum spinosum Several layers of keratinocytes unified by desmosomes. Stratum basale Deepest epidermal layer; one row of actively mitotic stem cells © 2013 Pearson Education, Inc. Dermis

Layers of Epidermis From deep to superficial: Stratum basale Stratum spinosum Stratum granulosum Stratum lucidum (only in thick skin) Stratum corneum

Stratum Basal (Germinativum) Deepest epidermal layer Attached to dermis Single row of stem cells, actively mitotic Produces two daughter cells One cell journeys from basal layer to surface One cell remains in stratum basale as stem cell 10-25% of layer is Melanocytes

Stratum Spinosum Several layers thick Cells contain web-like system of intermediate prekeratin filaments attached to desmosomes Abundant melanosomes and dendritic cells

Stratum Granulosum Thin - four to six cell layers Cells flatten Nuclei and organelles disintegrate Keratinization begins Help form keratin in upper layers Cell accumulate keratohyaline and lamellar granules Their water-resistant glycolipid slows water loss

Stratum Lucidum Only in thick skin Thin, translucent band superficial to the stratum granulosum A few rows of flat, dead keratinocytes

Stratum Corneum 20–30 rows of dead, flat, anucleate keratinized membranous sacs Three-quarters of epidermal thickness Though dead, its cells have functions Protect deeper cells from environment and water loss Protect from abrasion and penetration Barrier against biological, chemical, and physical assaults

Figure 5.2b The main structural features of the skin epidermis. Keratinocytes Stratum corneum Most superficial layer; 20–30 layers of dead cells, essentially flat membranous sacs filled with keratin. Glycolipids in extracellular space. Stratum granulosum Typically five layers of flattened cells, organelles deteriorating; cytoplasm full of lamellar 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. Dendritic cell Sensory nerve ending Dermis 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. Melanin granule Tactile (Merkel) cell Desmosomes Melanocyte © 2013 Pearson Education, Inc.

Keratinocytes and Melanocyte Network

The Walking Dead! Average person shed 50,000 dead cells every minute 40 lbs of skin in a lifetime

Dermis Strong, flexible connective tissue (proper) Contains: Fibroblasts, macrophages, mast cells and white blood cells Contains: nerve fibers; blood and lymphatic vessels, hair follicles, and oil and sweat glands Contains two layers This is the equivalent to the hide to make leather

Hair shaft Dermal papillae Figure 5.1 Skin structure. Hair shaft Dermal papillae Epidermis Subpapillary plexus Papillary layer Sweat pore Appendages of skin Dermis Reticular layer Eccrine sweat gland Arrector pili muscle Sebaceous (oil) gland Hair follicle Hair root Hypodermis (subcutaneous tissue; not part of skin) Cutaneous plexus Nervous structures Sensory nerve fiber with free nerve endings Adipose tissue Lamellar corpuscle Hair follicle receptor (root hair plexus) © 2013 Pearson Education, Inc.

Papillary Layer of the Dermis Areolar connective tissue with collagen and elastic fibers and blood vessels Phagocytes can patrol for microorganisms Home to dermal papillae Superficial peglike projections

Papillary Layer of the Dermis Dermal Papillae indent the superior epidermis conatin capillary loops, pain and touch receptors Friction ridges the collection of skin ridges created by dermal papillae enhance gripping and touching ability give us our fingerprint

Openings of sweat gland ducts Friction ridges Friction ridges of Figure 5.4a Dermal modifications result in characteristic skin markings. Openings of sweat gland ducts Friction ridges Friction ridges of fingertip (SEM 12x) © 2013 Pearson Education, Inc.

Reticular Layer of Dermis Majority of dermal thickness Dense fibrous connective tissue Elastic fibers provide stretch-recoil properties Collagen fibers Provide strength and resiliency Bind water

Reticular Layers form Cleavage Lines formed from the separation between thick bundles of interlacing collagen fibers Externally invisible Important to surgeons Incisions parallel to cleavage lines gap less and heal more readily

Cleavage lines in the reticular dermis Figure 5.4b Dermal modifications result in characteristic skin markings. Cleavage lines in the reticular dermis © 2013 Pearson Education, Inc.

Reticular Layer of the Dermis Cleavage lines Collagen gives skin strength Collagen binds water to keep skin hydrated Flexure lines dermal folds that occur at or new joints, where dermis is tightly secured to deeper structures

Flexure lines on digit Flexure lines on the palm Flexure lines of the Figure 5.4c Dermal modifications result in characteristic skin markings. Flexure lines on digit Flexure lines on the palm Flexure lines of the hand © 2013 Pearson Education, Inc.

Skin Color Three pigments contribute to skin color: Melanin Carotene Hemoglobin

Melanin Two forms Color differences due to amount and form Reddish-yellow to brownish-black Color differences due to amount and form Produced in melanocytes Same relative number in all people Migrates to keratinocytes to form "pigment shields" for nuclei Sun exposure stimulates melanin production. Freckles and moles are accumation of melanin

Carotene Yellow to orange pigment Most obvious in palms and soles (St. corneum thick) Accumulates in stratum corneum and hypodermis Yellowish-tinge of some asians – carotene and melanin variations Can be converted to vitamin A for vision and epidermal health

Hemoglobin Pinkish hue of fair skin Red blood cells circulating through the dermal capillaries Hemoglobin seen easier in lighter melanin Caucasians

Appendages of the Skin Derivatives of the epidermis Hairs and hair follicles Nails Sweat glands Sebaceous (oil) glands Function: Maintain body homeostasis

Hairs and Hair Follicles Functions are protective; Warn of insects on skin Physical trauma Heat loss Sunlight Hair pigments Melanins (yellow, rust, brown, black); trichosiderin in red hair Gray/white hair: decreased melanin production, increased air bubbles in shaft

Structure of a Hair Flexible strands produced by hair follicles and consist of dead, keratinized cells Hair shaft dictates properties of hair flat = hair is kinky oval = hair is silky, wavy round = hair is straight, course

Hair Follicle Supports the hair Extends down the epidermal surface into the dermis At base (hair bulb) knot of sensory nerves hair follicle receptors papilla contains capillary bed

Figure 5.5a Skin appendages: Structure of a hair and hair follicle. Follicle wall • Peripheral connective tissue (fibrous) sheath • Glassy membrane • Epithelial root sheath • External root sheath • Internal root sheath Hair • Cuticle Hair shaft • Cortex • Medulla Diagram of a cross section of a hair within its follicle Arrector pili Sebaceous gland Hair root Hair bulb © 2013 Pearson Education, Inc.

Figure 5.5c Skin appendages: Structure of a hair and hair follicle. Hair shaft Arrector pili Sebaceous gland Follicle wall Hair root • Peripheral connective tissue (fibrous) sheath Hair bulb • Glassy membrane • Epithelial root sheath • External root sheath • Internal root sheath Hair root • Cuticle • Cortex • Medulla Hair matrix Hair papilla Melanocyte Subcutaneous adipose tissue Diagram of a longitudinal view of the expanded hair bulb of the follicle, which encloses the matrix © 2013 Pearson Education, Inc.

Arrector pili Bundle of smooth muscle Associated with each hair follicle Contraction pulls hair follicle upright and dimples the skin surface goose bumps

Nails Scale-like modifications of epidermis Contain hard keratin Protective cover for distal, dorsal surface of fingers and toes Contain hard keratin Nail matrix at base of nail responsible for its growth

Sweat Glands ~3 million per person Two main types Eccrine (merocrine) sweat glands Apocrine sweat glands

Eccrin Sweat Glands Majority of sweat glands Abundant on palms, soles and forehead Simple, coiled, tubular glands that function in thermoregulation Regulated by sympathetic nervous system Their secretion is sweat (filtrate of the blood) 99% water, salts, vitamin c, antibodies, dermcidin (microbe-killing peptide), metabolic wastes

Figure 5.7a Photomicrograph of a sectioned sebaceous gland (90x). Sweat pore Dermal connective tissue Hair in hair follicle Sebaceous gland duct Eccrine gland Secretory cells Photomicrograph of a sectioned sebaceous gland (90x) © 2013 Pearson Education, Inc.

Apocrine Sweat Glands Roughly 2000 confined to axillary and anogenital areas of body Empty into hair follicles, rather than on the skin (eccrine) Contain sweat, fatty substances and protein with bacterial decomposition = body odor

Apocrine Sweat Glands Begin functioning at puberty possibly the human equivalent to animals’ sexual scent glands sexual foreplay increase their activity do not participate in body cooling (sweat) precise function not known activated by nerve fibers during pain and stress

Modified Apocrine Glands Ceruminous glands lining of external ear canal; secrete cerumen (earwax) Mammary glands secrete milk

Sebaceous Glands Widely distributed Not in thick skin of palms and soles Most develop from hair follicles and secrete into hair follicles Softens hair and skin Stimulated by hormones, especially androgens Secrete sebum consisting of lipids and cell fragments Acts as a bactericidal

Figure 5.7a Photomicrograph of a sectioned sebaceous gland (90x). Sweat pore Dermal connective tissue Hair in hair follicle Sebaceous gland duct Eccrine gland Secretory cells Photomicrograph of a sectioned sebaceous gland (90x) © 2013 Pearson Education, Inc.

Functions of the Skin Protection Body temperature regulation Cutaneous sensation Metabolic functions Blood reservoir Excretion

Protection Three types of barriers Chemical barriers Physical barriers secretions and melanin acid mantle: the low pH of secretion antibiotic properties of secretion Physical barriers only lipid solvents can dissolve through skin Biological barriers innate immunity (macrophages

Body Temperature Regulation Body temperature normal: ~500 ml/day of perspiration Body temperature rises: dilation of dermal vessels and increased sweat gland activity Cold external environment Dermal blood vessels constrict causing warm blood to bypass skin Skin temperature drops to slow passive heat loss

Cutaneous Sensatioin Cutaneous sensory receptors exteroceptors Part of nervous system detect temperature, touch, and pain

Metabolic Functions Fueled by sunlight Synthesis of: Vitamin D precursor Collagenase for collagen turnover Keratinocyte enzymes: Chemical conversion of carcinogens Activate some steroid hormones (cortisone to hydrocortison)

Blood Reservoir Dermal vascular supply can hold up to 5% of body’s blood volume Constriction of dermal blood vessels force blood to where its needed vascular shunts

Excretion Body eliminates some of the nitrogen wastes ammonia, urea, etc. Sweating also increases loss of water and salts that must be constantly added back Major function for liquid secretion is kidneys

Lab Exercise for Today Exercise 7