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

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

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

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

4 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

5 © 2013 Pearson Education, Inc. Figure 5.1 Skin structure. Hair shaft Epidermis Papillary layer Dermis Reticular layer Hypodermis (subcutaneous tissue; not part of skin) Dermal papillae Subpapillary plexus Sweat pore Cutaneous plexus Adipose tissue Nervous structures Sensory nerve fiber with free nerve endings Lamellar corpuscle Hair follicle receptor (root hair plexus) Appendages of skin Eccrine sweat gland Arrector pili muscle Sebaceous (oil) gland Hair follicle Hair root

6 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

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

8 Cells of Epidermis Keratinocytes – 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

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

10 © 2013 Pearson Education, Inc. Figure 5.2a The main structural features of the skin epidermis. Dermis Stratum spinosum Several layers of keratinocytes unified by desmosomes. Stratum basale Deepest epidermal layer; one row of actively mitotic stem cells Stratum granulosum Typically five layers of flattened cells, organelles deteriorating; Stratum corneum Most superficial layer; 20–30 layers of dead cells Flat membranous sacs filled with keratin.

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

12 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

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

14 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

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

16 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

17 © 2013 Pearson Education, Inc. Stratum spinosum Several layers of keratinocytes unified by desmosomes. Cells contain thick bundles of intermediate filaments made of pre-keratin. 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. Melanocyte Dendritic cell Keratinocytes Stratum corneum Most superficial layer; 20–30 layers of dead cells, essentially flat membranous sacs filled with keratin. Glycolipids in extracellular space. Dermis Melanin granule Sensory nerve ending Tactile (Merkel) cell Desmosomes Stratum granulosum Typically five layers of flattened cells, organelles deteriorating; cytoplasm full of lamellar granules (release lipids) and keratohyaline granules. Figure 5.2b The main structural features of the skin epidermis.

18 Keratinocytes and Melanocyte Network

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

20 Dermis Strong, flexible connective tissue (proper) – 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

21 © 2013 Pearson Education, Inc. Figure 5.1 Skin structure. Hair shaft Epidermis Papillary layer Dermis Reticular layer Hypodermis (subcutaneous tissue; not part of skin) Dermal papillae Subpapillary plexus Sweat pore Cutaneous plexus Adipose tissue Nervous structures Sensory nerve fiber with free nerve endings Lamellar corpuscle Hair follicle receptor (root hair plexus) Appendages of skin Eccrine sweat gland Arrector pili muscle Sebaceous (oil) gland Hair follicle Hair root

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

23 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

24 © 2013 Pearson Education, Inc. Figure 5.4a Dermal modifications result in characteristic skin markings. Openings of sweat gland ducts Friction ridges Friction ridges of fingertip (SEM 12x)

25 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

26 Reticular Layers form Cleavage Lines 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

27 © 2013 Pearson Education, Inc. Figure 5.4b Dermal modifications result in characteristic skin markings. Cleavage lines in the reticular dermis

28 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

29 © 2013 Pearson Education, Inc. Figure 5.4c Dermal modifications result in characteristic skin markings. Flexure lines of the hand Flexure lines on the palm Flexure lines on digit

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

31 Melanin Two forms – 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

32 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

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

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

35 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

36 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

37 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

38 © 2013 Pearson Education, Inc. Follicle wall Peripheral connective tissue (fibrous) sheath Glassy membrane Epithelial root sheath External root sheath Internal root sheath Hair Cuticle Cortex Medulla Diagram of a cross section of a hair within its follicle Hair shaft Arrector pili Hair root Hair bulb Sebaceous gland Figure 5.5a Skin appendages: Structure of a hair and hair follicle.

39 © 2013 Pearson Education, Inc. Figure 5.5c Skin appendages: Structure of a hair and hair follicle. Follicle wall Peripheral connective tissue (fibrous) sheath Glassy membrane 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 Epithelial root sheath External root sheath Internal root sheath Hair shaft Arrector pili Hair root Hair bulb Sebaceous gland

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

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

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

43 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

44 © 2013 Pearson Education, Inc. Figure 5.7a Photomicrograph of a sectioned sebaceous gland (90x). Dermal connective tissue Hair in hair follicle Sebaceous gland duct Sebaceous gland Eccrine gland Photomicrograph of a sectioned sebaceous gland (90x) Secretory cells Sweat pore

45 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

46 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

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

48 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

49 © 2013 Pearson Education, Inc. Figure 5.7a Photomicrograph of a sectioned sebaceous gland (90x). Dermal connective tissue Hair in hair follicle Sebaceous gland duct Sebaceous gland Eccrine gland Photomicrograph of a sectioned sebaceous gland (90x) Secretory cells Sweat pore

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

51 Protection Three types of barriers Chemical 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

52 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

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

54 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)

55 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

56 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

57 Lab Exercise for Today Exercise 7


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