The Integumentary System: Structure and Functions

1. 5 The Integumentary System Pages 101-108, 110-116

2. The Skin and the Hypodermis • Skin—our largest organ • Accounts for 7% of body weight • Varies in thickness from 1.5–4.4mm • Divided into two distinct layers • Epidermis • Dermis • Hypodermis—lies deep to the dermis

3. Skin Structure Hair shaft Dermal papillae Epidermis Subpapillary vascular plexus Papillary layer Pore Appendages of skin Dermis Eccrine sweat gland Reticular layer Arrector pili muscle Sebaceous (oil) gland Hair follicle Hair root Hypodermis (superficial fascia) Nervous structures Sensory nerve fiber Dermal vascular plexus Lamellar (Pacinian) corpuscle Adipose tissue Hair follicle receptor (root hair plexus) Figure 5.1

4. Figure 5.2 Gross structure of skin and underlying tissues. Epidermis Dermis Hypodermis Deep fascia Muscle

5. The Skin and Hypodermis • Functions • Protection—cushions organs and protects from bumps, chemicals, water loss, UV radiation • Regulation of body temperature • Excretion—urea, salts, and water lost through sweat

6. The Skin and Hypodermis • Functions (continued) • Production of vitamin D • Sensory reception—keeps us aware of conditions at the body’s surface

7. Epidermis • Contains four main cell types • Keratinocytes • Produce keratin a fibrous protein • Melanocytes • Location—basal layer; manufacture and secrete pigment

8. Epidermis • Contains four main cell types (continued) • Tactile epithelial cells • Location—basal layer; attached to sensory nerve endings • Dendritic cells • Location—stratum spinosum; part of immune system; macrophage-like

9. Epidermis • Keratinocytes—most abundant cell type in epidermis • Arise from deepest layer of epidermis • Produce keratin, a tough fibrous protein • Produce antibodies and enzymes • Keratinocytes are dead at skin's surface

10. Layers of the Epidermis • Stratum basale (stratum germinativum) • Stratum spinosum • Stratum granulosum • Stratum lucidum (only in thick skin) • Stratum corneum

11. Figure 5.3a Epidermal cells and layers of the epidermis. Stratum corneum Most superficial layer; 20–30layers of dead cells representedonly by flat membranous sacsfilled with keratin. Glycolipids inextracellular space. Stratum granulosum One to five layers of flattenedcells, organelles deteriorating;cytoplasm full of lamellargranules (release lipids) andkeratohyaline granules. Stratum spinosum Several layers of keratinocytesunified by desmosomes. Cellscontain thick bundles ofintermediate filaments madeof pre-keratin. Desmosomes Stratum basale Deepest epidermal layer; one rowof actively mitotic stem cells;some newly formed cells becomepart of the more superficiallayers. See occasionalmelanocytes and dendritic cells. Dermis

12. Figure 5.3b Epidermal cells and layers of the epidermis. Stratum corneum Keratinocytes Most superficial layer; 20–30layers of dead cells representedonly by flat membranous sacsfilled with keratin. Glycolipids inextracellular space. Stratum granulosum One to five layers of flattenedcells, organelles deteriorating;cytoplasm full of lamellargranules (release lipids) andkeratohyaline granules. Stratum spinosum Several layers of keratinocytesunified by desmosomes. Cellscontain thick bundles ofintermediate filaments madeof pre-keratin. Desmosomes Stratum basale Deepest epidermal layer; one rowof actively mitotic stem cells;some newly formed cells becomepart of the more superficiallayers. See occasionalmelanocytes and dendritic cells. Dermis Dendritic cell Sensorynerveending Melanocyte Melaningranule Tactileepithelial cell

13. Layers of the Epidermis • Stratum basale • Deepest layer of epidermis • Attached to underlying dermis • Cells actively divide • Stratum basale contains • Merkel cells—associated with sensory nerve ending • Melanocytes—secrete the pigment melanin

14. Layers of the Epidermis • Stratum spinosum (spiny layer) • “Spiny” appearance caused by: • Artifacts of histological preparation • Contains thick bundles of intermediate filaments (tonofilaments) • Resist tension • Contain protein prekeratin • Contains star-shaped dendritic cells • A type of macrophage • Function in immune system

15. Figure 5.3b Epidermal cells and layers of the epidermis. Stratum corneum Keratinocytes Most superficial layer; 20–30layers of dead cells representedonly by flat membranous sacsfilled with keratin. Glycolipids inextracellular space. Stratum granulosum One to five layers of flattenedcells, organelles deteriorating;cytoplasm full of lamellargranules (release lipids) andkeratohyaline granules. Stratum spinosum Several layers of keratinocytesunified by desmosomes. Cellscontain thick bundles ofintermediate filaments madeof pre-keratin. Desmosomes Stratum basale Deepest epidermal layer; one rowof actively mitotic stem cells;some newly formed cells becomepart of the more superficiallayers. See occasionalmelanocytes and dendritic cells. Dermis Dendritic cell Sensorynerveending Melanocyte Melaningranule Tactileepithelial cell

16. Layers of the Epidermis • Stratum granulosum • Consists of keratinocytes and tonofilaments • Tonofilaments contain: • Keratohyaline granules—help form keratin • Lamellated granules—contain a waterproofing glycolipid

17. Figure 5.3b Epidermal cells and layers of the epidermis. Stratum corneum Keratinocytes Most superficial layer; 20–30layers of dead cells representedonly by flat membranous sacsfilled with keratin. Glycolipids inextracellular space. Stratum granulosum One to five layers of flattenedcells, organelles deteriorating;cytoplasm full of lamellargranules (release lipids) andkeratohyaline granules. Stratum spinosum Several layers of keratinocytesunified by desmosomes. Cellscontain thick bundles ofintermediate filaments madeof pre-keratin. Desmosomes Stratum basale Deepest epidermal layer; one rowof actively mitotic stem cells;some newly formed cells becomepart of the more superficiallayers. See occasionalmelanocytes and dendritic cells. Dermis Dendritic cell Sensorynerveending Melanocyte Melaningranule Tactileepithelial cell

18. Layers of the Epidermis • Stratum lucidum (clear layer) • Occurs only in thick skin • Locations of thick skin—palms and soles • Composed of a few rows of flat, dead keratinocytes

19. Figure 5.4 Thick skin. Epidermis Stratum corneum Stratum lucidum Stratum granulosum Stratum spinosum Dermis Stratum basale Papillarydermis Dermalpapilla Reticulardermis Collagenfibers

20. Layers of the Epidermis • Stratum corneum (horny layer) • Thick layer of dead keratinocytes and thickened plasma membranes • Protects skin against abrasion and penetration

21. Dermis • Second major layer of the skin • Strong, flexible connective tissue • Richly supplied with blood vessels and nerves • Has two layers • Papillary layer—includes dermal papillae • Reticular layer • Deeper layer—80% of thickness of dermis

22. Figure 5.4 Thick skin. Epidermis Stratum corneum Stratum lucidum Stratum granulosum Stratum spinosum Dermis Stratum basale Papillarydermis Dermalpapilla Reticulardermis Collagenfibers

23. The Two Regions of the Dermis Dermis (b) Papillary layer of dermis, SEM (570) (a) Light micrograph of thick skin identifying the extent of the dermis, (100) (c) Reticular layer of dermis, SEM (430)

24. Hypodermis • Deep to the skin—also called superficial fascia • Contains areolar and adipose CT • Anchors skin to underlying structures • Helps insulate the body

25. Hair shaft Dermal papillae Epidermis Subpapillary vascular plexus Papillary layer Pore Appendages of skin Dermis Eccrine sweat gland Reticular layer Arrector pili muscle Sebaceous (oil) gland Hair follicle Hair root Hypodermis (superficial fascia) Nervous structures Sensory nerve fiber Dermal vascular plexus Lamellar (Pacinian) corpuscle Adipose tissue Hair follicle receptor (root hair plexus) Figure 5.1

26. Nails • Nails—scalelike modification of epidermis • Made of hard keratin • Parts of the nail • Free edge • Body • Root • Nail folds • Eponychium—cuticle

27. Structure of a Nail Lunule Lateral nail fold (a) Free edge of nail Body of nail Eponychium (cuticle) Root of nail Proximal nail fold Nail matrix (b) Nail bed Phalanx (bone of fingertip) Figure 5.6

28. Appendages of the Skin • Hair • Flexible strand of dead, keratinized cells • Hard keratin—tough and durable • Chief parts of a hair • Root—imbedded in the skin • Shaft—projects above skin's surface

29. Appendages of the Skin • Hair has three concentric layers of keratinized cells • Medulla—central core • Cortex—surrounds medulla • Cuticle—outermost layer

30. Figure 5.7a Structure of a hair and hair follicle. Hair shaft Arrector pili Sebaceousgland Follicle wall Peripheral connectivetissue (fibrous) sheath Hair root Glassy membrane Hair bulb Epithelial root sheath External root sheath Internal root sheath Hair Cuticle Cortex Medulla Diagram of a cross section of ahair within its follicle

31. Figure 5.7c Structure of a hair and hair follicle. Hair shaft Follicle wall Peripheral connective tissue (fibrous) sheath Glassy membrane Arrector pili Epithelial root sheath External root sheath Sebaceousgland Internal root sheath Hair root Hair root Cuticle Cortex Hair bulb Medulla Hair matrix Dermal papilla Melanocyte Subcutaneous adipose tissue Diagram of a longitudinal view of the expanded hairbulb of the follicle, which encloses the matrix

32. Appendages of the Skin • Hair follicles • Extend from epidermis into dermis • Hair bulb • Deep, expanded end of the hair follicle • Root plexus • Knot of sensory nerves around hair bulb

33. Skin Structure Hair shaft Dermal papillae Epidermis Subpapillary vascular plexus Papillary layer Pore Appendages of skin Dermis Eccrine sweat gland Reticular layer Arrector pili muscle Sebaceous (oil) gland Hair follicle Hair root Hypodermis (superficial fascia) Nervous structures Sensory nerve fiber Dermal vascular plexus Lamellar (Pacinian) corpuscle Adipose tissue Hair follicle receptor (root hair plexus) Figure 5.1

34. Appendages of the Skin • Arrector pili muscle • Bundle of smooth muscle • Hair stands erect when arrector pili contracts

35. Sebaceous Glands • Occur over entire body • Except palms and soles • Secrete sebum—an oily substance • Most associated with a hair follicle • Functions of sebum • Collects dirt; softens and lubricates hair and skin

36. Figure 5.8a Skin glands. Sweatpore Sebaceousgland Sebaceousgland duct Dermalconnectivetissue Hair inhair follicle Eccrinegland Secretory cells Photomicrograph of asectioned sebaceousgland (90)

37. Sweat Glands • Sweat glands (sudoriferous glands) widely distributed on body • Sweat—is a blood filtrate • 99% water with some salts • Contains traces of metabolic wastes • About 2% urea

38. Figure 5.8b Skin glands. Sweatpore Sebaceousgland Eccrinegland Duct Dermalconnective tissue Secretory cells Photomicrograph of a sectioned eccrinegland (140)

39. Sweat Glands • Two types of sweat gland • Eccrine gland • Most numerous—these produce true sweat • Apocrine gland • Confined to axillary, anal, and genital areas • Produce a special kind of sweat

40. Figure 5.1 Skin structure. Hair shaft Dermal papillae Epidermis Subpapillary vascularplexus Papillarydermis Sweat pore Appendages of skin Dermis Eccrine sweat gland Reticulardermis Arrector pili muscle Sebaceous (oil) gland Hair follicle Hair root Hypodermis(superficial fascia) Nervous structures Sensory nerve fiberwith free nerve endings Dermal vascular plexus Lamellar corpuscle Adipose tissue Hair follicle receptor(root hair plexus)