Integumentary System: Skin and adnexa

1. Integumentary System:Skin and adnexa Lecture 4 Tuesday, January 23, 2007 Refs. Ross and Pawlina Histology Chapter 15, Wheater’s Functional Histology Chapter 9 diFiore Atlas of Human Histology Medical Physiology p. 572, 352, 1231-7

2. Skin • Functions • Protection • Mechanical, dehydration, UV radiation • Immune system (innate and APC cells) • Largest sensory organ • Thermoregulation • Metabolism • Vitamin D synthesis • Adipose tissue

3. 3 Layers of the skin • Epidermis • Keratinizing stratified squamous epithelium • Self renewing, avascular • Dermis • Supporting and nourishing layer • Collagen, elastic fibers, vessels and nerves • Hypodermis or subcutis • Loose CT, adipose cells, variable thickness

4. Thin skin, full thickness diFiore Plate 46Trichrome stain, low magnification

5. Epidermal-dermal junction • Epidermal ridges (rete ridges) interdigitate with dermal papillae • Superficial dermis = papillary dermis • Fine collagen and elastic fibers • Vascular plexus • Deep dermis = reticular dermis • Thick collagen and elastic fibers • Larger vessels

6. Regional variations • Thick skin • Palmar and plantar surfaces (glabrous=hairless) • Epidermis is relatively thicker, keratinized layer is very thick, rete ridges more prominent • Thin skin • Most of body--especially eyelids and periorbital skin • Hair in thin skin is fine. • Scalp skin • Restricted to head • More numerous and larger hair follicles

7. Upper panel: thin skin (x 123) WFH 9.3 and lower panel thick skin (x104) WFH 9.2 H&E .

8. Epidermis • 4 layers from dermis to surface • Stratum basale • Germinal layer • Stratum spinosum • Stratum granulosum- keratohyalin granules • Stratum corneum • Keratinocytes= name for epithelial cells in skin • Do not confuse with keratocyte in the cornea. • Basal to desquamation - 25-50 days

9. Epidermis Trichrome stain, 600x WFH 9.4a

10. Stratum basale H&E stain, 1000x WFH 9.4b

11. Stratum spinosum toluidine blue, 1200x WFH 9.4c

12. Stratum spinosum EM, 5000x WFH 9.6a

13. Stratum spinosum EM, 25,000x WFH 9.6bD=desmosomeK=keratinocyte

14. Stratum granulosum EM, 5000x WFH 9.6cK= keratohyaline granules

15. Dermal-epidermal junction, EM 24000x WFH 9.5bHD= hemidesmosome3 zones of basement membraneL=lamina lucidaD=lamina densaF= fibroreticular lamina

16. Other cells in the epidermis • Melanocytes • Synthesize and release melanin • Premelanosome-melanosome • Langerhans cells • APC, Birbeck granules • Merkel cells • Touch receptors in basal layer

17. Melanocyte, premelanosome WFH 9.7 a,b

18. Langerhans cells and EM of Birbeck granules in cytoplasm of Langerhans cell.WFH 9.7c,d

19. Adnexa • Also referred to as skin appendages • Derived embryologically from epidermis • Hair follicles • Sweat glands • Merocrine-open onto surface • Apocrine-open into hair follicles • Sebaceous glands-open into hair follicles

20. Schematic of skin WFH 9.9

21. Hair follicle, longitudinal section WFH 9.11

22. Hair follicles • Longitudinal segments • Infundibulum--segment from the skin surface to the level of sebaceous ducts. • Isthmus--segment from sebaceous ducts to insertion of arrector pili muscle. • inferior segment-- ends in expanded hair bulb • Dermal papilla--tuft of connective tissue that invaginates the base of the bulb. • Matrix cells-- cells that surround the dermal papilla and proliferate generating hair.

23. Concentric layers of the hair and follicle • Medulla (often not present in fine hair) • Cortex- thick , highly keratinized layer • Cuticle-thin, hard, keratinized layer • Internal root sheath • External root sheath • Glassy membrane--thick basement membrane

24. Hair: types and growth • Hair thickness varies. • Vellus = fine hair • Terminal is coarse as in scalp hair. • Phases of hair growth: • Growing phase is anagen • Period in which growth stops is catagen • Resting phase is telogen • Follicles are shorter. • Hair bulb is smaller and lacks dermal papilla.

25. Hair follicle (transverse section) WFH 9.12

26. Pilosebaceous unit WFH 9.14aM= arrector pili musclesympathetic innervation

27. Hair follicle and sebaceous gland WFH 9.14b

28. Merocrine sweat gland WFH 9.15aSympathetic innervation:Cholinergic fibers

29. Merocrine sweat glands and ducts WFH 9.15b

30. Apocrine sweat gland WFH 9.16Misnomer- secretion is not apocrine.Sympathetic innervation byadrenergic fibers

31. Fingernail WFH 9.17

32. Skin circulation schematic WFH 9.18

33. Thermoregulation • Body core temperature remains almost constant. • Increase in body core temperature causes: • Vasodilation of dermal vessels and increased heat loss from skin. • Evaporation of sweat from surface increases heat loss. • Two types of skin in terms of thermoregulation: apical and nonapical: • Apical skin (nose, ears, fingers and toes) has many glomus bodies; has significant sympathetic tone • Nonapical skin has few, if any, glomus bodies; vessels respond mainly to local mediators.

34. Glomus body WFH 9.19

35. Control of blood flow in apical and nonapical skin MP 23.8

36. Summary of sensory receptors in the skin MP 13-23

37. Skin is the largest sensory organ • Mechanoreceptors • Meissner’s corpuscles in the epidermal ridges • Ruffini’s corpuscles • Pacini’s corpuscles are deep (subcutis) • Merkel’s cells/disks at junction of epidermis and dermis • Krause end bulbs • Chemoreceptors • Nociceptors respond to painful stimuli • Temperature receptors in skin • Respond to local heat by vasodilation or cold by vasoconstriction. • Send message about environment to hypothalamus-anticipatory feedback.