September 17 th Friday

1. September 17th Friday • Objective: Know the components of the skin • Homework: Read p. 138-141 (Skin Structure) • Agenda: • Hand out article • PPT • Sun block lab

2. The Integumentary System Chapter 4

3. Overview of the Integumentary System Guiding Question: What are the components of the integumentary system?

4. Overview of the Integumentary System • Not just a covering for the body • Largest organ • Blood vessels, connective tissue structures, glands, hair, nails, nerves, skin • Plays a large role in homeostasis • Has inherent and adaptive characteristics • Calluses • Darken in sun • Elasticity • Sensitive to moisture

5. The Integumentary System Guiding Questions: 1.) What embryonic layers form the integumentary system? 2.) Describe the development of the integumentary system. 3.) What are some various causes of hair loss?

6. 4-5 weeks: outermost layer of skin form a simple squamous tissue that becomes stratified as the embryo develops from the ectoderm • In some areas forms nervous tissue that later becomes integrated into the skin structure. • 6-7 weeks: deeper parts of skin begin to form from mesoderm. • 8-9 wks: mesenchyme begins to mature and fibroblasts form, and dents occur in the upper squamous layer—form lanugo. • 10 weeks: ridges form between the outer and inner layers of skin—so don’t separate when rubbed • 11 weeks: small nails at the tips of fingers & toes, followed by development of special blood vessels in the layers of skin • Angiogenic factors stimulate the production of these vessels • 20 weeks: Glandular structures form • Inward growths of the outermost squamous cell layer • Will eventually produce oils and sweat • 25 weeks: Pigmentation • About 26 weeks: melanoblasts mature into melanocytes, and nervous tissue structures develop

7. Development of the Integumentary System Ectoderm & mesoderm in origin Skin is a complex structure Many things can go wrong in its development Let’s make a timeline!

8. Skin Structure

9. Skin Structure Guiding ?’s: • What are the three major layers of the skin? • Describe the basic characteristics of the three major layers of the skin (recommend a chart)

10. Skin: Structure – 3 layers 1. Epidermis: Epithelial • Superficial & thinnest • cells are very tightly packed • New cells produced here 2. Dermis: Connective • Deep to epidermis & thick • Primarily connective tissue • loosely packed cells 3. Subcutaneous/Hypodermis (adipose tissue) • Deep to the skin/dermis • Layer of insulation

11. Diagrammatic vs. Histological view

12. Epidermis • Outermost: Stratum corneum • Dry, dead, • keratin filled (waterproof, tough) • Stratum Granulosum • Waterproof • Contains granules of keratin • Stratum Spinosum • “Prickly” layer • Contains Langerhans cells (fight infections)

13. Statumgerminativum / basale • Cells undergoing mitosis, move up and horizontally • Contains malpighian layer or “Pigment layer” with melanosomes • Forms epidermal ridges

15. Stratum corneum: Dead squamous cells Stratum lucidum: (only in thick skin); oils from lysosome disintegration Stratum granulosum: Granules with lipids and keratin – forms waterproof layer Stratum Spinosum: cuboidalcells, desmosomes hold together >> spiny Stratum Germanitivum/ Basale: dividing columnar cells

16. Epidermis • Specialized cells within epidermis: • Melanocytes • Melanin: pigment, inc. w/sun (protection) • Keratinocytes • Keratin: tough, waterproof material • Abrasion resistance for cells • Langerhans cells • Immune response against microbes invading the skin

17. Dermis Second layer of the skin

18. Dermis • Collagen, elastin fibers– scattered

19. Dermal Connective tissue • Dense, irregular connective tissue • Loose, connective tissue = areolar connective tissue • Binds blood vessels, membranes, muscles, nerves, and skin to other structures • Contains extensive meshwork of protein fibers (fibroblasts) • Involved primarily in body growth • Connective tissue maintenance • Wound healing

20. Dermal-epidermal junction Dermal papillae: parallel rows of peg-like projections • Unique to each individual; akin to fingerprints

21. Subcutaneous Layer Third layer of the skin

22. Subcutaneous layer • Third, innermost layer of the skin • Thickness, composition vary throughout body • Composed of loosely-arranged elastic fibers that anchor the skin to the fascia • Sheet of fibrous connective tissue • Covers muscles, skull bones, some organs • Large amount of adipose (fat) cells • Large network of blood vessels, capillaries, lymphatic vessels

23. Skin Appendages Glands Nerves Nails Hair

24. Glands • 3 Types: • Ceruminous • Sebaceous • Sweat

25. Ceruminous Produce cerumen (waxy secretion), an apocrine secretion (ear wax) Found lining ear canal

26. Sebaceous Holocrineglands (secrete whole dead cells) Produce, store abundance of fat, which burst and die, releasing sebum

27. Specialized Structures of the Dermis • Sebaceous Glands • Secrete oil (sebum) for hair/skin • Ducts open into hair follicles • Accumulated sebum enlarges ducts>>white heads • Darkened sebum>>black head

28. Specialized Structures of Dermis • Sudoriferous Glands • Eccrine Glands • Widespread • Watery Fluid • Apocrine Glands • Armpits/Genitals • Thick/milky fluid

29. Sweat • Aprocrine • Odorous, sweat-like material in armpits, navel, groin region, areolae • Inactive until puberty • Contain phermones • Broken down by bacteria, creating odor • Eccrine • Skin of armpits, foreheads, palms, soles • Mostly secrete water, w/ salts, organic compounds, and wastes (like urea) • Microbes feed on these as well, producing odors

31. Nerves • Sensory receptors • Communicate information from environment to the body • Found in all skin layers • Mostly in innermost regions, fascia • Free nerve endings • Pain-sensing structures • Found throughout inner part of epidermis • Detect chemicals associated with tissue damage and bleeding

33. Encapsulated receptors • Merkel cells • Sensitive to gentle physical sensation • Found in stratum germinativum • Abundant in fingertips

34. Meissner’s (tactile) corpuscles • Elongated, club-shaped pile of connective tissue • Upper region of dermis (in dermal papilla) • Respond to touch

35. Pacinian (lamellated) corpuscle Look like onions Deeper parts of hypodermis Hard pressure, vibrations

36. Ruffini receptors • Pressure, constant touch

37. Krause end bulbs • Sensitive touch receptors • Found mostly in mucous membrane of mouth

38. Nails • Merely a keratin secretion • Nail root • Lies beneath skin-nail fold • Grow back as long as nail root and skin-nail fold are not severely damaged • Grow 1/8 in per month

39. Dermis • Specialized structures: • Hair follicle: cells of the epidermis extend into the dermis forming a small tube • Hair bulb: base of the follicle • Hair papilla: cluster of cells (live); nourished by BV’s • Root: part of hair hidden in follicle • Shaft: visible part of hair

40. Hair Modified stratum corneum Grows from an individual follicle buried in subcutaneous layer

43. Dermis • Specialized Structures (continued) • Arrector pili: tiny, smooth muscle attached to base of dermal papillae & side of hair follicle • Contracts: pulls on both simultaneously>>goosebumps