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

2. Chapter 4

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

4.  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. 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.  Ectoderm & mesoderm in origin  Skin is a complex structure  Many things can go wrong in its development  Let’s make a timeline!

9.  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. 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

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

16.  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. Second layer of the skin

18.  Collagen, elastin fibers– scattered

19.  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 papillae: parallel rows of peg-like projections Unique to each individual; akin to fingerprints

21. Third layer of the skin

22.  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.  Glands  Nerves  Nails  Hair

24.  3 Types: Ceruminous Sebaceous Sweat

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

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

27.  Sebaceous Glands Secrete oil (sebum) for hair/skin Ducts open into hair follicles Accumulated sebum enlarges ducts>>white heads Darkened sebum>>black head

28.  Sudoriferous Glands Eccrine Glands  Widespread  Watery Fluid Apocrine Glands  Armpits/Genitals  Thick/milky fluid

29.  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.  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.  Merkel cells Sensitive to gentle physical sensation Found in stratum germinativum Abundant in fingertips

34.  Elongated, club-shaped pile of connective tissue  Upper region of dermis (in dermal papilla)  Respond to touch

35.  Look like onions  Deeper parts of hypodermis  Hard pressure, vibrations

36.  Pressure, constant touch

37.  Sensitive touch receptors  Found mostly in mucous membrane of mouth

38.  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.  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.  Modified stratum corneum  Grows from an individual follicle buried in subcutaneous layer

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