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

Chapter 4

Guiding Question: What are the components 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

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?

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

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

 What are the three major layers of the skin?  Describe the basic characteristics of the three major layers of the skin (recommend a chart)

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

 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)

 Statum germinativum / basale Cells undergoing mitosis, move up and horizontally Contains malpighian layer or “Pigment layer” with melanosomes Forms epidermal ridges

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

 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

Second layer of the skin

 Collagen, elastin fibers– scattered

 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

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

Third layer of the skin

 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