Skin & The Integumentary System Chapter 6 Learning Targets: By the end of this lecture, you should be able to: List functions of skin. Describe the various layers of the skin. Explain the physiology behind skin and hair color. List and describe the various accessory organs of the skin. Hypertrichosis https://www.youtube.com/watch?v=7WDyMW0LN2g

The Skin Organs are body structures composed of two or more different tissues. The skin and its accessory organs make up the integumentary system. Skin is also known as the cutaneous membrane Cutis – skin in Latin Cutaneous – anything relating to the skin

SHAPES The Skin Sensation (housing sensory receptors) Functions of the skin include: Sensation (housing sensory receptors) Heat regulation (maintains homeostasis) Absorption (certain chemicals/ medications) Protecting underlying tissues Excreting wastes Synthesizing certain chemicals & vitamins

Skin Layers The skin consists of: Epidermis Dermis Epithelial tissue Dermis Connective tissue Smooth muscle tissue Nervous tissue Blood Subcutaneous layer (hypodermis) Loose connective tissue Adipose Tissue

Epidermis Lacks blood vessels As cells divide and grow, older cells are pushed away from the dermis Farther the cells move, poorer their nutrient supply becomes, and in time, they die and are shed In humans, it is thinnest on the eyelids at 0.05 mm (0.0020 in) and thickest on the palms and soles at 1.5 mm (0.059 in).

Epidermis Keratinization - cytoplasm of older cells fills with keratin protein (tough and waterproof) as they move to the outer layers Normally, production of epidermal cells is balanced with the loss of dead cells (so skin doesn’t wear away) Where skin is rubbed or pressed regularly, cell division increases… causes calluses Life span of a typical epidermal cell is about 2-4 weeks

Skin Color Melanocytes - specialized cells in epidermis produce melanin Melanin - a dark pigment that absorbs UV radiation & prevents mutations in DNA of skin cells Melanin is produced because of UV light exposure Melanocytes found in deepest portion of epidermis, cellular extensions pass between epidermal cells

Skin Color Largely due to melanin All people have the same number of melanocytes Differences result from amount of melanin produced and size of pigment granules

Skin Color More pigment located near equator to protect from UV radiation More pigment near the equator to protect from UV radiation which damages B-vitamin, folate, needed for DNA synthesis and cell division. Less pigment away from the equator needed to help our bodies make more vitamin D for health and reproduction.

Tanning As your body is exposed to UV light, your melanocytes produce more melanin to block the UV light. The melanin moves outside of the melanocytes to protect you, tanning your skin or making it freckle in the process.

Tanning Sunburn results when your skin cannot produce melanin quickly enough to prevent UV rays from injuring blood vessels near kin’s surface

Melanoma Most deadly type of skin cancer Uncontrolled production of melanocytes Usually starts on or near a mole For women, most common on legs; for males, on the back Click image for 4 min video

Melanoma

Dermis Boundary with epidermis is uneven because epidermal ridges project internally Dermal papillae then extend into spaces Fingerprints - determined by genes and changes slightly as fetus moves during pregnancy (so identical twins usually don’t have exact same fingerprints)

Dermis Composed of dense connective tissue with fibers that give the skin toughness and elasticity Dermal blood vessels supply nutrients to all skin cells and help regulate body temperature Nerve cells and sensory receptors also present Hair follicles, sebaceous (oil-producing), and sweat glands also present

How do tattoos work? Ink is injected into dermis Tattoo visible through epidermis Tattoo wouldn’t work on epidermis because it would shed quickly Click image for 1 min video

Dermal Growth & Repair Dermis doesn’t shed like epidermis It can regenerate when injured Starts to produce new tissue (has different texture and quality than surrounding tissue) Will become a scar Stretch marks are caused by rapid growth and tearing of elastic tissue; causes scarring

Subcutaneous Layer (Hypodermis) Binds skin to underlying organs No sharp boundary between dermis and hypodermis Adipose tissue for insulation Blood vessels supply nutrients

Accessory Organs of the Skin Nails Protective coverings on ends of digits The whitish, thickened, half-moon shaped region (lunula) covers the most actively growing region Cells here divide and become keratinized; pushes nail plate forward Thumbnail grows slowest; middle nail fastest Nails & Hair are dead cells filled with keratin Hair pigment = melanin Both nails & hair are derived from epidermal cells

Accessory Organs of the Skin Hair Present on all skin surfaces except palms, soles, lips, nipples and parts of external reproductive organs Each hair develops from a group of epidermal cells called hair follicles As the epidermal cells divide and grow, older cells are pushed up These cells become keratinized and die (remains are hair) Hair= dead epidermal cells Nails & Hair are dead cells filled with keratin Hair pigment = melanin Both nails & hair are derived from epidermal cells

Hair A bundle of smooth muscle cells attaches to each hair follicle  called the arrector pili muscle The muscle is positioned so that a short hair w/in the follicle stands on end when the muscle contracts If person is emotionally upset or cold, nerve impulses may stimulate the arrector pili muscles to contract, causing goose bumps Nails & Hair are dead cells filled with keratin Hair pigment = melanin Both nails & hair are derived from epidermal cells

The Origin of Hair Humans have as many hair follicles per square inch of skin as a chimpanzee All of the 5 million hair follicles form during the 5th month of prenatal development Perhaps humans evolved to have less hair for hunting(could run for longer times); perhaps to avoid parasites. Click for video on Hypertrichosis..6 min

Hair Color Genes determine hair color by directing amount of pigment melanocytes produce A lot of melanin= darker hair No melanin= white

Accessory Organs of the Skin Sebaceous Glands Associated with hair follicles Secrete sebum to keep hair and skin soft, pliable and waterproof Sweat Glands Lined with sweat- secreting epithelial cells

Sweat Glands Eccrine Glands Apocrine Glands Modified sweat glands Most numerous Forehead, neck, back Produce sweat Water, Salt and Waste (Urea and Uric Acid) Apocrine Glands Responsible for natural body odor Become active at puberty Axillary regions and groin Usually connect to hair follicles Modified sweat glands Mammary glands secrete milk Ceruminous glands secrete ear wax T-shirt mate selection video ~3min - pbs Click image for t-shirt mate selection video—3 min