Integumentary System

1. Integumentary System

2. Structure of the Skin • Epidermis • The surface layer of the skin • Lacks blood vessels in the outermost layers • The deepest layer, the stratum germinativum, is the only living layer of cells • As these cells divide, daughter cells are constantly pushed to the surface as they develop large amounts of keratin • These cells also produce melanin, a dark pigment that protects skin cells from damage by ultraviolet radiation; irregular patches of melanin are called freckles • As the daughter cells reach the surface, they become flattened and form the uppermost layer of the epidermis called the stratum corneum

3. Dermis • Also called the corium • Has a framework of elastic connective tissue and is supplied with blood vessels and nerves • Because of its elasticity, skin can stretch with little damage • Most of the appendages of the skin: hair, sweat glands, oil glands, are located in the dermis and may extend into the subcutaneous layer under the skin • Dermal thickness varies by location with thicker areas found in the soles of the feet and palms of the hands • Portions of the dermis that extend upward into the epidermis form extensions called papillae which produce the distinct patterns of ridges on the surface of thick skin to help prevent slipping

4. Subcutaneous layer • Sometimes called the hypodermis or the superficial fascia • Connects the skin to the surface muscles • Consists of loose connective tissue and large amounts of adipose tissue which serves as insulation and as a reserve supply of energy • Continuous bundles of elastic fibers connect the subcutaneous tissue with the dermis • Blood vessels that supply the skin and help to regulate body temperature run through this layer • It is thickest on the abdomen

5. The Skin

6. Appendages of the Skin • Sweat glands • Also known as the sudoriferous glands • Are coiled, tube-like structures located in the dermis and the subcutaneous layer • Each gland has an excretory tube that extends to the surface and opens at a pore • Function to regulate body temperature through evaporation • Another type of sweat gland is located mainly in the armpits and the groin area. These glands secrete cellular materials that are broken down by bacteria producing body odor. • Modified sweat glands called ceruminous glands produce earwax and other ciliary glands are located at the edges of the eyelids. Mammary glands produce breast milk in females.

7. Sebaceous glands • Sac-like structures that secrete sebum (oil) • Sebum lubricates the skin and hair preventing drying • Ducts of sebaceous glands open into the hair follicles • Babies are born with a covering produced by sebaceous glands called the vernixcaseosa, which looks like cottage cheese. • Hair • Hair is composed mainly of keratin and is not living • Develops within a sheath called a follicle and new hair is formed from cells at the bottom of the follicles • Each hair has a thin band of involuntary muscle attached to it • When this muscle contracts, the hair is raised forming “goose bumps” • This muscle is the arrectorpili muscle

8. Nails • Protective structures made of hardened keratin produced by cells in the stratum corneum • New cells form continually at the proximal end of the nail: the nail root

9. Functions of Skin • Protection against infection • Intact skin forms a primary barrier against invasion of pathogens • Surface cells are constantly being shed, causing the mechanical removal of pathogens • Also protects against bacterial toxins and harmful environmental chemicals • Protection against dehydration • Prevents water loss through keratin and sebum production • Regulation of body temperature • Perspiration cools the body through evaporation of sweat • Blood vessel dilation cools the body by bringing more heat to the surface to release it • To maintain warmth, blood vessels constrict limiting blood flow to the surface and arrectorpili muscles constrict pulling the hair upward to better insulate the body

10. Collection of sensory information • Skin is one of the chief sensory organs • It contains many nerve endings and other receptors for pain, touch, pressure, and temperature • Other activities • Some substances can be absorbed through the skin • A limited amount of excretion occurs through the skin • Vitamin D is manufactured in the skin via the absorption of ultraviolet light • Skin coloring can be an effective diagnostic tool for disease and disorders. Doctors look at the skin to determine the quality and quantity of blood circulating in the surface blood cells

11. Effects of Aging • Wrinkles • Develop as a result of fat and collagen loss • The dermis becomes thinner and more translucent as it loses its elasticity. • Hair loss • Hair becomes thinner and does not replace itself as rapidly as it did in youth • Lack of pigment cause the hair to become gray or white • Lack of sebum causes dryness of the hair and skin • Temperature • Sweat glands decrease in number and the ability to withstand heat is lost • Less fat in the skin and poor circulation increases the sensitivity to cold