1. 1 Skin and the Integumentary System Chapter 6 Anatomy & Physiology

2. 2 I. The Integumentary System A. The cutaneous membrane (the skin) and accessory organs make up the integumentary system B. Types of membranes of this system (4) 1. Serous membranes: line body cavities that do not open to the outside Line the thorax (parietal pleura), abdomen (parietal peritoneum), and cover the organs w/I these cavities (visceral pleura, visceral peritoneum) Consists: Layer of simple squamous epithelium and a thin layer of loose connective tissue Secrete serous fluid for lubrication

3. 3 2. Mucous membranes: line cavities and tubes that open to the outside Line the oral and nasal cavities, tubes of digestive, respiratory, urinary, and reproductive systems Consists: Epithelial tissue over loose connective tissue Goblet cells secrete mucus

4. 4 3. Synovial membrane: form the lining of the joint cavity between the end of bones at freely moving joints (aka synovial joints) Include dense connective tissue over loose connective tissue and adipose tissue Secrete synovial fluid into cavity for lubrication 4. Cutaneous membrane: THE SKIN, details follow.

5. 5 II. The Skin A. Functions: regulate homeostasis, forms protective covering, regulate body temperature, retard water loss from deeper tissues, house sensory receptors, synthesizes biochemicals, and excretes small quantities of wastes

6. 6 B. Layers of Skin 1. Epidermis (Figure 6.1-6.3) Composed of stratified squamous epithelium As cells divide, older ones are pushed toward the top layer of skin Keratinization: the development of the protein keratin in the outermost cells Stratum corneum: outermost layer Stratum basale: innermost layer Corns and calluses: regions on the palm and foot where cells are dividing at fast rates Functions to prevent water loss, mechanical injury, and harmful chemical effect of underlying tissues Melanin: dark pigment of the skin to protect from UV light; work by absorbing UV radiation; sometimes melanin is passed to other epidermal cells via cytocrine secretion

7. 7 Section of Skin

8. 8 Cross-section of skin showing layers

9. 9 2. Dermis Boundary between dermis and epidermis is uneven due to cellular projections Function: binds the epidermis to underlying tissues dense connective tissue creates the toughness of the skin and its elasticity Dermal blood vessels supply nutrients to all skin as well as regulate body temp Nerve cells, hair follicles, sebaceous glands, and sweat glands are scattered throughout

10. 10 3. Subcutaneous layer Layer beneath the dermis Loose connective tissue and adipose tissue Insulates to keep heat in and protects to keep heat out Contains major blood vessels for the skin

11. 11 III. Accessory Organs A. Hair follicles: develops hair; group of epidermal cells at the base of a tubelike depression Found on all body surfaces except palms, soles, lips, nipples, parts of external reproductive organs Contains the hair root; extends from surface to dermis Hair is composed of dead epidermal cells; cells become keratinized & die Genes determine hair color by the amount of melanin; epidermal melanocytes located at deep end of follicle Dark hair – lots of melanin Blonde hair – little melanin White hair – no melanin Gray hair – mixture of lots/no melanin Red hair - trichosiderin Arrector pili muscle: group of smooth muscle tissues at the base of the hair follicles causing short hairs to stand on end when stimulated Figure 6.4

12. 12 B. Sebaceous glands (holocrine glands) Associated with hair follicles Secrete an oily mixture of fatty material and other cellular debris called sebum Small ducts into the hair follicle Figure 6.6

13. 13 C. Nails Protective coverings: ends of fingers & toes Nail plate overlies skin surface called nail bed Lunula – white, half-moon shaped, actively producing new cells which are keratinized Grow from epithelial cells at the base Figure 6.7

14. 14 D. Sweat Glands (Sudoriferous glands) Exocrine gland Begins as ball-shaped coil in the deep dermis lined with epithelial cells that secrete sweat; a tube elongates from here to the surface Most numerous sweat glands (eccrine glands) respond to elevated body temperature (due to environment or exercise); located forehead, neck, back Opens in pore at skin surface Mostly water, some waste, urea, uric acid Other sweat glands (apocrine glands) become active when individual is upset, frightened, in pain. Numerous in axially region and groin Some are more specialized - glands in the ear secrete wax (ceruminous glands), mammary glands secrete milk

15. 15 Click on the link and try the 4 labeling exercises: Labeling excercises 1 and 2 The average square inch of human skin contains 650 sweat glands, 20 blood vessels, 60,000 melanocytes, in excess of 1,000 nerve endings.

16. 16 IV. Regulation of Body Temp A. normal: 37  C or 98.6  F B. Metabolic rate drives internal body temperature; active tissues/organs such as cardiac and skeletal muscle & liver produce lots of heat C. Incr heat warms blood, when it reaches hypothalamus which controls temp set point for body. Muscles in surface blood vessels relax causing vasodilation As warm blood enters these vessels, heat escapes to surface Evaporative cooling occurs as sweat absorbs heat and vaporizes from surface D. Shivering is a response to too much heat loss, response is to rapidly increase cellular respiration producing heat as by- product & increase muscle groups to contract rhythmically to create more heat E. Figure 6.8 shows the feedback loop for temperature regulation

17. 17 V. Healing A. Inflammation: painful swelling around a wound due to blood vessel dilation creating more fluid in the tissue Brings needed nutrients, oxygen, cells to aid healing B. Superficial cuts/injury stimulate epithelial cells to divide C. Deeper wounds often cause blood vessels to break, forming clots (scab); fibroblasts migrate to injury forming collagenous fibers to bind wound edges; a suture of superficial skin aids healing Phagocytic cells “eat” dead tissue/debris New cells replace damaged cells, scar replaces scab D. Granulations often form over large open wounds Consists of new blood supply, clusters of fibroblasts making collagenous fibers to aid healing As healing proceeds, fibroblasts migrate away, new blood supply resorbed, scar tissue left E. Table 6.1