The integumentary system, primarily consisting of skin, serves vital functions such as heat regulation, vitamin D synthesis, and protection against various damage. The skin is the largest organ, composed of the epidermis and dermis, with various structures including hair follicles, glands, and nails that aid in its functions. Melanin production, which determines skin and hair color, occurs in the epidermis, particularly in the stratum basale.

1. Integumentary System Anatomy & Physiology Essentials of Human Anatomy & Physiology Seventh Edition

2. Skin Functions Aids in heat regulation Synthesizes vitamin D Protects deeper tissues from : Mechanical damage - shape Antigens Thermal damage Ultraviolet radiation Dehydration

3. Skin Characteristics Skin is the largest organ in the body 25 square feet of surface area 40 pounds of skin shed in lifetime 30-40 thousand cells shed per minute 50 percent of heat lost through head 45 miles of nerves are in the skin 15 feet of blood vessels per 1 sq inch

4. Skin Structure Slide 4.13b Figure 4.4

5. Skin Structure Epidermis – outer layer forms finger prints Stratified squamous epithelium Often keratinized (hardened by keratin) Dermis – middle bilayer Hypodermis Anchors skin to underlying organs Composed mostly of adipose tissue

6. Layers of the Epidermis Stratum basale - cells undergoing mitosis, contain melaninocytes Stratum spinosum Stratum granulosum Stratum lucidum - occurs only in thick skin Stratum corneum – Shingle- like dead cells

7. Melanin Pigment (melanin) produced by melanocytes Color is yellow to brown to black Melanocytes are mostly in the stratum basale Amount of melanin produced depends upon genetic and exposure to sunlight

8. Dermal Bilayer Papillary layer Projections called dermal papillae Pain receptors Capillary loops Reticular layer Blood vessels Glands Nerve receptors

9. Dermal Structures Hair follicle Dermal and epidermal sheath surround hair root Arrector pilli Smooth muscle Sebaceous gland Sweat gland Figure 4.7a

10. Dermal Oil Glands Slide 4.15 Sebaceous glands Produce oil Lubricant for skin Kills bacteria Most with ducts that empty into hair follicles Glands are activated at puberty

11. Dermal Sweat Glands Slide 4.16 Sweat glands Widely distributed in skin Two types Eccrine Open via duct to pore on skin surface Apocrine Ducts empty into hair follicles

12. Dermal Hair Scalp alone has 100,000 hairs Strands are produced by hair bulb 40-100 strands fall out each day Melanocytes provide pigment for hair color Blonds have more hair than dark

13. Skin Color Determinants Slide 4.14 Melanin Yellow, brown or black pigments Carotene Orange-yellow pigment from some vegetables Hemoglobin Red coloring from blood cells in dermis capillaries Oxygen content determines the extent of red coloring

14. Appendages of the Skin Nails Scale-like modifications of the epidermis Heavily keratinized Stratum basale extends beneath the nail bed Responsible for growth Lack of pigment makes them colorless

15. Nail Structures Slide 4.22 Free edge Body Root of nail is where growth takes place Grow 1/8 inch per month Figure 4.9