5 The Integumentary System

An Introduction to the Integumentary System Learning Outcomes 5-1 Describe the main structural features of the epidermis, and explain the functional significance of each. 5-2 Explain what accounts for individual differences in skin color, and discuss the response of melanocytes to sunlight exposure. 5-3 Describe the interaction between sunlight and vitamin D3 production. 5-4 Describe the roles of epidermal growth factor.

An Introduction to the Integumentary System Learning Outcomes 5-5 Describe the structure and functions of the dermis. 5-6 Describe the structure and functions of the hypodermis. 5-7 Describe the mechanisms that produce hair, and explain the structural basis for hair texture and color.

An Introduction to the Integumentary System Learning Outcomes 5-8 Discuss the various kinds of glands in the skin, and list the secretions of those glands. 5-9 Describe the anatomical structure of nails, and explain how they are formed. 5-10 Explain how the skin responds to injury and repairs itself. 5-11 Summarize the effects of aging on the skin.

Integumentary Structure/Function Integumentary System Components (1) Cutaneous membrane Epidermis Dermis (2)Accessory structures (3) Subcutaneous layer (hypodermis) Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Integumentary Structure/Function Main Functions of the Integument Protection- from impact, infection, fluid loss Temperature maintenance – heat exchange Synthesis and storage of nutrients – vitamin D3 Sensory reception – touch, pressure, pain, temp. Excretion and secretion – salt, water, milk Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Integumentary Structure/Function Components of the Integumentary System Figure 5-1

Integumentary Structure/Function The Epidermis Stratified squamous epithelium Several distinct cell layers Thick skin (.5 mm) - five layers On palms and soles Thin skin (.08) - four layers On rest of body Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Integumentary Structure/Function Cell Layers (strata) of The Epidermis Stratum germinativum – attaches to b.m. Stratum spinosum Stratum granulosum Stratum lucidum (in thick skin) Stratum corneum – top layer Dying superficial layer Keratin accumulation – keratinized cells Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Integumentary Structure/Function The Structure of the Epidermis Figure 5-2

Integumentary Structure/Function Cell Layers of The Epidermis Stratum germinativum – deepest layer attaches with hemidesmosomes Basal layer – “finger prints” Stem cells – (germinative cells) Cell division layer Source of replacement cells Melanocytes Synthesize melanin Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Integumentary Structure/Function Cell Layers of the Epidermis Intermediate strata Stratum spinosum (spiny layer) Cells divide and add to layers of thickness Superficial to stratum germinativum Stratum granulosum (grainy layer) Keratin granules in cytoplasm No cell division Stratum lucidum (clear layer) – only in thick skin. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Integumentary Structure/Function Cell Layers of the Epidermis Stratum corneum (dead, dry) Most superficial layer Flattened (squamous) cells - 25 – 30 layers Dead cells Abundant keratin Keratinized (also, cornified) Tough, water-resistant protein Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Integumentary Structure/Function Sources of Skin Color Melanocytes Make melanin Melanin provides UV protection Gives reddish-brown to brown-black color Carotene Contributes orange-yellow color Provided from diet Hemoglobin Blood pigment Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Integumentary Structure/Function Melanocytes Figure 5-3

Integumentary Structure/Function Effects of UV Radiation Beneficial effect Activates synthesis of vitamin D3 Harmful effects Sun burn Wrinkles, premature aging Malignant melanoma Basal cell carcinoma Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Integumentary Structure/Function Two Important Types of Skin Cancer Figure 5-4 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Integumentary Structure/Function Key Note The epidermis is a multi-layered, flexible, self-repairing barrier that prevents fluid loss, provides protection from UV radiation, produces vitamin D3, and resists damage from abrasion, chemicals, and pathogens Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Integumentary Structure/Function Layers of the Dermis Composed of two layers: -Papillary layer - Reticular layer Papillary layer Underlies epidermis Named for dermal papillae Loose connective tissue Supports, nourishes epidermis Provides sensory nerves, lymphatics, and capillaries Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Integumentary Structure/Function Layers of the Dermis Reticular layer Tough, dense, fibrous layer Collagen fibers Limit stretch Elastic fibers Provide flexibility Blends into papillary layer (above) Blends into subcutaneous layer (below) Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Integumentary Structure/Function Other Dermal Components Epidermal accessory organs (hair, nails, etc.) Cells of connective tissues proper (mast, etc.) Communication with other organ systems Cardiovascular Lymphatic Nervous Sensation Control of blood flow and secretion Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Integumentary Structure/Function The Subcutaneous Layer (not actual integument) Composed of loose connective tissue Stabilizes skin position Loosely attached to dermis Loosely attached to muscle Contains many fat cells Provides thermal insulation Cushions underlying organs Safely receives hypodermic needles Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Integumentary Structure/Function Key Note The dermis provides mechanical strength, flexibility, and protection for underlying tissues. It is highly vascular and contains a variety of sensory receptors that provide information about the external environment. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Integumentary Structure/Function Accessory Structures - Include hair, glands, and nails Hair follicle – project into the dermis and often subcutaneous layer. Hair root – portion that anchors the hair Hair shaft – the part we see Cells die and become keratinized halfway to the surface of the skin marking the boundary of hair root and shaft. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Integumentary Structure/Function Hair components include medulla, cortex, cuticle Arrector pili muscle attaches follicle to dermis “goose bumps”. Hair color reflects melanocyte activity and different forms of melanin (decreased production and air bubbles contribute to gray hair)

Integumentary Structure/Function Hair Follicles Figure 5-5(a)

Integumentary Structure/Function Hair Follicles Figure 5-5(b)

Integumentary Structure/Function Hair Follicles Figure 5-5(c)

Integumentary Structure/Function Accessory Structures Hair growth cycle 0.3 mm/day growth rate 2–5 years growth 2–5 years follicle rest Follicle reactivation Old hair shedding Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Integumentary Structure/Function Accessory Structures Sebaceous glands (oil glands) Holocrine gland Oily secretion Sebum Hair shaft lubricant Sebaceous follicle Skin lubricant Skin waterproofing Becomes acne when clogged Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Integumentary Structure/Function The Structure of Sebaceous Glands and Their Relationship to Hair Follicles Figure 5-6

Integumentary Structure/Function Sweat Glands Apocrine – (communication) Odorous secretion (“funky”) Absent before puberty Present in axilla, areola, groin Merocrine – primarily to cool the surface of the skin through evaporation. Watery sweat (~1% NaCl) For heat loss Widely present in skin (up to 500/cm2) Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Integumentary Structure/Function Sweat Glands Figure 5-7

Integumentary Structure/Function Key Note The skin plays a major role in controlling body temperature. It acts as a radiator, with the heat being delivered by the dermal circulation and removed primarily by the evaporation of sweat or perspiration. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Integumentary Structure/Function Accessory Structures: Nails Nail body Dense mass of keratinized cells Nail bed area of epidermis covered by nail body Nail root site of nail production Cuticle - (eponychium) Portion of stratum corneum that extends over the exposed nail. Lunula Obscured blood vessels that leave a pale crescent. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Integumentary Structure/Function The Structure of a Nail Figure 5-8

Skin Injury and Repair Four Stages in Skin Healing Inflammation Blood flow increases Phagocytes attracted Scab formation Formed from insoluble network of fibrin Cell division and migration Stratum germinativum cells replace missing epidermal cells Scar formation Abnormally large amount of collagen fibers Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Bleeding occurs at the site of injury immediately after the injury, and mast cells in the region trigger an inflammatory response. After several hours, a scab has formed and cells of the stratum germinativum are migrating along the edges of the wound. Phagocytic cells are removing debris, and more of these cells are arriving with the enhanced circulation in the area. Clotting around the edges of the affected area partially isolates the region. Epidermis Scab Migratory epithelial cells Macrophages and fibroblasts Dermis Sweat gland Granulation tissue One week after the injury, the scab has been undermined by epidermal cells migrating over the meshwork produced by fibroblast activity. Phagocytic activity around the site has almost ended, and the fibrin clot is disintegrating. After several weeks, the scab has been shed, and the epidermis is complete. A shallow depression marks the injury site, but fibroblasts in the dermis continue to create scar tissue that will gradually elevate the overlying epidermis. Scar tissue Fibroblasts Figure 5-9 1 of 5 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Bleeding occurs at the site of injury immediately after the injury, and mast cells in the region trigger an inflammatory response. Epidermis Dermis Figure 5-9 2 of 5 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Macrophages and fibroblasts Bleeding occurs at the site of injury immediately after the injury, and mast cells in the region trigger an inflammatory response. After several hours, a scab has formed and cells of the stratum germinativum are migrating along the edges of the wound. Phagocytic cells are removing debris, and more of these cells are arriving with the enhanced circulation in the area. Clotting around the edges of the affected area partially isolates the region. Epidermis Scab Migratory epithelial cells Macrophages and fibroblasts Dermis Sweat gland Granulation tissue Figure 5-9 3 of 5 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

One week after the injury, the scab has been undermined by epidermal cells migrating over the meshwork produced by fibroblast activity. Phagocytic activity around the site has almost ended, and the fibrin clot is disintegrating. Fibroblasts Figure 5-9 4 of 5 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

One week after the injury, the scab has been undermined by epidermal cells migrating over the meshwork produced by fibroblast activity. Phagocytic activity around the site has almost ended, and the fibrin clot is disintegrating. After several weeks, the scab has been shed, and the epidermis is complete. A shallow depression marks the injury site, but fibroblasts in the dermis continue to create scar tissue that will gradually elevate the overlying epidermis. Scar tissue Fibroblasts Figure 5-9 5 of 5 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Skin Injury and Repair Table 5-1

Aging of the Skin Major Age-Related Changes Injury and infection increase Immune cells decrease Sun protection diminishes Skin becomes dry, scaly Hair thins, grays Sagging, wrinkles occur Heat loss decreases Repair slows Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Figure 5-17 System Integrator: The Integumentary System The integumentary system provides mechanical protection against environmental hazards. It forms the external surface of the body and provides protection from dehydration, environmental chemicals, and external forces. The integument (skin) is separated and insulated from the rest of the body by the subcutaneous layer, but it is interconnected with the rest of the body by an extensive circulatory network of blood and lymphatic vessels. As a result, although the protective mechanical functions of the skin can be discussed independently, its physiological activities are always closely integrated with those of other systems. Skeletal Page 275 Muscular Page 369 Nervous Page 543 Endocrine Page 632 ABOUT THE SYSTEM INTEGRATORS Since each body system interacts with every other body system, no one system can be completely understood in isolation. The integration of the various systems allows the human body to function seamlessly, and when disease or injury strikes, multiple systems must respond to heal the body. These charts will introduce the body systems one by one and show how each influences the others to make them function more effectively, and in turn how other body systems influence the system you are studying. As we progress through the organ system, the complementary nature of these interactions will become clear. Homeostasis depends on the thorough integration of all the body systems working as one. Cardiovascular Page 759 Lymphatic Page 807 Respiratory Page 857 Digestive Page 910 Urinary Page 992 Reproductive Page 1072 45