The Integumentary System

The Integumentary System

The Integumentary System (Introduction)
Two major parts of the integumentary system (or integument) Cutaneous membrane, or skin Accessory structures Hair Exocrine glands Nails © 2017 Pearson Education, Inc.

Cutaneous Membrane (Introduction)
Consists of two layers Superficial epithelium, or epidermis Underlying connective tissues of the dermis Hypodermis, or subcutaneous layer Loose connective tissue beneath the dermis Separates integument from deeper tissues Not part of the integumentary system, yet interwoven with connective tissue of the dermis © 2017 Pearson Education, Inc.

Figure 5-1 The General Structure of the Integumentary System.
Accessory Structures Cutaneous Membrane Hair shaft Epidermis Pore of sweat gland duct Papillary layer Dermis Touch receptor Reticular layer Sebaceous gland Arrector pili muscle Sweat gland duct Hair follicle Pressure receptor Hypodermis Nerve fibers Sweat gland Artery Subpapillary plexus Cutaneous plexus Vein Fat © 2017 Pearson Education, Inc.

Five General Functions of the Integument (Introduction)
Protection Skin covers and protects underlying tissues Prevents fluid loss Temperature maintenance Skin regulates heat exchange with the environment Synthesis and storage of nutrients Epidermis synthesizes vitamin D3 Dermis stores lipids in adipose tissue © 2017 Pearson Education, Inc.

Five General Functions of the Integument cont. (Introduction)
Sensory reception Receptors detect touch, pressure, pain, and temperature and relay information to nervous system Excretion and secretion Glands excrete salts, water, and organic wastes Specialized integumentary (mammary) glands secrete milk © 2017 Pearson Education, Inc.

Checkpoint (Introduction)
List five major functions of the integumentary system. © 2017 Pearson Education, Inc.

The Epidermis (5-1) Composed of layered epithelial tissue
Avascular (contains no blood vessels) Relies on diffusion from underlying connective tissue for nutrients and oxygen Deepest cells (closest to the dermis) are most active Cells in outer, superficial layers are dead Majority of the cells are keratinocytes Contain the protein keratin © 2017 Pearson Education, Inc.

Thick and Thin Skin (5-1) Terms “thick” and “thin” refer to thickness of epidermis (not whole integument) Thick skin – five layers of cells Found on palms of hands and soles of feet Very thick stratum corneum Total thickness about 0.5 mm (standard paper towel) Thin skin – four layers of cells Covers the rest of the body Total thickness about 0.08 mm (plastic sandwich bag) © 2017 Pearson Education, Inc.

Figure 5-2a-b The Epidermis
Surface Stratum corneum Stratum corneum Basement membrane Dermis Stratum lucidum Thin skin LM × 200 Dermal papilla Basement membrane Epidermal ridge Thick skin LM × 200 © 2017 Pearson Education, Inc.

Strata of the Epidermis (5-1)
Five cell layers (strata) of thick skin from deep to superficial Stratum basale Stratum spinosum Stratum granulosum Stratum lucidum Stratum corneum © 2017 Pearson Education, Inc.

Figure 5-2b The Epidermis
Surface Stratum corneum Stratum lucidum Stratum corneum Stratum granulosum Stratum spinosum Stratum lucidum Stratum basale Dermal papilla Basement membrane Epidermal ridge Dermis Thick skin LM × 200 © 2017 Pearson Education, Inc.

Stratum Basale (5-1) Deepest layer of the epidermis
Also called stratum germinativum Attached to basement membrane by hemidesmosomes Cells in the stratum basale Basal cells or germinative cells Stem cells that continually divide to replace cells lost at the surface Merkel cells (sensitive to touch) Melanocytes (synthesize melanin, a pigment) © 2017 Pearson Education, Inc.

Epidermal Ridges (5-1) Formed by cells of the stratum basale extending down into dermis Dermal projections (dermal papillae) extend up into epidermis between ridges Ridges and papillae interlock Increasing surface area for diffusion Strengthening bond between layers Contours of skin surface follow ridge patterns Basis for fingerprints © 2017 Pearson Education, Inc.

Figure 5-2a-e The Epidermis
Pores of sweat gland ducts Epidermal ridge Epidermis Thick skin SEM × 20 Basement membrane Epidermal ridge Dermal papilla Dermis © 2017 Pearson Education, Inc.

Intermediate Strata (5-1)
New daughter cells formed in stratum basale migrate upward toward skin surface Cells progress through three intermediate layers Stratum spinosum Stratum granulosum Stratum lucidum © 2017 Pearson Education, Inc.

Stratum Spinosum (5-1) Stratum spinosum (spiny layer)
Cells may continue to divide Consists of keratinocytes held together by desmosomes Contains branched dendritic cells (involved in the immune response) © 2017 Pearson Education, Inc.

Stratum Granulosum and Stratum Lucidum (5-1)
Stratum granulosum (grainy layer) Cells have stopped dividing Cells have started making keratin Durable, water-resistant protein Coats surface of skin and forms hair and nails Stratum lucidum (clear layer) Composed of flattened, densely packed cells filled with keratin © 2017 Pearson Education, Inc.

Stratum Corneum (5-1) Contains 15–30 layers of flattened, dead cells packed with keratin Called keratinized or cornified cells Cells tightly connected by desmosomes Because of connections, are generally shed in large groups or sheets © 2017 Pearson Education, Inc.

Cell Progression in the Epidermis (5-1)
Generally takes 7–10 days for cell to move from stratum basale to stratum corneum In the process, cells fill with keratin and die Dead cells stay in the stratum corneum for two more weeks before being shed or washed away © 2017 Pearson Education, Inc.

Checkpoint (5-1) Identify the five layers of the epidermis.
Dandruff is caused by excessive shedding of cells from the outer layer of skin in the scalp. Thus, dandruff is composed of cells from which epidermal layer? Some criminals sand their fingertips to avoid leaving recognizable fingerprints. Would this practice permanently remove fingerprints? Why or why not? © 2017 Pearson Education, Inc.

Skin Color – Pigmentation (5-2)
Carotene and melanin are the two pigments that influence skin color Carotene Orange-yellow pigment Accumulates in epidermal cells Found in orange-colored foods (carrots, squashes) © 2017 Pearson Education, Inc.

Skin Color – Pigmentation cont. (5-2)
Two types of melanin, red-yellow and brown-black Made by melanocytes Store melanin in vesicles called melanosomes Activity increases in response to sunlight (ultraviolet radiation) exposure Melanin absorbs UV radiation, protecting deeper layers of epidermis and dermis © 2017 Pearson Education, Inc.

LM × 600 Figure 5-3 Melanocytes. Melanocytes in stratum basale Melanin
pigment Basement membrane Melanocytes LM × 600 Melanosome Melanin pigment Melanocyte Basement membrane © 2017 Pearson Education, Inc.

Dermal Circulation and Skin Color (5-2)
Oxygenated blood is bright red Increase in body temperature dilates superficial blood vessels in dermis Result is a flushed, red skin color Temporary constriction of the same vessels results in pale skin Cyanosis, a bluish coloration, occurs when blood oxygen supplies are diminished © 2017 Pearson Education, Inc.

Checkpoint (5-2) Name the two pigments in the epidermis.
Why does exposure to sunlight or sunlamps darken skin? Why does the skin of a light-skinned person appear red during exercise in hot weather? © 2017 Pearson Education, Inc.

Beneficial Effects of Sunlight on Skin (5-3)
Vitamin D3 Formed by epidermal cells Converted from a cholesterol-related steroid when epidermal cells exposed to sunlight Liver and kidneys convert vitamin D3 into calcitriol Essential for absorption of calcium and phosphorus Inadequate vitamin D3 can lead to weak and flexible bones © 2017 Pearson Education, Inc.

Detrimental Effects of Sunlight on Skin (5-3)
Skin cancers Any cancer of epithelial tissue is a carcinoma Basal cell carcinoma is most common skin cancer Originates in stratum basale Squamous cell carcinoma found in more superficial layers Malignant melanoma is most dangerous Usually begins from a mole Can metastasize through the lymphatic system © 2017 Pearson Education, Inc.

Basal cell carcinoma Melanoma a b Figure 5-4 Skin Cancers.
© 2017 Pearson Education, Inc.

The Dermis (5-4) Lies between the epidermis and hypodermis
Contains two major layers Superficial papillary layer Deeper reticular layer © 2017 Pearson Education, Inc.

The Dermal Papillary Layer (5-4)
Named after the dermal papillae Consists of areolar tissue Supports and nourishes epidermis Contains capillaries, lymphatic vessels, and sensory neurons supplying skin surface © 2017 Pearson Education, Inc.

The Dermal Reticular Layer (5-4)
Interwoven meshwork of dense irregular connective tissue Elastic fibers provide flexibility Collagen fibers limit flexibility and so prevent damage to tissue Dominant cell type is fibroblast Accessory organs derived from epidermis (hair follicles, sweat glands) extend into this layer Also contains: blood vessels, lymphatic vessels, nerve fibers, and sensory receptors © 2017 Pearson Education, Inc.

Blood Supply in the Dermis (5-4)
Networks of arteries called plexuses Cutaneous plexus Lies along border of hypodermis Supplies adipose tissue in hypodermis and tissues of the integument Subpapillary plexus Provides blood to capillary loops along epidermis-dermis boundary © 2017 Pearson Education, Inc.

Figure 5-1 The General Structure of the Integumentary System.
Accessory Structures Cutaneous Membrane Hair shaft Epidermis Pore of sweat gland duct Papillary layer Dermis Touch receptor Reticular layer Sebaceous gland Arrector pili muscle Sweat gland duct Hair follicle Pressure receptor Hypodermis Nerve fibers Sweat gland Artery Subpapillary plexus Cutaneous plexus Vein Fat © 2017 Pearson Education, Inc.

Checkpoint (5-4) Describe the location of the dermis.
Where are the capillaries that supply the epidermis located? © 2017 Pearson Education, Inc.

The Hypodermis (5-5) Also called the subcutaneous layer
Deep to the dermis Fibers intermixed with dermis, so no clear delineation Not actually part of the integument But stabilizes position of the skin relative to underlying tissues Consists of areolar tissue with many fat cells No vital organs in area make it an ideal site for subcutaneous injections © 2017 Pearson Education, Inc.

Hair and Hair Follicles (5-6)
Accessory structures of the integumentary system Hairs Nonliving, keratinized structures Produced by hair follicles Project above the skin surface everywhere except: The sides and soles of the feet, palms of the hands, sides of the fingers and toes, the lips, and portions of the external genitalia © 2017 Pearson Education, Inc.

Hair Follicle Structure (5-6)
Project into dermis and usually into hypodermis Walls contain all cell layers found in epidermis Epithelium at the base of follicle forms cap over the hair papilla Connective tissue that contains capillaries and nerves Hair matrix surrounds hair papilla Contains epithelial stem cells Cells divide and push daughter cells toward surface © 2017 Pearson Education, Inc.

Figure 5-5b Hair Follicles and Hairs.
Connective tissue sheath of hair Cortex Medulla Hair matrix Hair papilla Hypodermis Hair follicle LM × 60 b In this section of skin of the scalp, notice that the hair follicle extends into the hypodermis. © 2017 Pearson Education, Inc.

Hair Structure (5-6) As hair cells move toward surface, they become keratinized and die Point of keratinization is about halfway to skin surface and marks boundary between hair root and shaft Hair root – portion that anchors hair into skin Hair shaft – hair part we see on the surface © 2017 Pearson Education, Inc.

Figure 5-5a Hair Follicles and Hairs.
Sebaceous gland Hair shaft Arrector pili muscle Hair root Connective tissue sheath Hair matrix Hair papilla a This drawing shows a longitudinal section of a single hair follicle and hair. © 2017 Pearson Education, Inc.

Hair Shaft Structure (5-6)
Three layers of dead, keratinized cells Cuticle (surface layer) Made of an overlapping shingle-like layer of cells Contains hard keratin, giving hair stiffness Cortex – also contains hard keratin Medulla Makes up the core Contains flexible soft keratin © 2017 Pearson Education, Inc.

Figure 5-5c Hair Follicles and Hairs.
Connective tissue sheath Wall of hair follicle Cuticle of hair Cortex of hair Medulla of hair C This cross section through a hair follicle was taken at the boundary between the hair shaft and hair root. © 2017 Pearson Education, Inc.

Hair Growth (5-6) Hair growth cycle Grows for two to five years
Follicle becomes inactive for same time frame When new growth cycle begins, follicle produces new hair Old hair gets pushed to surface and shed © 2017 Pearson Education, Inc.

Functions of Hair (5-6) Protects the scalp from UV light
Provides insulation for the skull Prevents entry of foreign particles into nose, eyes, and ears Provides early-warning system to prevent injury due to sensory fibers at base of hair follicles Expresses emotional state by hair standing up due to contraction of arrector pili muscle Produces “goose bumps” © 2017 Pearson Education, Inc.

Hair Color (5-6) Differences due to type and amount of melanin from melanocytes Hair color varies from black to blond Genetically determined and influenced by hormones and environmental factors Pigment production declines with age causing gray or white hair © 2017 Pearson Education, Inc.

Checkpoint (5-6) Describe a typical strand of hair.
What happens when the arrector pili muscle contracts? If a burn on the forearm destroys the epidermis and the deep dermis and then heals, will hair grow again in the affected area? © 2017 Pearson Education, Inc.

Exocrine Glands of the Skin (5-7)
Two types of exocrine glands in the integument Sebaceous glands Sweat glands © 2017 Pearson Education, Inc.

Sebaceous Glands (5-7) Also called oil glands
Discharge oily lipid secretion (sebum) into hair follicles through holocrine secretion Sebum inhibits growth of bacteria, lubricates the hair, and conditions surrounding skin Sebaceous follicles discharge sebum directly onto skin of face, back, chest, nipples, and external genitalia © 2017 Pearson Education, Inc.

Sebaceous Glands and Acne (5-7)
Sebaceous glands are sensitive to changes in concentrations of sex hormones Secretions accelerate at puberty Acne Blocked sebaceous ducts causes inflammation and raised “pimple” © 2017 Pearson Education, Inc.

Figure 5-6 Sebaceous Glands and Their Relationship to Hair Follicles.
Hair removed Sebaceous follicle Sebaceous gland Wall of hair follicle Basement membrane Epidermis Discharge of sebum Dermis Breakdown of cell membranes Mitosis and growth Hypodermis Basal cells Sebaceous gland LM × 150 © 2017 Pearson Education, Inc.

Sweat Glands (5-7) Also called sudoriferous glands Include two types
Apocrine sweat glands Merocrine sweat glands © 2017 Pearson Education, Inc.

Apocrine Sweat Glands (5-7)
Become active at puberty Secrete into hair follicles in armpits, around nipples, and in pubic region Secretion is sticky, cloudy, and potentially odorous Sweat is food source for bacteria on skin, increasing odor Deodorants are used to mask this odor © 2017 Pearson Education, Inc.

Merocrine Sweat Glands (5-7)
Also called eccrine sweat glands Coiled tubular structure secretes watery perspiration directly onto surface of skin Very numerous with high numbers on soles and palms Sweat is 99 percent water with electrolytes, urea, and organic nutrients Sodium chloride gives it the salty taste Function is to cool body through evaporation © 2017 Pearson Education, Inc.

Merocrine duct Sweat pore Hair shaft Arrector pili muscle
Figure 5-7 Sweat Glands. Merocrine duct Sweat pore Hair shaft Arrector pili muscle Apocrine duct Epidermis Dermis Hypodermis Artery Vein Merocrine sweat gland (sectioned) Apocrine sweat gland Merocrine sweat gland © 2017 Pearson Education, Inc.

Modified Sweat Glands (5-7)
Mammary glands Structurally related to apocrine sweat glands Secrete milk Ceruminous glands Located in passageway of external ear Secretions combine with sebaceous gland secretions to form cerumen, or earwax © 2017 Pearson Education, Inc.

Checkpoint (5-7) Identify two types of exocrine glands found in the skin. What are the functions of sebaceous secretions? Deodorants are used to mask the effects of secretions from which type of skin gland? © 2017 Pearson Education, Inc.

Nails (5-8) Protect dorsal surfaces of tips of fingers and toes
Visible nail body Made of dense, keratinized cells Recessed beneath surrounding epithelium Bordered by lateral nail folds Nail bed Deeper level of epidermis covered by nail body © 2017 Pearson Education, Inc.

Nail Structure (5-8) Nail root Lunula
Epithelial fold not visible from the surface Site of nail production Covered by the cuticle, or eponychium Portion of the stratum corneum Lunula Pale crescent near nail root © 2017 Pearson Education, Inc.

Figure 5-8 The Structure of a Nail.
Direction of growth Lateral nail groove Nail body Free edge Lateral nail fold Nail bed Nail body Lunula Phalanx (bone of fingertip) b Cuticle (eponychium) A cross-sectional view a A superficial view Cuticle (eponychium) Lunula Nail body Nail root (site of growth) Epidermis Dermis Phalanx c A longitudinal section © 2017 Pearson Education, Inc.

Repair of the Integument (5-9)
Skin regeneration occurs because: Stem cells of epithelium and connective tissue undergo cell division Replacing lost or damaged tissue Four phases of skin regeneration Inflammatory phase Migratory phase Proliferation phase Scarring phase © 2017 Pearson Education, Inc.

Inflammatory Phase (5-9)
Mast cells released at bleeding injury site trigger inflammatory response Result is increased blood flow to region and increased numbers of phagocytes © 2017 Pearson Education, Inc.

Figure 5-9 Repair of Injury to the Skin.
1 Inflammatory Phase Bleeding occurs at the site of injury immediately after the injury, and mast cells in the region trigger an inflammatory response. Epidermis Dermis Mast cell © 2017 Pearson Education, Inc.

Migratory Phase (5-9) Blood clot or scab forms at surface
Stratum basale cells migrate along wound edges to replace missing cells More phagocytes clear debris and pathogens If wound covers extensive area or involves a region of thin skin: Granulation tissue forms in deeper tissue Combination of blood clot, fibroblasts, and extensive capillary network © 2017 Pearson Education, Inc.

2 Migratory Phase After several hours, a scab has formed and cells of the stratum basale 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. Migrating epithelial cells Macrophages and fibroblasts Granulation tissue © 2017 Pearson Education, Inc.

Proliferation Phase (5-9)
Deeper parts of the clot dissolve Number of capillaries declines Fibroblasts have formed extensive meshwork of collagen fibers © 2017 Pearson Education, Inc.

3 Proliferation Phase About a week after the injury, the scab has been undermined by epidermal cells migrating over the collagen fiber meshwork produced by fibroblast activity. Phagocytic activity around the site has almost ended, and the fibrin clot is dissolving. Fibroblasts © 2017 Pearson Education, Inc.

Scarring Phase (5-9) Scab is shed and epidermis is complete
Shallow depression marks injury site Fibroblasts create fibrous, noncellular scar tissue to elevate epidermis Degree of scar formation dependent on severity and location of injury and age of patient Keloids are thickened areas of scar tissue covered by shiny, smooth epidermal surface © 2017 Pearson Education, Inc.

4 Scarring Phase 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 © 2017 Pearson Education, Inc.

1 Inflammatory Phase Bleeding occurs at the site of injury immediately after the injury, and mast cells in the region trigger an inflammatory response. Epidermis Dermis Mast cell 2 Migratory Phase After several hours, a scab has formed and cells of the stratum basale 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. Migrating epithelial cells Macrophages and fibroblasts Granulation tissue 3 Proliferation Phase About a week after the injury, the scab has been undermined by epidermal cells migrating over the collagen fiber meshwork produced by fibroblast activity. Phagocytic activity around the site has almost ended, and the fibrin clot is dissolving. Fibroblasts 4 Scarring Phase 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 © 2017 Pearson Education, Inc.

Figure 5-9 Repair of Injury to the Skin. Slide 1
Inflammatory Phase Bleeding occurs at the site of injury immediately after the injury, and mast cells in the region trigger an inflammatory response. Epidermis Dermis Mast cell © 2017 Pearson Education, Inc.

1 Inflammatory Phase Bleeding occurs at the site of injury immediately after the injury, and mast cells in the region trigger an inflammatory response. Epidermis Dermis Mast cell 2 Migratory Phase After several hours, a scab has formed and cells of the stratum basale 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. Migrating epithelial cells Macrophages and fibroblasts Granulation tissue © 2017 Pearson Education, Inc.

1 Inflammatory Phase Bleeding occurs at the site of injury immediately after the injury, and mast cells in the region trigger an inflammatory response. Epidermis Dermis Mast cell 2 Migratory Phase After several hours, a scab has formed and cells of the stratum basale 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. Migrating epithelial cells Macrophages and fibroblasts Granulation tissue 3 Proliferation Phase About a week after the injury, the scab has been undermined by epidermal cells migrating over the collagen fiber meshwork produced by fibroblast activity. Phagocytic activity around the site has almost ended, and the fibrin clot is dissolving. Fibroblasts © 2017 Pearson Education, Inc.

1 Inflammatory Phase Bleeding occurs at the site of injury immediately after the injury, and mast cells in the region trigger an inflammatory response. Epidermis Dermis Mast cell 2 Migratory Phase After several hours, a scab has formed and cells of the stratum basale 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. Migrating epithelial cells Macrophages and fibroblasts Granulation tissue 3 Proliferation Phase About a week after the injury, the scab has been undermined by epidermal cells migrating over the collagen fiber meshwork produced by fibroblast activity. Phagocytic activity around the site has almost ended, and the fibrin clot is dissolving. Fibroblasts 4 Scarring Phase 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 © 2017 Pearson Education, Inc.

Effects of Burns (5-9) Burns result from exposure of skin to heat, radiation, electrical shock, or strong chemicals Severity depends on depth into the tissues and the total area affected Skin functions affected by burns Fluid and electrolyte balance Thermoregulation Protection from infection © 2017 Pearson Education, Inc.

Classification by Depth of Burn (5-9)
Partial-thickness burns First-degree burn Only the epidermis is affected Causes erythema or redness from inflammation Example: sunburn Second-degree burn Entire epidermis and part of the dermis damaged Causes blistering, pain, and swelling Some scar tissue may form © 2017 Pearson Education, Inc.

Classification by Depth of Burn cont. (5-9)
Full-thickness burns Third-degree burn Epidermis and dermis are destroyed Damage may extend into the hypodermis Sensory nerves destroyed Cannot repair themselves and usually require skin grafting © 2017 Pearson Education, Inc.

Checkpoint (5-9) What term describes the combination of fibrin clots, fibroblasts, and the extensive network of capillaries in healing tissue? Why can skin regenerate effectively even after considerable damage? © 2017 Pearson Education, Inc.

Effects of Aging on the Integument (5-10)
Skin injuries and infections are more common Likely due to a thinning of the epidermis as stem cells become less active Sensitivity of immune system is reduced Mainly due to a decrease of macrophages residing in the skin Muscles become weaker and bone strength decreases Due to a decline in vitamin D3 © 2017 Pearson Education, Inc.

Sensitivity to sun exposure increases Due to lower amount of melanin production Skin becomes dryer and often scaly Due to reduction in glandular secretions Hair thins and changes color Due to low-functioning follicles and decreased melanocyte activity © 2017 Pearson Education, Inc.

Sagging and wrinkling of the skin occurs Due to decrease in elastic network, more noticeable when skin has been exposed to a lot of sunlight Ability to lose heat is reduced Due to reduced dermal blood supply and less active sweat glands Skin repairs take place more slowly Due to slower stem cell division, increasing the threat of infection in cuts © 2017 Pearson Education, Inc.

Checkpoint (5-10) Older individuals do not tolerate summer heat as well as they did when they were young, and they are more prone to heat-related illnesses. What accounts for these changes? Why does hair turn gray or white with age? © 2017 Pearson Education, Inc.

Unnumbered Figure, Page 138
Integumentary System The integumentary system performs five major functions for the human body. It: covers and protects underlying tissues and organs from impacts, chemicals, and infections, and it prevents the loss of body fluids maintains normal body temperature by regulating heat exchange with the environment synthesizes vitamin D3 in the epidermis, which aids calcium uptake, and stores large reserves of lipids in the dermis detects touch, pressure, pain, and temperature stimuli excretes salts, water, and organic wastes ABOUT THE BUILD YOUR KNOWLEDGE FIGURES Because each organ system, or simply, body system, interacts with all the others, no one system can be completely understood in isolation. Their integration allows the human body to function seamlessly, and when disease or injury strikes, multiple systems must respond to heal the body. Homeostasis depends on all the body systems working as one. These figures will introduce the body systems one by one and show how each influences the others to make them function more effectively. As we progress through the organ systems, you will build your knowledge about the functional relationships between the various body systems. © 2017 Pearson Education, Inc.

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