Chapter 5: The Integumentary System

Question 1

How does the integumentary system contribute to homeostasis?

Answer 1

• Protect body, help regulate body temperature.
• Sense pleasure, pain, and other stimuli from external environment.

Question 2

What is the integumentary system?

Structure of the Skin

Answer 2

• Skin consists of superficial, thin epidermis and a deep, thicker dermis.
• Deep to the skin is subcutaneous layer, attaches dermis to underlying fascia.
  Includes:
  1. Skin.
  2. Hair.
  3. Oil and sweat glands.
  4. Nails.
  5. Sensory receptors.

Structure of the Skin

Question 3

What is the skin?

Structure of the Skin

Answer 3

• Cutaneous membrane, covers external surface of body.
• Largest organ of the body in weight.

Skin consists of two main parts:
1. Epidermis (superficial, thinner portion, composed of epithelial tissue. Vascular).
2. Dermis (deeper, thicker connective tissue portion. Avascular).

• Deep to dermis, but not part of skin is the subcutaneous layer (hypodermis).

Structure of the Skin

Question 4

What is the subcutaneous layer (hypodermis)?

Structure of the Skin

Answer 4

• Layer consists of areolar and adipose tissues.
• Fibers extend from dermis anchor the skin to subcutaneous layer, which is turn attaches to underlying fascia, the connective tissue around muscles and bones.
• Layer serves as storage for fat, contains large blood vessels that supply the skin.

Structure of the Skin

Question 5

What is lamellated corpuscles (pacinian corpuscles)?

Structure of the Skin

Answer 5

• Nerve endings that are sensitive to pressure.

Structure of the Skin

Question 6

What are the functions of the integumentary system?

Structure of the Skin

Answer 6

1. Regulates body temperature.
2. Stores blood.
3. Protects body from external environment.
4. Detects cutaneous sensations.
5. Excretes and absorbs substances.
6. Synthesizes vitamin D.

Structure of the Skin

Question 7

What is the epidermis?

Structure of the Skin

Answer 7

• Composed of keratinized stratified squamous epithelium.

Contains four principal types of cells:
1. Keratinocytes.
2. Melanocytes.
3. Intraepidermal macrophages.
4. Tactile epithelial.

Structure of the Skin

Question 8

What are keratinocytes?

Structure of the Skin

Answer 8

• About 90% of epidermal cells are keratinocytes.
• Arranged in 4 or 5 layers, produce the protein keratin.
• Produce lamellar granules, which release a water-repellent sealant that decreases water entry/loss and inhibits entry of foreign materials.

Structure of the Skin

Question 9

What are melanocytes?

Structure of the Skin

Answer 9

• About 8% of epidermal cells are melanocytes.
• Develop from ectoderm of developing embryo, produce the pigment melanin.
• Long, slender projections extend between karatinocytes and transfer melanin granules to them.

Structure of the Skin

Question 10

What is melanin?

Structure of the Skin

Answer 10

• Yellow-red/brown-black pigment, contributes to skin color and absorbs damaging ultraviolet (UV) light.
• Shield nuclear DNA from damage from UV light.
• Melanin granules effectively protect keratinocytes.
• Melanocytes are particularly susceptible to damage by UV light.

Structure of the Skin

Question 11

What are intraepidermal macrophages?

Structure of the Skin

Answer 11

• From red bone marrow, migrate to the epidermis.
• Participate in immune responses against microbes that invade skin, and easily damaged by UV light.
• Help cells of immune system recognize invading microbe and destroy it.
• Also called Langerhans cells.

Structure of the Skin

Question 12

What are tactile epithelial cells?

Structure of the Skin

Answer 12

• Located in deepest layer of epidermis, where they contact the flattened process of a sensory neuron (nerve cell), a structure called a tactile disc (or merkel disc).
• Detect touch sensations.

Structure of the Skin

Question 13

What are the four layers of the epidermis of thin skin?

Structure of the Skin

Answer 13

• Several distinct layers of keratinocytes in various stages of development form epidermis.

Most regions of body, epidermis has four strata (or layers):
1. Stratum basale.
2. Stratum spinosum.
3. Stratum granulosum.
4. Thin stratum corneum.

Structure of the Skin

Question 14

What are the five layers of the epidermis of thick skin?

Structure of the Skin

Answer 14

Where expose to friction is greatest (fingertips, palms, and soles, epidermis) has five layers:
1. Stratum basale.
2. Stratum spinosum.
3. Stratum granulosum.
4. Stratum lucidum.
5. Thick stratum corneum.

Structure of the Skin

Question 15

What is stratum basale?

Structure of the Skin

Answer 15

• Deepest layer of epidermis.
• Single row of cuboidal or columnar keratinocytes.
• Some are stem cells that undergo cell division to continually produce new keratinocytes.
• Nuclei of keratinocytes in stratum basale are large, cytoplasm contains many ribosomes, small Golgi complex, few mitochondria and some rough ER.

Structure of the Skin

Question 16

What is stratum spinosum?

Structure of the Skin

Answer 16

• Superficial to stratum basale.
• Consists of keratinocytes arranged in 8-10 layers.
• Cells somewhat flattened.
• Keratinocytes in stratum spinosum, (produced by stem cells in basal layer), have same organelles as cells of stratum basale and some retain ability to divide.
• Keratinocytes produce coarser bundles of keratin in intermediate filaments.

Structure of the Skin

Question 17

What is stratum granulosum?

Structure of the Skin

Answer 17

• About the middle of the epidermis.
• Consists of 3-5 layers of flattened keratinocytes that are undergoing apoptosis.
• Nuclei and other organelles of these cells begin to degenerate as they move farther from source of nutrition (dermal blood vessels).
• Presence of darkly staining granules of a protein called keratohyalin (assembles keratin intermidiate filaments into keratin).
• Membrane-enclosed lamellar granules, fuse with plasma membrane and release a lipid-rich secretion.
• Marks transition between deeper, metabolically active strata and dead cells of more superficial strata.

Structure of the Skin

Question 18

What is stratum lucidum?

Structure of the Skin

Answer 18

• Present only in thick skin of areas such as fingertips, palms, and soles.
• Consists of 4-6 layers of flattened clear, dead keratinocytes that contain large amounts of keratin and thickened plasma membranes.

Structure of the Skin

Question 19

What is stratum corneum?

Structure of the Skin

Answer 19

• 25-30 layers of flattened dead keratinocytes, can range in thickeness.
• Extremely thin, flat, plasma membrane-enclosed packages of keratin that no longer contain a nucleus or any internal organelles.
• Final product of differentiation process of keratinocytes.
• In outer stratum of epidermis, cells are continuously shed and replaced by cells from deeper strata.
• Multiple layers of dead cells help protect deeper layers from injury and microbial invasion.

Structure of the Skin

Question 20

What is a callus?

Structure of the Skin

Answer 20

• Abnormal thickening of stratum corneum.
• Results due to constant exposure to friction.
• Stimulates increased cell production and keratin production.

Structure of the Skin

Question 21

What is Stratum basale?

Structure of the Skin

Answer 21

• Deepest layer, composed of single row of cuboidal or columnar keratinocytes that contain scattered keratin intermediate filaments (tonofilaments).
• Stem cells undergo cell division to produce new keratinocytes.
• Melanocytes and tactile epithelial cells associated with tactile discs are scattered among keratinocytes.

Structure of the Skin

Question 22

What is Stratum spinosum?

Structure of the Skin

Answer 22

• 8-10 rows of many-sided keratinocytes with bundles of keratin intermediate filaments.
• Contains projections of melanocytes and intraepidermal macrophages.

Structure of the Skin

Question 23

What is Stratum granulosum?

Structure of the Skin

Answer 23

• 3-5 rows of flattened keratinocytes, organelles are beginning to degnerate.
• Cells contain protein keratohyalin (converts keratin intermediate filaments into keratin) and lamellar granules (releases lipid-rich, water-repellent secretion).

Structure of the Skin

Question 24

What is Stratum lucidum?

Structure of the Skin

Answer 24

• Present only in skin of fingertips, palms, and soles.
• Consists of 4-6 rows of clear, flat, dead keratinocytes with large amounts of keratin.

Structure of the Skin

Question 25

What is Stratum corneum?

Structure of the Skin

Answer 25

• Few-50 or more rows of dead, flat keratinocytes.
• Contain mostly keratin.

Structure of the Skin

Question 26

What is keratinization?

Structure of the Skin

Answer 26

• Process where cells move from one epidermal layer to the next.
• They accumulate more and more keratin.
• Newly formed cells in stratum basale slowly pushed to surface.
• Eventually, keratinized cells slough off.
• Replaced by underlying cells that in turn become keratinized..

Structure of the Skin

Question 27

What is epidermal growth factor (EGF)?

Structure of the Skin

Answer 27

• Protein that stimulates cell growth and differentiation.

Structure of the Skin

Question 28

What is the dermis?

Structure of the Skin

Answer 28

Is the second, deeper part of the skin. Is composed of dense irregular connective tissue containing collagen and elastic fibers. Woven network of ibers has great tensile strength. Has ability to stretch and recoil easily. Much thicker than epidermis. Few vells present in dermis include predominantly fibroblasts, with some macrophages, and a few adipocytes near its boundary with subcutaneous layer. Blood vessels, nerves, glands, hair follicles are embedded in dermal layer. Can be divided into a thin superficial papillary region and a thick deeper reticular region.

Structure of the Skin

Question 29

What is the papillary region of the dermis?

Structure of the Skin

Answer 29

Makes up about one-fifth of the tickness of the total layer. Contains thin collagen and fine elastic fibers. Surface area is greatly increased by dermal papillae (small, nipple-shaped structures that project into the undersurface of the epidermis). All dermal papillae contain capillary loops (blood vessels). Some contain tactile receptors called corpuscles of touch (or Meissner corpuscles), nerve endings that are sensitive to touch. Other dermal papillae also contain free nerve endings, dendrites that lack any apparent structural specialization.

Structure of the Skin

Question 30

What is the reticular region of the dermis?

Structure of the Skin

Answer 30

Reticular region which is attached to the subcutaneous layer, contains bundles of thick collagen fibers, scattered fibroblasts, and various wandering cells (such as macrophages). Some adipose cells can be present in deepest part of the layer, along with some coarse elastic fibers. Collagen fibers in reticular region are arranged in netlike manner and have a more regular arrangement. Hekps the skin resist stretching. Blood vessels, nerves, hair follicles, sebaceous (oil) glands, and sudoriferous (sweat) glands occupy the spaces between fibers.

Structure of the Skin

Question 31

Papillary region

Structure of the Skin

Answer 31

Superficial portion of dermis (about one-fifth); consists of areolar connective tissue with thin collagen and fine elastic fibers; contains dermal ridges that house blood capillaries, corpuscles of touch, and free nerve endings.

Structure of the Skin

Question 32

Reticular region

Structure of the Skin

Answer 32

Deeper portion of dermis (about four-fifths); consists of dense irregular connective tissue with bundles of thick collagen and some coarse elastic fibers. Spaces between fibers contain some adipose cells, hair follicles, nerves, sebaceous glands, and sudoriferous glands.

Structure of the Skin

Question 33

What are epidermal ridges?

Structure of the Skin

Answer 33

Are produced during third month of fetal development as downward projections of the epidermis into the dermis between the dermal papillae of the papillary region. Epidermal ridges create a strong bond between the epidermis and dermis in a region of high mechanical stress. Also increase the surface area of the epidermis and thus increase the grip of the hand or foot by increasing friction. Increases tactile sensitivity. Because ducts of sweat glands open on the tops of epidermal ridges as sweat pores, the sweat and ridges form fingerprints (or footprints) on touching a smooth object.

Structure of the Skin

Question 34

What are the three pigments of skin color?

Structure of the Skin

Answer 34

1. Melanin
2. Hemoglobin
3. Carotene
   The amount of melanin causes skins color to vary from pale yellow to reddish-brown to black. Melanocytes, the melanin-producing cells, are most plentiful in epidermis of penis, nipples of breasts, area just around nipples (areolae), face and limbs. Differences in skin color are due mainly to the amount of pigment the melanocytes produce and transfer to keratinocytes.

Structure of the Skin

Question 35

What are accessory structures of the skin?

Accessory Structures of the Skin

Answer 35

Hair, skin glands and nails are accessory structures of the skin. Develop from the embryonic epidermis.

Accessory Structures of the Skin

Question 36

What is hair?

Accessory Structures of the Skin

Answer 36

Are present on most skin surfaces except palms, palmar surfaces of fingers, the soles, and plantar surfaces of feet. In adults, hair most heavily distributed across scalp, in eyebrows, in axillae and around external genitalia. Hairs function in sensing light tough, protection from foreign particles. Hairs are growth of epidermis comprosed of dead, keratinized epidermal cells.

Accessory Structures of the Skin

Question 37

What is the hair shaft?

Accessory Structures of the Skin

Answer 37

The superficial portion of the hair, which projects above the surface of the skin.

Accessory Structures of the Skin

Question 38

What is the hair root?

Accessory Structures of the Skin

Answer 38

The portion of the hair deep to the shaft that penetrates into the dermis, and sometimes into sibcutaneous layer. The shaft and root of the hair both consist of three concenrtic layers of cells:
1. Medulla
2. Cortex
3. Cuticle

Accessory Structures of the Skin

Question 39

Describe the anatomy of the hair.

Accessory Structures of the Skin

Answer 39

Hair shaft is the superficial portion of the hair.
Hair root is portion of the hair deep to the shaft that penetrates into the dermis.
Shaft and root of hair consist of 3 subcutaneous layers of cells: medulla, cortex, and cuticle of the hair.
Inner medulla is composed of 2-3 rowas of irregularly shaped cells that contain large armount of pigment granules in dark hair, small amounts of pigment granules in gray hair, and a lack of pigment granules and present of air bubbles in white hair.
Middle cortex forms major part of shaft and consists of elongated cells.
Cuticle of the hair, the outermost layer, consists of a single layer of thin, flat cells that are most heavily keratinized.

Accessory Structures of the Skin

Question 40

Describe the anatomy of the hair?

Accessory Structures of the Skin

Answer 40

Surrounds the root of the hair, which is made up of an external root sheath and an internal rooth sheath. The external root sheath is a downward continuation of the epidermis. The internal root sheath is produced by the matrix and forms a cellular tubular sheath of epithelium between the external root sheath and the hair. Together, external and internal root sheaths are referred to as the epithelial root sheath. Dense dermis surrounding the hair follicle is called the dermal root sheath. Base of each hair follicle and its surrounding dermal root sheath is an onion-shaped structure, the hair bulb. This structure houses a nipple-shaped indentation, the papilla of the hair, which contains areolar connective tissue and many blood vessels that nourish the growing hair follicle. Bulb also contains a germinal layer of cells called hair matrix. Sebaceous (oil) glands and a bundle of smooth muscle cells are also assiated with hairs. The smooth muscle is the arrector pili. Surrounding each hair follicle are dendrites of neurins that form a hair root plexus, which is sensitive to touch. Hair root plexuses generate nerve impulses if their hair shafts are moved.

Accessory Structures of the Skin

Question 41

What are sebaceous glands?

Accessory Structures of the Skin

Answer 41

Also called oil glands, are simple, branched acinar (rounded) glands. WIth few exceptions, they are connected to hair follicles. Secreting portion of a sebaceous gland lies in the dermis and usually opens into the neck of hair follicle. Secrete oily substance called sebum, a mixture of triglycerides, cholesterol, proteins, and inorganic salts.

Accessory Structures of the Skin

Question 42

What are sudoriferous glands?

Accessory Structures of the Skin

Answer 42

There are 3-4 million in the body. Also called sweat glands. Cells of these glands release sweat, or perspiration, into hair follicles or onto skin surface through pores. Sweat glands are divided into 2 main types, eccrine and apocrine, based on their structure and type of secretion.

Accessory Structures of the Skin

Question 43

What are eccrine sweat glands?

Accessory Structures of the Skin

Answer 43

Are simple, coiled tubular glands that are much more common than apocrine sweat glands. Distributed throughout the skin of most regions of the body, especially in the skin of forehead, palms, and soles. Secretory portion of eccrine sweat glands is located mostly in deep dermis. Excretory duct projects through dermis and epidermis and ends as a pore at surface of epidermis.

Accessory Structures of the Skin

Question 44

What is thermoregulation?

Accessory Structures of the Skin

Answer 44

The homeostatic regulation of body temperature.

Accessory Structures of the Skin

Question 45

What are apocrine sweat glands?

Accessory Structures of the Skin

Answer 45

Simple, coiled tubular glands but have larger ducts and lumens than eccrine glands. Found mainly in skin of axilla, groin, areolae of the breasts, and bearded regions of the face in adult males. Their secretion is via exocytosis, which is chanracteristic of eccrine glands. Secretory portion of these sweat glands is located in the lower dermis or upper subcutaneous layer, and the excretory duct opens into hair follicles. Sweat appears milky or yellowish in color.

Accessory Structures of the Skin

Question 46

What are ceruminous glands?

Accessory Structures of the Skin

Answer 46

Are modified sweat glands in the external ear. Produce a waxy lubricating secretion. Secretory portions of ceruminous glands lie in the subcutaneous later, deep to sebaceous glands. Excretory ducts open either directly onto surface of the external auditory canal or into ducts of sebaceous glands. Combined secretion of ceruminous and sebaceous glands is a yellowish material called cerumen or earwax.

Accessory Structures of the Skin

Question 47

Sebaceous (oil) glands

Accessory Structures of the Skin

Answer 47

Distribution: Largely in lips, glans penis, labia minora, and tarsal glands; small in trunk and limbs; absent in palms and soles.
Location of secretory portion: Dermis.
Termination of excretory duct: Mostly connected to hair follicle.
Secretion: Sebum (mixture of triglycerides, cholesterol, proteins, and inorganic salts).
Functions: Prevent hairs from drying out, prevent water loss from skin, keep skin soft, inhibit growth of some bacteria.
Onset of function: Relatively inactive during childhood; activated during puberty.

Accessory Structures of the Skin

Question 48

Eccrine sweat glands

Accessory Structures of the Skin

Answer 48

Distribution: Throughout skin of most regions of body, especially skin of forehead, palms, and soles.
Location of secretory portion: Mostly in deep dermis (sometimes in upper subcutaneous layer).
Termination of excretory duct: Surface of epidermis.
Secretion: Perspiration, which consists of water, ions (Na+, Cl-), urea, uric acid, ammonia, amino acids, glucose, and lactic acid.
Function: Regulation of body temperature, waste removal, stimulated during emotional stress.
Onset of function: Soon after birth.

Accessory Structures of the Skin

Question 49

Apocrine sweat glands

Accessory Structures of the Skin

Answer 49

Distribution: Skin of axillae, groin, areolae, bearded region of face, clitoris, and labia minora.
Location of secretory portion: Mostly in deep dermis and upper subcutaneous layer.
Termination of excretory duct: Hair follicles.
Secretion: Perspiration, which consists of same components as eccrine sweat glands plus lipids and proteins.
Functions: Stimulated during emotional stress and sexual excitement.
Onset of function: Puberty.

Accessory Structures of the Skin

Question 50

Ceruminous glands

Accessory Structures of the Skin

Answer 50

Distribution: External auditory canal.
Location of secretory portion: Subcutaneous layer.
Termination of excretory duct: Surface of external auditory canal or into ducts of sebaceous glands.
Secretion: Cerumen, a waxy material.
Functions: Impede entrance of foreign bodies and insects into external ear canal, waterproof canal, prevent microbes from entering cells.
Onset of function: Soon after birth.

Accessory Structures of the Skin

Question 51

What are nails?

Accessory Structures of the Skin

Answer 51

Are plates of tightly packed, hard, dead, keratinized epidermal cells that form a clear, solid covering over the dorsal surfaces of the distal portions of the digits. Each nail consists of nail body, a free edge and a nail root.

Accessory Structures of the Skin

Question 52

What is the nail body (plate)?

Accessory Structures of the Skin

Answer 52

The visable portion of the nail. Is comparable to the stratum corneum of the epidermis of the skin with exception that its flattened, keratinized cells fill with a harder type of keratin and the cells are not shed. Below nail body is a region of epithelium and a deeper layer of dermis. Nail body appears pink because blood flowing through capillaries in the underlying dermis.

Accessory Structures of the Skin

Question 53

What is the free edge of the nail?

Accessory Structures of the Skin

Answer 53

The part of the nail body that may extend past the distal end of the digit. Free edge is white because there are no underlying capillaries.

Accessory Structures of the Skin

Question 54

What is the nail root?

Accessory Structures of the Skin

Answer 54

The portion of the nail that is buried in a fold of skin. The whitish, crescent-shaped area of the proximal end of the nail body is called the lunula. Appears whitish beacause the vascular tissue underneath does not show through due to a thickened region of epithelium in the area. Beneath the free edge is a thickened region of stratum corneum called hyponychium.

Accessory Structures of the Skin

Question 55

What is the nail bed?

Accessory Structures of the Skin

Answer 55

Is the skin below the nail plate that extends from the lunula to the hyponychium. Epidermis of the nail bed lacks a stratum granulosum. The eponychium or cuticle is a narrow band of epidermis that extends from and adheres to margin of the nail wall.

Accessory Structures of the Skin

Question 56

What is a hangnail?

Accessory Structures of the Skin

Answer 56

It is a small torn piece of skin at the side or base of a fingernail or toenail, usually caused by dryness of the eponychium.

Accessory Structures of the Skin

Question 57

What is the nail matrix?

Accessory Structures of the Skin

Answer 57

Is the portion of the epithelium proximal to the nail root. The superficial nail matrix cells divide mitotically to produce new nail cells. Growth rate of nails is determined by the rate of mitosis in matrix cells, which is influenced by factors such as a person’s age, health and nutritional status.

Accessory Structures of the Skin

Question 58

What are the functions of nails?

Accessory Structures of the Skin

Answer 58

1. Protect the distal end of the digits.
2. Provide support and counterpressure to the palmar surface of the fingers to enhance touch perception and manipulation.
3. Allow us to grasp and manipulate small objects, and they can be used to scratch and groom the body in various ways.

Accessory Structures of the Skin

Question 59

What are the functions of the integumentary system?

Functions of the Skin

Answer 59

Include thermoregulation, storage of blood, protection, cutaneous sensations, excretion and absorption, and synthesis of vitamin D.

Functions of the skin

Question 60

What is thermoregulation?

Functions of the Skin

Answer 60

The homestatic regulation of body temperature. Skin contributes in 2 ways: by liberating sweat at its surface and by adjusting the flow of blood in the dermis. In response to low environmental temperature, production of sweat from eccrine sweat glands is decreased, which helps conserve heat. Blood vessels in the dermis of skin constrict, which decreases blood low through the skin and reduces heat loss from body. Skeletal muscle contractions generate body heat.

Functions of the Skin

Question 61

What is blood reservoir?

Functions of the Skin

Answer 61

Extensive network of blood vessels that carry 8-10% of the total blood flow in a resting adult, is located in the dermis. For this reason, the skin acts as a blood reservoir.

Functions of the Skin

Question 62

How does the skin provide protection?

Functions of the Skin

Answer 62

Skin provides protection in various ways. Keratin protects underlying tissues from microbes, abrasions, heat, and chemicals, and the tightly interlocked keratinocytes resist invasion by microbes. Lipids released by lamellar granules inhibit evaporation of water from skin surface, thus guarding against dehydration. Oily sebum from sebaceous glands keeps skin and hairs from drying out and contains bactericidal chemicals. Acidic pH of perspiration retards the growth of some microbes. Pigment melanin helps shield against effects of UV light.

Functions of the Skin

Question 63

What is the function of cutaneous sensations of the skin?

Functions of the Skin

Answer 63

There is a wide variety of nerve endings and receptors distributed throughout the skin, including tactile discs of the epidermis, the corpuscles of touch in the dermis, and hair root plexuses around each hair follicle. Sensation of pain, is usually an indication of impending or actual tissue damage.

Functions of the Skin

Question 64

What is the function of excretion and absorption of the skin?

Functions of the Skin

Answer 64

Skin normally has small role in exretion and absorption. About 400mL of water evaporates through skin daily. Sweat removes water and heat from the body, also is the vehicle for excretion of small amounts of salt, carbon dioxide, and two organic molecules that result from breakdown of proteins-ammonia and urea. Certain lipid-soluble materials do penetrate the skin. These include fat-soluble vitamines (A, D, E, and K), certain drugs, and gases oxygen and carbon dioxide.

Functions of the Skin

Question 65

Describe synthesis of Vitamin D in the skin.

Functions of the Skin

Answer 65

Synthesis of Vitamin D requires activation of a precursor molecule in the skin by UV rays in sunlight. Enzymes in liver and kidneys then modify the activated molecule, finally producing calcitriol, the most active form of vitamin D. Calcitriol is a hormone that aids in absorption of calcium from foods in GI tract into blood. Vitamin D is believed to enhance phagocytic activity, increase production of antimicrobial substances in phagocytes, regulate immune functions, and help reduce inflammation.

Functions of the Skin