5 The Integumentary System

Question 1

What are the major components of the integumentary system?

Answer 1

The skin and its appendages (hair, nails, sweat glands, sebaceous/oil glands)

Question 2

What are the two distinct layers of the skin?

Answer 2

The epidermis and the dermis

Question 3

The layer of tissue lies deep to the skin? What are some other commonly used names for it?

Answer 3

Subcutaneous tissue (also known as the hypodermis or the superficial fascia)

Question 4

What is the range of thickness for the skin?

Answer 4

The skin ranges from 1.5 mm thick (in the eyelids) to 4 mm thick (in the palms and soles) to even 6 mm thick in some places (skin between the shoulder blades)

Question 5

What is the average surface area of the skin in adults?

Answer 5

The surface area of the skin ranges from 1.2 to 2.2 square meters

Question 6

Around what percentage of total adult body weight does the skin contribute to?

Answer 6

Around 7-8%

Question 7

‘Integument’ refers to what?

Answer 7

The skin (‘integument’ = ‘covering’)

Question 8

The epidermis is composed of what type of tissue?

Answer 8

Stratified squamous epithelial tissue

Question 9

The dermis is composed of what type of tissue?

Answer 9

Mainly dense (fibrous) irregular connective tissue (in the reticular layer)

The thin papillary layer contains areolar connective tissue

Question 10

Which layer of the skin is vascularized?

Answer 10

The dermis

Question 11

Which layer of the skin is avascular?

Answer 11

The epidermis

Question 12

How do nutrients reach the epidermis?

Answer 12

Nutrients reach the epidermis by diffusion through tissue fluid from blood vessels in the underlying dermis

Thus, the deeper layers of the epidermis are nourished by the underlying dermis

Question 13

Is the hypodermis considered part of the skin?

Answer 13

No, the hypodermis (aka subcutaneous tissue, aka superficial fascia) is not part of skin but shares some functions

Question 14

What tissue type is the subcutaneous tissue composed of?

Answer 14

Mostly adipose tissue, but some areolar tissue as well

Question 15

How does the tissue composition of the hypodermis contribute to its function?

Answer 15

Adipose tissue in the subcutaneous tissue/hypodermis stores fat, absorbs shock (thus protecting underlying tissues) and insulates underlying tissues (preventing heat loss)

The subcutaneous tissue also anchors skin to underlying structures (mostly skeletal muscles), but loosely enough that the skin can slide freely over those structures (which makes it so grazing blows to the skin don’t result in damage)

Question 16

Fill in the blanks

Answer 16

Question 17

Which layer of the skin - the epidermis or dermis - is better nourished?

Answer 17

The dermis is better nourished than the epidermis because it is vascularized (contains many blood vessels), while the epidermis is avascular (no blood vessels)

Question 18

What are the four cell types found in the epidermis?

Answer 18

1) Keratinocytes
2) Melanocytes
3) Dendritic (Langerhans) cells
4) Tactile epithelial cells (Merkel cells)

Question 19

What is the most abundant cell type in the epidermis?

Answer 19

Keratinocytes make up vast majority of cells in epidermis

Question 20

What cell-cell junctions are present in the epidermis? How does this contribute to skin function?

Answer 20

Keratinocytes in the epidermis are tightly connected by desmosomes, which gives the epidermis strength and makes it better resist physical damage, penetration; in some layers, there are tight junctions between keratinocytes, which prevents the passage of water or pathogens between cells and helps make the epidermis a waterproof barrier

Question 21

What major protein is produced by keratinocytes? What role does it play?

Answer 21

As keratinocytes are pushed up toward the surface of the epidermis, they produce keratin, a tough, fibrous protein that gives skin its protective properties; by the time keratinocytes reach the surface, they are dead, scale-like flat sacs completely filled with keratin

Question 22

Describe the life cycle of a keratinocyte

Answer 22

Keratinocytes arise in the stratum basale (deepest layer) of the epidermis, when stem cells there undergo mitosis

Division of stem cells in the basal layer of the epidermis goes on continuously, with newly formed keratinocytes pushing older ones upward toward the surface of the epidermis

As keratinocytes are pushed upward from deeper layers of the epidermis towards the surface, they begin to produce keratin, they secrete waxy glycolipids that help form a waterproof barrier, they die, and they flatten

When keratinocytes reach the surface of the epidermis, they are dead, flattened, scale-like sacs of keratin. The cell-cell junctions holding them together weaken and they are sloughed off. Millions of keratinocytes are sloughed off every day.

This whole process is continuous and continuously replaces the epidermis with new cells. A totally new epidermis arises every 25 to 45 days

Question 23

How does the epidermis respond to persistent pressure or friction?

Answer 23

Persistent friction (from a poorly fitting shoe, for example) accelerates both cell production in the basal layer of the epidermis and keratin formation, which causes a thickening of the epidermis at that site called a callus or corn

Question 24

What is a callus?

Answer 24

A callus is a small area of thickened skin (the epidermis is the part that thickens), the formation of which is caused by continued friction, pressure, or other physical or chemical irritation; smaller, deeper version is known as a corn

Question 25

How often are new keratinocytes formed through cell division in the stratum basale?

Answer 25

Mitosis in the stratum basale is essentially continuous, and new keratinocytes are continuously being formed to replace older ones

Question 26

What are keratinocytes?

Answer 26

Keratinocytes represent the major cell type of the epidermis, the outermost of the layers of the skin, making up about 90 percent of the cells there. They originate in the deepest layer of the epidermis, the stratum basale and move up to the final barrier layer of the skin, the stratum corneum

Question 27

What are melanocytes? What is their main function?

Answer 27

Melanocytes are spider-shaped cells located in the deepest layer of the epidermis (stratum basale).

They produce the important pigment melanin, which is packaged into vesicles called melanosomes that are transferred to keratinocytes through melanocyte cell processes.

Melanosomes accumulate in keratinocytes, where they protect the nucleus against UV damage and contribute to the protective role of skin as a barrier to ultraviolet radiation

Question 28

What is melanin? What is its role?

Answer 28

Melanin is a pigment that is synthesized by melanocytes in the epidermis and then transferred to keratinocytes, where it clusters on the superficial side of the keratinocyte nucleus, forming a pigment shield that protects against UV damage.

It also is a major contributor to skin color, with darker colored skin being a function of a higher concentration of melanin in the skin

In terms of chemical structure, it consists of oligomers or polymers arranged in a disordered manner

Question 29

In which layer of the epidermis are keratinocytes located?

Answer 29

All layers

Question 30

In which layer of the epidermis are melanocytes located?

Answer 30

The stratum basale

Question 31

What are Dendritic (Langerhans) Cells?

Answer 31

Langerhans cells are star-shaped tissue-resident macrophages of the epidermis once thought to be resident dendritic cells. They ingest foreign substances and are key activators of the immune system. They have slender processes that extend among surrounding keratinocytes, forming a network

Question 32

In which layer of the epidermis are dendritic (Langerhans) cells located?

Answer 32

They are most prominent in the stratum spinosum but they can be located in other layers as well

Question 33

What are tactile epithelial cells? What is another name for them?

Answer 33

Tactile epithelial cells (Merkel cells) are mechanoreceptors (a type of sensory receptor) located the epidermal-dermal junction and associated with a sensory nerve ending (on the dermal side). They are essential for light touch sensation.

Question 34

In which layer of the epidermis are tactile epithelial (Merkel) cells located?

Answer 34

The stratum basale (at the epidermal-dermal junction)

Question 35

In which layer of the epidermis are stem cells located?

Answer 35

The stratum basale

Question 36

Thick skin and Thin skin differ based on the thickness of which layer of the skin?

Answer 36

Thick skin and thin skin differ based on the thickness of the epidermis, not the dermis

This can be confusing because the dermis can also vary in thickness and it is a greater contributor to the overall thickness of the skin. When taking into consideration both the epidermis and the dermis, the thickest skin is located on the back between the shoulder blades (although this skin would still be classified as ‘thin skin’ based on the thickness of the epidermis alone)

Question 37

What is the difference between thick skin and thin skin?

Answer 37

In Thick skin, the epidermis is thicker and composed of 5 layers; it is located in sites that are frequently subject to abrasion (the palms, fingertips, and soles of the feet)

In Thin skin, the epidermis is thinner and composed of 4 layers; it is located everywhere else in the body

Thick skin has an extra layer in the epidermis called the stratum lucidum, while thin skin does not have this layer. The other layers are also thicker in thick skin than in thin skin

Question 38

What are the layers of the epidermis (from deep to superficial) in thick skin?

Answer 38

Stratum basale
Stratum spinosum
Stratum granulosum
Stratum lucidum
Stratum corneum

Question 39

What are the layers of the epidermis (from deep to superficial) in thin skin?

Answer 39

Stratum basale
Stratum spinosum
Stratum granulosum
Stratum corneum

Question 40

Where is thick skin located on the body?

Answer 40

Fingertips, palms of the hand, soles of the feet (areas subject to abrasion)

Question 41

Where is thin skin located on the body?

Answer 41

Everywhere except the fingertips, palms of the hand, soles of the feet

Question 42

What are the five layers of the epidermis? (from deep to superficial)

Answer 42

Stratum basale
Stratum spinosum
Stratum granulosum
Stratum lucidum (only in thick skin)
Stratum corneum

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Question 43

What is the stratum basale?

Answer 43

Stratum basale (Basal Layer)
- Basal (deepest) layer of the epidermis
- Also called stratum germinativum (germinating layer)
- Firmly attached to underlying dermis along a wavy border (like corrugated carboard)
- Consists of a single row of stem cells, interspersed with melanocytes
- Stem cells in this stratum continually undergo mitosis, with one daughter cell being pushed upwards as a new keratinocyte, and the other daughter cell remaining in the stratum basale as a stem cell to produce more cells
- 10-25% of cells in the stratum basale are melanocytes

Question 44

What is the key process that occurs in the stratum basale?

Answer 44

Division of stem cells, production of new keratinocytes

Question 45

What cells can be found in the stratum basale?

Answer 45

Most are stem cells, 10-25% are melanocytes, and tactile epithelial (Merkel) cells can also be found

Question 46

How many cell layers thick is the stratum basale?

Answer 46

One cell layer thick

Question 47

What is the stratum spinosum?

Answer 47

Stratum spinosum (Prickly/Spiny layer)
- second deepest layer of the epidermis
- several cell layers thick
- gets its name because under the microscope cells look like they have spikes; this is an artifact of specimen preparation because the cells shrink will still being attached at their desmosomes; with the attachments between cells looking like little prickles
- Keratinocytes in this layer contain a weblike system off bundles of intermediate filaments called prekeratin attached to desmosomes
- This layer also contains dendritic (Langerhans) cells scattered among the keratinocytes; Of all the layers of the epidermis, dendritic cells are most abundant in this layer

Question 48

What cells are located in the stratum spinosum?

Answer 48

Mostly keratinocytes, some dendritic (Langerhans) cells scattered throughout, melanocyte thin cell processes extend through this layer and form a network

Question 49

How many cell layers thick is the stratum spinosum?

Answer 49

Several cell layers thick

Question 50

What is the stratum granulosum?

Answer 50

Stratum granulosum (Granular layer)
- The third deepest layer in the epidermis
- Four to six cells thick, but cells are flattened, so the layer is thin
- Drastic changes to keratinocytes occur in this layer: cells flatten, nuclei and organelles begin to disintegrate, keratinization begins, cells begin to accumulate two types of granules (keratohyaline granules, which help produce keratin fibers in the upper layers, and lamellar granules, which contain a water-resistant glycolipid that the cells secrete into the extracellular space, which along with tight junctions helps form a waterproof barrier between cells
- Cells above this layer die because: 1) they are too far from the dermal capillaries which supplies the nourishment and 2) they are surrounded by glycolipids which also prevent water and nutrients from diffusing to them

Question 51

What key changes to keratinocytes occurs in the stratum granulosum?

Answer 51

• Cells flatten
• Nuclei and organelles begin to disintegrate
• Keratinization begins
• Cells begin to accumulate two types of granules:
• keratohyaline granules, which help produce keratin fibers in the upper layers
• lamellar granules, which contain a water-resistant glycolipid that the cells secrete into the extracellular space, which along with tight junctions helps form a waterproof barrier between cells

Question 52

What are the two types of granules that begin to accumulate in keratinocytes in the stratum granulosum? What is the function of each?

Answer 52

-keratohyaline granules, which help produce keratin fibers in the upper layers
- lamellar granules, which contain a water-resistant glycolipid that the cells secrete into the extracellular space, which along with tight junctions helps form a waterproof barrier between cells

Question 53

Above which layer in the epidermis are all cells dead?

Answer 53

Stratum granulosum

Question 54

How many cell layers thick is the stratum granulosum?

Answer 54

4-6 cell layers thick (but cells are flattened, so the layer is thin)

Question 55

What is the stratum lucidum?

Answer 55

Stratum lucidum (Clear layer)
- Present only in thick skin
- Second most superficial layer of epidermis (just deep to stratum corneum)
- Appears under microscope as a thin, translucent band
- two or three rows of clear, flat, dead keratinocytes
- Keratinocytes are almost identical to those in the more superficial stratum corneum

Question 56

How many cell layers thick is the stratum lucidum?

Answer 56

Two to three cell layers thick (appears as a thin, translucent band)

Question 57

What is the stratum corneum?

Answer 57

Stratum corneum (Horny layer)
- Surface layer of the epidermis
- 20-30 rows of flat/scaly, anucleated, keratinized (cornified)dead cells
- Accounts for most of the thickness of the epidermis (around 3/4)
- Cells are filled with keratin filaments embedded in the “glue” from the keratohyaline granules, and the result is tough cells that resist abrasion and penetration and form a thick, fibrous protective layer that protects deeper layers from the environment
- Though the cells are dead, they perform many functions:
- Cells are surrounded by hydrophobic glycolipid and connected by tight junctions, which makes this layer nearly waterproof, prevents water loss
- Acts as a barrier against biological, chemical, and physical assaults
- Cells at the surface are constantly being shed, making up dander and dandruff

Question 58

Describe the morphology of keratinocytes in the stratum corneum and how that contributes to the function of the skin

Answer 58

• Flat/scaly
• Anucleated
• No organelles
• Filled with tough keratin filaments (cornified) embedded in gluey matrix; connected by desmosomes
• ^This forms shieldprotects deeper layer against physical assaults, abrasion, penetration
• Connected by tight junctions, surrounded by hydrophobic glycolipid matrix
• ^this forms a nearly waterproof barrier that prevents water loss from deeper tissues, while also preventing water and chemicals from outside environment from entering body

Question 59

How many cell layers thick is the stratum corneum?

Answer 59

20-30 cell layers thick

Question 60

What is the thickest layer of the epidermis?

Answer 60

Stratum corneum

Question 61

Which layer of the epidermis contributes most to the protective and barrier functions of skin?

Answer 61

Stratum corneum

Question 62

Which layers of the epidermis are completely composed of dead cells?

Answer 62

Stratum corneum, stratum lucidum

Question 63

What happens to keratinocytes that reach the surface of the stratum corneum?

Answer 63

They are shed into the environment; humans can shed around 50,000 cells every minute

Question 64

Fill in the blanks

Answer 64

Question 65

Keratohyaline granules

Answer 65

Granules found in the cells of the stratum granulosum of the epidermis and which contribute to the keratin content of the cornified cells. Mainly consist of keratin, profilaggrin, and other proteins which contribute to cornification or keratinization, the process of the formation of epidermal cornified cell envelope

Question 66

Lamellar granules

Answer 66

(also known as lamellar bodies) Vesicles that are secreted from keratinocytes, resulting in the formation of an impermeable, lipid-containing membrane that serves as a water barrier and is required for correct skin barrier function

Question 67

Why are the desmosomes and tight junctions connecting keratinocytes so important?

Answer 67

The skin is subjected to a lot of abrasion and physical trauma. The desmosomes, which are connecting junctions, help to hold the cells together during such stress. The tight junctions help to reduce water movement though the skin

Question 68

Suppose that the dead cells of the stratum corneum did not shed from your body, but rather stuck to it and continued to accumulate. What problems might this cause?

Answer 68

Some possible answers to this question are: (1) You would either be unable to grow, or there would be big cracks in the stratum corneum as you grew. (2) The thickness of the skin would impede joint movement so it would be hard to move. (3) You would not be able to lose heat through your skin as effectively as you do now. (4) Your skin would be very heavy to carry around after a while

Question 69

What are the two layers of the dermis?

Answer 69

• The papillary dermis : the more superficial layer; directly deep to the epidermis
• The reticular dermis : the deeper layer; makes up most of the dermis

Question 70

What type of tissue is the papillary dermis composed of?

Answer 70

Areolar connective tissue

Question 71

What type of tissue is the reticular dermis composed of?

Answer 71

Dense (fibrous) irregular connective tissue

Question 72

What is the dermis?

Answer 72

• Strong, flexible connective tissue layer that underlies the epidermis
• Makes up most of the thickness of the skin
• embedded with fibers, binds the entire body together like a body stocking
• It is your “hide” and corresponds to animal hides used to make leather
• Made up of two layers: papillary dermis and reticular dermis

Question 73

What are some differences between the epidermis and the dermis?

Answer 73

• The dermis is vascularized, innervated, has lymphatic vessels; the epidermis is avascular
• The epidermis is composed of epithelial tissue while the dermis is composed mostly of connective tissue
• Epidermis is superficial to the dermis
• Dermis is thicker than the epidermis

Question 74

What cells can be found in the dermis?

Answer 74

Its cells are typical of those found in any connective tissue proper: fibroblasts, macrophages, and occasional mast cells and white blood cells

Question 75

Fill in the blanks

Answer 75

Question 76

What is the papillary dermis?

Answer 76

Thin superficial layer of the dermis; composed of areolar connective tissue, consisting of fine collagen fibers and elastic fibers; fine fibers allow phagocytes to move through the tissue, patrol for pathogens; contains blood vessels that nourish the overlying epidermis, nerve endings, touch receptors (tactile corpuscules aka Meissner’s corpuscles)

So named because this is the part of the dermis that contains dermal papillae that project up into epidermis

Question 77

What are dermal papillae?

Answer 77

Small, nipple-like extensions (or interdigitations) of the dermis into the epidermis; form a wavy boundary between the epidermis and dermis that looks like corrugated cardboard

Composed of areolar connective tissue, contain capillary loops, free nerve endings, tactile (Meissner’s) corpuscules

Question 78

What are tactile corpuscles?

Answer 78

Also known as Meissner’s corpuscles; oval sense organs made of flattened cells and encapsulated nerve endings, occurring in hairless skin, as the tips of the fingers and toes, and functioning as a touch receptor

Question 79

What are some differences between the papillary dermis and the reticular dermis?

Answer 79

• Papillary dermis is composed of areolar connective tissue, while the reticular dermis is composed of dense irregular connective tissue
• Papillary dermis has finer collagen fibers, greater ratio of ground substance to fiber, which allows phagocytes to move around in it; reticular dermis has coarse collagen fibers, lesser ratio of ground substance to fiber, making it tough and leathery
• Papillary dermis is superficial to the reticular dermis, just deep to the epidermis; it contains the blood vessels that nourish the overlying epidermis
• Reticular dermis is much thicker than papillary dermis; makes up around 80% of dermis thickness

Question 80

What are friction ridges?

Answer 80

The ridges present on thick skin (the skin of the fingers and toes, and on the palms and soles of the feet, which make contact with an incident surface under normal touch). On the fingers, the distinctive patterns formed by the friction ridges that make up the fingerprints

In thick skin, dermal papillae lie on top of dermal ridges, which give rise to epidermal ridges; collectively, the ridges make up friction ridges

Friction ridges enhance gripping ability, contribute to sense of touch; Sweat pores on the crests of the ridges leave unique fingerprint pattern

Question 81

What is the reticular dermis?

Answer 81

• Deeper layer of the dermis
• Makes up around 80% of dermal thickness
• Made up of dense irregular connective tissue, with isolated pockets of adipose cells
• Coarse collagen fibers provide strength and resiliency
• Elastic fibers provide stretch-recoil properties
• Nourished by the dermal vascular plexus, which lies between the dermis and the subcutaneous tissue
• Named for the network of collagen fibers (reticulum = network), not for reticular fibers

Question 82

What are flexure lines?

Answer 82

Dermal folds that occur at or near joints where dermis is tightly attached to deeper underlying structures

• Skin’s inability to slide easily for joint movement causes deep creases
• Visible on hands, wrists, fingers, soles, toes

Question 83

What are cleavage (tension) lines?

Answer 83

also known as Langer’s linesare topological lines drawn on a map of the human body. They are parallel to the natural orientation of collagen fibers in the dermis. They have relevance to surgeons because incisions made parallel to these lines heal better than those made perpendicular to them

Question 84

What is the difference between friction ridges, flexure lines, and cleavage (tension) lines?

Answer 84

Question 85

What are the three types of dermal modifications that result in characteristic skin markings?

Answer 85

Friction ridges, Flexure lines, and Cleavage (tension) lines

Question 86

What are striae?

Answer 86

Scars or marks left on the skin due to dermal tears caused by extreme stretching of the skin (like that during rapid weight gain/loss, pregnancy); colloquially known as ‘stretch marks’

Question 86

What are blisters?

Answer 86

Fluid-filled pockets that separate the epidermal and dermal layers; caused by acute, short-term traumas

Occurs when fluid fills space between the two layers of skin (epidermis and dermis)

Question 87

Extreme stretching of skin (like that caused by rapid weight gain/loss) can cause tears of fibers in the dermis, leaving silvery white scars called what?

Answer 87

Striae (“stretch marks”)

Question 88

You have just gotten a paper cut. It is very painful, but it doesn’t bleed. Has the cut penetrated into the dermis or just the epidermis?

Answer 88

Because there is no bleeding, the cut has penetrated into the avascular epidermis only

Question 88

Stefan’s front bike tire slipped on a patch of gravel as he rode to work. He needed five stitches to close the cut above his left eye. The split skin ran along a cleavage line. Is Stefan likely to have a major scar or is the wound likely to heal cleanly? Explain.

Answer 88

Because Stefan’s wound runs along a cleavage line, it is likely to heal much more cleanly than it would if it ran perpendicular to the cleavage
lines

Question 88

Draw a wavy line to represent the junction between the dermis and epidermis. Draw and label the layer of epidermal cells next to the dermis. Label the layer of dermis that is next to these epidermal cells and label the projections from this layer that indent the epidermis.

Answer 88

Question 88

What are three important pigments that influence skin color?

Answer 88

1) melanin
2) carotene
3) hemoglobin

Question 89

What is the only pigment produced by the epidermis? Which cells produce it?

Answer 89

Melanin; it is produced by melanocytes, packaged into melanosomes, andd then sent to keratinocytes to shield DNA from sunlight

Question 90

What are two common/important forms of melanin? Which colors does each contribute?

Answer 90

1) eumelanin - brownish black; responsible for darker colored skin; most common type
2) pheomelanin - reddish yellow; responsible to the red or yellow tint given to certain skin/hair colors

Question 91

Which amino acid is melanin derived from?

Answer 91

Tyrosine (Tyr, Y)

Question 92

Which enzyme is critical to melanin biosynthesis?

Answer 92

Tyrosinase

Question 93

Which environmental signal can trigger melanin synthesis?

Answer 93

When skin is exposed to sunlight for prolonged, keratinocytes secrete chemicals that stimulate melanin production in melanocytes, causing a substantial melanin buildup, which helps protect the DNA of skin cells from UV radiation by absorbing the rays and dissipating the energy as heat.

The initial signal for speeding up melanin synthesis seems to be a faster repair rate of DNA that has suffered photodamage

In all but the darkest-skinned people, this defensive response causes skin to darken visibly (tanning occurs)

Question 94

What is responsible for the tanning of skin after prolonged sun exposure?

Answer 94

When skin is exposed to sunlight for prolonged, keratinocytes secrete chemicals that stimulate melanin production in melanocytes, causing a substantial melanin buildup, which helps protect the DNA of skin cells from UV radiation by absorbing the rays and dissipating the energy as heat.

The initial signal for speeding up melanin synthesis seems to be a faster repair rate of DNA that has suffered photodamage

Question 95

Most differences in skin color (like that between those with dark- vs fair-colored skin) is largely attributed to differences in:

Answer 95

• The amount of melanin produced by melanocytes
• How long melanosomes are retained in keratinocytes before being degraded

Question 96

What is one of the major functions of melanin in the skin?

Answer 96

Melanin, packaged into melanosomes that aggregate on the superficial “sunny” side of the nucleus, absorb potentially harmful ultraviolet (UV) radiation, protect the DNA of keratinocytes and protecting underlying tissues from UV damage

Question 97

Describe what happens to melanin from the time it is synthesized to when it is degraded

Answer 97

Melanin is synthesized in melanocytes of the stratum basale, where it is packaged into vesicles called melanosomes

Melanosomes are transferred by the long network of melanocyte cell processes to keratinocytes in the lower layers of the epidermis

Once transferred to keratinocytes, melanosomes aggregate on the superficial “sunny” side of the keratinocyte nucleus

Melanosomes are eventually degraded by keratinocytes, so in lighter-skinned people only keratinocytes in the deepest layers of the epidermis contain them, while in darker-skinned people, melanosomes may be more widespread throughout the layers of the epidermis

Question 98

What are some examples of local accumulations of melanin in the skin that produce dark spots on the skin?

Answer 98

• Freckles
• Pigmented moles (nevi)

Question 99

What are freckles?

Answer 99

Freckles are small brown spots on your skin, often in areas that get sun exposure. In most cases, freckles are harmless. They form as a result of overproduction of melanin. Overall, freckles come from ultraviolet (UV) radiation stimulation

Question 100

What are moles?

Answer 100

Moles, also known as nevi, are a common type of skin growth. They often appear as small, dark brown spots that are caused by clusters of pigment-forming cells called melanocytes. Most people have 10 to 45 moles that appear during childhood and the teenage years. How these moles look may change over time. They also may fade over time.

Most moles are harmless. Rarely, they become cancerous.

Question 101

What are the effects of excessive exposure to sunlight?

Answer 101

Despite melanin’s protective effects, excessive sun exposure eventually damages the skin. It causes elastic fibers to clump, which results in leathery skin; temporarily depresses the immune system; and can alter the DNA of skin cells, lead- ing to skin cancer.

Question 102

What is the deadliest form of skin cancer?

Answer 102

Melanoma

Although darker-skinned people are less likely to get melanoma, the deadliest form of skin cancer, they are not immune and still need to have suspicious skin changes evaluated.

Question 103

What is carotene?

Answer 103

• Yellow to orange pigment
• Accumulates in stratum corneum and in subcutaneous tissue (responsible for yellow color of adipose tissue)
• Most obvious in palms and soles
• Found in certain plant producrts like carrots
• Can be converted to vitamin A, which is important for vision and epidermal health

Question 104

How does hemoglobin contribute to skin color?

Answer 104

In those with fair skin, lack of melanin in the epidermis makes it more transperent, so the crimson color of hemoglobin in the blood shows through, creating the pinkish hue of fair skin

Question 105

What is photosensitivity?

Answer 105

Photosensitivity is the skin’s increased sensistivity to sunlight

Some drugs (e.g., antibiotics, antihistamines) and perfumes cause photosensitivity, leading to skin rashes

Question 106

Skin color can be used by clinicians to better diagnose certain conditions. What are some common alterations in skin color that can indicate disease?

Answer 106

• Cyanosis: blue skin color (shows best under the nails, in mucous membranes), caused by low oxygenation of hemoglobin
• Erythema (redness): can be caused by fever, hypertension, inflammation, allergy; due to increased concentration of hemoglobin in site
• Pallor (blanching; paleness): can be caused by anemia, low blood pressure, fear, anger
• Jaundice (yellow cast): Due to an accumulation of the pigment bilirubin in the blood, an intermediate of red blood cell degradation that is taken up by the liver to be secreted in bile; thus, jaundice is a sign of potential liver failure; most obvious in the sclera of the eyes
• Red/purple/green/yellow marks can be due to bruises, which are caused by physical trauma
• Brown or black “necklace”, or bruises: Dark areas in the axillae and around the neck are sometimes mistaken for a lack of cleanliness. These areas of velvety hyperpigmentation may be a sign of insulin resistance and elevated blood glucose.

Question 107

Melanin and carotene are two pigments that contribute to skin color. What is the third and where is it found?

Answer 107

The third pig-
ment that contributes to skin
color is hemoglobin, the pig-
ment contained in red blood
cells found in blood vessels of the dermis

Question 108

Which alteration in skin color may indicate a liver disorder?

Answer 108

Jaundice, a yellow cast to the skin due to the deposit of yellow bile pigments in body tissues, may indicate a liver disorder.

Question 109

What are the skin appendages? They are all derivatives of which layer of the skin?

Answer 109

Skin appendages include hair, hair follicles, nails, sweat glands, and sebaceous (oil) glands

They all derive from the epithelial cells of the epidermis (i.e., they are epidermal derivatives), but they all extend into the dermis

Question 110

Which parts of the body are covered with hair? Which are not?

Answer 110

All parts of the body except the palms of the hand, soles of the feet, lips, nipples, and portions of external genitalia (like the head of the penis) are covered in hair; although hair is much more sparse in humans than in many other mammals

Question 111

What are some functions of hair in humans?

Answer 111

• Increased touch sensation that warns of insects on skin before they bite or sting us
• Hair on the scalp guards against physical trauma, heat loss, and skin damage due to sunlight
• Hair can trap debris or serve as a filter; ex. eyelashes shield the eyes, nose hairs prevent large particles or insects from entering

Question 112

What is the difference between the hair and the hair follicle?

Answer 112

Hairs (aka pili) are the long filaments, and the hair follicles are tubular invaginations of the epidermis from which the hairs grow

Question 113

What are hairs?

Answer 113

Hairs (also known as pili) are flexible strands produced by hair follicles and consist largely of dead, keratinized cells

Question 114

What is the difference between the keratin found in hair and nails in comparison to the keratin found in the epidermis? What advantages does it offer?

Answer 114

The hard keratin that dominates hairs and nails has two advantages over the soft keratin found in typical epidermal cells: (1) It is tougher and more durable, and (2) its individual cells do not flake off

Question 115

What are the two main regions of a hair?

Answer 115

1) The hair shaft is the part of the hair that projects above the skin’s surface
2) The hair root is the part of the hair embedded in the skin

Question 116

What are some different hair types?

Answer 116

Different hair types are caused by different morphology of the hair filaments

Question 117

What is hair composed of?

Answer 117

Dead, keratinized cells

Question 118

What are the three concentric layers of keratinized cells that make up a hair?

Answer 118

(from inner to outer)
Medulla: central core of large cells and air spaces
Cortex: several layers of flattened cells surrounding medulla
Cuticle: outer layer consisting of overlapping layers of single cells

Question 119

Describe each concentric layer of a hair

Answer 119

The medulla, its central core, consists of large cells and air spaces; the only part of the hair that contains soft keratin; is absent in fine hairs.

The cortex, a bulky layer surrounding the medulla, consists of several layers of flattened cells

The outermost cuticle is formed from a single layer of cells overlapping one another like shingles on a roof. This arrangement helps separate neighboring hairs so the hair does not mat. (Hair conditioners smooth out the rough surface of the cuticle and make hair look shiny.) The cuticle is the most heavily keratinized part of the hair, providing strength and keeping the inner layers tightly compacted. Because it is subjected to the most abrasion, the cuticle tends to wear away at the tip of the hair shaft. This allows keratin fibrils in the cortex and medulla to frizz, creating “split ends.”

Question 120

What is responsible for the pigmentation of hair?

Answer 120

Melanocytes at the base of the hair follicle synthesize pigments like eumelanin and pheomelanin and transfer them to the cortical cells, which contributes to the unique hair color of an individual. The pigments are packaged into melanin granules that exist throughout the cortex of the hair

Combinations of different melanins (yellow, rust, brown, black) creat all the hair colors

Grey/white hair results when melanin production decreases and air bubbles replace melanin in the shaft

Question 121

Fill in the blanks

Answer 121

Question 122

What is a hair follicle?

Answer 122

a tube-like structure (pore) that surrounds the root and strand of a hair

Question 123

What are some important structural parts of a hair follicle?

Answer 123

Hair bulb: expanded area at the deep end of follicle

Hair follicle receptor (or root hair plexus): a knot of sensory nerve endings that wraps around the hair bulb. Bending the hair stimulates these endings, allowing our hairs act as sensitive touch receptors

Hair papilla: a dermal papilla that protrudes into the hair bulb. This papilla contains a knot of capillaries that supplies nutrients to the growing hair and signals it to grow. If the hair papilla is destroyed by trauma, the follicle permanently stops producing hair

Hair matrix: the part of the hair follicle where matrix keratinocytes proliferate to form the hair shaft of growing hair

Follicle Wall: composed of a peripheral connective tissue sheath (fibrous sheath) derived from the dermis, a glassy membrane (thickened basement membrane), and an epithelial root sheath derived from the epidermis

Question 124

What are the layers of the hair follicle wall (from external to internal)?

Answer 124

1) Peripheral connective tissue sheath (fibrous sheath): This connective tissue sheath is derived from the dermis. It forms the external layer of the follicle wall
2) Glassy membrane: The glassy membrane is at the junction of the fibrous sheath and the epithelial root sheath. It is, in essence, the basement membrane of the follicle epithelium.
3) Epithelial root sheath: The epithelial root sheath is derived from the epidermis. It has two components: The external root sheath, a direct continuation of the epidermis, and the internal root sheath, which is derived from the matrix cells

Question 125

What is the hair bulb?

Answer 125

The hair bulb comprises the expanded portion of the inferior hair follicle and contains the dermal papilla and hair matrix

Question 126

What is the hair follicle receptor (root hair plexus)?

Answer 126

A knot of sensory nerve endings that wraps around the hair bulb. Bending the hair stimulates these endings, allowing our hairs act as sensitive touch receptors

Question 127

What is the hair papilla?

Answer 127

A dermal papilla that protrudes into the hair bulb. This papilla contains a knot of capillaries that supplies nutrients to the growing hair and signals it to grow. If the hair papilla is destroyed by trauma, the follicle permanently stops producing hair

Question 128

What is the hair matrix?

Answer 128

The hair matrix, which contains the proliferating cells that generate the hair and the internal root sheath, is just above the dermal papilla, and separated from it by a basement membrane. Like the basal layer of the epidermis, the cells in the hair matrix proliferate and move upwards, gradually becoming keratinized to produce the hair

Question 129

What is going on at a tissue/cellular level that causes hair to grow?

Answer 129

Hair grows because cells in the bulb of the follicle divide rapidly. These dividing cells make up the hair matrix and lie immediately adjacent to the hair papilla. As the matrix produces new hair cells, the older part of the hair is pushed upward, and its fused cells become increasingly keratinized and die. As they divide, hair matrix cells are replenished by stem cells that mi- grate down to the bulb from a region closer to the skin surface called the hair bulge

Question 130

What is the name of the muscle that causes hair to stand up (causing the effect known as “goosebumps”)?

Answer 130

Arrector pili

Question 131

What is the arrector pili?

Answer 131

Associated with each hair follicle is a bundle of smooth muscle cells called an arrector pili muscle. Most hair follicles approach the skin surface at a slight angle. The arrector pili muscle is attached in such a way that its contraction pulls the hair follicle upright and dimples the skin surface to produce goose bumps in response to cold temperatures or fear

Question 132

What are some of the functional roles of the arrector pili muscle

Answer 132

The arrector pili muscle is attached in such a way that its contraction pulls the hair follicle upright and dimples the skin surface to produce goose bumps in response to cold temperatures or fear. This “hair-raising” response is not very useful to humans, with our short sparse hairs, but it is an important way for other animals to retain heat and protect themselves. Furry animals stay warmer by trapping a layer of insulating air in their fur; and a scared animal with its hair on end looks larger and more formidable to its enemy. The more important role of the arrector pili in humans is that its contractions force sebum out of hair follicles to the skin surface where it acts as a skin lubricant.

Question 133

What are two main types of hair in humans?

Answer 133

1) Vellus hair: “peach fuzz”
2) Terminal hair: “true” hair

Question 134

What is the difference between vellus hair and terminal hair?

Answer 134

The body hair of children and adult females is pale, fine The body hair of children and adult females is pale, fine vellus hair

The coarser, longer hair of the eyebrows, eye- lashes, and scalp is terminal hair, which may also be darker.

At puberty, terminal hairs appear in the axillary and pubic regions of both sexes and on the face and chest (and typically the arms and legs) of males. These terminal hairs grow in response to the stimulating effects of androgens (male sex hormones of which testosterone is the most important).

Question 135

What is hirsutism?

Answer 135

Hirsutism is a condition in women that results in excessive growth of dark or coarse hair in a male-like pattern — face, chest and back. Hirsutism is a cosmetic problem that may signal an underlying medical issue. In polycystic ovary syndrome, the ovaries secrete larger amounts of androgens, stimulating hair growth. Less frequently, ovarian or adrenal tumors can secrete androgens. In many cases, no clinical problem is found.

Question 136

Explain hair growth cycles

Answer 136

Hairs grow an average of 2 mm per week, although this rate varies widely among body regions as well as with sex and age. Each follicle goes through growth cycles. In each cycle, an active growth phase is followed by a resting phase in which the hair matrix is inactive and the follicle shinks somewhat. At the start of each active phase, the newly growing hair pushes out the old hair, which is shed. The life span of hairs varies. In the scalp, the follicles stay active for an average of four years, so individual hairs grow quite long before being shed. The follicles in eye- brows, in contrast, are active for only a few months so the eye- brows never grow very long. Fortunately, the cycles of adjacent hair follicles are not synchronized. For this reason, humans shed only a small percentage of their hairs at any one time.

Question 137

On average, how fast do hairs grow?

Answer 137

Hairs grow an average of 2 mm per week, although this rate varies widely among body regions as well as with sex and age.

Question 138

What factors affect hair growth?

Answer 138

Hair growth is affected by hormones (especially sex hormones) and nutrition

Question 139

Why do we lose hair as we grow older?

Answer 139

Given ideal conditions, hair grows fastest from the teen years to the 40s. When hairs are no longer replaced as quickly as they are shed, the hair thins. By age 60 to 65, both sexes usually experience some degree of balding. Coarse terminal hairs are replaced by vellus hairs, and the hair becomes increasingly wispy.

Question 140

What is the medical term for hair loss?

Answer 140

Alopecia

Question 141

What is male pattern baldness?

Answer 141

Male pattern baldness, distinct from the normal hair loss that occurs as we age, is a genetically determined, gender-influenced condition that changes the response of the hair follicles to androgens. The hair follicles respond to androgens with shorter and shorter growth cycles. The cycles become so short that many hairs never even emerge from their follicles before being shed, and those that do are fine vellus hairs that look like peach fuzz in the “bald” area. The drugs used to treat male pattern baldness either inhibit the production of androgens or increase blood flow to the skin and hair follicles. These treatments are only partly successful.

Question 142

Aside from male pattern baldness, what may be some causes behind hair loss?

Answer 142

Abrupt hair thinning may be distressing, and determining its cause can be challenging. Telogen effluvium, or TE, occurs when too many hair follicles enter the resting phase at the same time. TE often occurs after a “shock to the system,” such as surgery, a car crash, hormonal changes with childbirth, crash dieting, or emotional stress.

Hair loss or a change in texture may also signal low thyroid hormone levels. Drugs, including some antidepressants and cancer chemotherapy drugs, may cause hair thinning. Finally, severe dietary deficiencies of protein or minerals may result in thin, brittle hair.

Question 143

Why is having your hair cut painless?

Answer 143

There are no nerves in a hair, so cutting hair is painless

Question 144

Use the image below to answer the following questions.
What are the names of the parts of the hair labeled a and c? What are the names of structures b and d and what is the function of each of these structures?

Answer 144

The parts of the hair labeled a and c are the hair shaft and hair root, respectively. Structures b and d are the arrector pili muscle and the hair papilla, respectively. Arrector pili muscles pull the hair (normally slanted) to the upright position (when cold or scared). Hair papillae
contain a knot of capillaries that supplies nutrients to cells of the hair bulb.

Question 145

Draw a cross section of a hair shaft and label its three concentric regions

Answer 145

Question 146

Fill in the blanks

Answer 146

Question 147

Fill in the blanks

Answer 147

Question 148

What are nails?

Answer 148

A nail forms a clear protective covering on the dorsal surface of the distal part of a finger or toe

Nails correspond to the hooves or claws of other animals, and are useful as “tools” to help pick up small objects or scratch an itch.

In contrast to soft keratin of the epidermis, nails (like hairs) contain hard keratin

Question 149

Describe the structure of nails

Answer 149

Each nail has a proximal nail root (embedded in the skin), a **nail plate or body (visible attached portion), and a free edge**.

The nail rests on a bed of epidermis called the nail bed. This bed contains only the deeper layers of the epidermis, because the nail itself corresponds to the superficial keratinized layers.

The thickened proximal portion of the nail bed, the nail matrix, is responsible for nail growth. As the nail cells produced by the matrix become heavily keratinized, the nail body slides distally over the nail bed.

Nails normally appear pink because of the rich bed of capillaries in the underlying dermis. However, the region that lies over the thick nail matrix appears as a white crescent called the lunule (“little moon”).

The proximal and lateral borders of the nail are overlapped by skin folds, called nail folds. The proximal nail fold projects onto the nail body as the cuticle or eponychium

The thickened region beneath the free edge of the nail where dirt and debris tend to accumulate is the hyponychium. It secures the free edge of the nail plate at the tip of the finger or toe.

Question 150

What are some clinically relevant changes in nail appearance?

Answer 150

Changes in nail appearance
can help diagnose certain
conditions. For example,
yellow-tinged nails may
indicate a respiratory or
thyroid gland disorder.
(Thickened yellow nails
are usually due to a fungus
infecting the nail.) An out-
ward concavity of the nail
(koilonychia or “spoon nail,”) may signal an iron deficiency. Horizontal lines (Beau’s lines) across the nails can be a sign of severe illness that affects the whole body such as uncontrolled diabetes, a heart attack, or cancer chemotherapy.

Question 151

Why is the lunule of a nail white instead of pink like the rest of the nail?

Answer 151

The lunule of the nail is white
because the thick nail matrix that under-
lies it blocks the rosy color of the dermal
blood supply from showing through

Question 152

Why are nails so hard?

Answer 152

Nails are hard because the keratin they contain is the hard keratin variety

Question 153

What are the three main categories of cutaneous glands (skin glands)?

Answer 153

1) Eccrine sweat glands (eccrine sudoriferous glands)
2) Apocrine sweat glands (apocrine sudoriferous glands)
3) Sebaceous (Oil) glands

Question 154

What parts of the skin surface are covered by sweat glands?

Answer 154

The entire skin surface except for the nipples and parts of the external genitalia

Question 155

What are the two types of sweat glands?

Answer 155

1) Eccrine sweat glands
2) Apocrine sweat glands

Question 156

How do eccrine and apocrine sweat glands differ?

Answer 156

Eccrine sweat glands are:
- Far more numerous, cover almost entire skin surface
- Especially abundant on palms of hands, soles of feet, forehead
- Reach less deep into the dermis
- Secrete watery fluid plus some salts, wastes, and antimicrobial peptides

Apocrine sweat glands are:
- Far less numerous (only around 2000 of them)
- Present mainly in axillary (armpit) and anogenital areas
- Larger than eccrine glands, extend deeper into dermis and even into subcutaneous tissue
- Secrete fatty substances and proteins in addition to the same secretions as eccrine glands (these substances are odorless on their own, but when metabolized by bacteria on the skin surface produce the odors commonly associated with body odor)
- Begin functioning at puberty

Despite the confusing name of apocrine sweat glands, both are merocrine glands (meaning that they secrete substances through exocytosis)

Question 157

What are eccrine sweat (sudoriferous) glands?

Answer 157

Eccrine sweat glands also called merocrine sweat glands, are far more numerous than apocrine sweat glands and are particularly abundant on the palms, soles of the feet, and forehead. Each is a simple, coiled, tubular gland. The secretory part lies coiled in the dermis, and the duct extends to open in a funnel-shaped pore at the skin surface

Question 158

Characterize the composition of eccrine sweat gland secretions

Answer 158

Eccrine gland secretion, commonly called sweat, is a hypotonic filtrate of the blood that passes through the secretory cells of the sweat glands and is released by exocytosis. It is 99% water, with some salts (mostly sodium chloride), traces of metabolic wastes (urea, uric acid, and ammonia), and a microbe-killing peptide called dermcidin. Normally, sweat is acidic with a pH between 4 and 6.

Question 159

What are sweat glands?

Answer 159

Sweat glands, also called sudoriferous glands, are distributed over the entire skin surface except the nipples and parts of the external genitalia. Their number is staggering—up to 3 million per person.

We have two types of sweat glands: eccrine and apocrine. In both types, the secretory cells are associated with myoepithelial cells, specialized cells that contract when stimulated by the nervous system. Their contraction forces the sweat into and through the gland’s duct system to the skin surface. Sweating is regulated by a branch of the autonomic (involuntary) nervous system.

Question 160

Characterize the composition of apocrine sweat gland secretions

Answer 160

Apocrine secretion contains the same basic components as true sweat, plus fatty substances and proteins. Consequently, it is viscous and sometimes has a milky or yellowish color. The secretion is odorless, but when bacteria on the skin decom- pose its organic molecules, it takes on a musky and generally unpleasant odor, the basis of body odor.

Question 161

What are apocrine sweat (sudoriferous) glands?

Answer 161

The approximately 2000 apocrine sweat glands are largely confined to the axillary (armpit) and anogenital areas. In spite of their name, they are merocrine glands, which release their product by exocytosis like the eccrine sweat glands. Larger thaneccrine glands, they lie deeper in the dermis or even in the sub- cutaneous tissue, and their ducts empty into hair follicles.

Apocrine glands begin functioning at puberty under the influence of the male sex hormones (androgens) and play little role in maintaining a constant body temperature

Question 162

What is the main function of eccrine sweat (sudoriferous) glands?

Answer 162

Sweating’s major role is to prevent the body from overheat- ing. Heat-induced sweating begins on the forehead and spreads inferiorly over the remainder of the body. Emotionally induced sweating—the so-called “cold sweat” brought on by fright or nervousness—begins on the palms, soles, and axillae (armpits) and then spreads to other body areas.

Question 163

What is the main function of eccrine sweat (sudoriferous) glands?

Answer 163

Their precise function is not yet known. Three lines of evidence suggest that they may be the human equivalent of other animals’ sexual scent glands: (1) Sexual foreplay increases their activity; (2) they enlarge and recede with the phases of a woman’s menstrual cycle; and (3) behavioral studies show that their secretions may act as pheromones (chemical messengers released by one indi- vidual that trigger a response in other members of the same species).

Question 164

What are two important types of modified apocrine glands?

Answer 164

1) Ceruminous glands
2) Mammary glands

Question 165

What are ceruminous glands?

Answer 165

** Ceruminous glands** are modified apocrine glands found in the lining of the external ear canal. Their secretion mixes with sebum produced by nearby sebaceous glands to form a sticky, bitter substance called cerumen, or earwax, that is thought to deter insects and block entry of foreign material.

Question 166

Where are apocrine sweat glands found?

Answer 166

• Axillary region (armpit)
• Anogenital region

Question 167

What type of gland are sweat glands? (based on method of secretion)

Answer 167

Merocrine glands (They secrete substances through exocytosis)

Question 168

What type of gland are sudoriferous glands? (based on method of secretion)

Answer 168

Holocrine glands (They accumulate oily lipids until they become so engorged that they burst) The accumulated lipids and cell fragments constitute sebum.

Question 169

What are sebaceous glands?

Answer 169

The sebaceous glands, or oil glands, are simple branched alveolar glands that are found all over the body except in the thick skin of the palms and soles. They are small on the body trunk and limbs, but quite large on the face, neck, and upper chest.

These glands secrete an oily substance called sebum. The central cells of the alveoli accumulate oily lipids until they become so engorged that they burst, so functionally these glands are holocrine glands The accumulated lipids and cell fragments constitute sebum.

Most, but not all, sebaceous glands develop as outgrowths of hair follicles and secrete sebum into a hair follicle, or occasionally to a pore on the skin surface.

Arrector pili contractions force sebum out of the hair follicles to the skin surface.

Question 170

Where are sebaceous glands located on the skin surface?

Answer 170

Everywhere except the thick skin of the palms of the hand and the soles of the feet

They are small on the body trunk and limbs, but quite large on the face, neck, and upper chest.

Question 171

What do sebaceous glands secrete?

Answer 171

Sebaceous glands secrete an oily substance called sebum

Question 172

What is the major function of sebaceous glands?

Answer 172

Sebum softens and lubricates the hair and skin, prevents hair from becoming brittle, and slows water loss from the skin. Perhaps even more important is its bactericidal (bacterium-killing) action. Sebaceous glands increase their activity during puberty under the influence of male sex hormones.

Question 173

What is acne? What are whiteheads? What are blackheads?

Answer 173

Acne, also known as acne vulgaris, is a long-term skin condition that occurs when dead skin cells and oil from the skin clog hair follicles. Typical features of the condition include blackheads or whiteheads, pimples (pustules), oily skin, and possible scarring

A comedo is a clogged hair follicle (pore) in the skin. Keratin (skin debris) combines with oil to block the follicle. A comedo can be open (blackhead) or closed by skin (whitehead) and occur with or without acne

Acne is associated with infection by Propionibacterium acne. It can range from mild to so severe that it leads to permanent scarring.

Question 174

What is seborrhea?

Answer 174

Overactive sebaceous
glands can cause seborrhea, known
as “cradle cap” in infants. Seborrhea begins on the scalp as pink, raised lesions that gradually become yellow to brown and begin to slough off oily scales.

Question 175

Fill in the blanks

Answer 175

Question 176

What are the main functions of the skin and its appendages?

Answer 176

1) Protection (chemical, physical, biological)
2) Body temperature regulation
3) Cutaneous sensation
4) Metabolic functions
5) Blood reservoir
6) Excretion

Question 177

What are the three major types of skin barriers?

Answer 177

1) Chemical barriers
2) Physical barriers
3) Biological barriers

Question 178

What are the chemical barriers of the skin?

Answer 178

Skin secretions and melanin

Low pH:
Although the skin’s surface teems with bacteria, the low pH of skin secretions—the acid mantle—retards their multiplication.

Antimicrobial peptides/agents:
Dermcidin in sweat and bactericidal substances in sebum kill many bacteria outright. Skin cells also secrete natural antibiotics called defensins that literally punch holes in bacteria, making them leak like sieves. Wounded skin releases large quantities of protective peptides called cathelicidins that are particularly effective in preventing infection by group A streptococcus bacteria.

Melanin:
Melanin provides a chemical pigment shield to prevent UV damage to skin cells

Question 179

What is the acid mantle?

Answer 179

The acid mantle is a very fine, slightly acidic film on the surface of human skin acting as a barrier to bacteria, viruses and other potential contaminants that might penetrate the skin

Question 180

What are the physical barriers of the skin?

Answer 180

The continuity of skin and the hardness of its keratinized cells provide physical barriers.

The outstanding barrier capacity of the skin arises from the structure of its stratum corneum, which has been compared to bricks and mortar. Multiple layers of dead flat cells are the bricks and the glycolipids surrounding them are the mortar

Epidermal continuity prevents bacteria from being able to reach underlying tissues

Waterproof barrier: The water-resistant glycolipids of the epidermis block most diffusion of water and water-soluble substances between cells, preventing both their loss from and entry into the body through the skin. However, there is a continual small loss of water through the epidermis.

Some lipid-soluble substances and other compounds can penetrate the skin in limited amounts, however

Question 181

In what way is the skin a compromise as a physical barrier?

Answer 181

As a physical barrier, the skin is a remarkable compromise. A thicker epidermis would be more impenetrable, but we would pay the price in loss of suppleness and agility.

Question 182

What are the biological barriers of the skin?

Answer 182

1) Dendritic (Langerhans) Cells: part of the immune system. They patrol beneath the skin’s surface, engulfing any foreign invaders that have penetrated the epidermis. Once they have captured their prey, they leave the skin and migrate to the nearest lymph node. There they display their prey to other immune cells, triggering an immune response.

2) Dermal macrophages constitute a second line of defense. They dispose of viruses and bacteria that manage to pen- etrate the epidermis. Like dendritic cells, macrophages can initiate an immune response.

Question 183

What are some substances that can penetrate the skin in limited amounts?

Answer 183

• Lipid-soluble substances, such as oxygen, carbon dioxide, fat- soluble vitamins (A, D, E, and K), and steroids (estrogens)
• Oleoresins of certain plants, such as poison ivy and poison oak
• Organic solvents, such as acetone (can be very harmful, even lethal), dry-cleaning fluid, and paint thinner, which dissolve the cell lipids
• Salts of heavy metals (can be very harmful, even lethal), such as lead and mercury
• Selected drugs (nitroglycerine, seasickness medications)
• Drug agents called penetration enhancers that help ferry other drugs into the body

Question 184

In what ways does the skin regulate body temperature?

Answer 184

1) Vasodilation/vasoconstriction

When body temperature rises, the nervous system stimulates blood vessels in the skin to dilate, resulting in more flow of warm blood to the skin and more heat being lost to the environment (cooling the body)

2) Perspiration (Sweating)

Under normal resting conditions, and as long as the environmental temperature is below 31–32°C, sweat glands secrete about 500 ml (0.5 L) of sweat per day. This routine and unnoticeable sweating is called insensible perspiration. When body temperature rises, the nervous system stimulates the sweat glands into vigorous secretory activity. On a hot day, sweat becomes noticeable and can account for the loss of up to 12 L of body water in one day. This visible output of sweat is called sensible perspiration. Evaporation of sweat from the skin surface dissipates body heat and efficiently cools the body (evaporative cooling), preventing overheating.

Question 185

What are the cutaneous sensory receptors?

Answer 185

The skin is richly supplied with cutaneous sensory receptors, which are actually part of the nervous system. The cutaneous receptors are classified as exteroceptors because they respond to stimuli arising outside the body. For example:

● Tactile (Meissner’s) corpuscles (in the dermal papillae) and tactile epithelial cells with their associated sensory nerve endings allow us to become aware of a caress or the feel of our clothing against our skin.
● Lamellar (also called Pacinian) corpuscles (in the deeper dermis or subcutaneous tissue) alert us to bumps or contacts involving deep pressure.
● Hair follicle receptors report on wind blowing through our hair and a playful tug on a ponytail.
● Free nerve endings that meander throughout the skin sense painful stimuli (irritating chemicals, extreme heat or cold, and others).

Question 186

What roles does the skin play in body metabolism?

Answer 186

**The skin is a chemical factory, fueled in part by the sun’s rays.

1) Vitamin D Synthesis
When sunlight bombards the skin, modified cholesterol molecules are converted to a vitamin D precursor. This precursor is transported via the blood to other body areas to be converted to vitamin D, which plays various roles in calcium metabolism. For example, calcium cannot be absorbed from the digestive tract without vitamin D.

2) Among its other metabolic functions, the epidermis makes chemical conversions that supplement those of the liver. For example, keratinocyte enzymes can:
- “Disarm” many cancer-causing chemicals that penetrate the epidermis
- Activate some steroid hormones—for instance, they can transform cortisone applied to irritated skin into hydrocortisone, a potent anti-inflammatory drug

3) Skin cells also make several biologically important proteins, including collagenase, an enzyme that aids the natural turnover of collagen (and deters wrinkles)

Question 187

How does the skin act as a blood reservoir?

Answer 187

The dermal vascular supply is extensive and can hold about 5% of the body’s entire blood volume. When other body organs, such as vigorously working muscles, need a greater blood supply, the nervous system constricts the dermal blood vessels. This constriction shunts more blood into the general circula- tion, making it available to the muscles and other body organs.

Question 188

How does the skin play excretory roles?

Answer 188

The body eliminates limited amounts of nitrogen-containing wastes (ammonia, urea, and uric acid) in sweat, although most such wastes are excreted in urine. Profuse sweating is an important avenue for water and salt (sodium chloride) loss.

Question 189

What chemicals produced in the skin help provide barriers to bacteria? List at least three and explain how the chemicals are protective.

Answer 189

The low pH of skin secretions (acid mantle) inhibits division of bacteria, and many bacte- ria are killed by dermcidin in sweat, bactericidal substances in sebum, or natural antibiotics called defensins produced by skin cells. Damaged skin secretes cathel- icidins that are effective against a certain strain of strep bacteria.

Question 190

Which epidermal cells play a role in body immunity?

Answer 190

The epidermal dendritic cells play a role in body immunity

Question 191

How is sunlight important to bone health?

Answer 191

Sunlight causes the skin
to produce a precursor of vitamin D from cholesterol. Vitamin D is essential for absorption of calcium from the diet, and calcium is a major component of bone.

Question 192

What are the most common skin disorders?

Answer 192

Bacterial, viral, or yeast infections

Question 193

What is the most common kind of cancer?

Answer 193

Skin cancer is the most common kind of cancer—one in five of us will develop skin cancer at some point

Question 194

What are some risk factors for skin cancer?

Answer 194

The single most important risk factor for skin cancer is exposure to the UV radiation in sunlight and tanning beds, which damages DNA bases. Adjacent pyrimidine bases often respond by fusing, forming lesions called dimers. UV radiation also appears to disable a tumor suppressor gene. In limited numbers of cases, frequent irritation of the skin by infections, chemicals, or physical trauma seems to be a predisposing factor.

Question 195

What are the three major forms of skin cancer?

Answer 195

1) Basal cell carcinoma
2) Squamous cell carcinoma
3) Melanoma

Question 196

What is basal cell carcinoma?

Answer 196

• The least malignant and most common type of skin cancer, accounts for nearly 80% of cases
• Stratum basale cells proliferate, invading the dermis and subcutaneous tissue
• The cancer lesions occur most often on sun-exposed areas of the face and appear as shiny, dome-shaped nodules that later develop a central ulcer with a pearly, beaded edge
• Relatively slow-growing, and metastasis seldom occurs
• Full cure by surgical excision is the rule in 99% of cases.

Question 197

What is squamous cell carcinoma?

Answer 197

• The second most common skin cancer
• Arises from the keratinocytes of the stratum spinosum
• The lesion appears as a scaly reddened papule (small, rounded elevation) that arises most often on the head (scalp, ears, and lower lip), and hands
• Tends to grow rapidly and metastasize if not removed
• If it is caught early and removed surgically or by radiation therapy, the chance of complete cure is good

Question 198

What is melanoma?

Answer 198

• Cancer of melanocytes
• The most dangerous skin cancer because it is highly metastatic and resistant to chemotherapy
• Accounts for only about 1% of skin cancers, but most skin cancer deaths
• Incidence is increasing rapidly
• Melanoma can begin wherever there is pigment. Most such cancers appear spontaneously, and about one-third develop from preexisting moles
• Usually appears as a spreading brown to black patch that metastasizes rapidly to sur- rounding lymph and blood vessels

Question 199

What is the key to preventing/suriving melanoma?

Answer 199

The key to surviving melanoma is early detection. Survival rates decline with increasing thickness of the melanoma, degree of involvement of nearby lymph nodes, and extent of metastasis. In advanced cases, surgical treatment is followed by immunotherapy, radiation therapy, or, more recently, targeted gene therapy that has had promising results by shrinking tumors and/ or prolonging life.

The American Cancer Society suggests that we regularly examine our skin for new moles or pigmented spots.
Apply the ABCD rule for recognizing melanoma:
Asymmetry: The two sides of the pigmented spot or mole do not match.
Border irregularity: The borders of the lesion exhibit indentations.
Color: The pigmented spot contains several colors (blacks, browns, tans, and sometimes blues and reds).
Diameter: The spot is larger than 6 mm in diameter (the size of a pencil eraser).

Some experts add an E, for evolution or evolving (changes with time).

Question 200

What is the ABCD rule for recognizing melanoma?

Answer 200

The American Cancer Society suggests that we regularly examine our skin for new moles or pigmented spots.
Apply the ABCD rule for recognizing melanoma:
Asymmetry: The two sides of the pigmented spot or mole do not match.
Border irregularity: The borders of the lesion exhibit indentations.
Color: The pigmented spot contains several colors (blacks, browns, tans, and sometimes blues and reds).
Diameter: The spot is larger than 6 mm in diameter (the size of a pencil eraser).

Some experts add an E, for evolution or evolving (changes with time).

Question 201

What is a burn?

Answer 201

A burn is tissue damage inflicted by intense heat, electricity, radiation, or certain chemicals, all of which kill cells in the affected areas.

Question 202

What is the most immediate threat to life resulting from severe burns?

Answer 202

The immediate threat to life resulting from severe burns is a catastrophic loss of body fluids containing proteins and electrolytes. This leads to dehydration and electrolyte imbalance, and then renal failure (kidney shutdown) and circulatory shock (inadequate blood circulation due to reduced blood volume). To save the patient, the lost fluids must be replaced immediately by administration of intravenous (IV) fluids.

Question 203

How are burns classified?

Answer 203

Burns are classified according to their severity:

In first-degree burns, only the epidermis is damaged. Symptoms include localized redness, swelling, and pain. First-degree burns tend to heal in two to three days without special attention. Sunburn is usually a first-degree burn.

Second-degree burns injure the epidermis and the upper region of the dermis. Symptoms mimic those of first-degree burns, but blisters also appear. The burned area is red and painful, but skin regeneration occurs with little or no scarring within three to four weeks if care is taken to prevent infection

First- and second-degree burns are considered partial-thickness burns

Third-degree burns are full-thickness burns, involving the entire thickness of the skin (Figure 5.12b). The burned area appears gray-white, cherry red, or blackened, and initially there is little or no edema. Since the nerve endings have been destroyed, the burned area is not painful. Although skin might eventually regenerate, it is usually impossible to wait that long because of fluid loss and infection. Skin grafting is advised.

Question 204

Under what criteria are burns deemed to be critical?

Answer 204

In general, burns are considered critical if any of the follow- ing conditions exists:
● Over 25% of the body has second-degree burns
● Over 10% of the body has third-degree burns
● There are third-degree burns of the face, hands, or feet (facial burns introduce the possibility of burned respiratory passageways, which can swell and cause suffocation)

Question 205

What is the rule of nines? What is it used for?

Answer 205

In adults, the percentage of body surface burned is estimated using the rule of nines. This method divides the body into 11 areas, each accounting for 9% of total body area, plus an addi- tional area surrounding the genitals accounting for 1% of body surface area. The rule of nines is only approximate, so special tables are used when greater accuracy is desired.

Question 206

How are severe burns usually treated?

Answer 206

• Patients with severe burns need thousands of extra food calories daily to replace lost proteins and allow tissue repair. Burn patients are given supplementary nutrients through gastric tubes and IV lines.
• Replacing lost fluid by IV hydration is also critical
• After the initial crisis has passed, infection becomes the main threat and sepsis (widespread bacterial infection) is the leading cause of death in burn victims. Bacteria, fungi, and other pathogens easily invade areas where the skin barrier is destroyed, and they multiply rapidly in the nutrient-rich environment of dead tissues. As you might expect, antibiotics play an important role in burn treatment.
• Longer-term treatment of full-thickness burns usually involves a skin graft

Question 207

What is a skin graft?

Answer 207

Surgical operation in which a piece of healthy skin is transplanted to a new site on the body.

To prepare a burned area for a skin graft, the eschar, or burned skin, must first be debrided (removed).

Then healthy skin is transplanted to the burned site. If possible, the skin is the patient’s own (an autograft). Otherwise, there is a good chance that the patient’s immune system will reject the foreign skin.

Even if the graft “takes,” extensive scar tissue often forms—a major problem because it can limit mobility at joints and other critical areas.

Alternatively, synthetic skin—a silicone “epidermis” bound to a spongy “dermal” layer composed of collagen and ground cartilage—can be applied to the debrided area. In time, the patient’s own dermal tissue absorbs and replaces the artificial one. Then the silicone sheet is peeled off and replaced with a network of epidermal cells cultured from the patient’s own skin.

Research is currently under way where three-dimensional bioprinting is used to create skin grafts that can be used as alternatives to a patient’s own skin. This tissue engineering technology makes use of a bio ink comprising a combination of keratinocytes, fibroblasts, pericytes, and endothelial cells to construct a multilayered skin graft. The advantage of using this technology is that it produces a functional epidermis and vascularized dermis, which improve the chances of graft survival and integration with the patient’s own tissue. Skin grafts created with 3D bio-printing could potentially be used to treat patients with diabetic and pressure ulcers where smaller pieces of skin are required

Question 208

Which type of skin cancer develops from the youngest epidermal cells?

Answer 208

Basal cell carcinoma develops from the youngest epidermal cells

Question 209

What name is given to the rule for recognizing the signs of melanoma?

Answer 209

The ABCD rule helps one to recognize signs of melanoma

Question 210

The healing of burns and epidermal regeneration is usually uneventful unless the burn is a third-degree burn. What accounts for this difference?

Answer 210

First- and second-degree burns can heal uneventfully by regeneration of epidermal cells as long as infection does not occur. Third-degree burns destroy the entire depth of skin and regeneration is usually not possible. Infection and loss of body fluid and proteins make recovery problematic.

Question 211

Although the anterior head and face represent only a small percentage of the body surface, burns to this area are often more serious than those to the body trunk. Why?

Answer 211

Burns to the face are serious because damage to the respiratory passageways can occur in such burns.

Question 212

Which embryonic germ layer is the epidermis derived from? The dermis?

Answer 212

The epidermis is derived from the ectoderm, while the dermis and subcutaneous tissue is derived from the mesoderm

Question 213

Describe development of the skin during fetal development and infancy

Answer 213

The epidermis develops from the embryonic ectoderm and the dermis and subcutaneous tissue develop from mesoderm.

By the end of the fourth month of development, the skin is fairly well formed. The epidermis has all its strata, dermal papillae are obvious, fingerprints have developed, and rudimentary epidermal appendages have formed by downward projections of cells from the basal layer.

During the fifth and sixth months, the fetus is covered with a downy coat of delicate color- less hairs called the lanugo coat. This hairy cloak is shed by the seventh month, and vellus hairs appear.

When a baby is born, its skin is covered with vernix caseosa , a white, cheesy-looking substance produced by the sebaceous glands that protects the fetus’s skin within the water-filled amnion. The newborn’s skin is very thin and often has accumulations in the sebaceous glands on the forehead and nose that appear as small white spots called milia. These normally disappear by the third week after birth.

Question 214

What is the lanugo coat?

Answer 214

Lanugo is the delicate and downy hair that covers a fetus within the uterus (womb). It is very fine hair. It aids in their protection and keeps them warm as they grow. Some neonates, particularly those delivered pre-term, have lanugo on their bodies during birth.

Question 215

What is the vernix caseosa?

Answer 215

Vernix caseosa, also known as vernix, is the waxy white substance found coating the skin of newborn human babies. It is produced by dedicated cells and is thought to have some protective roles during fetal development and for a few hours after birth.

Question 216

Describe the development of the skin from infancy to adulthood

Answer 216

During infancy and childhood, the skin thickens, and more subcutaneous fat is deposited.

Although we all have approximately the same number of sweat glands, the number that func- tion increases in the first two years after birth and is determined by climate. For this reason, people who grow up in hot climates have more active sweat glands than those raised in cooler areas.

During adolescence, the skin and hair become oilier as sebaceous glands increase their activity, and acne may appear. Acne generally subsides in early adulthood, and skin reaches its optimal appearance when we reach our 20s and 30s.

Thereafter, the skin starts to show the effects of cumulative environmental assaults (abrasion, wind, sun, chemicals). Scaling and various kinds of skin inflammation, or dermatitis, become more common.

Question 217

Describe the aging process of skin

Answer 217

• Epidermal replacement slows; skin becomes thin, dry, and itchy (decreases sebaceous gland activity)
• Subcutaneous fat and dermal elasticity decrease leading to cold intolerance and wrinkles
• Increased risk of cancer due to decreased numbers of melanocytes and dendritic cells
• Hair thinning

Question 218

Are there any ways to avoid skin aging?

Answer 218

Although there is no known way to avoid skin aging, one of the best ways to slow the process is to shield your skin from the sun’s rays of both UVA (aging rays) and UVB (rays that burn) light. Aged skin that has been protected from the sun, while it grows thinner and loses some elasticity, still remains unwrinkled and unmarked.

Question 219

What is the difference between UVA and UVB radiation?

Answer 219

Ultraviolet A (UVA) has a longer wavelength. It is associated with skin aging. Ultraviolet B (UVB) has a shorter wavelength. It is associated with skin burning.

Question 220

What causes wrinkling?

Answer 220

Wrinkles are a by-product of the aging process. As people age, skin cells divide more slowly, and the middle layer of your skin — the dermis — begins to thin. The dermis has a network of elastin and collagen fibers, which offer support and elasticity. As this network loosens and unravels with time, depressions form on your skin’s surface. Aging skin is also less able to retain moisture, less efficient in secreting oil and slower to heal. All of these factors contribute to the development of wrinkles.

Question 221

What is albinism?

Answer 221

Inherited condition in which melanocytes do not synthesize melanin owing to a lack of tyrosinase. An albino’s skin is pink, the hair pale or white, and the irises of the eyes unpigmented or nearly so.

Question 222

What is alopecia?

Answer 222

bsence of hair from areas of the body where it would normally occur. May be partial or complete (baldness). In alopecia areata, the immune system attacks the hair follicles, leading to hair loss.

Question 223

What are boils and carbuncles?

Answer 223

Inflammation of hair follicles and sebaceous glands in which an infection has spread to the underlying subcutaneous tissue; common on the dorsal neck. A carbuncle is a cluster of boils. A common cause is bacterial infection.

Question 224

What are cold sores (fever blisters)?

Answer 224

Small fluid-filled blisters that itch
or hurt; usually occur around the lips and in the mucosa of the mouth; caused by a herpes simplex infection. The virus localizes in a cutaneous nerve, where it remains dormant until activated by emotional upset, fever, or UV radiation.

Question 225

What is contact dermatitis?

Answer 225

Itching, redness, and swelling, progressing to blister formation; caused by exposure of the skin to chemicals (e.g., poison ivy oleoresin) that provoke an allergic response in sensitive individuals.

Question 226

What is a decubitus ulcer?

Answer 226

(Aka pressure ulcer) Localized breakdown and ulceration of skin due to interference with its blood supply. Usually occurs over a bony prominence, such as the hip or heel, that is subjected to continuous pressure; also called a bedsore.

Question 227

What is dermatology?

Answer 227

The branch of medicine that studies and treats disorders of the skin.

Question 228

What is eczema?

Answer 228

(Aka atopic dermatitis) A skin rash characterized by itching, blistering, oozing, and scaling of the skin. A common allergic reaction in children, but also occurs in adults. Frequent causes include allergic reactions to certain foods (fish, eggs, and others) or to inhaled dust or pollen. Treated by methods used for other allergic disorders.

Question 229

What is epidermolysis bullosa?

Answer 229

A group of hereditary disorders characterized by inadequate or faulty synthesis of keratin, collagen, and/or basement membrane “cement” that results
in lack of cohesion between layers of the skin and mucosa.
A simple touch causes layers to separate and blister. In severe cases fatal blistering occurs in major vital organs. Because the blisters rupture easily, people with EB suffer frequent infections. Treatments are aimed at relieving the symptoms and preventing infection.

Question 230

What is impetigo?

Answer 230

Pink, fluid-filled, raised lesions (common around the mouth and nose) that develop a yellow crust and eventually rupture. Caused by staphylococcus infection, it is contagious, and common in school-age children.

Question 231

What is porphyria?

Answer 231

A group of inherited disorders in which certain enzymes needed to form the heme of hemoglobin of blood are abnormal. Because these enzymes do not work properly, metabolic intermediates of the heme pathway called porphyrins build up, spill into the circulation, and eventually damage various parts of the body. Some porphyrias make the skin very sensitive to sunlight. The skin becomes lesioned and scarred. In some cases, fingers, toes, and nose are disfigured; gums degenerate and teeth become prominent. Believed to be the basis of folklore about vampires.

Question 232

What is psoriasis?

Answer 232

A chronic autoimmune condition characterized by raised, reddened epidermal patches covered with silvery scales that itch or burn, crack, and sometimes bleed or become infected. When severe, it may be disfiguring and debilitating. Trauma, infection, hormonal changes, or stress often trigger the autoimmune attacks. Cortisone-containing topicals (medications applied to the skin surface) may control mild cases. For more severe cases, self-injected drugs called biologicals and/or phototherapy with UV light in conjunction with chemotherapeutic drugs provides some relief.

Question 233

What is rosacea?

Answer 233

A chronic skin eruption produced by dilated small blood vessels of the face, particularly the nose and cheeks. Papules and acne-like pustules may or may not occur. More common in women. Cause is unknown, but stress, some endocrine disorders, and anything that produces flushing (hot beverages, alcohol, sunlight, etc.) can aggravate this condition.

Question 234

What is vitiligo?

Answer 234

The most prevalent skin pigmentation disorder, characterized by a loss of melanocytes and uneven dispersal of melanin, so that unpigmented skin regions (light spots) are surrounded by normally pigmented areas. An autoimmune disorder.

Question 235

What is scleroderma?

Answer 235

An autoimmune disorder characterized by stiff, hardened skin due to abnormal amounts of collagen in the dermis that severely limit joint movements and facial expressions. A classic sign of the disorder is Raynaud’s phenomenon in which the fingers and toes become white and painful because of poor blood flow to those areas. The fibrosis that occurs in systemic cases may affect a variety of organs including the lungs (eventually leading to difficulty breathing) and the kidneys (leading to renal hypertension because of blood vessel constriction and occlusion).

Question 236

What are dermatomes?

Answer 236

A dermatome is an area on your body that relies on a specific spinal nerve. That spinal nerve is critical for its dermatome because it carries all the nerve signals traveling between the dermatome and your brain.

Usually, this is a two-way connection. Your brain sends signals out to dermatomes, which is how you control your muscles. The nerves in the dermatomes also send signals back, which is how you have your sense of touch, the sensations of hot and cold, and your ability to feel pain. However, some conditions can make this a one-way connection, or that can completely cut off the connection.

Question 237

What is an allergy?

Answer 237

An allergy or allergic reaction is an individually unique hypersensitivity response to certain types of antigens known as allergens

The basis of all allergic reactions is the release of histamine from basophils in the blood and mast cells in the connective tissue

Allergic reactions anywhere in the body almost always involve the skin or mucuous membranes

A local reaction occurs when an allergen touches the skin or mucuous membranes of a hypersensitive individual and is accompanied by inflammation and redness (erythema), swelling (edema), irritation, and itching (pruritus)

A systemic reaction occurs when allergens are inhaled by, ingested by, or injected into a hypersensitive person, causing symtomps in several body systems. Can lead to anaphylaxis, a severe systemic allergic reaction that can be life threatening

Question 238

What are common allergens?

Answer 238

Allergens include cells from plant and animal sources (food, pollens, molds, animal dander), as well as dust, chemicals, and drugs

Question 239

What is anaphylaxis?

Answer 239

Anaphylaxis is a severe systemic allergic reaction that can be life threatening. Symptoms include respiratory distress, hypotension, and shock. Examples: eating peanuts, being stung by a bee, taking a drug that has caused a past allergic reaction, or being exposed to latex gloves. This is also known as anaphylactic shock