5 The Integumentary System Flashcards

Question

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

Answer 1

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

Answer 2

**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*

Answer 3

**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

Answer 4

**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

Answer 5

All layers

Answer 6

The *stratum basale*

Answer 7

**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

Answer 8

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

Answer 9

**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.

Answer 10

The *stratum basale* (at the epidermal-dermal junction)

Answer 11

The *stratum basale*

Answer 12

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)

Answer 13

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

Answer 14

**Stratum basale** **Stratum spinosum** **Stratum granulosum** ***Stratum lucidum*** **Stratum corneum**

Answer 15

**Stratum basale** **Stratum spinosum** **Stratum granulosum** **Stratum corneum**

Answer 16

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

Answer 17

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

Answer 18

**Stratum basale** **Stratum spinosum** **Stratum granulosum** **Stratum lucidum** (only in thick skin) **Stratum corneum** MNEMONIC: **B**rittany **S**pears **G**lows **L**ike **C**andy

Answer 19

**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

Answer 20

Division of stem cells, production of new keratinocytes

Answer 21

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

Answer 22

One cell layer thick

Answer 23

**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

Answer 24

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

Answer 25

Several cell layers thick

Answer 26

**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

Answer 27

- 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

Answer 28

-***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

Answer 29

**Stratum granulosum**

Answer 30

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

Answer 31

**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

Answer 32

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

Answer 33

**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

Answer 34

- 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

Answer 35

20-30 cell layers thick

Answer 36

Stratum corneum

Answer 37

Stratum corneum

Answer 38

Stratum corneum, stratum lucidum

Answer 39

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

Answer 40

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

Answer 41

(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

Answer 42

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

Answer 43

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

Answer 44

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

Answer 45

Areolar connective tissue

Answer 46

Dense (fibrous) irregular connective tissue

Answer 47

- 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

Answer 48

- 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

Answer 49

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

Answer 50

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

Answer 51

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**

Answer 52

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

Answer 53

- 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

Answer 54

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

Answer 55

- 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

Answer 56

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

Answer 57

also known as *Langer's lines*are 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

Answer 58

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

Answer 59

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'

Answer 60

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)

Answer 61

**Striae** ("stretch marks")

Answer 62

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

Answer 63

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

Answer 64

1) **melanin** 2) **carotene** 3) **hemoglobin**

Answer 65

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

Answer 66

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

Answer 67

**Tyrosine (Tyr, Y)**

Answer 68

**Tyrosinase**

Answer 69

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)

Answer 70

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

Answer 71

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

Answer 72

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

Answer 73

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

Answer 74

- **Freckles** - Pigmented **moles (*nevi*)**

Answer 75

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

Answer 76

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.

Answer 77

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.

Answer 78

**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.

Answer 79

- 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

Answer 80

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

Answer 81

Photosensitivity is the skin's increased sensistivity to sunlight Some drugs (e.g., antibiotics, antihistamines) and perfumes cause photosensitivity, leading to skin rashes

Answer 82

- **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.

Answer 83

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

Answer 84

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

Answer 85

**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

Answer 86

**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

Answer 87

- 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

Answer 88

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

Answer 89

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

Answer 90

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

Answer 91

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

Answer 92

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

Answer 93

Dead, keratinized cells

Answer 94

(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

Answer 95

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.”

Answer 96

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

Answer 97

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

Answer 98

**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

Answer 99

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

Answer 100

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

Answer 101

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

Answer 102

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

Answer 103

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

Answer 104

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*

Answer 105

**Arrector pili**

Answer 106

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

Answer 107

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.

Answer 108

1) **Vellus hair**: "peach fuzz" 2) **Terminal hair**: "true" hair

Answer 109

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).

Answer 110

**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.

Answer 111

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.

Answer 112

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

Answer 113

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

Answer 114

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.

Answer 115

**Alopecia**

Answer 116

**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.

Answer 117

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.

Answer 118

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

Answer 119

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.

Answer 120

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**

Answer 121

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.

Answer 122

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.

Answer 123

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

Answer 124

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

Answer 125

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

Answer 126

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

Answer 127

1) Eccrine sweat glands 2) Apocrine sweat glands

Answer 128

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)

Answer 129

**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

Answer 130

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.

Answer 131

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.

Answer 132

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.

Answer 133

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

Answer 134

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.

Answer 135

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).

Answer 136

1) **Ceruminous glands** 2) **Mammary glands**

Answer 137

** 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.

Answer 138

- Axillary region (armpit) - Anogenital region

Answer 139

**Merocrine glands** (They secrete substances through exocytosis)

Answer 140

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

Answer 141

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.

Answer 142

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.

Answer 143

Sebaceous glands secrete an oily substance called **sebum**

Answer 144

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.

Answer 145

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.

Answer 146

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.

Answer 147

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

Answer 148

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

Answer 149

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

Answer 150

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

Answer 151

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

Answer 152

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.

Answer 153

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.

Answer 154

- **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

Answer 155

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.

Answer 156

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).

Answer 157

****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)

Answer 158

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.

Answer 159

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.

Answer 160

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.

Answer 161

The epidermal dendritic cells play a role in body immunity

Answer 162

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.

Answer 163

Bacterial, viral, or yeast infections

Answer 164

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

Answer 165

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.

Answer 166

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

Answer 167

- 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.

Answer 168

- 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

Answer 169

- 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

Answer 170

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 **e**volving (changes with time).

Answer 171

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 **e**volving (changes with time).

Answer 172

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

Answer 173

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.

Answer 174

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.

Answer 175

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)

Answer 176

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.

Answer 177

- 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**

Answer 178

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

Answer 179

Basal cell carcinoma develops from the youngest epidermal cells

Answer 180

The ABCD rule helps one to recognize signs of melanoma

Answer 181

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.

Answer 182

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

Answer 183

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

Answer 184

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.

Answer 185

**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.

Answer 186

**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.

Answer 187

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.

Answer 188

- 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

Answer 189

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.

Answer 190

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.

Answer 191

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.

Answer 192

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.

Answer 193

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.

Answer 194

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.

Answer 195

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.

Answer 196

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.

Answer 197

(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**.

Answer 198

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

Answer 199

(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.

Answer 200

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.

Answer 201

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.

Answer 202

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.

Answer 203

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.

Answer 204

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.

Answer 205

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.

Answer 206

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).

Answer 207

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.

Answer 208

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

Answer 209

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

Answer 210

**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**