Chapter 5 (Skin)

Question 1

Integumentary system consists of:

Answer 1

– Skin
– Hair
– Nails
– Sweat glands
– Sebaceous (oil) glands

Question 2

Skin consists of two distinct regions:

Answer 2

Epidermis and Dermis

Question 3

Epidermis

Answer 3

superficial region
 Consists of epithelial tissue and is avascular

Question 4

Dermis

Answer 4

underlies epidermis
 Mostly fibrous connective tissue, vascular

Question 5

Hypodermis (superficial fascia)

Answer 5

 Subcutaneous layer deep to skin
 Not part of skin but shares some functions
 Mostly adipose tissue that absorbs shock and insulates
 Anchors skin to underlying structures: mostly muscles

Question 6

Epidermis consists mostly of what epithelium

Answer 6

keratinized stratified squamous epithelium

Question 7

Keratinocytes

Answer 7

 Produce fibrous keratin (protein that gives skin its protective
properties)
 Major cells of epidermis
 Tightly connected by desmosomes
 Millions slough off every day

Question 8

Melanocytes

Answer 8

 Spider-shaped cells located in deepest epidermis
 Produce pigment melanin, which is packaged into melanosomes
– Melanosomes are transferred to keratinocytes, where they protect
nucleus from UV damage

Question 9

Dendritic (Langerhans) cells

Answer 9

 Star-shaped macrophages that patrol deep epidermis
– Are key activators of immune system

Question 10

Tactile (Merkel) cells

Answer 10

 Sensory receptors that sense touch

Question 11

Five layers of skin

Answer 11

1. Stratum basale
2. Stratum spinosum
3. Stratum granulosum
4. Stratum lucidum (only in thick skin)
5. Stratum corneum

Question 12

Stratum basale (basal layer)

Answer 12

– Deepest of all epidermal layers (base layer)
– Layer that is firmly attached to dermis
– Consists of a single row of stem cells that actively divide (mitotic),
producing two daughter cells each time
 One daughter cell journeys from basal layer to surface, taking 25–45
days to reach surface
– Cell dies as it moves toward surface
 Other daughter cell remains in stratum basale as stem cell
– Layer also known as stratum germinativum because of active mitosis
– 10–25% of layer also composed of melanocyte

Question 13

Stratum spinosum (prickly layer)

Answer 13

– Several cell layers thick
– Cells contain weblike system of intermediate prekeratin filaments attached
to desmosomes
 Allows them to resist tension and pulling
– Keratinocytes in this layer appear spikey, so they are called prickle cells
– Scattered among keratinocytes are abundant melanosomes and dendritic cells

Question 14

Stratum granulosum (granular layer)

Answer 14

– Four to six cells thick, but cells are flattened, so layer is thin
– Cell appearance changes
 Cells flatten, nuclei and organelles disintegrate
 Keratinization begins
– Cells accumulate keratohyaline granules that help form keratin
fibers in upper layers
 Cells also accumulate lamellar granules, a water-resistant glycolipid
that slows water loss
– Cells above this layer die
 Too far from dermal capillaries to survive

Question 15

Stratum lucidum (clear layer)

Answer 15

– Found only in thick skin
– Consists of thin, translucent band of two to three rows of clear, flat, dead
keratinocytes
– Lies superficial to the stratum granulosum

Question 16

Stratum corneum (horny layer)

Answer 16

– 20–30 rows of flat, anucleated, keratinized dead cells
– Accounts for three-quarters of epidermal thickness
– Though dead, cells still function to:
 Protect deeper cells from the environment
 Prevent water loss
 Protect from abrasion and penetration
 Act as a barrier against biological, chemical, and physical assaults

Question 17

Dermis

Answer 17

 Strong, flexible connective tissue
 Cells include fibroblasts, macrophages, and occasionally mast cells and white
blood cells
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 Fibers in matrix bind body together
– Makes up the “hide” that is used to make leather
 Contains nerves, blood vessels, and lymphatic vessels
 Contains epidermal hair follicles, oil glands, and sweat glands

Question 18

2 layers of dermis

Answer 18

– Papillary
– Reticular

Question 19

Papillary Layer

Answer 19

 Superficial layer of areolar connective tissue consisting of loose, interlacing
collagen and elastic fibers and blood vessels
 Loose fibers allow phagocytes to patrol for microorganisms
 Dermal papillae: superficial region of dermis that sends fingerlike projections
up into epidermis
– Projections contains capillary loops, free nerve endings, and touch
receptors (tactile corpuscles, also called Meissner’s corpuscles)
 In thick skin, dermal papillae lie on top of dermal ridges, which give rise to
epidermal ridges
– Collectively ridges are called friction ridges
 Enhance gripping ability
 Contribute to sense of touch
 Sweat pores in ridges leave unique fingerprint pattern

Question 20

Reticular Layer

Answer 20

 Makes up ~80% of dermal thickness
 Consists of coarse, dense fibrous connective tissue
– Many elastic fibers provide stretch-recoil properties
– Collagen fibers provide strength and resiliency
 Bind water, keeping skin hydrated
 Cutaneous plexus: network of blood vessels between reticular layer and
hypodermis
 Extracellular matrix contains pockets of adipose cells
 Cleavage (tension) lines in reticular layer are caused by many collagen
fibers running parallel to skin surface
– Externally invisible
– Important to surgeons because incisions parallel to cleavage lines heal
more readily
 Flexure lines of reticular layer are dermal folds at or near joints
– Dermis is tightly secured to deeper structures
– Skin’s inability to slide easily for joint movement causes deep creases
– Visible on hands, wrists, fingers, soles, toes

Question 21

Striae

Answer 21

Extreme stretching of skin can cause dermal tears, leaving silvery white scars (stretch marks)

Question 22

Blisters

Answer 22

fluid-filled pockets that
separate epidermal and dermal layers

Question 23

Three pigments contribute to skin color

Answer 23

Melanin, Carotene, and Hemoglobin

Question 24

Melanin

Answer 24

 Only pigment made in skin; made by melanocytes
– Packaged into melanosomes that are sent to keratinocytes to shield
DNA from sunlight
– Sun exposure stimulates melanin production
 Two forms: reddish yellow to brownish black
 All humans have same number of keratinocytes, so color differences
are due to amount and form of melanin
 Freckles and pigmented moles are local accumulations of melanin

Question 25

Carotene

Answer 25

 Yellow to orange pigment  Most obvious in palms and soles  Accumulates in stratum corneum and hypodermis  Can be converted to vitamin A for vision and epidermal health

Question 26

Hemoglobin

Answer 26

 Pinkish hue of fair skin is due to lower levels of melanin – Skin of Caucasians is more transparent, so color of hemoglobin shows through

Question 27

Hair

Answer 27

 Consists of dead keratinized cells  None located on palms, soles, lips, nipples, and portions of external genitalia  Functions: – Warn of insects on skin – Hair on head guards against physical trauma – Protect from heat loss – Shield skin from sunlight

Question 28

Structure of a Hair

Answer 28

 Hairs (also called pili): flexible strands of dead, keratinized cells  Produced by hair follicles  Contains hard keratin, not like soft keratin found in skin – Hard keratin is tougher and more durable, and cells do not flake off

Question 29

Regions of a Hair

Answer 29

– Shaft: area that extends above scalp, where keratinization is complete – Root: area within scalp, where keratinization is still going on

Question 30

Three parts of hair shaft:

Answer 30

– 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 31

Structure of a Hair Follicle

Answer 31

 Extends from epidermal surface to dermis  Hair bulb: expanded area at deep end of follicle  Hair follicle receptor (or root hair plexus): sensory nerve endings that wrap around bulb – Hair is considered a sensory touch receptor  Wall of follicle composed of: – Peripheral connective tissue sheath  Derived from dermis  Also called fibrous sheath – Glassy membrane: thickened basal lamina – Epithelial root sheath  Derived from epidermis  Hair matrix: actively dividing area of bulb that produces hair cells – As matrix makes new cells, it pushes older ones upward  Arrector pili: small band of smooth muscle attached to follicle – Responsible for “goose bumps”  Hair papilla – Dermal tissue containing a knot of capillaries that supplies nutrients to growing hair

Question 32

Nails

Answer 32

 Scale-like modifications of epidermis that contain hard keratin  Act as a protective cover for distal, dorsal surface of fingers and toes  Consist of free edge, nail plate, and root  Nail bed is epidermis underneath keratinized nail plate  Nail matrix: thickened portion of bed responsible for nail growth  Nail folds: skin folds that overlap border of nail  Eponychium: nail fold that projects onto surface of nail body  Also called cuticle  Hyponychium: area under free edge of plate that accumulates dirt  Nails normally appear pink because of underlying capillaries – Lunule: thickened nail matrix, appears white  Abnormal color or shape can be an indicator of disease

Question 33

Sweat Glands

Answer 33

 Also called sudoriferous glands  All skin surfaces except nipples and parts of external genitalia contain sweat glands – About 3 million per person  Two main types – Eccrine (merocrine) sweat glands – Apocrine sweat glands  Contain myoepithelial cells – Contract upon nervous system stimulation to force sweat into ducts

Question 34

Eccrine (Merocrine) Sweat Glands

Answer 34

 Most numerous type  Abundant on palms, soles, and forehead  Ducts connect to pores  Function in thermoregulation – Regulated by sympathetic nervous system  Their secretion is sweat – 99% water, salts, vitamin C, antibodies, dermcidin (microbe-killing peptide), metabolic wastes

Question 35

Apocrine Sweat Glands

Answer 35

 Confined to axillary and anogenital areas  Secrete viscous milky or yellowish sweat that contains fatty substances and proteins – Bacteria break down sweat, leading to body odor  Larger than eccrine sweat glands with ducts emptying into hair follicles  Begin functioning at puberty – Function unknown but may act as sexual scent gland – Ceruminous glands: lining of external ear canal; secrete cerumen (earwax) – Mammary glands: secrete milk

Question 36

Sebaceous (Oil) Gland

Answer 36

 Widely distributed, except for thick skin of palms and soles  Most develop from hair follicles and secrete into hair follicles  Relatively inactive until puberty – Stimulated by hormones, especially androgens  Secrete sebum – Oily holocrine secretion – Bactericidal (bacteria-killing) properties – Softens hair and skin

Question 37

Functions of Skin

Answer 37

– Protection – Body temperature regulation – Cutaneous sensations – Metabolic functions – Blood reservoir – Excretion of wastes

Question 38

Three major types of skin cancer

Answer 38

– Basal cell carcinoma – Squamous cell carcinoma – Melanoma

Question 39

Basal cell carcinoma

Answer 39

– Least malignant and most common – Stratum basale cells proliferate and slowly invade dermis and hypodermis – Cured by surgical excision in 99% of cases

Question 40

Squamous cell carcinoma

Answer 40

– Second most common type; can metastasize – Involves keratinocytes of stratum spinosum – Usually is a scaly reddened papule on scalp, ears, lower lip, or hands – Good prognosis if treated by radiation therapy or removed surgically

Question 41

Melanoma

Answer 41

– Cancer of melanocytes; is most dangerous type because it is highly metastatic and resistant to chemotherapy – Treated by wide surgical excision accompanied by immunotherapy – Key to survival is early detection: ABCD rule  A: asymmetry; the two sides of the pigmented area do not match  B: border irregularity; exhibits indentations  C: color; contains several colors (black, brown, tan, sometimes red or blue)  D: diameter; larger than 6 mm (size of pencil eraser)

Question 42

To evaluate burns, the Rule of Nines is used

Answer 42

– Body is broken into 11 sections, with each section representing 9% of body surface (except genitals, which account for 1%) – Used to estimate volume of fluid loss

Question 43

First-degree burn

Answer 43

 Epidermal damage only – Localized redness, edema (swelling), and pain

Question 44

Second-degree burn

Answer 44

 Epidermal and upper dermal damage – Blisters appear – First- and second-degree burns are referred to as partial-thickness burns because only the epidermis and upper dermis are involved

Question 45

Third-degree burn

Answer 45

 Entire thickness of skin involved (referred to as full-thickness burns)  Skin color turns gray-white, cherry red, or blackened  No edema is seen and area is not painful because nerve endings are destroyed  Skin grafting usually necessary

Question 46

Cyanosis

Answer 46

Blue skin color – low oxygenation of hemoglobin

Question 47

Erythema (redness)

Answer 47

Fever, hypertension, inflammation, allergy

Question 48

Pallor (blanching or pale color)

Answer 48

Anemia, low blood pressure, fear, anger

Question 49

Jaundice (yellow cast)

Answer 49

Liver disorders

Question 50

Bronzing

Answer 50

Inadequate steroid hormones (example: Addison’s disease)

Question 51

Bruises (black-and-blue marks)

Answer 51

Clotted blood beneath skin

Question 52

Appendages of skin

Answer 52

* Eccrine sweat gland * Arrector pili muscle * Sebaceous (oil) gland * Hair follicle * Hair root

Question 53

Dermis

Answer 53

Papillary and Reticular layer

Question 54

Hypodermis

Answer 54

(subcutaneous tissue; not part of skin)

Question 55

Nervous structures

Answer 55

* Sensory nerve fiber with free nerve endings * Lamellar corpuscle * Hair follicle receptor (root hair plexus)

Question 56

Stratum corneum

Answer 56

Most superficial layer; 20–30 layers of dead cells, essentially flat membranous sacs filled with keratin. Glycolipids in extracellular space

Question 57

Stratum granulosum

Answer 57

Typically one to five layers of flattened cells, organelles deteriorating; cytoplasm full of lamellar granules (release lipids) and keratohyaline granules

Question 58

Stratum spinosum

Answer 58

Several layers of keratinocytes unified by desmosomes. Cells contain thick bundles of intermediate filaments made of pre-keratin.

Question 59

Stratum basale

Answer 59

Deepest epidermal layer; one row of actively mitotic stem cells; some newly formed cells become part of the more superficial layers. See occasional melanocytes and dendritic cells

Question 60

Severity of burns

Answer 60

Anterior and posterior head and neck, 9% Anterior and posterior upper limbs, 18% Anterior and posterior trunk, 36% Perineum, 1% Anterior and posterior lower limbs, 36%