Skin

Question 1

What is the epidermis?

Answer 1

The superficial layer of the skin classified as stratified squamous keratinized epithelium

Primarily of ectodermal origin and composed predominantly of keratinocytes, melanocytes, Langerhans cells, and Merkel cells.

Question 2

How often is the epidermis regenerated?

Answer 2

Approximately every 30 days

Regeneration is carried out by the mitotic activity of keratinocytes, which normally divide at night.

Question 3

What are epidermal ridges?

Answer 3

Deep downgrowths of the epidermis that interdigitate with projections of the dermis

Resulting in a highly irregular interface with dermal ridges.

Question 4

What are surface ridges and where are they visible?

Answer 4

Ridges produced where the epidermis overlies the dermal ridges, visible as fingerprints on fingertips

The configuration of fingerprints is genetically determined and unique to each individual.

Question 5

What role do keratinocytes play in immune reactions?

Answer 5

They manufacture and release various signaling molecules

Such as interleukins, interferons, tumor necrosis factors, and colony-stimulating factors that stimulate the immune system.

Question 6

Fill in the blank: The epidermis is composed predominantly of _______.

Answer 6

keratinocytes

Question 7

True or False: The epidermis is not involved in immune reactions.

Answer 7

False

Question 8

What types of cells are found in the epidermis?

Answer 8

Keratinocytes, melanocytes, Langerhans cells, Merkel cells

These cells have distinct roles in skin function and health.

Question 9

Fill in the blank: The mitotic activity of _______ is responsible for the regeneration of the epidermis.

Answer 9

keratinocytes

Question 10

What is the deepest layer of the epidermis?

Answer 10

The stratum basale (stratum germinativum)

Composed mostly of keratinocytes that are cuboidal to columnar in shape

Question 11

What type of cells are primarily found in the stratum basale?

Answer 11

Keratinocytes, melanocytes, and Merkel cells

Keratinocytes manufacture and house keratins 5 and 14

Question 12

How are keratinocytes in the stratum basale attached to the basal lamina?

Answer 12

By hemidesmosomes

They are also attached to each other by desmosomes

Question 13

What is the composition of the stratum spinosum?

Answer 13

A few layers of polyhedral keratinocytes (prickle cells)

Their extensions are known as intercellular bridges that terminate in desmosomes

Question 14

What occurs in the deeper aspects of the stratum spinosum?

Answer 14

Mitotic activity of keratinocytes

Keratinocytes and their nuclei become larger and flatter

Question 15

What is the malpighian layer?

Answer 15

The stratum spinosum and stratum basale

Nearly all mitotic activity occurs in this region, primarily at night

Question 16

Which factors facilitate and suppress mitotic activity in the epidermis?

Answer 16

Facilitated by interleukin-1 and epidermal growth factor; suppressed by transforming growth factor

These factors influence cell division in the malpighian layer

Question 17

What characterizes the stratum granulosum?

Answer 17

Three to five layers of flattened keratinocytes with keratohyalin granules

Contains thick bundles of keratin filaments (tonofibrils) and membrane coating granules

Question 18

What is the stratum lucidum?

Answer 18

A clear, homogeneous layer just superficial to the stratum granulosum

Found only in palmar and plantar skin, consisting of keratinocytes without nuclei or organelles

Question 19

What is the composition of the stratum corneum?

Answer 19

15 to 20 layers of flattened, nonnucleated dead cells filled with keratohyalin keratin complex

These nonviable structures are called squames or horny cells

Question 20

What is the shape of the squames in the stratum corneum?

Answer 20

14-sided polygon

These structures are scale-like and nonviable

Question 21

What is the papillary layer of the dermis?

Answer 21

Superficial thin layer of connective tissue that interdigitates with epidermal ridges of the epidermis

Forms dermal papillae where Meissner corpuscles and capillary loops may be found

Question 22

What types of collagen fibers are found in the papillary layer?

Answer 22

Delicate collagen (type I and type III) fibers

Also contains anchoring fibrils (type VII collagen), microfibrils (fibrillin), and elastic fibers

Question 23

What is the reticular layer of the dermis?

Answer 23

Extensive part of the dermis, lying deep to the papillary layer

Contains thick bundles of collagen (type I) fibers and elastic fibers

Question 24

What structures are present in the reticular layer of the dermis?

Answer 24

Arteries, veins, lymphatics, sweat glands, Pacinian corpuscles, and nerves

In thin skin, contains hair follicles, sebaceous glands, and arrector pili muscles

Question 25

Fill in the blank: The papillary layer contains _______ corpuscles.

Answer 25

Meissner

Question 26

What type of collagen fibers are predominant in the reticular layer?

Answer 26

Thick bundles of collagen (type I) fibers ## Footnote Also contains elastic fibers

Question 27

What can exposure of unprotected skin to UV light cause?

Answer 27

Harmful effects to the cells, even in the absence of sunburn. ## Footnote UV radiation can lead to skin damage and increase the risk of skin cancer.

Question 28

What SPF rating does sunscreen need to have to protect against UVB wavelengths?

Answer 28

15 or higher. ## Footnote SPF measures the level of protection against UVB radiation, which is primarily responsible for sunburn.

Question 29

Does sunscreen with SPF 15 or higher protect against UVA wavelengths?

Answer 29

No. ## Footnote UVA rays penetrate the skin more deeply and are associated with aging and long-term skin damage.

Question 30

Fill in the blank: Sunscreen with a sun protection factor (SPF) rating of _______ or higher may protect against UVB wavelengths.

Answer 30

15

Question 31

True or False: Sunscreen protects against both UVA and UVB radiation.

Answer 31

False. ## Footnote Most sunscreens primarily offer protection against UVB rays, and additional protection against UVA requires broad-spectrum formulations.

Question 32

What are melanocytes and where are they located?

Answer 32

Melanocytes are present in the stratum basale ## Footnote Melanocytes originate as melanoblasts from the neural crest.

Question 33

What do melanoblasts become upon reaching the epidermis?

Answer 33

Premelanocytes ## Footnote Premelanocytes enter the stratum basale and form hemidesmosomes with the basal lamina.

Question 34

What binds to premelanocytes to influence their differentiation?

Answer 34

Stem cell factor

Question 35

What structure do melanocytes extend that occupy the extracellular spaces?

Answer 35

Dendrites

Question 36

What is the group of cells formed by the dendrites of a single melanocyte and stratum spinosum cells called?

Answer 36

Epidermal-melanin unit

Question 37

What pigment do melanocytes synthesize?

Answer 37

Melanin

Question 38

In what organelles is melanin synthesized?

Answer 38

Melanosomes

Question 39

What hormone influences melanin synthesis in melanocytes?

Answer 39

Melanocyte-stimulating hormone (MSH)

Question 40

What does MSH bind to in melanocytes to trigger melanin synthesis?

Answer 40

Receptors on the melanocyte plasma membrane

Question 41

What factor is activated in melanocytes as a result of MSH binding?

Answer 41

Microphthalmia-associated transcription factor

Question 42

What enzyme is contained within melanosomes that is directly involved in melanin synthesis?

Answer 42

Tyrosinase

Question 43

How are mature melanosomes transported into dendrites?

Answer 43

Along microtubule pathways powered by myosin Va

Question 44

What pathways deliver melanosomes to the dendrite’s plasma membrane?

Answer 44

F-actin pathways

Question 45

What occurs when melanosomes are released into the extracellular space?

Answer 45

Cells of the stratum spinosum phagocytose the released melanosomes

Question 46

What protective role do melanosomes play once inside keratinocytes?

Answer 46

They form a physical barrier between the keratinocyte’s nucleus and UV rays

Question 47

What percentage of the entire epidermal cell population do melanocytes account for?

Answer 47

Approximately 3%

Question 48

What factors contribute to pigmentation differences among individuals?

Answer 48

* Rate of melanin synthesis * Melanosome size * Content * Rate of transfer * Degradation patterns

Question 49

What are Langerhans cells?

Answer 49

Dendritic cells that originate in the bone marrow and migrate to the epidermis ## Footnote Named for their long processes, Langerhans cells play a crucial role in the immune response.

Question 50

Where are Langerhans cells primarily located?

Answer 50

In the stratum spinosum of the epidermis ## Footnote They contain characteristic paddle-shaped Birbeck granules.

Question 51

What are Birbeck granules associated with in Langerhans cells?

Answer 51

The integral protein langerin ## Footnote These granules are characteristic of Langerhans cells.

Question 52

What immune-related proteins are expressed on the cell membranes of Langerhans cells?

Answer 52

* CD1a * MHC I * MHC II * C3b receptors * Receptors for IgG ## Footnote These proteins play important roles in immune responses.

Question 53

What role does the protein CD1a play in Langerhans cells?

Answer 53

Defends against Mycobacterium leprae ## Footnote It works in association with langerin to provide immunity against leprosy.

Question 54

What function do Langerhans cells serve in immune responses?

Answer 54

They act as antigen-presenting cells ## Footnote They are involved in contact allergies and some skin graft responses.

Question 55

What happens after Langerhans cells phagocytize antigens?

Answer 55

They travel to a lymph node to present the epitope to T cells ## Footnote This initiates a delayed-type hypersensitivity reaction.

Question 56

True or False: Langerhans cells make adhesive junctions to keratinocytes.

Answer 56

False ## Footnote Langerhans cells are independent and do not form such junctions.

Question 57

Merkel cells are present in small numbers in the _____________________ near areas of well vascularized, richly innervated connective tissue.

Answer 57

stratum basale,

Question 58

____________ receive afferent nerve terminals and are believed to function as sensory mechanoreceptors.

Answer 58

merkel cells

Question 59

Merkel cells appear to be more abundant in areas of acute sensory perception, as at the ________________

Answer 59

tips of fingers

Question 60

What is the thickness range of the epidermis in thick skin?

Answer 60

400 to 600 μm

Question 61

Q: What are the characteristic layers of thick skin?

Answer 61

A: Prominent stratum corneum, well-developed stratum granulosum, and often a distinct stratum lucidum.

Question 62

Where is thick skin found on the body?

Answer 62

A: On the palms of the hands and the soles of the feet.

Question 63

What structures are absent in thick skin?

Answer 63

A: Hair follicles, sebaceous glands, and arrector pili muscles.

Question 64

What is the thickness range of the epidermis in thin skin?

Answer 64

A: 75 to 150 μm

Question 65

How does the stratum corneum in thin skin compare to that in thick skin? .

Answer 65

A: It is less prominent

Question 66

Which layers are generally absent in thin skin?

Answer 66

A: Stratum granulosum and stratum lucidum (though similar cells may be present).

Question 67

What structures are present in thin skin that are absent in thick skin?

Answer 67

A: Hair follicles, sebaceous glands, and arrector pili muscles.

Question 68

What are the two main types of sensory receptors in the skin?

Answer 68

A: Unencapsulated and encapsulated receptors.

Question 69

What are Merkel cells and what do they detect?

Answer 69

A: Unencapsulated receptors that detect sustained light touch and texture.

Question 70

What do free nerve endings respond to?

Answer 70

A: Temperature, pain, itching, and tactile stimuli.

Question 71

What is the function of root hair plexuses?

Answer 71

A: Detect movement of hair.

Question 72

What type of response do encapsulated receptors exhibit?

Answer 72

A: Phasic (rapid) responses to stimuli.

Question 73

Where are Meissner corpuscles located and what do they sense?

Answer 73

A: In dermal papillae; sense light touch and low-frequency vibrations.

Question 74

What do Pacinian (lamellated) corpuscles detect?

Answer 74

A: Coarse touch, pressure, and vibration.

Question 75

Where are Krause end bulbs found and what do they sense?

Answer 75

A: In genital skin; sense low-frequency vibrations.

Question 76

What stimuli do Ruffini corpuscles respond to?

Answer 76

A: Skin stretch and twisting.

Question 77

What type of glands are eccrine sweat glands? .

Answer 77

A: Simple coiled tubular glands

Question 78

Where are eccrine sweat glands absent?

Answer 78

A: Lips and parts of the external genitalia.

Question 79

What are the primary functions of eccrine sweat glands?

Answer 79

A: Thermoregulation, conserving electrolytes, and excreting urea and lactic acid.

Question 80

What are the three cell types in the secretory unit of eccrine sweat glands?

Answer 80

A: Dark cells, clear cells, and myoepithelial cells

Question 81

What do dark cells secrete?

Answer 81

A: Mucinogen-rich secretory granules.

Question 82

What is the role of clear cells in eccrine glands?

Answer 82

A: Secrete watery, electrolyte-rich fluid; rich in mitochondria and glycogen.

Question 83

What is the function of myoepithelial cells?

Answer 83

A: Contract to help expel gland secretions into the duct

Question 84

What happens as sweat passes through the dermal duct?

Answer 84

A: Electrolytes are reabsorbed, and substances like urea and drugs are excreted.

Question 85

How is eccrine sweat gland activity regulated?

Answer 85

A: By parasympathetic innervation in response to temperature changes.

Question 86

What is hyperhidrosis?

Answer 86

A: A condition of excessive sweating due to overactive eccrine glands.

Question 87

How can hyperhidrosis be treated? A: Botox injections block sympathetic signals, reducing sweat secretion.

Answer 87

A: Botox injections block sympathetic signals, reducing sweat secretion.

Question 88

Where are apocrine sweat glands located?

Answer 88

A: Axilla, areola of the nipple, perianal region, and external auditory canal (ceruminous glands).

Question 89

When do apocrine glands begin to function?

Answer 89

A: At puberty, under hormonal influence.