Module 2: Skin

Question 1

4 major functions of skin

Answer 1

Protection
Sensation
Thermoregulation
Metabolic functions

Question 2

Protection

Answer 2

against UV lights, mechanical, chemical, thermal damage
Prevent excess water uptake/loss
Physical barrier to invasion by microbes

Question 3

Sensation

Answer 3

Largest sensory organ in the body

Receptors for touch, pain, pressure, temp

Question 4

Thermoregulation

Answer 4

Major organ of thermoregulation
Body is insulated against heat loss by presence of hairs and subcutaneous fat tissue
Heat loss is through evaporation of sweat from skin surface and increased blood flow to dermis

Question 5

Metabolic functions

Answer 5

subcutaneous adipose makes just major store of energy (used in synthesis of Vit D; synthesized from ergosterol, a derivative of cholesterol and requires exposure of skin to UV light)

Question 6

3 layers of skin

Answer 6

Epidermis
Dermis
Subcutis or Hypodermis

Question 7

Thick/thin skin refers to the thickness of

Answer 7

the epidermal layer

Question 8

Thick skin

Answer 8

in areas with large amounts of abrasion
Palms of hands, soles of feet
Characterized by prominent granular layer and an increase in amount of keratin in outer layer of epidermis

Question 9

Thin skin

Answer 9

covers remaining body surface
Smaller amount of keratin
Basically same structure as thick skin

Question 10

Furrow

Answer 10

“dip” that separates narrow epidermal ridges
In both thick and thin skin

Epidermal/dermal layer has regular arrangement of ridges (adds to skins ability to resist abrasion and friction)
Fingerprints

Question 11

Interpapillary peg

Answer 11

AKA Rete ridges

Question 12

Dermal ridges

PICTURE*****

Answer 12

Primary dermal ridge mirrors primary epidermal ridge and are divided into 2 secondary ridges by interpapillary pegs of epidermis

Pegs are most prominent in soles and palms

Question 13

Epidermis layers (Bottom to surface)

Answer 13

Stratum Basal
Stratum Spinosum
Stratum Granulosum
Stratum Lucidum (Only in thick skin)
Stratum Corneum

Question 14

What classification is skin

Answer 14

stratified squamous keratinizing epithelia

Question 15

Epidermis

Answer 15

epithelium layer
Waterproof, bacteria and wear resistant
Cells constantly being replaced
Most cells are keratinocytes
Undergo gradual transformation into scales of keratin as they become displaced from the basal layer below (4wks in healthy individual)

Question 16

Stratum Basal

Answer 16

AKA Germinal or Basal Layer

Low columnar
Form single layer separated from the dermis by a basement membrane
Evidence of mitosis is occasionally present

Hemidesmosomes provide anchor between basement membrane and the cells of basal layer

Question 17

Desmosomes

Answer 17

cells between basal and spinosum layer to provide attachment holding the two layers together

Question 18

Stratum Spinosum

Answer 18

AKA Spinosum or Prickle cell layer

Layer is several cells thick; polyhedral in shape
Cells appear to have elongated spines joining the cells (are actually artifact/broken desmosomes due to shrinkage during tissue processing)
Tonofibrils present between cells that give tensile strength

Question 19

Stratum Granulosum

Answer 19

AKA Granular Layer

A few cells thick
Flattened cells filled with granules (involved in production of keratin)
Outer cells of layer die, losing nucleus and cytoplasm and produce a layer of keratin (released upon death)

Question 20

Stratum Lucidum

Answer 20

AKA Lucidum Layer

Only present in thick skin In between granular and cornified layers

Cells are essentially a cell membrane containing keratin

Question 21

Stratum Corneum

Answer 21

AKA Corneum or Cornified Layer

Layer of keratin formed from flattened fused cells without any organelles or nuclei

Question 22

3 other cells in epidermis

Answer 22

Melanocytes
Langerhans
Merkel

Question 23

Melanocytes

Answer 23

produce melanin granules from tyrosine in presence of tyrosinase
Between keratinocytes of stratum basal
Granules produced are transferred to keratinocytes
Function of melanin is to be protection from UV light

Question 24

What is a mole the result of

Answer 24

benign accumulation of melanocytes

Malignant melanoma is a malignant tumor of melanocytes

Question 25

Langerhans cells

Answer 25

lie in stratun spinosum
Antigen presenting cells (part of immune system)
When stimulated, migrate to regional lymph nodes and present antigen to T lymphocytes

Question 26

Merkel cells

Answer 26

sensory receptors for touch

Located in stratum basal

Question 27

Summary of Layers of Epidermis

Answer 27

BOTTOM
Stratum Basal: Single layer, cuboidal or low columnar, mitosis, hemidesmosomes attach to basement membrane, desmososmes attach to each other, melanocytes found between keratinocytes, Merkel cells sparsely scattered

Stratum Spinosum: Several layers, polyhedral, artifact gaps with filaments, desmosome attached, Langerhans cells prominent

Stratum Granulosum: Few layers, flattened cells, basophilic granules of keratinohyaline

Stratum Lucidum: Barely distinguishable, flattened cells (mostly cell membrane), translucent cytoplasm, nuclei undergoing karylolysis, thick skin only

Stratum Corneum: Compact layer of soft keratin, flat scales, anucleate, desmosome attachment, waterproof
OUTER SURFACE

Question 28

Basement Membrane

Answer 28

separates epidermis from dermis

Question 29

2 Layers of dermis

Answer 29

Papillary dermis: Adjacent to epidermis, thin layer of delicate fibrocollagenous support tissue with many fine branched elastic fibers and reticular fibers, blood vessels, sensory nerve endings

Reticular dermis: Forms bulk of dermis, denser than papillary, contains fibrocollagenous tissue with many elastic fibers and cells (fibroblasts, macrophages, occasional fat cells, nerve endings, arterioles, capillaries, venules, lymphatics and skin appendages throughout)

Question 30

Hypodermis or Subcutis

Answer 30

Rich vascular network that branches into dermis
Lymphatics and nerves present
Lots of adipose tissue
Downward extensions of collagen or septae (from dermis)

attaches the skin to the deep fascia, muscles and bone

Question 31

Hair follciles

Answer 31

tubular epithelial structure opening onto the epidermis
External root sheath is modified epidermis
Base is a hair bulb where cells proliferate to form hair shaft and internal root sheath

Associated with arrector pili muscle (attaches to connective tissue surrounding hair sheath; allows hair to stand erect; not in thick skin) and sebaceous glands

Question 32

Sebaceous Glands

Answer 32

holocrine, simple, branches acinar glands
Flask shaped, stain pale
outgrowth of external root sheath of hair follicle
Composed of cell cluster with polyhedral cells in center, and cuboidal around edges

Produce an oily substance, sebum, which coats hair and thin skin surface

Question 33

Eccrine (merocrine) sweat glands

Answer 33

simple coiled tubular glands
Ducts are stratified cuboidal epi
Secretory portion is large cuboidal or simple columnar epi with associated myoepithelial cells (responsible for expulsion of sweat into excretory ducts)
Glands originate in dermis and rise through epidermis to skin surface

Numerous in thick skin

Question 34

Apocrine Sweat glands

Answer 34

become prominent and functional after puberty
Areolae of breast, axillae, genital regions
Produce a slightly milky secretion with some loss of fragments of the cell in response to external stimuli
Secretory portion has large lumen line with simple cuboidal epi
Duct is similar to eccrine glands
Ducts open into hair follicles

Question 35

Nails

Answer 35

highly specialized dense keratinized plate which sits on nail bed made of stratified squamous epi
Nail root is at proximal end of nail plate and extends deep into dermis (attached to periosteum of distal phalanx)
nail growth occurs through differentiation and proliferation of epi under the nail root
Nail plate slides along nail bed as it grows