Histology of the skin

Question 1

functions of the skin

Answer 1

protection (UV, water, chemical/thermal/mechanical insults, micro-organisms)
sensation
thermoregulation
metabolic functions (sc fat, vitamin D synthesis)

Question 2

Thick epidermitesis

Answer 2

found on palms and soles (acral skin

Question 3

thinner epidermis

Answer 3

hair-bearing boyd

Question 4

Epidermis structure

Answer 4

stratified keratinizing squamous epithelium
4 layers:
Stratum corneum
S granulosum
S spinosum
S basale

Question 5

Stratum basale

Answer 5

single layer of cuboidal cells resting on BM
mitotically active - give rise to other keratinocytes
usually pigmented as a result of pigment transfer from neighbouring melanocytes
attached to the BM via hemidesmosomes

Question 6

Stratum spinosum

Answer 6

large, polyhedral cells with visible intercellular connections (desmosomes)

Question 7

stratum granulosum

Answer 7

1-3 layers of flattened cells containing keratohyaline granules

Question 8

Stratum corneum

Answer 8

Fused, flattened, keratinized cells in multiple layers
Cells lose their nucleus and cytoplasmic organelles and are composed almost entirely of keratin filaments
forms the principal diffusion barrier of skin

Question 9

Keratinocytes

Answer 9

ectodermal origin
stem cells in the basal layer of epidermis
cytoplasm has numerous tonofilametns composed of keratin intermediate filaments
held together by desmosomores
flatten and lose nucleus in stratum corneum
rich source of cytokines

Question 10

melanocytes

Answer 10

neural crest origin
melanin protects against UV radiation and scavenges cytotoxic radicals
one melanocyte/4-10 basal keratinocytes
Cell bodies located in the stratum basale with dendritic processes extending upward into more superficial epidermis

Question 11

Melanin production

Answer 11

enzyme tyrosinase
melanin packaged into melanosomes, then melanin granules for transfer to keratinocytes
one melanocyte “feeds” melanin to ~36 keratinocytes
granules accumulate in the supranuclear region of keratinocyte cytoplasm, protecting the nucleus from UV radiation

Question 12

Langerhans cells

Answer 12

Dendritic monocyte-macrophage derived from bone marrow
located within epidermal spinous layer
immune surveillance; antigen-presenting
Birbeck granules: distinct tennis racquet-shaped intracytoplasmic organelles visible on electron microscopy
chronic UV exposure decreases Langerhans cell numbers

Question 13

Merkel cells

Answer 13

located in basal epidermis
associated with free nerve endings - may serve as sensory receptors
most abundant in thick skin of palms and soles and in mucous membranes of lips and oral cavity

Question 14

Dermis zones

Answer 14

papillary dermis: immediately beneath epidermis; finely woven collagen and delicate elastic fibers
Reticular dermis: thick bundles of type I collagen, thick elastic fibers

Question 15

Cells in the dermis

Answer 15

fibroblasts
dermal dendritic cells
histiocytes (macrophages)
mast cells
occasionally - lymphocytes

Question 16

Basement membrane zone function

Answer 16

scaffold for tissue organization and repair
physical barrier between cell types
anchor for the epidermis

Question 17

Vessels in the dermis

Answer 17

two plexi: between papillary and reticular dermis
- between dermis and subcutaneous tissue
rate of skin bloodflow can be controlled to vary from almost 0 to 30% of the Cardiac output
Exposed areas: also direct arteriovenous anastomoses, flow controlled by surrounding smooth muscles

Question 18

Lymphatics in dermis

Answer 18

begin as closed sacs in papillary dermis and converge into two plexi like blood vessels

Question 19

Nerves in the dermis

Answer 19

Encapsulated - sense of touch
Free nerve endings - pain and T
Specialized nerve end organs

Question 20

Meissner corpuscles

Answer 20

papillary dermis

touch receptors

Question 21

Pacinian corpuscles

Answer 21

deep dermis, subcutaneous fat
pressure and vibration receptors
onion-like

Question 22

Pilar unit

Answer 22

hair follicle
sebaceous gland
arrector pili muscle
apocrine gland (when present)

Question 23

Hair follicle

Answer 23

infundibulum: from opening of hair follicle to opening of sebaceous duct
Isthmus: opening of sebaceous duct to insertion of arrector pili
Inferior segment: to the base of the follicle
Hair bulb: base of the hair follicle, surrounds the dermal papilla

Question 24

Sebaceous glands

Answer 24

lobulated, branched acinar glands
Mass of rounded cells containing lipid-filled vacuoles
Holocrine secretion
Palms and soles devoid of sebaceous glands

Question 25

Eccrine glands

Answer 25

unbranched tubular glands
Secretory portion forms a compact coil deep in the dermis or superficial subcutis
secretory portion lined by two layers of cuboidal cells; surrounded by myoepithelial cells

most numerous in the palms and soles

Question 26

Eccrine coil

Answer 26

1) convoluted duct in close association with the secretory unit
2) straight dermal component
3) spiral intraepidermal component (acrosyringium)

Question 27

Apocrine sweat glands

Answer 27

located in the axilla, groin, genital region
empty into hair follicles
under the control of adrenergic receptors and function as scent glands
Duct is histologically identical to that of the eccrine gland

Question 28

Normal scalp skin

Answer 28

hair follicle extending through dermis into sc fat

Question 29

Ear skin

Answer 29

bundant vellus hairs

Question 30

face skin

Answer 30

numerous sebaceous galnds

Question 31

nose skin

Answer 31

large sebaceous glands

Question 32

eyelid skin

Answer 32

thin epidermis
spinous layer only 2-3 cell layers thick
modified apocrine glands (Moll’s glands)

Question 33

Back skin

Answer 33

thick reticular dermis

Question 34

Palms and soles skin

Answer 34

thick compact stratum corneum
numerous eccrine glands
nerve end organs
glomus structures
no pilosebaceous units

Question 35

Lower leg skin

Answer 35

thick vessels in the papillary dermis as a result of gravity and stasis

Question 36

Genitalia/areola/nipple skin

Answer 36

smooth muscle bundles

Question 37

Nail function

Answer 37

protects distal phalanx from trauma
helps in picking up small objects
aids in the appreciation of fine touch
used for scratching
aesthetic organ
animals - locomotion/prehensile

Question 38

Components of the human nail

Answer 38

nail plate

nail unit: nail fold, nail matrix, nail bed

Question 39

Wound healing phases

Answer 39

1) hemostasis: bleeding –> v/c, coagulation, scab
2) inflammation: within first 6-8 hours; PMN cleanse the wound
3) Granulation: fibroplasia, matrix deposition, angiogenesis and re-epithelialization. Change from type III to type I collagen
4) Remodelling