EPIDERMIS
stratum corneum
stratum lucidum
stratum granulosum
stratum spinosum
stratum germinativum (basalis)
DERMIS
papillary layer
(loose CT)
layer of dense CT
HYPODERMIS
subcutaneous tissue
• fully keratinized (dead) epithelial cells, no nuclei, low H2O content
• sealed extracellular space
a) prevents evaporation
b) barrier against pathogens
• sqames, most superficial cells, sloughed off
• only in thick skin; advanced keratinization
• keratinocytes here contain basophilic granules of keratohyalin
a) leaks into extracellular space and acts to seal
b) this aids in waterproofing and protection of skin
• lamellar bodies with glycolipids (same function as keratohyalin)
• cells attached to each other via desmosomes which gives spiny
appearance to keratinocytes under LM
• spaces in between cells allow fluid from vessels in the dermis to
nourish the cells (epidermis is avascular!)
• Langerhans cells (involved in the immune system) found here
• contains stem cells from which new keratinocytes arise by mitosis
a) these cells are relatively small, cuboidal to low columnar
b) look for mitotic cells with basophilic appearance
• melanocytes are dendritic cells that synthesize melanin
a) melanin protects from UV radiation
b) can be distributed to surrounding keratinocytes
• blood vessels, nerves, lymphatics found here
• dermal papillae project into the epidermis
• Meissner’s corpuscles (in dermal papillae); mostly in fingertips
a) encapsulated; two point discrimination
• bulb of the hair follicle
a) germinative matrix cells adjacent to the CT papilla – shaft,
sheath formed
b) melanocytes contribute melanin granules
c) sebaceous glands
i.
secret sebum between shaft and follicle
ii.
holocrine secretion
d) arrector pili (smooth muscle bundle)
i.
hair pulled to vertical position
ii.
goosebumps due to skin depression
• eccrine sweat glands (coiled tubular glands)
a) secretion contains salts and IgA
b) secretory portion in subcutaneous tissue
i.
secretory tubules: acidophilic layer of
myoepithelium contracts to expel secretion
ii.
myoepithelium – sympathetic innervation
c) ducts extend to epidermis
i.
excretory ducts: TWO layers of cuboidal cells
ii.
remove salt – final sweat hypotonic
iii.
corkscrew path in epidermis
d) Pacinian corpuscle (boundary b/w dermis and hypodermis)
i.
encapsulated
ii.
senses vibration
• loose CT, many glands, ducts, blood vessels, lymphatics
• abundant adipose tissue
EXTRA Questions (These questions were from last year’s SSN workshop – they are not part of the slidebased practice practical:
1) Melanoma is likely to originate in the ___________ layer, from a mutated ___________.
a.
b.
c.
d.
stratum spinosum, melanocyte
stratum basalis, keratinocyte (with melanin granules)
stratum basalis, melanocyte
stratum basalis, stem cell
answer: c
2) ____________ are found in stratum basalis. They attach keratinocytes to _____________.
a.
b.
c.
d.
Hemidesmosomes, basal lamina
Desmosomes, basal lamina
Hemidesmosomes, other keratinocytes
Desmosomes, Langerhans cells
answer: a
3) Excreted sweat is isotonic / Sebum is secreted by holocrine secretion / Pacinian corpuscles detect two
point touch
a.
b.
c.
d.
F/F/F
T/T/F
F/T/F
T/F/T
answer: c