Histology SSN
October 27, 2003
SKIN
Vinny: Km2101
Anand: apd2104
Functions: Resists Abrasion, Immunological Defense, Prevents Fluid Loss, Prevents
Fluid Absorption From Environment, and UV Protection.
Refer to Chapter 14 in Ross
EPIDERMIS
stratum corneum  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
stratum lucidum  only in thick skin; advanced keratinization
stratum
 keratinocytes here contain basophilic granules of keratohyalin
granulosum
a) leaks into extracellular space and acts to seal cell
b) this aids in waterproofing and protection of skin
 lamellar bodies with glycolipids are secreted (same function as
keratohyalin)
stratum
 cells attached to each other via desmosomes which gives spiny
spinosum
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
 in upper part synthesis of keratohyalin granules and lamellar
bodies begins
stratum
 contains stem cells from which new keratinocytes arise by mitosis
germinativum
a) these cells are relatively small, cuboidal to low columnar
(basalis)
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
DERMIS
papillary layer
(loose CT)
 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 (see page 385 in Ross)
a) matrix of hair follicle is equivalent to the basal layer of
epidermis
b) melanocytes contribute melanin granules
c) sebaceous glands (always associated with hair follicle)
i.
secrete sebum between shaft and follicle
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Histology SSN
October 27, 2003
ii.
holocrine secretion—cell is stuffed with product
and necroses
d) arrector pili (smooth muscle bundle)
i.
hair pulled to vertical position
ii.
goosebumps due to skin depression
Reticular layer
(dense CT)
 eccrine sweat glands (coiled tubular glands—not associated with
hair follicles)
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
 Pacinian corpuscle (found in deeper dermis and hypodermis)
i.
encapsulated
ii.
senses vibration, deep pressure
HYPODERMIS
subcutaneous
tissue
 loose CT, many glands, ducts, blood vessels, lymphatics
 abundant adipose tissue
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Histology SSN
October 27, 2003
SKIN QUESTIONS
1. In the stratum basalis, ________ are found. They attach keratinocytes to _________.
a.
b.
c.
d.
Hemidesmosomes, basal lamina
Desmosomes, basal lamina
Hemidesmosomes, other keratinocytes
Desmosomes, Langerhans cells
2. What is the function of the structure at the pointer?
a.
b.
c.
d.
senses light touch.
pain and temperature sensation.
deep pressure and vibration sensation.
increases rate of neuronal transmission.
3. The structure is a(n) ________; it is located in the _________ layer, and its ducts
terminate in the ________.
a.
b.
c.
d.
sebaceous gland, hypodermal, stratum granulosum.
eccrine sweat gland, dermal, stratum granulosum.
eccrine sweat gland, dermal, stratum corneum.
sebaceous gland, hypodermal, stratum corneum.
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Histology SSN
October 27, 2003
SKIN ANSWERS
1. Lab 8, slide 2
a) Choice A is correct
b) Choice B is not correct because desmosomes attach keratinocytes to other
keratinocytes.
c) Choice C is not correct because hemidesmosomes attach keratinocytes to
the basal lamina.
d) Choice D is not correct because Langerhans cells are involved in the
immune response and does not form desmosomes with neighboring
keratinocytes.
2. Lab 8, slide 17 (pointer on Pacinian Corpuscle)
a) senses light touch – NO. This better describes a Meissner’s corpuscle,
which senses 2 point discrimination.
b) pain and temp. sensation – NO. This describes free nerve endings in the
epidermis.
c) deep pressure and vibration sensation – YES.
d) increases rate of neuronal transmission – partly true. At best, this answer
is only partly correct, as the STRUCTURE is the corpuscle. A myelin
sheath (composed of Schwann cells) surrounds the nerve axon entering the
corpuscle and does ensure an increased rate of transmission relative to
transmission in unmyelinated nerves – but the myelin sheath only extends
for one or two nodes. The inner core of the corpuscle is composed of
lamellae of attenuated Schwann cells, while the outer core of the corpuscle
is composed of lamellae of extra-corpuscular endoneurial cells. Lymphlike fluid and collagen sit between the lamellae; displacement of lamellae
causes an action potential – so the Schwann cells are also involved in
whether the transmission will happen at all (their role is not limited to
ensuring speed).
3. Lab 8, slide 14
a) Choice A is not correct because sebaceous glands are only associated with
hair follicles.
b) Choice B is not correct because if this were true, sweat would have to
percolate to the outer surface of the epidermis.
c) Choice C is correct.
d) Choice D is not correct because, again, sebaceous glands are only
associated with hair follicles.
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