Lecture 11 skin Flashcards
Skin functions
maintains body temperature
vitamin D synthesis (hormone, not a vitamin)
barrier
- loss of body fluid
- mechanical injury
- noxious agents
- immunological barriers against pathogen
layers of skin
epidermis
dermis
hypodermis (sub Q)
Development of skin
epidermis and its appendages are derived from ectoderm
dermis, hypodermis and vascular elements of these tissues are derived from mesoderm
5 layers of epidermis
- stratum corneum
- stratum lucidum
- stratum granulosum/ granular layer
- stratum spinosum/spinous layer
- stratum basale/basal layer
the main parenchymal cell type of the epidermis
epidermal keratinocytes
Keratinocytes are characterized by expression of ___
cytokeratin genes
keratins proteins encoded by a large ___
gene family (54 in humans)
epidermal keratinocytes are considered prototypical ___
intermediate filaments
- larger than actin filaments and microtubules but smaller than myosin
- play a basic structural role/ provide mechanical strength
type 1 (acid) and type 2 (basic) cytokeratins always form ___
heterodimers
basal layer of epidermis expresses Keratin ___
5 and 14
granular layer of epidermis expresses keratin ___
1 and 10
cytokeratin filaments are anchored by ___
desmosomes
DIFC
desmosome-intermediate filament complexes
Desmocollin and desmoglein
bind to plakophilin and plakoglobin
which bind to desmoplakin
which bind to intermediate filaments
main categories of skin
thick or thin
layers of thin skin
stratum basale
stratum spinosum
stratum granulosum
stratum corneum
layers of thick skin
stratum basale
stratum spinosum
stratum granulosum
stratum lucidum (extra layer)
stratum corneum
differences between thin and thick skin
thick:
5 layers (stratum lucidum)
lack most appendages (hair follicles, sebacous glands, smooth muscle) but does have eccrine sweat glands
Basal Layer
germinativum
deepest layer of epidermis
single layer of columnar or cuboidal cells directely attached to the basement membrane by hemidesmosomes
basal cells (basal keratinocytes) are the stem cells of the epidermis
mitosis occurs in vertical manner, one daughter cell ramins basal while the other moves into the stratum spinosum asymmetric division
mitotic activity replenished the cells in the intermediate layers while the most superficial cells (stratum corneum) are shed (homeostasis)
stratum basale are attached to basement membrane by ___
hemidesmosomes
what are the stem cells of the epidermis
basal cells (basal keratinocytes)
mitosis occurs in a vertical manner in stratum basale, one daughter cell remains basal the other moved into the stratum spinosum. This is called ___
asymmetric division
Stratum spinosum
“Spiny layer”
irregular, heterogenous
can see “bridges(desmosomes)” between cells
why can you see the desmosomes of stratum spinosum
artifact from making the slide
cells retract from each other but stuck at “bridges”
stratum granulosum
in thick skin: several layers of flattened cells
in thin skin: can be one layer of cells
keratohyalin granules
-also contain membrane coating lipid granules, secreted by exocytosis onto the surface of the cells, providing a hydrophobic barrier to water
keratohyalin granules
found in stratum granulosum
contain filaggrin, which associates the cross links keratin filaments
Stratum lucidum
only present in thick skin
- several layer of flattened dead cells
- nuclei begin to degenerate, only faint nuclear outlines present here
- cells are constantly shedding from most superficial layer
in statrum lucidum, ___ begin to degenerate
nuclei
stratum corneum
outermost layer of epidermis
cells are completely filled by keratin filaments
no longer have nuclei
very flat
space between cells filled with lipids, giving the appearance of continuous sheet of keratin
JEB
junctional epidermolysis bullosa
junctional epidermolysis bullosa
-defect in the formation of effective hemidesmosomes
severe and often lethal genetic disease
- very fragile skin, blisters, sloughing, prone to infection
- monogenic disease caused by mutations in any:
laminin
collagen XVII
integrin a6B4
mutations in what genes leads to junctional epidermolysis bullosa
laminin
collagen XVII
Integrin alpha6Beta4 (what hemidesmosomes are made out of)
loss of function mutation in LAMB3 caused
blistering and infection (staph) and loss of 60% of skin
junctional epidermolysis bullosa was treated by
making skin graphs that had the LAMB3 gene corrected
melanocytes
neural-crest derived cells
produce the dark brown pigment melanin from tyrosine
Melanin is synthesized in melanosomes, which then transit along the cytoplasmic extension and are transferred into keratinocytes
lie on basal membrane, attached by hemidesmosomes
melanin is synthesized in
melanosomes
melanosomes transit along the cytoplasmic extensions and are transferred into ___
keratinocytes
melanocytes lie upon the basement membrane between the ___ of the stratum basale
keratinocytes
melanocytes send fine processes between other cells and transfer melanin to ___, mainly to the basal cells
keratinocytes
the fine processes of melanocytes invade the ___ and bud off part of the melanocyte cytoplasm, including the ___
keratinocytes
melanosomes
melanin protects the chromosomes of the mitotically active basal cells against ___
UV-induced damge
__ produced by the pituitary and the adrenal glands affect pigmentation
hormones
langerhans cells
morphologically similar to melanocytes, but are actually immune cells
Dendritic cells
fine processes form a network between cells where they can eat antigens which enter the epidermis
after langerhans cells eat antigen, they will migrate to lymph nodes to “present” antigen to T cells which will initiate an immune response
Merkel Cells
neuroendocrine cells
derived from epithelial proto-basal cells
scattered throughout the stratum basale, mostly found in thick skin
“touch cells”- transmit sensory information via direct innervation
merkel cells are found mostly in ___
thich skin
Merkel cells act as ___
touch sensors- transmit sensory information via direct innervation
it is hard to see merkel cells using ___, easier to see using ___
light microscope
electron microscopy - dense core granules
by their immunocytochemical staining profile (express keratin 8)
Dermis
thick layer of connective tissue to which the epidermis is attached
dermis is akin to ___ in mucosal tissue
lamina propria
two sublayers of dermis
papillary layer
reticular layer
Papillary layer of dermis
wavy surface
loose-cell rich connective tissue which fills the gaps (dermal papillae) at the deep surface of the epidermis
contains nerve endings, fibroblast, macrophages ect.
frequent capillaries
fine, not very dense collagen fibers
ridges of papillary layer of dermis
dermal papillae
reticular layer of dermis
deeper layer of dermis
dense and fewer cells
thick type 1 collagen fibers, often aggregate into bundles
interlacing collagen network, mostly parallel to the epidermis
deeper layer of dermis
recticular layer
reticular layer of dermis has ___ which form into bundles
Type 1 collagen fibers
hypodermis
layer of connective tissue that anchors the dermis to the underlying bone and muscle
loose arrangment of collagen and elastin matrix
lots of adipose tissue (adipocytes) in the form of small clusters of large masses that make up a cushion of fat
hypodermis has lots of ___ tissue that form a “cushion”
adipose
loose arrangement of collagen and elastin matrix
hypodermis
___ anchors the dermis to the underlying bone and muscle
hypodermis
Hair follicles
in mammals- covers the entire body except foot pads, penis and nipples
- flexible and keratinized structure
- root of the hair is anchored in a tubular invagination of the epidermis, hair follicle
the root of each hair is anchored in a tubular invagination of the epidermis called the ___
hair follicle
what are some appendages of the epidermis
hair follicle
sebaceous gland
sweat gland
arrector pilli muscle
label the hair follicle
Hair growth stages
anagen (active growth)
catagen (regression)
telogen (silent/quiescence)
exogen(hair shedding)
anagen
active hair growth
in mice: lasts around 3 weeks
humans: scalp hair: last several years
eyelashases/eyebrows 1-4 months
catagen
regression hair growth
telogen
3rd stage of hair growth
quiescence/silent
exogen
4th stage of hair growth
shedding of hair
hair growth is controlled by ___ and ___ factors
hormonal and hereditary
in anagen phase of hair growth
stem cells get activated that move deeper into skin and trigger proliferating progenitor cells which make hair
the bulge of the hair follicle contains the ___
follicular epithelial stem cells
the bulge of the hair follicle resides in the ___ and is the deepest and most protected place within the epithelial compartment
base of the permanent portion of the follicle
induction of a new anagen phase occurs when the dermal papilla recruits one or more ___
bulge cells
in humans hair growth occurs in a ___ pattern
mosaic
each individual hair develops independently of its neighbor
In species other than humans, hair growth occurs in a ___
wave pattern (mice)
cycles of growth and rest, starting at the head and move towards the tail
__ can initiate hair growth
plucking- leads to apoptosis-a bunch of stuff- wave of hair growth
quorum sensing
sinus hair follicles
whiskers (vibrissae)
large hairs modified to act as mechanosensors
thicker and stiffer then normal hairs
hair follicle - surrounded by blood sinus
what am I
___ amplifies the movement and allows the mechanoreceptors at the base of the vibrissa to detect extremely small deflections
blood
(sinus hair follicle)
(whiskers)
___ offer an advantage to animals when use of non tactile senses is limited
vibrissae
(whiskers)
Two types of sweat glands
eccrine (merocrine) sweat glands
apocrine sweat glands
sebaceous glands
holocrine gland
empty their secretory product into the upper part of the hair follicle
found in thin skin hair follicles and lips and genitalia
alveoli
type of gland that the secretory product is essentially the dead cells of the gland itself
an example is ___
holocrine
sebaceous glands
hair follicle and its associated sebaceous gland form the ___
pilosebaceous unit
What am I
sebaceous gland
explain how sebaceous glands work
live in alveoli
basal cells are flattened and mitotically active
daughter cells accumulate lipids and grow until they break and release their contents (holocrine secretion)
Sweat glands
Eccrine (merocrine) sweat glands
- empty onto surface of epidermis
- found in footpads of dogs and cats, nasolabial region of ruminants
- found all over in human
- watery secretion
-Apocrine Sweat Glands
- non actually aprocine- misnomer
- milk and odorless secretion
- empties into the upper part of the hair follicle (pilosebaceous unit)
What is this
eccrine sweat gland
where are eccrine sweat glands found
footpads of dogs and cats, the nasolabial region of ruminants
all over in humans
Eccrine sweat glands is a ___ duct
excretory - empty directly onto the surface of the skin
A layer of ___ cells is found between the secreotory cells of the epithelium and the basement membrane in eccrine sweat glands
myoepithelial
Apocrine sweat glands
non actually apocrine- misnomer
milk and odorless secretion
empties into the upper part of the hair follicle (pilosebaceous unit)
