block III: Skin video 1 Flashcards
What are the layers of the skin?
epidermis
dermis
Describe epidermis
outer layer maximally keratinized stratified squamous
epithelium.
Describe dermis
fibroelastic connective(CT) underlying the epidermis
WHat are epidermally-derived appendages?
include hair, eccrine sweat glands, appocrine sweat glands, sebaceous glands, nails, and mammary glands
Where do epidermally-derived appendages come from?
They derive from invaginations of epidermis into CT and remain attached to epidermis throughout life.
What is hypodermis?
not a layer of skin; skin sits here (Loose CT)
identify
What is the total body weight of skin?
16%
What are some functions of skin?
- barrier protection: from water loss/gain, mechanical abrasion, UV radiation or chemicals
- Immunological info: Through antigen processing & presentation
- HOMEOSTASIS: By thermoregulation and regulation of water loss
- SENSORY INPUT: Through nerve endings in skin.
Receptors for pleasure, pain, temperature, and
pressure - ENDOCRINE FUNCTIONS: By secretion of
hormones, cytokines, growth factors, and vitamin D - EXCRETION: Through exocrine secretion of
sweat, sebaceous, and apocrine glands - SEXUAL: Through appearances and tactile
senses
What are the two types of skin?
Thick skin and thin skin
What is thick skin? where is it found?
thick epidermis and no hairs. Found on palmar and plantar surfaces. (eccrine sweat glands)
What is thin skin? where is it found?
thin epidermis, typically with hairs. Found over most of rest of body
identify
thick skin
identify
thin skin
WHat are the layers of the epidermis
- Stratum basale
- Stratum spinosum
- Stratum granulosum
- Stratum lucidum -Only seen in thick skin (in some cases).
- Stratum corneum
identify
What are epidermal ridges?
(rete ridges) extend down into dermis. Dermal
Papillae project up into epidermis. Capillary loops are here; reduces distance of epithelium reaching blood vessels
What are the 4 main cell types of the epidermis?
- Keratinocyte (major cell type)
- Melanocytes
- Langerhans cells
- Merkel cells
What is keratinization?
It is important to recognize that the different layers of
epidermis actually represent stages in the differentiation of the keratinocyte
What is the turnover for epithelium?
47 days
identify
startum basale, EM image of hemidesmosomal junctions (arrows) at the basal plasma membrane of an epithelial cells. Note the intermediate filaments binding to the hemidesmosomes
what is the classificatin of stratum basale (germinativum?
A single layer of columnar cells attaching the epidermis to the dermis
* Cells divide to replenish those sloughed off at
surface
WHat organelles can we find in the SB?
- Numerous hemidesmosomes to attach to dermis. Irregular basal surface.
- Small bundles of tonofilaments containing keratin
in cytoplasm - Cells frequently contain melanin pigment granules
identify
Micrograph of epidermis with stratum basales
labeled. Inset: showing the very irregular basal
surface of epidermal cells
WHat are pathologies involving hemidesmosomes?
- Epidermolysis bullosa
- Bullous pephmigoid
What are the 3 types of epidermolysis bullosa?
1.epidermolyosis bullosa simplex (typically due to a defect in keratins 5 and 14)
- junctional epidermolysis bullosa (defects in either collagen XVII or laminin 332 of the hemidesmosome);
3.dystrophic epidermolysis bullosa (defect in collagen type VII of the anchoring fibrils attaching lamina densa to underlying CT)
In what does epidermolysis bullosa result?
blistering and fragility of the skin. Babies or children
with this disorder are frequently said to be “Butterfly children” (skin fragile as a butterfly wing), “cotton wool babies” (because of need to protect the skin with soft cushioning), or “crystal skin babies” [South America] (probably referring to fragility of skin)
What is bullous pemphigoid?
(due to high levels of auto-antibodies against
components of the hemidesmosome; especially BP230 and collagen XVII).
Similar in effect to epidermolysis bullosa in that have severe blister formation
in response to touch or irritation
identify
Image (middle panel) of blistering of
skin in bulbous pemphigoid
CC of bulbous pemphigoid?
result from autoimmune reactions against the
proteins of the hemidesmosome such as
collagen XVII.
This results in the autoimmune destruction of the hemidesmosome allowing separation of the basal layer of the epidermis from the underlying connective tissue of the dermis thus allowing for the formation of massive blistering of the skin.
Which epidermal layer does skin is still able to divide?
stratum spinosum
What can we find in stratum spinosum?
- More extensive desmosomes. The interdigitating cell processes with desmosomes give cells a spiny
appearance - Increasing numbers of bundles of tonofilaments. The bundles are called tonofibrils
identify
Stratum spinosum cells showing the interdigitating processes with desmosomes; cytokeratin
identify
stratum spinosum
Where do do keratinocytes appear and how they characterize?
startum granulosum; basophilic staining keratohyalin granules
how are Keratohyalin granules appearance and what do they contain?
are nonmembrane bound and amorphous
in shape and size;
contain filaggrin & trichohyalin which are intermediate filament associated proteins that promote the aggregation of keratin filaments into
tonofibrils (soft keratin)
identify
EM of keratihyaline granules with intermediate filaments
identify
EM of stratum spinosum cell and stratum granulosum cell with keratohyalin granule
identify
Micrograph of epidermis with stratum granulosum
Where is stratum lucidum found? how does it look?
Only present in thick skin such as found on palmar and plantar surfaces. Not always seen or recognizable
Appears as a paler staining region between stratum granulosum and stratum corneum
Is sometimes considered a subdivision of the Stratum Corneum
what happens to organelles in stratum lucidum?
have lysed (died by apoptosis)
what is prominent in stratum lucidum?
eleidin, a refractile keratin precursor
identify
What happens to cells and organelles in the stratum corneum?
The cells die by apoptosis in this layer, but cells remain intact
- All of the organelles are lysed. The cell is transformed into essentially a bag of crosslinked keratin
what is cornification of cell membrane?
The cell membrane is thickened and the extraellular space made impermeable to water [stratum corneum]
What happens to the desmosomes in the stratum corneum?
Cells at surface lose desmosomes
and are sloughed off (desquamated).
identify
identify
What structure is not present in human skin in the stratum corneum?
There are no zonula occludens (tight junctions)
How does waterproofing depends upon on?
- Filling of the intercellular space with lipid exocytosed from small granules called lamellar bodies (membrane coating granules)that are first formed in the cells of the stratum spinosum, but are not exocytosed until the stratum corneum
- Cornification (thickening) of the plasma membrane of the cells in the stratum corneum to form the cornified cell envelope which is also impermeable to water
identify
EM of keratinocytes (top) showing cell in statum spinosum with membrane coating granules and cell in stratum granulosum with
keratohyalin granule
identify
lamellar body - membrane coating granule
identify
Thickening of the cell envelop and contents of membrane coating granule in intercellualar space between cells in stratum corneum
