Skin Flashcards
What is skin (x8)?
1) protective barrier against chemical, physical and infectious insults
2) accounts for 16% of the body’s weight
3) thickness & structure varies
4) mobile & elastic
5) involved in thermoregulation (via sweat & vasculature)
6) important in blood pressure reg (uses capillary beds)
7) sense organ (touch/pain)
8) tells you stuff as physician about state of the patient
Skin layers?
1) epidermis = epithelium = keratinized stratified squamous
2) dermis = connective tissue under epithelium
3) hypodermis = looser connective tissue under that
How nourish the epidermis?
- same as all epithelia
- nourished by diffusion from capillaries under the basement membrane
- the capillaries are in the dermis layer
where is the basement membrane at in a skin tissue slide?
- basement membrane is at the dermal/epidermal junction
what does Retin A do?
-stimulates neovascularization in the dermis which increases rate of basal cell proliferation
How do you increase basal cell proliferation?
-by increase the amount of nutrients being absorbed by the basal cells
Where are the capillaries that nourish the epithelial layer?
-the capillaries are in the dermis layer
what do you know about the relative activity of the cells closest versus farthest from the source of nutrients?
the closer cells (on the basement membrane; nearest the dermis which houses the capillaries) are most actively dividing since receive the most nutrients
thick vs thin skin?
- refers only to the dermis
- can have thin epidermis and thick dermis, but is still thin skin
Thick skin found?
- areas of high wear and tear (palms, soles of feet)
- is usually highly keratinized
- is crucial to keep dermial-epidermis layers together but is harder to do w/ thick skin
how keep dermial-epidermis layers together?
- need extensive epidermal-dermal junctions (layers)
- done by forming lots of epidermal pegs/dermal papillae (3D ridges)
Thin skin?
- is typical of most other parts of body besides those that get a lot of wear & tear
- skin very thin to retain flexibility & elasticity
- membrane is wavy
Why is thin skin basement membrane wavy?
- increased access to capillaries
- increases stretchy/elasticity of tissue
- increase tissue mobility, required for skin
Papillae/ridges pattern?
- seen in the keratin layer (epidermis layer)
- produces finger prints
How get separation between cells in the epidermis (epithelial cells)?
-repetitive movements causes a separation between cells in the epidermis
What happens when get separation between cells in the epidermis?
- blister (fluid-filled pocket) will form
- if viruses/ bacteria can get in can form pustules
How get blood blister?
- if have separation between the epidermis & dermis
- small capillaries will break giving you blood blister
Purpose of the dermis? Composition?
- located just under the epidermis
- is composed of loose connective tissue (lots of elastin, collagen T1 &T3) smooth muscle cells
- gives mobility to the surface layers of the skin
Which components of connective tissue are being referred to as loose or dense?
-collagen, elastic fibers, smooth muscle, fat all work together to determine dense vs loose connective tissue
What happens to elastic fibers as we age?
We begin to loose elastin/fibril so our elastic fibers loose their ping back, our skin gets saggy
What fibers stop you from over-stretching the skin? What happens if you rip these?
- the elasticity of elastin fibers
- if rip the elastic fibers, skin looses ability to ‘ping back’ is get saggy skin
- collagen also puts thresholds on skin stretching, if loose collagen T1/T2 now can overstretch the skin
Dermis Pathology?
-a connective tissue disease
-due to defects in dermis collagen deposition
-dermis usually loose;
ex 1: excessive fibrosis (fibroid) cause abnormal (intense) wound healing
ex 2: scleroderma
excessive fibrosis (fibroid) due to?
connective tissue dermis layer have fibroblast that lay down collagen; if over active get fibrosis
- cause scars/scar tissue,
- an exaggerated wound healing response, cause organ damage
scleroderma due to?
- inflammatory infiltrates drive excessive collagen deposition leading to loss of skin elasticity
What are the layers of the epidermis in the skin?
1) Keratin layer: cornified (tough protective layers) of cells are dead
2) stratum spinosum
3) basal lamina layer of epithelial cels
Keratin layer of the skin
- outer most skin layer; epithelial cells
- cornified (tough protective layers) of cells are dead
- can be 1 or 2 cells thick or very thick
stratum spinosum layer?
- granular and prickle cell layer
- provide separation between dividing cells and dead cornified cells at the top
- often times have lost nuclei in this layer
cornified mean?
tough protective layer of the skin
basal lamina layer of epithelial cels?
- divide to give rise to the cells above, but they only do so at night
- create water tight seal by constantly dividing and making differentiating cell types
How basal lamina create water tight seal?
- by establishing intercellular conenctions
- by forming dehydrated, keratin layer of cells that are dead and
clear cells? what are the 4 types?
- in basal and prickle cell layers
- all dendritic, w/ cytoplasmic extensions in & among other cells
- involved in immune responses
1) melanocyte
2) Merkel cell
3) Langerhans cell
4) gamma delta T lymphocyte
How are clear cells distinguishable?
-have central nuclei with (colored) with a clear cytoplasm around it, different than epithelial cells
Melanocytes
- a clear cell
- responsible for skin&hair color
- melanin-producing neural crest-derived cells
- under dermis layer of skin
- embryologically late migrating cells from the neural crest
- retain their mobile characteristics & plasticity throughout life.
Melanocytes mechanism?
- in -early development, neural crest-derived melanocyte progenitor cells line up down spine, migrate through body from there
- lots of genes effect melanin
Melanocytes and neurotransmitters?
- have similar movements to neurons
- way pigment granuels are move & deopisited in skin/hair follicles, similar to how neurotransmitter pushed arund in neurons
- often see pigment & neurotranmitter diseases because of it
Melanin
- made from tyrosine in granules which budded off the Golgi
- Mature melanin granules exocytosed from melanocytes (in dermis) their content is endocytosed by basal cells and prickle cell
What is a melanoma vs. basal cell carcinoma severity?
melanoma is worse because has mobile characteristics throughout life
-so can move through body; basal cells do not
Melanocytes and wound healing?
-wounds initially white, take time to develop color because takes time for melanocyte cells to migrate from neural crest to reach the injury
Variations in skin color occur because of?
- All races have same # of melanocytes variation depends on:
1) rate of synthesis of melanin
2) size of melanin granule
3) ability of other cells to endocytose melanin granule core
4) types of melanin produced
Two types of melanin?
pheomelanin versus eumelanin
pheomelanin versus eumelanin
1) blondes produce more light pheomelanin
2) darker skinned peoples produce more eumelanin
advantage/disadvantage of fair skin?
- can absorb more UV to make Vitamin D
- is easily damaged by too much UV
advantage/disadvantage of dark skin?
- protection from UV
- reduced ability to make Vitamin D
Merkel cell?
- clear cell
- modified nerve endings
- contain neurotransmitter granules (amount varies w/ skin region)
- mechanoreceptors in hair follicles (tell you if your face is being touched)
Langerhans cells
- clear cell
- born in bone marrow; constitute 4% of epithelial cells
- are self-renewing in skin, have slow turnover/replacement from bone marrow
- are skin dendritic cells
Langerhans cells & immune response? Unstimulated vs stimulated state?
- are the skin’s Dendritic Cells
- express immune Antigen Presenting Cell markers such as MHC Class II antigens
- typicallly reside in an nstimulated resident state,
Langerhans cells cytoplasm?
-tennis racket-shaped Birbeck “granules”which can appear appear in regular macrophages in some disease states
Langerhans cells in unstimulated state?
-in unstimulated resident state, they are not as potent as lymphoid tissue Dendritic Cells
Langerhans cells in activation?
activation by inflammation or cytokines
- causes upregulation in stimulatory molecules
- induces their migration into draining lymph nodes to trigger immune responses
What do tissue dendritic cells (Langerhans) stimulate?
-trigger organ graft rejection
Gamma-delta T Cells?
- found in all epithelia, but in diff variations depending on the tissue
- produce growth factors important for wound healing/ tissue repair from inflammation & infections
What clear cells have similar morphologies
malanocytes, gamma delta T cells and langerhans have similar morphologies
Prickle Cell layer ?
- also called stratum spinosum
- cells remain stuck together by desmosomes, can’t shrink
- main structural cells of the epidermis
- when dehydrated; form tight connections, in H20 would swell if they were only cells in the epidermis
why called prickle cell layer?
- cells appear to have prickles at under light microscope
- is an artifact of tissue dehydration & shrinkage
Keratinization
- keratins produced in all normal epidermal cells;
- increasing #; type & distribution; and amount of cross linking change w/ distance from the basement membrane
- form waterproof barrier
- form cornfield layer and are dead at this pint
thicker keratin layer?
the greater the protection
creating of the cornfield layer?
- as cells move through layers of prickle cells, they produce molecules that act as a glue between cells
- sticks cells to one another over entire surface, forms waterproof barrier
- lysosomal digestion of organelles make cells dead bags of keratin
- thicker keratin=more protection
keratin & expression of tight junctions?
-Is limited and transient.
Warts
example of Keratinocyte patholology
-HPV drive keratinocyte proliferation leading to thickening at the dermoepidermal junction
Epidermal Involutions (papila) of the skin?
- provide sites for skin repair if the surface epithelium is lost
- body can do it on own, also seen in treatment of burns
- allows for split skin grafting.
split skin grafting process?
do basememnt membrane transplant to give burn victims an active epithelial cell layer
-the epithelial cells will grow out of glands & hair follicles, provide new skin tissue
Hair
- a type of holocrine secretion
- cells remain stuck together
- cell division in basal layer gives rise to cells above that gain more & more keratin.
hair color?
Melanocytes contribute color to the hair in the same way as in the rest of the skin
-grey hair due to melanocytes not migrating anymore
estrogen/ testosterone and hair growth?
- head hair, estrogen stimulates growth
- in presence of some pituitary factors, testosterone inhibits growth
- castration cure balding
- estrogen treatment increases hair growth
Abnormal hair growth in women
-most often due to adrenal production of androgens
Goosebumps
- Cold initiates contraction of smooth muscle
- squishes skin in angle to make a goose bump
- squeezes sebum out of the sebaceous gland & makes hair stand up straight
Sebaceous Glands
- empty into hair follicles
- testosterone promotes cell division; estrogen inhibits
- secret oily material
- are sacs of lipids
- natures moisturizers
Sebaceous Glands secretions?
- as cells move farther from basement membrane, they accumulate lipid & die
- dead bags of lipid move onto the skin surface
- easy for exit of glands to get blocked
Sebaceous Glands blockage?
- blockage w/ increased cell division, may result in cells bursting through basement membrane
- initiates an inflammatory response in the dermis(acne)
- clogging& inflammatory responses are exacerbated by bacteria in hair follicle
Follicle Mites
- can block sebaceous glands
- many black heads are follicle mites (demodex folliculorum). )
Sweat Glands
-simple coiled tubular glands
-secretions=H20, ions & nitrogenous waste
-Stratified cuboidal
-
Sweat Glands secretions provess?
- secretory portion produces initial product
- duct modifies product ( by reuptake of sodium)
- specific chloride channels are required for reuptake, are dysfunctional/absent in CF
- is why CF patients have very salty skin, cells can’t uptake Na from skin
Sweat Glands & thermoregulation?
- Sweat comes up through ducts & empties onto the surface
- Evaporation cools skin surface, which cools blood in capillary beds in the dermal papillae
Apocrine Sweat Glands
- secrete in both apocrine & merocrine fashion
- large secretory regions
- empty into hair follicles, which serve as the ducts
- found in axillary regions (not useful for thermoregulation) & produce pheromones
Apocrine Sweat Glands
secretions?
- water, ions, protein and lipid
- bacteria cause apocrine secretions to smell bad
- release pheromones
- secretions accelerated by contraction of myoepithelial cells
Fingernails
- nail similar to hair but w/ harder keratin
- white part (lunulae) due to active dividing epithelium, younger & healthier people have larger ones
- Cells divide in basal layer & move at angle to surface during keratinization
nail clubbing?
- excessive nail curvature due to circulatory disorders and insufficient oxygenation of blood in extremities
- may show as blue nail beds
Nerve Endings In Skin?
- pain and fine motion detectors
- have different functions
- often require special stains
1) Meissner’s Corpuscle
2) Pacinian Corpuscles
1) Krause end bulbs?
2) Ruffini corpuscles?
1) cold receptors
2) sit on collagen fibers, stretch receptors
Meissner’s Corpuscle
- responsible for sensitivity to light touch
- Schwann cells are parallel to skin surface
- Lateral movement of skin distorts the cell and is transmitted to a nerve fiber
- common in dermal papillae/ridges
Pacinian Corpuscles
- large deep pressure receptors
- push on your skin; these tell you where pushing
- mostly in hypodermis
- tell you when your bladder is full
Pacinian Corpuscles mechanism?
Schwann cells are arranged at 90 degrees to skin surface so pressure will compress them
- this communicated to the afferent fiber
