Terms in this set (42)
1. Epidermis (stratum corneum, granulosum, spinosum, and basalis)
2. Dermis (papillary, reticular)
3. Subcutis/panniculus/hypodermis/superficial fascia
What are the two layers of skin and the layer below?
corneum: cornified cells and horny cells
granulosum: granular cells (blue granules)
spinosum: spiny cells (desomosomes)
basalis: basal cells, melanocytes, stem cells
what cell types are found in each layer of the epidermis?
layers of the epidermis (from superficial to deep):"Come Let's Get Sun Burned"
1. stratum corneum
- flattened, dessicated, anucleate cells that are filled with keratin. These cells have a thick plasma membrane that's coated with an extracellular lipid layer - this gives the epidermis its water barrier component.
2. stratum lucidum
- doesn't stain well + is seen in thick skin only. is considered a division of the stratum corneum.
3. stratum granulosum
- cells contain numerous, highly-staining keratohyalin granules of irregular shape and size within the cell cytoplasm
4. stratum spinosum
- several layers of cells with lots of short, cytoplasmic processes extending from the cells. These processes attach to other cell processes via desmosomes.
5. stratum basale (lamina lucida, lamina densa)
- single layer of cuboidal epithelial cells which are mitotically active and rest on the basement membrane
what are the layers of the epidermis? what types of cells + structures are they made of?
skin is thick in the palm and and soles of feet (~5 mm)
where is skin the thickest?
rete ridges: epidermal extensions into the dermis around dermal papillae
what structure is indicated by the arrows?
dermal papilla: blood vessels in the dermis; note that rete ridges will extend down around them
what structure is indicated by the arrows?
the majority of keratin synthesis occurs in the stratum spinosus
in which layer of the epidermis does the majority of keratin synthesis occur?
In the stratum corneum,
cells are completely filled with keratin filaments (horny cells) which are embedded in a dense matrix of proteins. Individual cells are difficult to observe because (1) nuclei can no longer be identified, (2) the cells are very flat and (3) the space between the cells has been filled with lipids, which cement the cells together into a continuous membrane. In the EM, the cell membranes appear thickened and interdigitate with those of neighbouring cells. Closest to the surface of the epidermis, the stratum corneum has a somewhat looser appearance. Horny cells are constantly shed from this part of the stratum corneum.
The protection of the body by the epidermis is essentially due to the functional features of the stratum corneum.
what are characteristics of cells in the stratum corneum?
granular cells in the stratum granulosum contain kaeratohyalin granules that aggregate keratin as well as lamellar bodies for waterproofing
Official version: The stratum granulosum consists, in thick skin, of a few layers of flattened cells. Only one layer may be visible in thin skin. The cytoplasm of the cells contains numerous fine grains, keratohyalin granules. The keratohyalin is not located in membrane-bound organelles but forms "free" accumulations in the cytoplasm of the cells. The cells begin to release the contents of the lamellar granules. The lipids contained in the granules come to fill the entire interstitial space, which is important for the function of the epidermis as a barrier towards the external environment.
what are characteristics of cells in the stratum granulosum?
In the stratum spinosum,
the cells become irregularly polygonal. The cells are often separated by narrow, translucent clefts. These clefts are spanned by spine-like cytoplasmatic extensions of the cells (hence the name of the layer and of its cells: spinous cells), which interconnect the cells of this layer. Spines of cells meet end-to-end or side-to-side and are attached to each other by desmosomes. In addition to the usual organelles of cells, EM shows membrane-bound lamellar granules in the cytoplasm of the spinous cells.
what are characteristics of cells in the stratum spinosum?
the stratum basalis contains the following cells:
keratinocyte stem cells
keratinocytes with melanosomes
melanocytes (synth melanin)
what cells are found in the stratum basalis?
shown here is a tight cell junction between two cells via desmosomes
keratinocytes are firmly attached to each other by desmosomes
what is shown in this micrograph of the epidermis?
desmosomes are composed of the following:
extracellular cadherins attaching to each other anchoring cell-to-cell (DSG and DSC)
desmosome plaques: serve as attachment of cadherin and intracellular intermediate filaments (Plaks)
what are the structure of desmosomes?
the stratum basale is composed of the lamina lucida and lamina densa
densa: interacts w/ upper dermis via hemidesmosomes
what are the two layers of the stratum basalis?
the stratum basalis is composed of 2 layers:
1. lamina lucida: electron lucent layer between basal cells and lamina densa
2. lamina densa: electron dense due to ECM interaction with papillary layer of dermis
what are characteristics of the two layers of the stratum basalis?
basal keratinocytes are attached to the basement membrane via hemidesomes
anchoring filaments bind hemidesmosomes to lamina densa
anchoring fibrils bind lamina densa to papillary dermis
"KFil, HemiD, AFil, AFib"
how are basal keratinocytes attached to the basement membrane and lamina densa?
melanocytes are found in the stratum basalis of the epidermis
synth melanin from tyrosine, store in melanosomes, and transfer to keratinocytes
neural crest derivatives
pale with no desmosomes
what are characteristics of melanocytes?
melanocytes do not contain many melanosomes (transfer them to keratinocytes)
keratinocytes contain abundant melanosomes
how are melanosomes and keratinocytes differentiated from one another histologically?
the majority of melanin is found in basal and spinous keratinocytes
it is located above the nucleus to protect it from UV light
in what cell is the majority of melanin found, and where is it found intracellularly?
melanin is synthed from tyrosine by tyrosinase
tyrosine -> DOPA -> melanin
from what amino acid is melanin synthesized?
melanocytes are found in the same number in both light and dark skinned people; the difference in color is from increased synthesis
how do the number of melanocytes differ in light and dark skinned people?
langerhan cells are involved in the immune response
recognize, phagocytose, and process antigen processing cells
found in the basal layer of cells
what is the function of langerhans cells, and in what layer of the epidermis are they found?
merkel cells are mechanorecptors involved in touch
found in the basal layer of the epidermis
neural crest derivatives
what is the function of merkel cells, and in what layer of the epidermis are they found?
2 layers of the dermis:
1. papillary: superficial layer; includes dermal papillae; loose CT with vertically oriented collagen and reticular fibers
2. reticular: deeper layer; dense irregular CT
what are the two layers of the dermis?
hair follicles have sebaceous and apocrine glands opening into their root
what two glands open into a hair follicle?
hair is composed of:
shaft: portion of hair outside of epidermis
root: portion of hair below epidermis
arrector pilli muscle: smooth muscle which causes hair to "stand up"
follicle: root runs through this; apocrine and sebaceous glands open into it
what are the components of hair?
sebaceous glands demonstrate holocrine secretion of sebum, an oily/waxy substance
opens into hair follicle
what do sebaceous glands secrete, and how do they secrete it?
eccrine glands secrete sweat in a merocrine manner directly onto skin surface
myoepithelial cells propel secretion
what are characteristics of eccrine sweat glands?
apocrine glands secrete sweat in a merocrine manner into hair follicle
found in axilla and genitals
what are characteristics of apocrine sweat glands, where do they open, and where are they found?
the epidermis is avascular, and receives its blood supply and nutrients from the subcutis and dermis layers
where does the epidermis receive its blood supply from?
glomus bodies are specialized vessels between arterioles and veins that bypass capillaries and form a shunt in the dermis
used for temperature regulation
what are glomus bodies?
the lamina densa is attached to the papillary dermis by anchoring fibrils
how is the lamina densa attached to the papillary dermis?
maximally keratinized stratified squamous epithelium composed mainly of keratinocytes
what are components of epithelium?
the dermis contains the arterioles, lymphatics, and nerves of the skin
where are the arterioles, nerves, and lymphatics of the skin found?
the subcutis layer (deep to the dermis) contains the main arterial supply of the skin
what layer contains the main arterial supply of the skin?
myoeptihelial cells are found in the outer circumferential layers of apocrine and eccrine sweat glands of the skin
contract to propel secretion
where are myoepithelial cells found?
epidermis = stratified squamous epithelium
dermis = irregular dense connective tissue
how would you classify the epidermis + dermis?
what layer does the epidermis develop from?
what layer does the dermis develop from?
binds skin to underlying structures.
what's the function of the hypodermis?
dermal papillae - the superficial layer creates an irregular border between the epidermis and the dermis.
in thick skin, what feature would you expect to see between the dermis and the epidermis?
they are the stem cells of the epithelium. They lie along the basement membrane in a single layer. They are mitotic - they replace the cells in more superficial layers as these get shed from the epidermis.
what is the function of basal cells?