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Páginas: 5 (1034 palabras) Publicado: 18 de noviembre de 2012
BDT13 Owens Skin Synopsis:

Suggested reading:
Larsen’s 4e: 193-208

Ectoderm makes the epidermis of the skin (top layer of skin).
Mesoderm forms the dermis of the skin (deep layers of the skin)

Epidermis from Ectoderm:
Keratinocytes They are ectodermal cells. They are layered, basal cells are stem cells, above are spinosum, and the top layer has died and represents the barrier.Melanocytes are derived from the ectodermal layer via the dorsal neural crest
Merkel cells are ectoderm and differentiate from keratinocytes. They are columnar shaped keratinocytes sitting in the basal layer. Merkel cells are touch receptors and are sensory innervated.
Langerhans are mesodermal ie they come from hematopoietic stem cells. Langerhans are professional Antigen PresentingCells that take up foreign bodies and present antigen to Tcells. These cells are abundant in the skin and broadly cover large areas of the keratinocyte layers—they appear to be uniformly spaced out in the skin.
T cells Gamma/Delta subtype receptors. They live in the epidermis. They do not reproduce and are not replenished from thymus. They are important for wound healing and for antimicrobialdefense.

No blood vessels in epidermis.

The most interesting point in the lecture was that the skin has many different types of tissues and consistently there are multiple types of stem cells serving these populations. The basal level of the epidermis includes the proliferative zone for the epidermis. In the hair there are stem cells in the bulge for hair production. Hence, these stemcells are regionalized in different and non-overlapping microdomains and service their respective populations only. The different stem cells do not communicate with one another.

Dermis: hair cells are part of the epidermis reaching down into the dermis, the rest of the dermis is connective tissues, collagen from mesoderm. The papillary dermis has loose irregular collagen fibers just below theepidermis. In the reticular dermis are bigger bundles of collagen fibers that have an orientation. Also there is a neural plexus. Blood vessels in dermis remove wastes from the dermis and the epidermis.

Hypodermis: adipocytes and smooth muscles.









Development of Skin:
A. Ectoderm progenitors ( Senses Wnt*, BMP(embryonic epidermis
*Wnt signaling is critical to direct thecells away from neurogenesis toward epidermal morphogenesis
This mechanism of epidermis specification might seem a little different from the previous lectures (CNS and NC), which said that BMP ( epidermis, BMP lo (NC and no BMP( neural, but in fact they are fairly similar (and there is considerable debate in the field). Here is the unifying idea: BMPs are everywhere (not just peripheral),FGF signaling blocks the ability of a cell to respond to BMP, which is equivalent to no BMP, and thus these cells become neural. Wnt signaling blocks the FGF signaling thus allowing BMP signaling, so these cells become epidermis. Intermediate ( NC.

B. Embryonic epidermis can undergo two possible outcomes: no hair vs hair

(1) Induction by BMP, Notch=> a stratified epidermis forms, becauseNotch inhibits Wnt

(2) Induction by Wnt10b, EGF, BMP’s and FGF=> a thinner layer of skin with a hair follicle.

How to make Hairy Skin:
The mesenchyme (dermatome ie mesoderm-derived) signals the surface ectoderm to regulate hair (or tooth formation or mammary gland ie appendage) formation.

Embryonic epidermis=>placode formation by condensing of ectodermal cells and mesenchymal cellmigration to the middle of the ectodermal cluster to make a mound of cells called a placode. The mesenchymal cells condense underneath the placode and induce Wnt10a. Together the placode and the mesenchymal condensate form the “bud”. The bud elongates to form the “peg”. The dermal condensate becomes a special cluster called the dermal papilla. The dermal papilla becomes engulfed by the base of the...
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