Skin development Flashcards
what types of cells comprise the epidermis?
keratinoytes, melanocytes, merkel cells and langerhans cells.
what are melanocytes derived from?
Neural crest
the first primordial hair follicles form on the eyebrows, upper lip and chin at what gestational age?
9-12 weeks
when does epidermal stratification occur?
8 weeks
what is required for epidermal stratification to occur?
TP63 expression
when do melanocytes, langerhan cells, and merkel cells migrate into the epidermis?
9-12 weeks
when does terminal differentiation wiht full stratification occur?
late second trimester
when in the epidermis similar to adult skin morphologically?
third trimester
When does epidermal melanin production start?
12-16 weeks
what markers do langerhan cell precursors express?
CD45, HLA-DR, CD1c. @ 13 weeks CD1a, langerin, and birbeck granules present
what directs the migration of melanocytes?
KIT and KIT ligand
when are melanocytes in the epidermis?
12 weeks
when does melanin production begin?
12-16 weeks
when are melanocytes fully functional and can transfer melanosomes to keratinocytes?
16-20 weeks
where is dermal mesenchyme of face and anterior scalp derived from?
neuroal crest ectoderm
where does dermal mesenchyme of the back orignate from?
dermomyotome of embryonic somite
where does dermal mesenchyme of extremities and ventral trunk arise from?
lateral plate mesoderm
what types of collagen are made by embryonic dermal cells?
Tyeps I, III, IV
what type of collagen is most common in embryonic dermal cells
type III
When does the dermis shift from non-scarring to scarring?
end of second trimester
when do fibroblasts appear in the dermis?
6-8 weeks
when does a distinct border between the epidermis and dermis occur
9 weeks
when does primordial vasculature form?
9-12 weeks
when does fat form in the subcutis?
16-18 weeks
when does mature thickness of dermis occur with dermal ridges present?
20 weeks
when does mature thickness of dermis occur with dermal ridges present?
20 weeks
what two overal structures make up the DEJ?
lamina lucida and lamina dense
what types of collagen are present in the lamina lucida?
XVII and IV
what types of collagen are present in the lamina dense?
IV
when do epidermal placodes induce dermal papilla formation?
18-20 weeks
when is hair canal fully formed?
18-20 weeks
when do hairs start cycling between anagen, catagen, and telogen?
24-28 weeks
what signalling molecule is important for telogen to anagen transition?
sonic hedghog
what is the down stream mediator of WNT signalling?
beta catenin
there are two parts ot the superior bulge pair in the hair follicle. What one si the more superifical one?
the sebaceous gland
there are two parts ot the superior bulge pair in the hair follicle. Which one is the more inferior one?
insertion point for the arrector pili muscle
when does nailbed demarcation occur?
8-10 weeks
when does proximal hail fild form?
12-13 weeks
when does nail plate form and cover the nail bed completely?
17-20 weeks
when does toenail formation start?
4 weeks after fingernails (12-14 weeks)
when does the eccrine gland begin formation
10 weeks
where does eccrine gland formation begin?
on the palms and soles
when does the eccrine primordia bud down and glands begin to develop?
14-16 weeks
when does apocrine gland formation begin?
22 weeks
when does sebaceous gland formation start?
13-16 weeks
where are keratinocyte stem cells located?
bulge region of the hair follicle and base of rete ridges of interfollicular epidermis
how long does complete renewal of epidermis take?
40-56 weeks
what helps control blood flow to the fingers (involved in hot and cold and resulting blood shunting)?
glomus body
what type of structures consists of endothelial cells attached to basement membrane w/o associated pericytes or smooth muscle?
lymphatic
basement membrane of both the epidermis and cutnaeous blodo vessels are composed of what tyep of collagen
type IV
what type of collagen is most abundant in the dermis?
type I (80%), collagen III makes up 10%
in the axillary and anogenital regions the outer root shieath froms 3 not 2 bulges. What is the most likely thing to develop from the most superifical bulge?
apocrine
What skin structures are derived from the ectoderm?
Epidermis, adnexal structures, merkel cells, melanocytes (neural crest), and nerves (neuroectoderm)
What skin structures arise from the mesoderm?
fibroblasts, Langerhans cells, vessels, and inflammatory cells
