Embryology & ontogeny Flashcards
Initially, the embryonic skin consists of how many layers and composed of what?
Single layer of ectodermal cells and a dermis containing mesenchymal cells in an interstitial ground substance.
The ectodermal covering develops into what two layers as a second step in development?
- basal cell layer (stratum germinativum) 2. outer layer (periderm).
What is the layer that develops between the basal cell layer (Stratum germinativum) and the periderm?
Stratum intermedium.
Where do melanocytes originate from?
Neural crest.
Where do Langherans cells originate?
Bone marrow.
Fetal skin contains a large percentage of what type of collagen compared with the skin of an adult?
Fetal: Type III.
Adult: Type I.
Lipocytes develop from what type of precursor cells?
prelipoblasts.
During what part of gestation do lipocytes form?
Second half.
Hair germs are AKA?
Primary epithelial germs.
The embryonal stratum germinativum (basal cell layer) differentiates into ___germs that give rise to what three structures?
Hair germs; 1. follicles 2. sebaceous glands 3. epitrichial (apocrine) sweat glands.
Hair germs initially consist of an area of crowding of deeply _____cells in the____layer of the epidermis.
Basophilic; basal.
The areas of crowding in the basal layer of the epidermis become buds known as ______?
Epidermal placodes.
What are epidermal placodes, where do they come from and what do they protrude into?
Epidermal placodes develop from areas of crowding in the basal layer of the epidermis which become buds which protrude into the dermis from the epidermis.
Where is the dermal condensate located and what structure is formed from it?
Located beneath each bud (epidermal placode); dermal hair papilla.
The epidermal placode (Bud) develops into what three structures? What do each of these structures form?
Three epithelial cylinders. Inner cylinder: hair shaft; Outer cylinder: outer root sheath (ORS); middle cylinder (inner root sheath)
What environmental and inflammatory factors are known to alter the amount of human epidermal profilaggrin, filaggrin and/or filaggrin-derived natural moisturizing factor components
Environmental factors
Humidity level
UV-B radiation
Mechanical damage (scratching, tape stripping) Ageing
Skin irritants (sodium lauryl sulfate, etc.)
Psychological stress Inflammatory factors
IL-4, IL-13, IL-17A, IL-22, IL-25, IL-31, TNF-a
What stimulates kertohyaline granules from being released?
Increased calcium levels
Where are keratohyaline granules stored?
Stratum granulosum
Describe the terminal differentiation of cornyeocytes with regards to filigrin
The FLG monomers aggregate keratin intermediate filaments forming tight bundles, and induce the collapse and flattening of corneocytes, an essential feature of cor- nified layer formation. Keratins and FLG are cross-linked to cornified envelopes, consolidating the structure.
Where do keratinocytes originate?
Stratum basale
How does filigrin contribute to the skin barrier/hydration?
Ultimately, FLG is deaminated and totally degraded by several pro- teases in the upper SC to release its constitutive amino acids [part of the ‘natural moisturizing factor’ (NMF)] which contributes to epidermal hydration and barrier function.
What cytoplasmic filaments make up the keratinocyte cytoskeleton?
Cytokeratin, actin & microtubules (tubulin).
How are keratinocytes characterised ultrastructurally? Immunohistochemically?
Keratin intermediate filaments (cytokeratin & tonofilaments) and desmosomes. Immunohistochemically= presence of cytokeratins.
What keratins are from the acidic subfamily?
Type 1 keratins, cytokeratins 9-20.
What keratins are from the neutral-basic subfamily?
Type 2 keratins, 1-8.
Which 6 major morphogenic family systems are important for hair follicle development:
1) Genes of the HOX cluster.
2) Fibroblast growth factor (FGF).
3) Transforming growth factor (TGF-Beta).
4) Sonic Hedgehog (shh).
5) Wingless/ wnt pathway.
6) Neurotrophins.
Initially embryonic skin consists of how many layers & is composed of what?
Single layer of ectodermal cells & dermis containing mesenchymal cells in an interstitial ground substance.
What enzyme is a marker of early anagen hair follicles
Transglutaminase
Two things that determine final length of the hair shaft
Rate of hair growth & duration of anagen.
What are non medullated hairs called
Lanugo.
What is the ratio of secondary to primary hairs in the cat dorsally & ventrally
10:1 dorsally, 24:1 ventrally.
What determines the shape of the hair fibre
Shape of the hair follicle.
When do puppies produce secondary hairs
12-28 weeks of life.
What is the yearly amount of hair growth that adult short haired cats produce
32.7g/kg per year.
What’s the yearly amount of hair growth that dogs produce
60-180g/kg per year depending on the breed.
What kind of sweat gland opens directly onto the skin surface
Eccrine (atrichial).
