Embryology & ontogeny

Question 1

Initially, the embryonic skin consists of how many layers and composed of what?

Answer 1

Single layer of ectodermal cells and a dermis containing mesenchymal cells in an interstitial ground substance.

Question 2

The ectodermal covering develops into what two layers as a second step in development?

Answer 2

1. basal cell layer (stratum germinativum) 2. outer layer (periderm).

Question 3

What is the layer that develops between the basal cell layer (Stratum germinativum) and the periderm?

Answer 3

Stratum intermedium.

Question 4

Where do melanocytes originate from?

Answer 4

Neural crest.

Question 5

Where do Langherans cells originate?

Answer 5

Bone marrow.

Question 6

Fetal skin contains a large percentage of what type of collagen compared with the skin of an adult?

Answer 6

Fetal: Type III.
Adult: Type I.

Question 7

Lipocytes develop from what type of precursor cells?

Answer 7

prelipoblasts.

Question 8

During what part of gestation do lipocytes form?

Answer 8

Second half.

Question 9

Hair germs are AKA?

Answer 9

Primary epithelial germs.

Question 10

The embryonal stratum germinativum (basal cell layer) differentiates into ___germs that give rise to what three structures?

Answer 10

Hair germs; 1. follicles 2. sebaceous glands 3. epitrichial (apocrine) sweat glands.

Question 11

Hair germs initially consist of an area of crowding of deeply _____cells in the____layer of the epidermis.

Answer 11

Basophilic; basal.

Question 12

The areas of crowding in the basal layer of the epidermis become buds known as ______?

Answer 12

Epidermal placodes.

Question 13

What are epidermal placodes, where do they come from and what do they protrude into?

Answer 13

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.

Question 14

Where is the dermal condensate located and what structure is formed from it?

Answer 14

Located beneath each bud (epidermal placode); dermal hair papilla.

Question 15

The epidermal placode (Bud) develops into what three structures? What do each of these structures form?

Answer 15

Three epithelial cylinders. Inner cylinder: hair shaft; Outer cylinder: outer root sheath (ORS); middle cylinder (inner root sheath)

Question 16

What environmental and inflammatory factors are known to alter the amount of human epidermal profilaggrin, filaggrin and/or filaggrin-derived natural moisturizing factor components

Answer 16

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

Question 17

What stimulates kertohyaline granules from being released?

Answer 17

Increased calcium levels

Question 18

Where are keratohyaline granules stored?

Answer 18

Stratum granulosum

Question 19

Describe the terminal differentiation of cornyeocytes with regards to filigrin

Answer 19

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.

Question 20

Where do keratinocytes originate?

Answer 20

Stratum basale

Question 21

How does filigrin contribute to the skin barrier/hydration?

Answer 21

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.

Question 22

What cytoplasmic filaments make up the keratinocyte cytoskeleton?

Answer 22

Cytokeratin, actin & microtubules (tubulin).

Question 23

How are keratinocytes characterised ultrastructurally? Immunohistochemically?

Answer 23

Keratin intermediate filaments (cytokeratin & tonofilaments) and desmosomes. Immunohistochemically= presence of cytokeratins.

Question 24

What keratins are from the acidic subfamily?

Answer 24

Type 1 keratins, cytokeratins 9-20.

Question 25

What keratins are from the neutral-basic subfamily?

Answer 25

Type 2 keratins, 1-8.

Question 26

Which 6 major morphogenic family systems are important for hair follicle development:

Answer 26

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.

Question 27

Initially embryonic skin consists of how many layers & is composed of what?

Answer 27

Single layer of ectodermal cells & dermis containing mesenchymal cells in an interstitial ground substance.

Question 28

What enzyme is a marker of early anagen hair follicles

Answer 28

Transglutaminase

Question 29

Two things that determine final length of the hair shaft

Answer 29

Rate of hair growth & duration of anagen.

Question 30

What are non medullated hairs called

Answer 30

Lanugo.

Question 31

What is the ratio of secondary to primary hairs in the cat dorsally & ventrally

Answer 31

10:1 dorsally, 24:1 ventrally.

Question 32

What determines the shape of the hair fibre

Answer 32

Shape of the hair follicle.

Question 33

When do puppies produce secondary hairs

Answer 33

12-28 weeks of life.

Question 34

What is the yearly amount of hair growth that adult short haired cats produce

Answer 34

32.7g/kg per year.

Question 35

What’s the yearly amount of hair growth that dogs produce

Answer 35

60-180g/kg per year depending on the breed.

Question 36

What kind of sweat gland opens directly onto the skin surface

Answer 36

Eccrine (atrichial).