5 - Development of the Skin and it's Derivatives

Question 1

The skin developes from what two early embryonic tissues? What is critical in directing the formation of all components of the skin?

Answer 1

Epithelium and mesenchyme.

Inductive interactions between these tissues at the epithelial-mesenchyme interface are critical in directing formation of all components of the skin.

Question 2

What does the epidermis form from?

Answer 2

The surface or non-neural ectoderm covering the embryo.

Question 3

What cells enter the epidemris? What is their derivation?

Answer 3

Melanocytes - neural crest

Langerhans - bone marrow

Merkel cells - epidermal stem cells in the basal layer

Question 4

The dermis is derived from what?

Answer 4

Mesenchyme of regional origin.

Question 5

During skin development, what cross-signaling is cessential?

Answer 5

Ectoderm-mesenchyme

Question 6

What protects the skin from amniotic fluid?

Answer 6

The vernix caseosa.

Question 7

Hair follicles, sweat glands, and nails are dervied from what?

Answer 7

Epidermal buds that extend into the forming dermis.

Question 8

The initial downy, _______ hair is replated near birth by ______ hair.

Answer 8

Lanugo hair is replaced by course hair

Question 9

What are nails derived from?

Answer 9

Epidermal thickenings at the tips of the digits.

Question 10

What is piebaldism caused by?

Answer 10

An absence of melanocytes in affected skin and hair follicles caused by an aut. dominant mutation of the KIT proto-oncogene.

Question 11

What are clinical manifestations of piebaldism?

Answer 11

• Depigmented patches (congenital - seen at birth) often with speckles within - often appear heart-shaped
• Stable spots, non-progressive
• White forelock typical (melanocytes dont make it to this location)

Question 12

What helps distinguish vitiligo from piebaldism?

Answer 12

History.

Question 13

What is the cause of Waardenburg syndrome?

Answer 13

Rare disease; multiple genes implicated, resulting in abnormal development of melanocytes (as opposed to a migration problem seen in piebaldism).

Question 14

What are the clinical manifestations of Waardenburg Syndrome?

Answer 14

Achromia (white patches of skin or hair) with

• deafness
• heterochromia irides (eyes are 2 colors)
• dystopia canthorum (wide distance between eyes)

Question 15

What is a port-wine stain? How common are they? Do they change?

Answer 15

Malformed, ectatic, dilated capillary to venule sized blood vessels.

• Always present at birth
• Occur in about 0.3-0.6% of newborns
• Tend to darken and thicken over time

Question 16

What are three potential distributions of facial port-wine stains?

Answer 16

• V1-Ophthalmic Branch: may extend to ocular conjunctive
• V2-Maxillary branch
• V3-mendibular branch: may extend to oral mucosa

Question 17

Capillary malformations (port-wine stains) in the V1 distribution can be associated with what? What are common findings?

Answer 17

Sturge-Weber syndrome.

Seizures, developmental delay, migraines, and tram track calcifications.

Ocular findings such as congenital glaucoma and increased choroidal vascularity (tomato ketchup spot).

Question 18

What isthe most common vascular tumor? What is it composed of?

Answer 18

Infantile hemangioma (incidence 4-5%)

Composed of proliferating endothelial-like cells that become clinically visible within first month of life.

Question 19

How do infantile hemangiomas change over time?

Answer 19

Appear as white flat patch with fine pink-red vessels.

The pallor may be due to local vasoconstriction.

1-2 wks of age proliferation begins; growth phase 3-9 months and then it slowly involutes.

Question 20

What clinical findings are associated with PHACE syndrome?

Answer 20

P: posterior fossa abnormailities

H: hemangioma (segmental)

A: arterial anomolies

C: cardiac anomolies

E: eye anomolies

S: sternal clefting/supraumbilicant raphe

Question 21

What causes hypohidrotric ectodermal dysplasia (HED)?

Answer 21

Most ofetn X linked recessive.

Most common form of ectodermal dysplasia.

Multiple genes can cause the condition and they are found in the ectodysplasin signaling pathway.

Question 22

What are the clinical manifestations of hypohidrotic ectodermal dysplasia (HED)?

Answer 22

• Squareforhead with frontal bossing.
• Flattened nasal bridge (saddle-nose)
• Low-lying ears
• Skin is thin and dry
• Sparse hair
• Hypo-anodontia/Peg teeth
• Decreased ability to sweat

Question 23

Patients with hypohidrotic ectodermal dysplasia have impaired ability to ______ and can _______.

Answer 23

Impaired ability to sweat and can overheat