Lecture 13: Development Of The Integument

Question 1

Appearance of keratohyalin is true of which layer of Epidermis in the fetus
A. Basal (germinative) layer
B. Peridermal layer
C. Stratum spinosum 
D. Stratum granulosum

Answer 1

Ans: C

Question 2

These type of immigrant cell migrate into dermis and then into epidermis and produce pigment by mid-pregnancy.
A. Melanoblasts
B. Langerhan’s cells
C. Merkel cells
D. Dermal cells

Answer 2

Ans: A
Immigrant Cells
Melanoblasts: From neural crest, Migrate into dermis and then into epidermis, Stain with HMB-45, Produce pigment by mid-pregnancy
Langerhans’ cells: Derived from bone marrow, Antigen-presenting cells
Merkel cells: From neural crest, Slow-adapting mechano-receptors

Question 3

Dorsal surface of the body is covered by
A. Mesenchyme mostly from cranial neural crest
B. Mesenchyme from dermatome
C. Mesenchyme from lateral plate mesoderm
D. Mesenchyme from the dorsal plate mesoderm

Answer 3

Ans: B

Origin of Dermal Cells
• Dorsal surface of body: • Mesenchyme from dermatome
• Ventral and lateral surfaces of body: • Mesenchyme from lateral plate mesoderm
• Cranial and anterior neck: • Mesenchyme mostly from cranial neural crest

Question 4

What signals are involved in the origin of Dermis?
A. Hox 12 and Dermo 1
B. Wnt and Pax
C. Wnt and Hox 1
D. Wnt and Dermo 1

Answer 4

Ans: D
Slide 12 and 13 of lecture 13
Mesenchymal cell —- Wnt—— dermal cell (Loosely aggregated; interconnected by tight junctions; secrete thin watery matrix rich in glycogen and hyaluronic acid;) ——— Dermo 1 — fibroblasts ——- [Type 1 collagen, type 3 collagen and elastic fibers- 3rd month]

Sensory innervation after week 8.

Question 5

This type of induction, where one germ layer instructs another on how to differentiate is referred to as
A. Instructive Induction.
B. Constructive induction
C. Selective induction 
D. Terminal induction

Answer 5

Ans A
A: Ectoderm and mesenchyme are separated. Neither differentiates any farther.
B: Abdominal ectoderm is combined with sole mesoderm. Abdominal ectoderm differentiates as thickened skin typical of the sole.
C: Sole ectoderm and scalp mesoderm are combined. Ectoderm differentiates as hi scalp epidermis with hair.
This type of induction, where one germ layer instructs another on how to differentiate is referred to as Instructive Induction.
Look at slide 15, lecture 13

Question 6

In the induction of the ectodermal placode, in the interfollicular zones ———————- blocks Wnt.
A. Dickkopf
B. BMP
C. Eda
D. Beta - catenins

Answer 6

Ans: A
Induction of ectodermal placode (thickening):
• Dermal induction
• Wnt-11 and FGF from mesoderm cause ectoderm to express Noggin
• Eda from mesoderm causes ectoderm to express Edar
• Edar and Noggin in ectoderm block BMP
• Other Wnts act through β-catenins
• In interfollicular zones: • Dickkopf blocks Wnt
• BMP inhibits follicle development

Question 7

During the induction of dermal papilla, expression of ————— via the signaling pathway involving Edar receptor stimulates formation of dermal papilla below epidermal placode.

A. Dickkopf
B. BMP
C. Shh
D. Beta - catenins

Answer 7

Ans C
Induction of dermal papilla: • Epidermal induction
• Expression of Shh via the signaling pathway involving Edar receptor stimulates formation of dermal papilla below epidermal placode.
Induction of hair germ: • Dermal induction
• Various inducers from dermal papilla along with Shh and Cyclin D1 in epidermal placode stimulate further downgrowth of proliferation of epidermal placode.
• Final differentiation of hair primordia involves Hox genes.