Lecture 13 - Dev of the Integument

Question 1

Periderm

Answer 1

• Single layer of ectodermal cells

* Formed by end of first mont

Question 2

Three-layered epidermis

Answer 2

• Formed by end of third month
• Basal (germinative) layer
• Intermediate layer
• Superficial peridermallayer

Question 3

Intermediate layer

Answer 3

Stratum spinosum
Stratum granulosum
Loss of integrins attached to basal lamina
Inactivation of p63

Question 4

Role of apoptosis

Answer 4

• Postnatal layers of epidermis during sixth month

* Peridermal cells undergo apoptosis

Question 5

Stratum granulosum

Answer 5

Interconnected by fillagrin

Question 6

Stratum spinosum

Answer 6

Appearance of keratohyalin granules

Question 7

Epidermal Ridges/Creases

Answer 7

fingerprints

by the end of the third month of gestation, fetuses have fingerprints

Question 8

Immigrant Cells

Answer 8

Melanoblasts
Langerhans’ cells
Merkel cells

Question 9

Melanoblasts:

Answer 9

• From neural crest
• Migrate into dermis and then into epidermis
• Stain with HMB-45
• Produce pigment by mid-pregnancy

Question 10

Langerhans’ cells:

Answer 10

• Derived from bone marrow

* Antigen-presenting cells

Question 11

Merkel cells

Answer 11

• From neural crest

* Slow-adapting mechanoreceptors

Question 12

Origin of Dermal Cells

Dorsal surface of body

Answer 12

Mesenchyme from dermatome

Question 13

Origin of Dermal Cells

Ventral and lateral surfaces of body

Answer 13

Mesenchyme from lateral plate mesoderm

Question 14

Mesenchymal cells can develop into ___ cells under influence of ___.

Answer 14

Dermal Cells

Wnt

Question 15

Dermal Cells

Answer 15

Loosely aggregated; Interconnected by tight junctions; Secrete thin watery matrix rich in glycogen and hyaluronic acid;
express Dermo1
can produce mesenchymal cells again, which give rise to fibroblasts

Question 16

Origin of Dermal Cells

Cranial and anterior neck

Answer 16

Mesenchyme mostly from cranial neural crest

Question 17

Origin of Dermis

Trunk Dermis

Answer 17

From somatic dermatomes

•Aggregated mesenchymal cells develop tight junctions

Question 18

Limb Dermis

Answer 18

from lateral plate mesoderm

Question 19

face and anterior neck

Answer 19

neural crest

Question 20

Dermal-Epidermal Interactions

Answer 20

• The underlying dermis influences the development of the epidermis and especially of the epidermal derivatives.
• There is a reciprocal influence by the epidermis on the dermis.

Question 21

By the third month: (three things happen)

Answer 21

fibroblasts develop from mesenchymal cells.
•Collagens I and III are secreted.
•Elastic fibers are secreted

Question 22

Instructive Induction

Answer 22

one germ layer instructs another on how to differentiate

A: Ectoderm and mesenchyme are separated. Neither differentiates any farther.
B: Abdominal ectoderm is combined with sole mesoderm. Abdominal ectoderm differentiate as thickened skin typical of the sole.
C: Sole ectoderm and scalp mesoderm are combined. Ectoderm differentiates as scalp epidermis with hair.

Question 23

Epidermal Derivatives:

Answer 23

• Hair
• Nails
• Mammary glands

Question 24

Commonalities: Epidermal Derivative

Answer 24

• Development of these derivatives involves ectodermal-mesodermal interactions and inductions.
• Hairs, nails, and mammary glands begin as epidermal down growths (ingrowths) into mesenchyme.
• Ectoderm contributes to the hair follicle, hair shaft, sebaceous glands, nails, eponychium, hyponychium, and secretory and duct components of the mammary glands.
• Mesenchyme contributes to the hair papilla, outer hair follicle and arrector muscles.

Question 25

``` What roles do the following play in hair development and distribution? •Wnt-1 •Wnt 11 •BMP •Eda/Edar •Noggin •Dickkopf •Shh ```

Answer 25

Refer to Figure 9.8B-D and text.

Question 26

Induction of ectodermal placode (thickening):

Answer 26

* Dermal induction * Wnt-11and 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 27

Induction of dermal papilla:

Answer 27

* Epidermal induction * Expression of Shhvia the signaling pathway involving Edar receptor stimulates formation of dermal papilla below epidermal placode.

Question 28

Induction of hair germ

Answer 28

* 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.

Question 29

Nails:

Answer 29

Refer to text and Figure 9.10.

Question 30

Mammary glands:

Answer 30

•Refer to text and Figures 9.12-9.14