Lecture 13: development of the integument

Question 1

Define and distinguish between cytodifferentiation and histogenesis.

Answer 1

cytodifferentiation- development of specialized cells as muscle, blood, or nerve cells

histogenesis- differentiation of cells into specialized tissues and organs during growth

Question 2

Describe the formation of a multiple layered epidermis, including the derivatives from the intermediate layer.

Answer 2

p63 must be activated and then miR-203 must be added in order to deactivate it which then forms what intermediate layer

The layers of the intermediate layer are the stratum spinous and stratum granulosum

Question 3

Relate pattern of epidermal ridges to morphology of volar pads and timing of ridge
formation.

Answer 3

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Question 4

List major groups of immigrant cells, tell where they are derived from, and list basic functions.

Answer 4

melanoblasts: from the neural crest and migrate into dermis then epidermis

langerhan’s cells; from the bone marrow and present antigens

Merkel cells: from the neural crest and are mechanoreceptors

Question 5

Describe the source of dermal cells in various parts of the skin.

Answer 5

Dorsal surface: mesenchyme from dermatome

Ventral and lateral surfaces: mesenchyme from the lateral plate mesoderm

cranial and anterior neck: mesenchyme from the cranial neural crest

Question 6

Describe the signaling pathways leading to the differentiation of dermal cells.

Answer 6

Wnt is secreted by mesenchymal cells which leads to the formation of dermal cells that secrete Dermo 1 and leads to mesenchymal cells.

Fibroblasts (type 1 and 3 collagen, elastic fibers) come from mesenchymal cells

Question 7

Compare characteristic of dermal cells and mesenchymal cells.

Answer 7

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Question 8

Describe how recombination experiments between mesoderm (source of dermis) and ectoderm (source of epidermis) demonstrate instructive induction?

Answer 8

one germ layer instructs another on how to differentiate;

Question 9

List commonalities in the development of epidermal derivatives.

Answer 9

1. involves ectodermal-mesodermal interactions and inductions
2. begin as down growths into mesenchyme
3. ectoderm contributes to a lot of the ducts; hair, mammary, etc
4. mesenchyme contributes to the follicle and arrestor muscles

Question 10

Describe the developmental pathway for hair development.

Answer 10

Wnt, Wnt11, BMP, Eda, Noggin, Dickkopf, Shh

Wnt-11 and FGF cause the ectoderm to express noggin

Eda causes expression of Eda which then blocks BMP which inhibits the follicle

Dickkopf blocks Wnt

Question 11

Describe the adult hair cycle including the specific stages: anagen, catagen, telogen, and
exogen

Answer 11

anagen-growth
catagen-follicular regression
telogen-resting
exogen-shedding

Question 12

Explain the importance of hormones in the development of mammary glands

Answer 12

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