Lect. 20 - Devpt. Of The Integument

Question 1

What are the 3 layers of the epidermis?

Answer 1

Basal (germinative) layer; intermediate layer; superficial peri dermal layer (derived from basal layer)

Question 2

Activation of what TF leads to development of the 3 layered epidermis?

Answer 2

p63

Question 3

What leads to formation of the intermediate layer?

Answer 3

Inactivation of p63 (blocked by miR-203)

Question 4

What are the derivatives of the intermediate layer?

Answer 4

Stratum Spinosum (loss of integrins attached to basal lamina and appearance of keratohyalin granules) and stratum granulosum (interconnected by fillagrin)

Question 5

What role does apoptosis play in epidermal development?

Answer 5

Postnatal layers of epidermis during sixth month; peri dermal cells undergo apoptosis

Question 6

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

Answer 6

Volar pads set the stage for the formation of epidermal ridges (occurs b/w 11-17 weeks); if a volar pad is high and round, the epidermal ridges for a whorl and if they pad is low, and arch results.

Question 7

Melanoblasts

Answer 7

From neural crest; migrate into dermis then to epidermis; produce pigment by mid-pregnancy

Question 8

Langerhan’s cells

Answer 8

Derived from bone marrow; APCs

Question 9

Merkel cells

Answer 9

From neural crest; slow-adapting mechano-receptors

Question 10

Origin of dermal cells in the dorsal surface of the body

Answer 10

Mesenchyme from dermatome

Question 11

Origin of dermal cells on ventral and lateral surfaces of body

Answer 11

Mesenchyme from lateral plate mesoderm

Question 12

Origin of dermal cells from cranial and anterior neck

Answer 12

Mesenchyme mostly from cranial neural crest

Question 13

Signaling pathways leading to differentiation of dermal cells

Answer 13

Mesenchymal cells –> Dermal cells by Wnt; Dermal cells –> Dermo 1 and mesenchymal cells; mesenchymal cells –> fibroblasts

Question 14

Characteristics of dermal cells

Answer 14

Loosely aggregated; interconnected by tight junctions; secrete thin watery matrix rich in glycogen and HA

Question 15

Trunk Dermis

Answer 15

From somitic dermatomes; aggregated mesenchymal cells develop tight junctions

Question 16

Limb dermis origin

Answer 16

Lateral plate mesoderm

Question 17

Face and anterior neck origin

Answer 17

Neural crest

Question 18

Instructive induction

Answer 18

One germ layer instructs another on how to differentiate

Question 19

How is instructive induction demonstrated?

Answer 19

Ectoderm and mesenchyme are separated; abdominal ectoderm is combined w/ sole mesoderm - abdominal ectoderm differentiate as thickened skin typical of the sole; sole ecto and scalp meso are combined - ecto differentiates as scalp epidermis w/ hair

Question 20

What are commonalities of the epidermal derivatives?

Answer 20

Development involves ectodermal-mesodermal interactions and inductions; begin as epidermal down growths; Ectoderm contributes to: hair follicle, shaft, sebaceous glands, nails, eponychium, hyponychium, mammary glands. Mesenchyme contributes to: hair papilla, outer hair follicles and arrector muscles

Question 21

Developmental pathway for hair development (induction of ectodermal placode (thickening))

Answer 21

Wnt 1 induces Wnt 11; Wnt 11 and FGF from meso cause ecto to express Noggin; Eda from meso causes ecto to express Edar; Edar and Noggin in ecto block BMP; in inter follicular zones: Dickkopf blocks Wnt and BMP inhibits follicle development

Question 22

Induction of dermal papilla

Answer 22

Epidermal induction; expression of Shh via signaling pathway involving Edar receptor stimulates formation of dermal papilla below epidermal placode

Question 23

Induction of hair germ

Answer 23

Dermal induction; various inducers from dermal papilla along w/ Shh and Cyclin D1 in epidermal placode stimulate further down growth of proliferation of epidermal placode; final differentiation of hair primordial involves Hox genes

Question 24

Adult hair cycle

Answer 24

Anagen - growth; catagen - follicular regression; telogen - resting; exogen - shedding

Question 25

Inductive interactions in hair

Answer 25

4th month - primary nail field overlies mesenchymal nail bed and extend proximally as proximal matrix; Close to term - nail has grown close to the end of the fingertip, much of the nail is covered by thin eponychium, which will degenerate

Question 26

What are milk lines and how are they related to Wnt expression?

Answer 26

The line where mammary glands form; marked by various expressions of Wnt w/I the ectodermal cells

Question 27

Mammary gland development

Answer 27

Newborn; young adult - estrogen stimulation of duct growth; adult - progesterone stimulation of formation of secretory alveoli; lactating adult; adult after lactation

Question 28

What is testicular feminization and what is its relation to mammary gland development?

Answer 28

Genetic males lack testosterone receptors; develop breasts but can’t respond to testosterone

Question 29

What role do neurogluin-3, Tbx-3, PTH, BMP-4, and Msx-2 play in mammary gland development?

Answer 29

BMP-4: stimulate downgrowth of mammillary epithelial bud and stimulate expression of Msx-2; Msx-2 inhibits formation of hair follicles in regression of nipple; PTH: increases sensitivity of underlying mesenchymal cells to BMP-4; Tbx-3: marks dorsi ventral location; neurogluin-3: induces mammary placode to form from ectodermal cells of the milk line

Question 30

What causes milk letdown?

Answer 30

Oxytocin release from posterior pituitary

Question 31

Cause of milk protein and fat synthesis?

Answer 31

Prolactin release from anterior pituitary

Question 32

Overall stimulator of prolactin and oxytocin release?

Answer 32

Neural stimulus from suckling

Question 33

Periderm

Answer 33

Single later of ectodermal cells; formed by the end of the first month