Lect. 20 - Devpt. Of The Integument Flashcards Preview

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Flashcards in Lect. 20 - Devpt. Of The Integument Deck (33):

What are the 3 layers of the epidermis?

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


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



What leads to formation of the intermediate layer?

Inactivation of p63 (blocked by miR-203)


What are the derivatives of the intermediate layer?

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


What role does apoptosis play in epidermal development?

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


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

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.



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


Langerhan's cells

Derived from bone marrow; APCs


Merkel cells

From neural crest; slow-adapting mechano-receptors


Origin of dermal cells in the dorsal surface of the body

Mesenchyme from dermatome


Origin of dermal cells on ventral and lateral surfaces of body

Mesenchyme from lateral plate mesoderm


Origin of dermal cells from cranial and anterior neck

Mesenchyme mostly from cranial neural crest


Signaling pathways leading to differentiation of dermal cells

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


Characteristics of dermal cells

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


Trunk Dermis

From somitic dermatomes; aggregated mesenchymal cells develop tight junctions


Limb dermis origin

Lateral plate mesoderm


Face and anterior neck origin

Neural crest


Instructive induction

One germ layer instructs another on how to differentiate


How is instructive induction demonstrated?

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


What are commonalities of the epidermal derivatives?

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


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

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


Induction of dermal papilla

Epidermal induction; expression of Shh via 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 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


Adult hair cycle

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


Inductive interactions in hair

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


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

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


Mammary gland development

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


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

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


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

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


What causes milk letdown?

Oxytocin release from posterior pituitary


Cause of milk protein and fat synthesis?

Prolactin release from anterior pituitary


Overall stimulator of prolactin and oxytocin release?

Neural stimulus from suckling



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