Lect. 20 - Devpt. Of The Integument Flashcards
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?
p63
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.
Melanoblasts
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
