Development Of The Integument Flashcards
What are the three layers of epidermis formed and when do they form?
- form by end of third month
- basal (germinative) layer, intermediate layer, superficial peridermal layer
What layers compose the intermediate layer? What are some features of these layers?
- stratum spinosum (loss of integrins attached to basal lamina, appearance of keratohyalin granules)
- stratum granulosum (interconnected by fillagrin)
What transcription factor plays a role in the development of the three layered epidermis?
- activation of p63 (deactivates miP-203)
- the intermediate layer deactivates p63 in order to grow
When and what undergoes apoptosis in the epidermis?
- postnatal layers of epidermis during 6th month
- peridermal cells undergo apoptosis
What are melanoblasts?
- from neural crest
- migrate into dermis and then into epidermis
- stain with HMB-45
- produce pigment by mid-pregnancy
What are Langerhans’ cells?
- derived from bone marrow
- antigen presenting cells
What are Merkel cells?
- from neural crest
- slow adapting mechanoreceptors
What are the three immigrant cells?
- Langerhans’ cells
- Merkel cells
- melanoblasts
What is the origin of dorsal surface of body dermal cells?
-mesenchyme from dermatome
What is the origin of ventral and lateral surfaces of body dermal cells?
Mesenchyme from lateral plate mesoderm
What is the origin of cranial and anterior neck dermal cells?
-mesenchyme mostly from cranial neural crest
What induces mesenchyme cells to differentiate into dermal cells?
Wnt
Describe dermal cells?
-loosely aggregated, interconnected by tight junctions, secrete thin watery matrix rich in glycogen and hyaluronic acid
What cells can dermal cells differentiate into?
- dermo 1
- mesenchymal cells -> fibroblasts (type 1 and 2 collagen, elastic fibers)
What is the origin of trunk dermis? Give a timeline of when specific features are developed.
- Somitic dermatomes induced via Wnt from the ectoderm to turn into dermo 1
- aggregated mesenchymal cells develop tight junctions
- sensory innervations after week 8
- vascularization
- by 3rd month fibroblasts develop from mesenchymal cells, collagens I and III, and elastic fibers are secreted
What is the origin of limb dermis?
-lateral plate mesoderm
What is the origin of face and anterior neck dermis?
-neural crest
The dermis and epidermis each have an influence on the development of each other.
:)
What is instructive induction?
-induction where one germ layer instructs another on how to differentiate
What are epidermal derivatives?
- hair
- nails
- mammory glands
What are some commonalities between the epidermal derivatives?
- development involves ectoderm all-mesodermal interactions and inductions
- hair, nails, and mammory glands begins as epidermal ingrowths into mesenchyme
- ectoderm contributes to the hair follicle, shaft, sebaceous glands, nails, eponychium, hyponychium, and secretory duct components of mammory glands
- mesenchyme contributes to the hair papilla, outer hair follicle, and arrector muscles
Describe the induction of the ectoderm all placode (thickening)?
- dermal induction
- Wnt-11 and FGF from mesoderm cause ectoderm to express Noggin
- Eda from mesoderm causes ectoderm to express Edar
- Edar and Noggin block BMP
- other Wnts act through beta-catenins
- in interfollicular zones: Dickkopf blocks Wnt, BMP inhibits follicle development
Describe induction of dermal papilla.
- epidermal induction
- expression of Shh via the signaling pathway involving Edar receptor which stimulates formation of dermal papilla below epidermal placode
Describe induction of hair germ.
- dermal induction
- various inducers: Shh and cyclin D1 in epidermal placode stimulate further downgrowth and proliferation of epidermal placode
- final differentiation of hair primordia involves Hox genes
What is the periderm and when is it formed?
- single layer of ectoderm all cells
- formed by end of first month
