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The apical ectodermal ridge (AER) is a structure that forms from the ectodermal cells at the distal end of each limb bud and acts as a major signaling center to ensure proper development of a limb. After the limb bud induces AER formation, the AER and limb mesenchyme —including the zone of polarizing activity (ZPA)—continue to communicate ...
Most of the barrier functions of the epidermis localize to this layer. [12] clear/translucent layer (stratum lucidum, only in palms and soles) This narrow layer is found only on the palms and soles. The epidermis of these two areas is known as "thick skin" because with this extra layer, the skin has 5 epidermal layers instead of 4.
The skin of the hands and fingers and the feet and toes is known by forensic scientists as friction ridge skin. It is known by anatomists as thick skin, volar skin or hairless skin. It has raised ridges, a thicker and more complex epidermis, increased sensory abilities, and the absence of hair and sebaceous glands.
The lateral plate mesodermal cells secrete fibroblast growth factors (FGF7 and FGF10) to induce the overlying ectoderm to form an organizer at the end of the limb bud, called the apical ectodermal ridge (AER), which guides further development and controls cell death. [8]
Limb bud development relies not only on the ZPA, but also many different genes, signals, and a unique region of ectoderm called the apical ectodermal ridge (AER). Research by Saunders and Gasseling in 1948 identified the AER and its subsequent involvement in proximal distal outgrowth. [ 1 ]
Both processes position neural crest cells between a superficial epidermal layer and the deep neural tube. During primary neurulation, the notochord cells of the mesoderm signal the adjacent, superficial ectoderm cells to reposition themselves into a columnar pattern to form cells of the ectodermal neural plate . [ 7 ]
Skin epithelium (purple) with lamina propria (underlying connective tissue) (pink) -- the epithelium exhibits rete pegs. Rete pegs protect the tissue from shearing. [1]Rete pegs (also known as rete processes or rete ridges) are the epithelial extensions that project into the underlying connective tissue in both skin and mucous membranes.
The epidermis, "epi" coming from the Greek language meaning "over" or "upon", is the outermost layer of the skin. It forms the waterproof, protective wrap over the body's surface, which also serves as a barrier to infection and is made up of stratified squamous epithelium with an underlying basal lamina.