WikiVisually
Infinite photos and videos for every Wiki article · Find something interesting to watch in seconds
Celebrities British Monarchs Tallest Buildings Crown Jewels Countries of the World Sports Famous Castles Rare Coins Presidents Supercars Recovered Treasures Great Cities Great Museums Kings of France Wonders of Nature Wars and Battles Great Artists Animals History by Country World Banknotes Largest Empires Largest Palaces Ancient Marvels Best Campuses Orders and Medals Richest US Counties
more top lists
History
Zone of polarizing activity
Videos
Photos
The zone of polarizing activity (ZPA) is an area of mesenchyme that contains signals which instruct the developing limb bud to form along the anterior/posterior axis. Limb bud is undifferentiated mesenchyme enclosed by an ectoderm covering. Eventually, the limb bud develops into bones, tendons, muscles and joints. 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. Twenty years later, the same group did transplantation studies in chick limb bud and identified the ZPA. It wasn't until 1993 that Todt and Fallon showed that the AER and ZPA are dependent on each other.
The apical ectodermal ridge is a thickened epithelium at the most distal end of the limb bud. The zone of polarizing activity is at the posterior part
The apical ectodermal ridge is a thickened epithelium at the most distal end of the limb bud. The zone of polarizing activity is at the posterior part of the limb bud.
Image: Zpa 1
Image: Zpa 1
Image: Zpa 2
Image: Zpa 2
Image: Limbbud
Image: Limbbud
Limb development
Videos
Photos
Limb development in vertebrates is an area of active research in both developmental and evolutionary biology, with much of the latter work focused on the transition from fin to limb.
9-week human fetus from ectopic pregnancy
9-week human fetus from ectopic pregnancy
The Turing reaction-diffusion mechanism illustrates the complex chemical interactions involved in developmental pattern formation. "A" activates itsel
The Turing reaction-diffusion mechanism illustrates the complex chemical interactions involved in developmental pattern formation. "A" activates itself and "B", while "B" inhibits "A". The model depicts a slowly diffusing activator's (A) interaction with a rapidly diffusing inhibitor (B). The reaction-diffusion system is responsible for the characteristic patterning of the autopod, zeugopod, and stylopod in limb development.