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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 ...
The climate and ecology of different locations on the globe naturally separate into life zones, depending on elevation, latitude, and location.The generally strong dependency on elevation is known as altitudinal zonation: the average temperature of a location decreases as the elevation increases.
Holdridge life zone classification scheme. Although conceived as three-dimensional by its originator, it is usually shown as a two-dimensional array of hexagons in a triangular frame. The Holdridge life zones system is a global bioclimatic scheme for the classification of land areas.
Fibroblast growth factor (FGF) induces the formation of an organizer at the end of the limb bud, called the apical ectodermal ridge (AER), which guides further development and controls cell death. Programmed cell death is necessary to eliminate webbing between digits.
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.
The term Goldilocks zone is used, as it is a fine balance between the two sites (heavy element and strong cosmic rays). Galactic habitable zone is the place a planet will have the needed parameters to support life. Not all galaxies are able to support life. [71] In many galaxies, life-killing events such as gamma-ray bursts can occur. About 90% ...
The development of the nervous system in humans, or neural development, or neurodevelopment involves the studies of embryology, developmental biology, and neuroscience.These describe the cellular and molecular mechanisms by which the complex nervous system forms in humans, develops during prenatal development, and continues to develop postnatally.
In this zone, the chondrocytes undergo hypertrophy (become enlarged). Chondrocytes contain large amounts of glycogen and begin to secrete vascular endothelial growth factor to initiate vascular invasion. Zone of calcification In this zone, chondrocytes are either dying or dead, leaving cavities that will later become invaded by bone-forming ...