Pattern of limb development, Biology

Pattern of Limb Development

The first visible sign of limb development is the appearance of ridge or thickening on each lateral side of the embryo of amniotes. The ridge called Wolffian Ridge extends antero-posteriorly between the brachial and pelvic regions; but only its anterior and posterior ends persist from which the forelimb and hindlimb develop respectively. In the amphibians there is no such ridge and separate pairs of ridges arise in the respective limb regions. The ridge is formed from proliferation of cells of the somatic (parietal) layer of lateral plate mesoderm. The mesodermal cells of the ridge or disc lose their epithelial connections and become mesenchymal migrate as separate cells and form a loose mass of mesenchyme beneath the embryonic ectoderm opposite the ridge or thickening.

Their continued proliferation elevates the covering ectoderm and a limb bud is formed.  The early limb bud has a core of mesoderm and a covering of ectoderm; the ectoderm is 2-cell layered. The outer, peridermal layer is of flattened cells and the inner layer has cuboidal cells, separated from the mesoderm by a basement membrane. The bud is at fist a small mound but soon grows in size due to proliferation of mesodermal cells; as this happens the cells of the inner layer of ectodermal covering along its distal, edge become tall columnar and form a pseudostratified layer. In the amniotes (lizard, birds, mammals) this thickening of the apical ectoderm appears as a prominent ridge running antero-posteriorly along the free distal margin of the bud. It is called the Apical Ectodermal Ridge (AER). It has also been described in xenopus and at least one frog (Rana tigrina) and may be present in other amphibians also, though not so prominently. In chick limb development AEU has been found to play a very important role.

Posted Date: 1/29/2013 6:04:27 AM | Location : United States







Related Discussions:- Pattern of limb development, Assignment Help, Ask Question on Pattern of limb development, Get Answer, Expert's Help, Pattern of limb development Discussions

Write discussion on Pattern of limb development
Your posts are moderated
Related Questions
The breakdown of ATP releases energy, which is utilized by other reactions that require energy. Identify other examples where inventions have utilized a similar principle, where en

If the generation time (t) is the incubation time (t) per generation (G), or t = t/G, rewrite the formula you derived in question 2 for bacterial population growth in terms of incu

Animal Reproduction - Reproduction is the ability to produce new organism of its own type. It is meant to increase their number. Reproduction includes - (i) Replication o

The methods that can be used for valuing biodiversity are still evolving at the global level, but studies have been done on how biodiversity values can be incorporated into the pro

Oxides of nitrogen:          These include nitrogen monoxide (NO) and nitrogen dioxide (NO2). NO is a colourless, odourless and inert gas but like CO it can also combine with

B o v i ne viral diarrhoea Bovine viral diarrhoea (BVD) and mucosal disease (MD) are clinically dissimilar disease syndrome yet have a common viral etiology. The acute dise

Digestive system is one of eleven major body organ systems in animals; it converts food from the external environment into the nutrient molecules which can be used and stored by t

How are mutagenic agents related to cancer incidence in a population? Is cancer a disease transmitted to the individual offspring? The exposition of a population to mutagenic a

Why are the recombinant DNA technology and the nucleus transplantation technology still dangerous? A recombinant DNA technology and the nucleus transplantation technology (clon

1. Briefly explain the dynamics in enzyme reaction mechanism with potential energy surface diagram. 2. How to find the rate constant of any enzymetic reaction? 3. Derivation