Pharyngula

Pharyngula is a stage in embryonic development in vertebrates. It is during this stage that the embryo takes on the basic structure of the vertebrate form. This stage occurs after the gastrulation process and is characterized by the formation of the pharyngeal arches.

Overview

The term "pharyngula" was coined by embryologist Karl Ernst von Baer in the 19th century. It is derived from the word "pharynx", which refers to the part of the throat where the pharyngeal arches form. The pharyngula stage is considered the most important stage in vertebrate embryology because it is when the basic body plan of the vertebrate is established.

Pharyngeal Arches

The pharyngeal arches are a series of outgrowths that form on the lateral sides of the embryo during the pharyngula stage. These arches give rise to various structures in the adult organism, including the jaws, the larynx, and parts of the ear and neck. Each arch contains a core of mesoderm that becomes the muscles and arteries, and is covered by ectoderm and endoderm which form the lining of the mouth and throat.

Development

During the pharyngula stage, the embryo undergoes significant morphological changes. The neural tube, which will become the central nervous system, begins to close. The somites, blocks of mesoderm that will form the vertebrae and muscles, begin to appear. The heart starts to beat and the circulatory system begins to function. The embryo also starts to show the first signs of a head, with the formation of the forebrain, midbrain, and hindbrain.

Significance

The pharyngula stage is significant because it is when the basic body plan of the vertebrate is established. This stage is also when the embryo is most resistant to birth defects caused by mutations. This is because the basic body plan has been established, and any changes to the plan can be compensated for by the organism's developmental plasticity.

See Also

• Embryonic development
• Gastrulation
• Neural tube
• Somites