Holonephros

Holonephros is a term used in embryological studies to refer to the primitive, undifferentiated kidney that is present in the earliest stages of vertebrate development. The holonephros is the first of three types of kidneys that develop in vertebrates, followed by the mesonephros and the metanephros.

Development

The holonephros develops from the intermediate mesoderm, a layer of cells that forms during the early stages of embryogenesis. The intermediate mesoderm differentiates into a series of tubules, which eventually form the holonephros.

The holonephros is a temporary structure and is not functional in most vertebrates. It degenerates as the mesonephros begins to form. However, in some lower vertebrates, such as lampreys and hagfish, the holonephros remains functional throughout the animal's life.

Structure

The structure of the holonephros is simple, consisting of a series of tubules that connect to a common duct, the nephric duct. Each tubule is composed of a single layer of epithelial cells, and is surrounded by a network of capillaries. The tubules and capillaries work together to filter waste products from the blood.

Function

Although the holonephros is not functional in most vertebrates, in those species where it remains functional, it serves as the primary organ for excretion and osmoregulation. It filters waste products from the blood and excretes them as urine.

See also

• Pronephros
• Mesonephros
• Metanephros
• Nephron