1. The earliest and most primitive type of kidney found in the embryos of vertebrates and in some adult aquatic animals; also called the head kidney.
Usage: biology; embryology; technical

Examples

• The pronephra develops early in embryonic life and is the first functional kidney structure.
• In fish larvae, the pronephra serves as the primary excretory organ.
• The pronephra is composed of a few tubules that drain into the pronephric duct.
• As the embryo develops, the pronephra is gradually replaced by the mesonephra.
• Marine organisms such as some fish retain functional pronephra throughout their lives.