Intermediate mesoderm

Intermediate mesoderm is a type of mesoderm that is situated between the paraxial mesoderm and the lateral plate mesoderm in the developing embryo. It plays a crucial role in the development of the urinary system and reproductive system, giving rise to structures such as the kidneys, ureters, gonads, and their associated ducts. Understanding the development and differentiation of the intermediate mesoderm is essential for comprehending the embryogenesis of these vital organ systems.

Development

During the third week of human embryogenesis, the intermediate mesoderm emerges as a distinct layer. It originates from the lateral edges of the paraxial mesoderm and extends along the longitudinal axis of the embryo, from the cervical regions to the hind end. As development progresses, the intermediate mesoderm differentiates into two main components: the nephrogenic cord and the gonadal ridge. The nephrogenic cord gives rise to the urinary system, while the gonadal ridge develops into the reproductive organs.

Structure and Function

The intermediate mesoderm is pivotal in forming the urogenital system. Initially, it forms a series of transient, primitive kidney structures known as the pronephros, mesonephros, and metanephros. The pronephros is the most cranial and temporary, degenerating early in development. The mesonephros serves as a temporary kidney during fetal life, while the metanephros develops into the permanent kidney. The differentiation of these structures is a complex process involving various signaling pathways and gene expressions.

Urinary System Development

The metanephros, derived from the intermediate mesoderm, begins its development around the fifth week of embryogenesis and eventually forms the adult kidneys and ureters. This process involves interactions between the metanephric mesenchyme and the ureteric bud, a critical step in kidney development.

Reproductive System Development

The gonadal ridge, also originating from the intermediate mesoderm, differentiates into either testes or ovaries, depending on the genetic sex of the embryo. This differentiation is influenced by the presence or absence of the SRY gene on the Y chromosome. The development of the reproductive ducts, including the Müllerian ducts and Wolffian ducts, is also closely associated with the intermediate mesoderm.

Clinical Significance

Abnormalities in the development of the intermediate mesoderm can lead to congenital anomalies of the kidney and urinary tract (CAKUT) and disorders of sexual development (DSD). Understanding the molecular and cellular mechanisms underlying the development of the intermediate mesoderm is crucial for diagnosing, managing, and potentially preventing these conditions.

See Also

• Mesoderm
• Human embryogenesis
• Urogenital system
• Congenital anomalies of the kidney and urinary tract (CAKUT)
• Disorders of sexual development (DSD)