What is the Difference Between Pronephric Mesonephric and Metanephric Kidney

The key difference between pronephric mesonephric and metanephric kidney is that pronephric kidney is the earliest nephric stage while mesonephric kidney develops between the sixth and tenth week and metanephric kidney develops and functions between fifth to the twelfth week in the embryonic development stage.

The kidneys and urinary tract develop simultaneously from the cloaca and intermediate mesoderm. In an embryo, the kidneys develop from three overlapping sequential systems. The stages are pronephric kidney, mesonephric kidney, and metanephric kidney. They are all derived from the urogenital ridge.

CONTENTS

1. Overview and Key Difference
2. What is Pronephric Kidney
3. What is Mesonephric Kidney
4. What is Metanephric Kidney
5. Similarities – Pronephric Mesonephric and Metanephric Kidney
6. Pronephric vs Mesonephric vs Metanephric Kidney in Tabular Form
7. Summary – Pronephric vs Mesonephric vs Metanephric Kidney

What is a Pronephric Kidney?

A pronephric kidney is a transient embryonic organ that serves as a kidney. It provides osmoregulation during the early developmental stages of an embryo. Later, it degenerates during the process of metamorphosis. Then the mesonephric kidney develops and becomes the functional kidney. The pronephric kidney is the basic excretory organ that develops in the vertebrates. The development of pronephric primordium is from the intermediate mesoderm. It is succeeded by a mesonephric kidney, which is present in Pisces and amphibians. Once the advanced kidney develops, the previous version degenerates by apoptosis and becomes a part of the male reproductive system.

Figure 01: Development of Embryonic Nephrons

The pronephric kidney is a paired organ that consists of a single giant nephron. Nephron processes blood filtrate produced by glomeruli. The filtrate is then deposited into the coelom and passes through thin ciliated tubules into the pronephric nephron, where the solutes are recovered. In humans, the pronephric kidney is rudimentary and appears at the end of the third week, and it is then replaced by the mesonephric kidney after three and a half weeks. The pronephric kidney is essential to develop the adult kidneys. It produces inductive signals that trigger the formation of adult kidneys.

What is Mesonephric Kidney?

A mesonephric kidney is also an embryonic organ that disappears in all mammals when the metanephric kidney or the permanent kidney is functional. The mesonephric kidney has a structure similar to that of the functional kidney in humans and starts its function between the sixth and tenth weeks of embryological life. It consists of a glomerulus, capillaries, and finally drains out into the Bowmen’s capsule. A unit that consists of a single glomerulus and Bowmen’s capsule is surrounded by the renal corpuscle, and this unit is associated with a mesonephric unit called an excretory mesonephric unit or nephron.

Figure 02: Mesonephric Kidney

These kidneys produce urine from the sixth to tenth week of development of the embryo. Even though their structure, function, and terminology are similar to a mature kidney, mesonephric nephron does not form any part of the mature kidney. In females, the mesonephric kidney degenerates entirely, while in males, few caudal tubules will survive and give rise to several structures of the male reproductive system.

A metanephric kidney is a highly complex organ present in mammals. It filters waste products from circulation. It also maintains electrolyte and pH balance in body fluids, mineralization of bones, blood pressure, and blood composition. Metanephric kidney develops during the fifth week of gestation period. The mesonephric duct develops, outpouching the ureteric bud. The bud is also known as a meta-nephrogenic diverticulum. An elongated stalk in the ureteric bud called the metanephric duct forms the ureter later.

Figure 03: Kidney

When the cranial end of the bud extends to the intermediate mesoderm, it forms a branching system and, finally, the collecting duct system of the kidney. It also forms the renal pelvis. Signals released from the ureteric bud also induce the differentiation of metanephrogenic blastema into renal tubules. During the growth of renal tubules, they join connecting tubules to form a continuous passage from the renal tubule to the collecting duct. Vascular endothelial cells form at the tips of renal tubules, and these cells differentiate into glomerular cells.

• All three are associated with the excretory system.
• They are involved in the embryonic developmental stage.
• They are all derived from the urogenital ridge.

The pronephric kidney is the earliest nephric stage, while the mesonephric kidney develops between the 6th and 10th week. Meanwhile, the metanephric kidney develops and functions between the 5th to 12th week in the embryonic development stage. Thus, this is the key difference between pronephric mesonephric and metanephric kidney. Moreover, the pronephric kidney is not functional in humans, but mesonephric and metanephric kidneys are functional in humans. Furthermore, the mesonephric kidney has a temporary function while the metanephric kidney is permanent.

The below infographic presents the differences between pronephric mesonephric and metanephric kidney in tabular form for side by side comparison.

Summary – Pronephric vs Mesonephric vs Metanephric Kidney

Mammalian kidney develops with three overlapping stages, and they are pronephric kidney, mesonephric kidney, and metanephric kidney. The pronephric kidney is a transient embryonic organ that serves as a kidney. It provides osmoregulation during the early developmental stages of an embryo. Later it degenerates. The mesonephric kidney is also an embryonic organ that disappears in all mammals when the metanephric kidney, the permanent kidney, is functional. Meanwhile, the metanephric kidney is a highly complex organ present in mammals that filters waste products from circulation. The metanephric kidney finally develops into the complex organ kidney. So, this summarizes the difference between pronephric mesonephric and metanephric kidney.

Reference:

1. “Pronephros.” Encyclopædia Britannica, Encyclopædia Britannica, Inc.
2. “Stages in Kidney Development: Pronephros, Mesonephros, and Metanephros.” LifeMap Discovery®.

Image Courtesy:

1. “Development of embryonic nephrons” By Ashley Sawle – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Gray986” By Henry Vandyke Carter – Henry Gray (1918) Anatomy of the Human Body. Bartleby.com: Gray's Anatomy, Plate 986, Public Domain) via Commons Wikimedia
3. “Blausen 0592 KidneyAnatomy 01” By Blausen.com staff (2014). “Medical gallery of Blausen Medical 2014”;  WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. – Own work (CC BY 3.0) via Commons Wikimedia

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