The evolution of the kidney is one of the most exciting topics in evolutionary biology and several fields of science. This is because the kidney offers clear evidence of the effect of evolutionary pressures on the development of organs and the ability of scientists to study the development of human metanephroi.
Kidneys are seen in all vertebrates, and just like the ones found in human beings, they are also made up of nephrons. But the thing is that there are differences in the structure and function of the several vertebrate kidneys that allow for adaptation to the environment that the animals are found.
The excretory system is responsible for regulating the chemicals found in the body by sorting the removal of metabolic wastes and seeing to the retention of the correct amounts of water, nutrients, and salts. The invertebrates’ excretory system is also categorized based on the differences in their morphology-based, and this is done in three kinds.
The evolution of the kidneys in vertebrates becomes an interesting tale when seen from the external osmotic environment in which the different classes have had their evolutionary trends. Marine, freshwater, and terrestrial habitats have several issues regarding the maintenance of internal water balance alongside nitrogenous wastes’ excretion. Hence, there are several variations in the evolution of the kidney and these are correlated with the factors of the environment.
A study of kidney’s evolution in vertebrates shows how the mesonephric, pronephric, and metanephric kidneys are representations of the success in evolution trends alongside correlation done with factors of the environment. Differences in the morphology of the vertebrate kidney from aquatic creatures to man are mainly changes in the number, structure, modification, and placement of the renal tubules.
When it comes to embryological origins, the kidney, as seen in all vertebrates, originates from what is known as the intermediate mesoderm. This layer is the one that will later form the kidney, and this is why it is called the nephrogenic mesoderm. The kidney itself overall has two elements, and these are the kidney tubules and the kidney duct.
The kidneys’ tubules are called nephrons and are referred to as the evolutionary modifications seen in the nephridia and are known as the functional units of the kidneys.
The development of the kidney is described as being complicated, and this is based on the premise that two or even three different kinds of kidneys are based on the species formed in spatial and temporal sequence. The largest, most anterior, and first part when it comes to development is the pronephric kidney. Then there is the second kidney in the formation sequence and it is known as the mesonephric kidney. In reptiles, mammals, and birds, a third kidney is known as the metanephric kidney and develops to the posterior of the mesonephros.
Even though the mesonephros is fundamentally an embryonic kidney seen in amniotes, it works for a limited time after birth, as seen in reptiles, marsupials, and monotremes. In the meantime, there is a new kidney utilized by amniotes utilized for life, and that is the metanephros. Once the metanephros takes over a kidney’s works, there is involution in the mesonephros and what is left after birth are just the remnants.
It has also been observed that the environment has affected the structure and function of the nephrons. The parts of the nephrons as seen in the higher vertebrates and humans are the Bowman’s capsule, glomerulus, the loop of Henle, the proximal convoluted tubule, and the course the distal convoluted tubule.
The main job of the glomerulus is to ensure the filtration of the blood. Then the Bowman’s capsule also contributes to the filtration of the blood and their cells, which are known as the podocytes, also see to the prevention of the passage of big molecules like blood proteins and the blood cells into the area known as the Bowman’s space.