What is the role of the kidneys and how does it function to do its job?

The main role of the kidney is to filter the blood, to remove toxins like urea and then via various methods, parts of the kidney are able to reabsorb many of these filtered substances back for example, glucose. The kidney is made up of various distinct parts- the first region is the Bowman's capsule with the glomerulus within it- the glomerulus is a bundle of capillaries within the capsule- which has an afferent capillary leading to it and efferent capillary leading from it. The blood is filtered and substances pass through the filtration surface into the kidney's tubule . From here, the filtrate passes through the proximal convoluted tubule, the loops of henle, the distal convoluted tubule and finally the collecting duct leading to the pelvis of the kidney. Each of these regions has adaptations to enable reabsorption of substances- for example the loop of henle via the countercurrent mechanism reabsorbs much water and the collecting duct responds to hormone ADH to allow aquaporins to penetrate through and again enable water reabsorption. So overall, the kidneys have various different regions, adapted in various ways to enable rebasorption of specific substances and allow toxins to be excreted- in order to clean the blood.