Nephron is the basic functional unit of the human kidney and a single kidney is made out of 800,000 to 1 million nephrons. These nephrons perform many functions and these include regulating the blood volume, blood pressure, metabolic status and more importantly electrolyte balance. Apart from these, it performs a vital function in excreting metabolic by products including certain medications once they are metabolized elsewhere in the body. Finally, the outcome of all these functions would be the formation of urine and the solute content in urine and the volume that the kidneys are producing would depict the various functional adaptations made by the nephrons according to the body needs.
The structure of the nephron:
Each nephron contains two sections and these are the ‘renal corpuscle’ and the ‘renal tubules’. Depending on the location in which the nephrons are places, these can be named as either cortical nephrons or juxta-medullary nephrons which will have slightly different functionality and anatomical characteristics of its own.
This can be named as the initial or beginning portion of the nephron and contains the bowman’s capsule and the glomerulus. The glomerulus is a tuft of capillaries coiled within the bowman’s capsule and the pressure build up within the glomerulus will determine the force at which the blood seeps in into the bowman’s capsule. It is said that, about 1/5th of the blood going through the glomerulus would get absorbed. The lining of the bowman’s capsule is adapted for its function with thin layers of cells as its wall between the blood and the space of the capsule. Thus, the podocytes are the ones which lines the inner layer or the visceral layer and simple epithelial cells would be lining the outer parietal layer.
There several anatomical regions throughout the renal tubules and it starts from the proximal convoluted tubules, proceeds to loop of henle and lastly in to distal convoluted tubules.
The tubules would be covered by peri-tubular capillaries and the inner layers of these tubules would also be specialized to perform a specific function. Thus, the proximal convoluted tubules would be lined by brush border cells which are cuboidal in structure. These cells with increased cell surface would facilitate re-absorption of the minerals and solutes, namely the sodium, glucose and the amino-acids, from the filtrate that passes on from the bowman’s capsule.
The loop of henle consist of a descending portion, the hairpin loop and the ascending portion which will create a concentration gradient through which more water would be re-absorbed and will make the urine more concentrated.
The distal convoluted tubules would perform an additional function to regulate the pH levels of the blood as well as regulate the calcium and potassium absorption from the filtrate.
Following the distal convoluted tubules, the filtrate or the urine would pass onto the collecting tubules which are not considered to be part of the nephron.