The functional unit of the kidney, there are approximately 1.3 million per kidney. They each consist of a glomerulus and a tubule.
Capillaries supplied by afferent arterioles pass by a blind end of the nephron. Blood is filtered by the capillary endothelium and the endothelium of Bowman's capsule. This makes up the glomerular membrane, and allows free filtration of neutral substances less than 4nm. Those over 8nm are excluded. The blood then leaves via efferent arterioles. Blood flow to the kidneys means they filter ~180 litres/day.
Proximal convoluted tubule
Exactly what the name suggests, this drains the glomerular filtrate. Sodium and water are reabsorbed, along with amino acids and glucose. Carbonic anhydrase inhibitors (eg acetazolamide) act here.
Loop of Henle
Using a countercurrent multiplier beloved of medical students, this manages to reabsorb vast quantities of both water and sodium. It has thin descending (reabsorb water) and thick ascending (reabsorb sodium) limbs. Loop diuretics act on the ascending limb.
As the afferent and efferent arterioles both pass near this part of the tubule, the cells in the afferent arteriole secrete renin according to the osmotic load (principally sodium and chloride) in the tubule, and the pressure in the arterioles.
Distal convoluted tubule
Another well named section of the nephron, this acts to fine tune the reabsorption of sodium. It also acidifies the filtrate. Thiazide diuretics act here.
Divided into cortical and medullary portions, there is more water resorption here. This is controlled by anti-diuretic hormone (ADH), which inserts aquaporins into the luminal membranes.