Urine Formation

Urine forms as some of the blood plasma spills out, some of these spilled plasma components are taken back up into the blood, and other material is selectively sent out to be added to the urine. In other words, there are three main things happening to form urine:

	glomerular filtration (blood plasma spills out)
	tubular reabsorption (some items are selectively reabsorbed into the blood)
	tubular secretion (some blood plasma items are selectively sent out into the tubules)

Of these three steps, glomerular filtration is the only one that happens in the renal capsule. You will see that I have devoted a web page to glomerular filtration. Throughout the renal tubule, both tubular reabsorption and tubular secretion are occurring. It is impossible to talk about one without also talking about the other. It makes more sense to me to talk about both together. As filtrate progresses through each region of the renal tubule (the proximal convoluted tubule, loop of Henle, and distal convoluted tubule & collecting duct), different methods are used for tubular reabsorption and secretion... therefore, I have separated what happens in each region out into individual web pages. You will find both tubular reabsorption and secretion in most regions.