Biology: How a Kidney Works

When you tutor biology or any science, often the basic concept is better without all the extra details thrown in.

The renal artery brings blood to the kidneys to be filtered.  Upon reaching a kidney, the renal artery branches into thousands of arterioles, each of which leads to a nephron.  A nephron is the basic working unit of the kidney; each kidney may contain around a million of them, according to wikipedia.

Upon entering the nephron, the blood is spun at high speed in the glomerulus.  The glomerulus is a “merry-go-round” of capillaries.   Water, glucose, amino acids, ions, urea, and uric acid can pass through it;  the high speed flings them out.  The solution thus expelled from the blood is called the filtrate.  It enters the convoluted tubule.  This phase of kidney function is called glomerular filtration.

The main point of the kidneys is excretion, which means ridding the blood of nitrogenous wastes – chiefly urea and uric acid.  Therefore, most of the filtrate now needs to be reclaimed.  Virtually all the glucose and amino acids, most of the water, and some of the ions are reabsorbed by the peritubular capillary network that surrounds the convoluted tubule.  This phase of kidney function is called tubular reabsorption.

At the same time, certain non-filtrable species (too big to exit the blood by glomerular filtration) are actively removed from the capillary into the convoluted tubule.  These non-filtrable species include drug remnants.  Filtrable ions that escaped glomerular filtration can also be removed from the blood in this way.  In either case, this phase of kidney function is called tubular secretion.

What remains of the filtrate after tubular reabsorption – with the targets of tubular secretion added in – flows into the collecting duct, the ureter, and finally into the urinary bladder.

There we have it:  basic kidney function.  It consists of three phases:  filtration, reabsorption, and secretion.  Of course, you can read further.  I use Sylvia S. Mader’s Inquiry into Life, 11th edition, McGraw-Hill.

I hope this gets you started, anyway:)

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC

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