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How the kidneys work: where they are, what they do, the nephrons, and how blood flows through them
For anyone who wants to understand their kidneys; anyone who was told something is wrong with their kidneys and wants to follow what their care team says; anyone reading a report full of words like nephron, glomerulus or renal; and anyone looking after someone who is. It passes on, by name, what the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK, part of the NIH) says: where the kidneys are and how big; what they do, from removing wastes to keeping the balance of water, salts and minerals, and the hormones they make; the million nephrons in each kidney, each with a filter and a tubule; how blood flows in and out; the numbers in a day; and the words, in plain language. It builds the words to say to your care team, so you do not have to find them, and prints a card.
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- On this site: Kidneys, bladder and urine: find the right page · When it’s your kidneys · Glomerular disease · A solitary kidney.
- Related: High blood pressure · Anemia in kidney disease · Mineral and bone disorder · Blood in the urine.
- Getting ready: Get ready for your appointment · Symptom diary · When you need a doctor and can’t pay.
- In a crisis: Help right now (988, 911). All our free tools.
Kidneys, bladder or urine, and not sure this is the right page? The pages on this site for bladder infections, kidney stones, blood in the urine, bladder pain, bladder leaks, the prostate, kidney disease and bedwetting, on one list.
This page and its wording were written with AI (Claude) for Scarlet Beast (our AI policy). No doctor or nurse has reviewed it. The facts were read on October 19, 2026 on NIDDK’s (NIH) page Your Kidneys & How They Work (last reviewed June 2018) and its Spanish page Los riñones y su funcionamiento (last reviewed June 2018), which says nearly the same (it says the blood vessel takes back 99 percent of the water where the English says almost all, and it leaves out the line on children). The numbers (about a half cup of blood a minute; about a million nephrons in each kidney; about 150 quarts of blood a day; 1 to 2 quarts of urine) are NIDDK’s. Ours: “if you believe it is an emergency, call 911” (NIDDK names no 911 on this page); 988; the plain-words list, which only gathers what NIDDK says each word means; that the page does not say what protein or blood in the urine means; the questions to ask; the links to our other pages; and the order of the steps. What we left out: the section on clinical trials, NIDDK’s video, and NIDDK’s links to other sites. Nothing you tick or type here is saved or sent.