Filtering — the Kidney Up Close
Each kidney filters your whole blood supply many times a day. This one is cut open — follow the blood in through the red vessel, and the urine out through the pale tube.
Each dot names a part of the kidney and says, in one line, what it does. This kidney is sliced in half, so the inside layers are on show.
Follow the filtrate
Blood arrives by the renal artery, is filtered in the cortex, fine-tuned in the medulla, and leaves two ways: cleaned blood out the renal vein, urine down the ureter.
What it is
A kidney is a filter with plumbing. Blood enters through the renal artery and spreads into the cortex, the outer layer packed with millions of glomeruli — tiny strainers that pull fluid and waste out of the blood. The fluid then travels through tubules in the medulla, the striped inner pyramids, where the body takes back the water and salts it still needs.
What is left is urine. It collects in the renal pelvis, the funnel at the kidney's center, and drains through the ureter to the bladder. The cleaned blood leaves by the renal vein. When kidneys fail, every step on this path matters — intake, output and the labs that track the filter.
The bedside link
- Urine output reports the filter. Falling output is often the first visible sign that the kidneys are struggling.
- Two exits, two problems. Block the ureter and urine backs up; fail the filter and waste stays in the blood — different causes, different care.
- The kidneys get a fifth of the heart's output. Low blood pressure starves the filter fast — perfusion is kidney protection.