Each kidney holds about a million nephrons. On the right is one of them. Blood arrives at a knot of capillaries — the glomerulus — cupped by Bowman's capsule. The fluid then snakes through the PCT, dives into the loop of Henle, returns through the DCT, and drains down the collecting duct. ▶ Play to trace the whole route.
Switch to the Urine formation tab. Blood enters the glomerulus under high pressure, because the exit vessel is narrower than the entry. Small molecules — water, glucose, salts, urea — are forced out into the capsule as filtrate. Blood cells and plasma proteins are too big and stay in the blood. ▶ Play to watch the filter at work.
The filtrate still holds substances the body needs. As it flows along the PCT, watch all the glucose and amino acids, most salts and most water move back into the surrounding capillaries — glucose and amino acids by active transport, water by osmosis. ⏭ Step through to see normal urine end up with no glucose.
At the DCT, extra H⁺ and K⁺ are actively secreted into the tubule to fine-tune blood pH and ions. Then in the collecting duct the last water is reabsorbed. What is left — water, urea and excess salts — is urine. ↻ Reset and ▶ Play to follow filtrate all the way to urine.
Open the Thermoregulation tab — first it shows the same loop logic for water. If blood is too concentrated, the hypothalamus releases more ADH, the collecting duct reabsorbs more water, and you make a little concentrated urine. Too dilute, and less ADH means a lot of dilute urine. ▶ Play to swing the dial and watch the correction.
Now the same dial drives temperature. When the body is too hot: vasodilation and sweating dump heat and the temperature falls. When too cold: vasoconstriction and shivering save and make heat, so it rises. The hypothalamus always pushes back toward 37 °C. ▶ Play to drive it hot, then cold, and watch it self-correct.