The diagram given below is that of a structure present in a human kidney. Study the same and answer the questions that follow: The diagram given below is that of a structure present in a human kidney. Study the same and answer the questions that follow:
Mention the three main steps involved in the formation of the fluid mentioned in (iii) above.
Topic: Steps in urine formation
Answer
- ULTRAFILTRATION (glomerular filtration) — blood is filtered under high pressure in the Malpighian capsule.
- SELECTIVE REABSORPTION — useful substances are reabsorbed from the tubule back into the blood.
- TUBULAR SECRETION — additional wastes and excess ions are actively secreted from the blood into the tubule.
The three names must be exact, and they happen in that ORDER.
The word SELECTIVE in step 2 is what makes the kidney intelligent rather than a mere sieve. Filtration is indiscriminate; the tubule then recovers what the body needs and leaves the rest.
STEP 3 RUNS IN THE OPPOSITE DIRECTION to step 2 — OUT of the blood INTO the tubule — which is the detail candidates most often get backwards. It removes substances that were not filtered out in the first place, such as excess potassium, hydrogen ions and creatinine.
Together the three explain how a filtrate of 180 litres a day becomes about 1.5 litres of urine.