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:
What is the fluid that comes to part ‘2’ called? Name the main nitrogenous waste in it.
Topic: Urine and urea
Answer
The fluid is URINE.
The main nitrogenous waste in it is UREA.
THE DISTINCTION between parts (ii) and (iii) is the point of the pair: the same liquid has two different names depending on WHERE it is. At the start of the tubule it is the GLOMERULAR FILTRATE — still full of useful substances. By the end, after selective reabsorption and tubular secretion, it is URINE — what remains once everything useful has been recovered.
UREA is formed IN THE LIVER from excess amino acids by deamination, carried in the blood to the kidneys, and excreted.
The pattern of nitrogenous wastes depends on water supply: AMMONIA (fishes), UREA (mammals), URIC ACID (birds and insects, needing least water).