The correct sequence of the movement of urea during urine formation is?

Analyzing the question: It asks for the path urea takes through the nephron as urine forms. Urea is filtered out of the blood and then travels along the nephron until it reaches the collecting duct.

Concept: The nephron is the functional unit of the kidney. Its parts, in order, are:

1. Glomerulus: a knot of capillaries where ultrafiltration happens. Water, urea, glucose, salts and amino acids are forced out of the blood.
2. Bowman's capsule: collects the filtrate (glomerular filtrate).
3. Proximal convoluted tubule: selective reabsorption of glucose, amino acids and much of the water and salts.
4. Loop of Henle: concentrates the filtrate by water and salt exchange.
5. Distal convoluted tubule: further adjustment of salts and water, and secretion.
6. Collecting tubule (duct): carries urine to the renal pelvis, then the ureter.

Solution:

• C and D are wrong. The convoluted tubule cannot come before the glomerulus or Bowman's capsule, because filtration happens first. "Nettle's loop" in C is also not a real structure.
• A skips the second convoluted tubule (the distal one). The filtrate must pass through the proximal convoluted tubule, the loop of Henle, and then the distal convoluted tubule before it enters the collecting tubule.
• B gives the complete and correct order:

glomerulus → Bowman's capsule → (proximal) convoluted tubule → loop of Henle → (distal) convoluted tubule → collecting tubule

Correct answer: B

Exam tip: Remember the nephron path as G-B-P-H-D-C: Glomerulus, Bowman's capsule, Proximal tubule, Henle's loop, Distal tubule, Collecting duct. If an option leaves out the second convoluted tubule, check whether a more complete option is available.