Final answer:
Osmolarity changes in the nephron during antidiuresis and diuresis reflect water reabsorption levels. In antidiuresis, water is conserved, leading to increased osmolarity as urine moves through the nephron, while in diuresis, reduced water reabsorption results in less concentrated urine.
Step-by-step explanation:
The sequence of osmolarity for antidiuresis (when the body is conserving water) and diuresis (when the body is getting rid of excess water) in different parts of the nephron would be different based on the body's hydration status and hormone influences such as Antidiuretic Hormone (ADH) levels. In antidiuresis, the osmolarity would increase as fluid moves through the nephron because water is being reabsorbed, concentrating the solutes. By contrast, in diuresis, less water reabsorption occurs, leading to a less concentrated urine.
Given the options provided and the typical physiology, one would expect in antidiuresis a blood osmolarity of 300 mOsmol/kg, isotonicity in the proximal convoluted tubule (300 mOsmol/kg), a hypertonic solution in the descending limb of the loop of Henle (1200 mOsmol/kg), very hypotonic solution in the ascending limb of the loop of Henle (100 mOsmol/kg), even further dilution in the distal convoluted tubule (70 mOsmol/kg), and finally, in the presence of ADH, a concentrated urine in the collecting ducts (1200 mOsmol/kg).
The correct sequence for antidiuresis based on the information and physiology described, and omitting incorrect values provided would be: Proximal convoluted tubule (300), Descending limb of the loop of Henle (1200), Ascending limb of the loop of Henle (100), Distal convoluted tubule (70), Collecting duct (variable but can be as high as 1200 depending on ADH influence). For diuresis, where less water is reabsorbed, osmolarity would decrease along the nephron following a similar starting point at the proximal tubule.