Question

Which of the following factors is responsible for the formation of concentrated urine.
A. Low levels of diuretic urine
B. Maintaining hyperosmolarity towards internal medullary interstitium in kidney
C. Secretion of erythropoietin by Juxtaglomerular complex
D. Hydrostatic pressure during glomerular filtration

Answer 1

Hint: The concentrated urine means that the concentration of the solute is more as compared to the water. Solutes present are dissolved particles, such as sugars, salts, and proteins. These are all again absorbed back into the body by different processes.

Complete answer:
The factors that are responsible for the formation of concentrated urine are a loop of Henle and antidiuretic Hormone. The loop of Henle creates a negative or low water potential in the medulla tissues to absorb more water from the fluids present in the collecting duct. The proximity between the loop of Henle and vasa recta as well as the countercurrent of fluids between them helps to maintain an increasing osmolarity towards the inner medullary interstitium. This process helps to maintain a concentration gradient in the medullary interstitium so human urine is usually four times more concentrated than the initial filtrate formed.
So, the right answer is option (B), Maintaining hyperosmolarity towards internal medullary interstitium in the kidney.

Additional information:-
Waste is excreted from our body in the form of urine. The urine formation takes place in three steps:- Glomerular Filtration, Reabsorption, and Secretion. Glomerular filtration occurs in the glomerulus where blood is filtered. This process occurs by crossing the three layers- epithelium of Bowman’s capsule, endothelium of glomerular blood vessels, and a membrane between these two layers. All the constituents of blood are filtered except the protein. Therefore, this process is known as ultrafiltration. The filtrate then moves to the Bowman’s capsule for more absorption of the filtrate. Maximum constituents of the filtrate present in it are reabsorbed by the renal tubules. This is known as reabsorption. This is achieved by active and passive transport. Then the urine is formed in the tubular secretion. Here, tubular cells release hydrogen ions, potassium ions, etc into the filtrate. The secreted ions in combination with the filtrate form urine. The urine passes through the nephron tubule to the collecting duct.

Note: Wastes such as urea, ammonia, uric acid are generally excreted in the urine. The potassium, sodium, and calcium ions are also excreted out of the body in the urine. Humans are called as ureotelic as the major component in urine is urea.