ANATOMY

Detailed explanation-1: -When water intake is large enough to dilute blood plasma, a urine more dilute than blood plasma is produced; when water intake is so small that blood plasma is concentrated, a urine more concentrated than blood plasma is produced.

Detailed explanation-2: -Movement of a large amount of urea across cell membrane is made possible by urea transporter proteins. Urea allows the kidney to create the hyperosmotic urine (higher concentration of ions), which implies that the urine has more concentration of urea than the plasma of the body.

Detailed explanation-3: -In the presence of ADH, both the outer and inner medullary collecting ducts increase their permeability to water; in the absence of ADH, the urine cannot be concentrated, causing polyuria.

Detailed explanation-4: -Increased urine concentration may be due to conditions, such as: Glucose (a type of sugar) in the urine. Heart failure. Loss of body fluids (dehydration) from diarrhea or excessive sweating.