Figure 23.27 depicts kidney osmolalities during excretion of a dilute urine, as occurs when plasma AVP levels are low. Tubular fluid is diluted along the ascending limb and becomes more dilute as solute is reabsorbed across the relatively water-impermeable distal portions of the nephron and collecting ducts. Since as much as 15% of filtered water is not reabsorbed, a high urine flow rate results. In these circumstances, the osmotic gradient in the medulla is reduced but not abolished. The decreased gradient results from several factors, including an increased medullary blood flow,
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.