Textbook Question
Mark the following statements as true or false. If a statement is false, correct it to make a true statement.
d. ADH triggers water reabsorption from the nephron loop.
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25. The Urinary System
Renal Physiology Step 2: Tubular Reabsorption
1:40 minutesProblem 5
Textbook Question
Glucose is not normally found in the urine because it
a. Does not pass through the walls of the glomerulus
b. Is kept in the blood by colloid osmotic pressure
c. Is reabsorbed by the tubule cells
d. Is removed by the body cells before the blood reaches the kidney
Verified step by step guidance1
Understand the role of the kidney in filtering blood: The kidney filters blood through structures called nephrons, which include the glomerulus and renal tubules. The glomerulus allows small molecules like glucose to pass into the filtrate, but larger molecules like proteins are retained in the blood.
Recall the process of reabsorption: After filtration in the glomerulus, the filtrate passes through the renal tubules. Essential substances like glucose are reabsorbed into the bloodstream by the tubule cells through active transport mechanisms.
Eliminate incorrect options: a) Glucose does pass through the walls of the glomerulus because it is a small molecule. b) Colloid osmotic pressure primarily retains proteins, not glucose, in the blood. d) Glucose is not removed by body cells before reaching the kidney; it circulates in the blood and is filtered by the kidney.
Focus on the correct mechanism: Glucose is reabsorbed by the tubule cells in the proximal convoluted tubule of the nephron. This prevents glucose from being excreted in the urine under normal conditions.
Conclude the reasoning: The correct answer is related to the reabsorption process, which ensures that glucose is retained in the body and not lost in the urine unless the reabsorption capacity is exceeded, such as in conditions like diabetes mellitus.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Glomerular Filtration
Glomerular filtration is the process by which blood is filtered in the kidneys, specifically in the glomeruli. During this process, small molecules, including glucose, can pass through the glomerular membrane into the renal tubules. However, glucose is typically reabsorbed later in the nephron, preventing its presence in urine under normal conditions.
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Tubular Reabsorption
Tubular reabsorption refers to the process by which the kidneys reclaim water, ions, and nutrients from the filtrate back into the bloodstream. In the case of glucose, it is actively reabsorbed in the proximal convoluted tubule through specific transporters, ensuring that it is not lost in urine and remains available for the body's energy needs.
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Colloid Osmotic Pressure
Colloid osmotic pressure is the pressure exerted by proteins in the blood plasma that helps retain water within the circulatory system. While it plays a role in fluid balance, it is not the primary mechanism for glucose retention in the blood. Instead, glucose's absence in urine is mainly due to its reabsorption in the renal tubules.
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