The Question is from neet-zoology excretory-products-and-their-elimination mechanism-of-concentration-of-the-filterate, and it was created by the author K SUNKANNA

Question

A patient presents with significantly reduced glomerular filtration rate and an inability to concentrate urine.  Damage to which specific part of the nephron is MOST likely responsible for this impaired concentrating ability?

K SUNKANNA · Accepted Answer

## CORE INFORMATION
✓ **Answer**: B
## CONCEPT FRAMEWORK
	**Primary Concept**: Nephron function and urine concentration
	**Related Topics**: Glomerular filtration rate (GFR), countercurrent mechanism, renal concentrating ability, hormonal regulation of water reabsorption.
	**Prerequisites**: Understanding of nephron anatomy and physiology, including the roles of different nephron segments in urine formation.
## SOLUTION PATHWAY
**Given Information**:
		Reduced glomerular filtration rate (GFR)
		Inability to concentrate urine
**Method & Steps**:
	1. **Understanding Urine Concentration:** The kidney's ability to concentrate urine depends primarily on the countercurrent mechanism within the Loop of Henle and the collecting duct. This mechanism establishes an osmotic gradient in the renal medulla, allowing for water reabsorption from the collecting duct.
	2. **Role of the Loop of Henle:** The thick ascending limb of the Loop of Henle is crucial for establishing the medullary osmotic gradient.  It actively transports sodium, potassium, and chloride ions out of the tubule lumen into the interstitial fluid, creating a hyperosmolar environment in the medulla.
	3. **Impact of Damage:** Damage to the thick ascending limb of the Loop of Henle would impair the ability to generate this osmotic gradient. This would directly lead to a reduced ability to concentrate urine, resulting in the production of dilute urine. The reduced GFR is a separate issue, possibly related to damage in a different part of the nephron or to systemic factors.  However, the question specifically asks about the impaired concentrating ability.
	4. **Other Nephron Segments:** The proximal convoluted tubule reabsorbs most of the filtered water and solutes. The distal convoluted tubule plays a role in fine-tuning electrolyte balance and some water reabsorption, but it's not the primary site for establishing the medullary osmotic gradient. The collecting duct is crucial for the final adjustments to water reabsorption under the influence of antidiuretic hormone (ADH), but it relies on the osmotic gradient established by the Loop of Henle. 
	5. **Conclusion:** Therefore, damage to the thick ascending limb of the Loop of Henle is the most likely cause of the described impaired urine concentrating ability.
		Result: Loop of Henle, specifically the thick ascending limb
		Verification:  The symptoms directly correlate with the disruption of the countercurrent mechanism, which is largely dependent on the thick ascending limb's function.
## OPTION ANALYSIS
A :x: The proximal convoluted tubule's primary function is reabsorption, not establishing the medullary osmotic gradient.
B ✓: The thick ascending limb actively transports ions, creating the medullary osmotic gradient essential for concentrating urine.
C :x: The distal convoluted tubule plays a role in electrolyte balance but is not the primary site for establishing the medullary osmotic gradient.
D :x: The collecting duct reabsorbs water under ADH influence but relies on the medullary osmotic gradient already established by the Loop of Henle.
## LEARNING AIDS
	**Common Mistakes**:
		1. Confusing the roles of different nephron segments: Thorough understanding of each segment's function is crucial.
			How to avoid: Create a chart summarizing the key functions of each nephron segment.
		2. Focusing solely on GFR reduction: While relevant, the question specifically asks about the impaired concentrating ability.
			How to avoid: Carefully read and understand the question's specific focus.
	**Quick Tips**:
		1. Remember the countercurrent mechanism and its dependence on the Loop of Henle's thick ascending limb.
		2. Relate symptoms directly to the specific function of each nephron segment.

K SUNKANNA · Answer

Proximal convoluted tubule

K SUNKANNA · Answer

The correct Option is "Loop of Henle, specifically the thick ascending limb"

K SUNKANNA · Answer

Distal convoluted tubule

K SUNKANNA · Answer

Collecting duct

NEET Zoology Excretory Products And Their Elimination Mechanism Of Concentration Of The Filterate MCQs

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