To determine which statement is correct regarding the functioning of the nephron, we will analyze each option based on our knowledge of nephron structure and function.
### Step-by-Step Solution:
1. **Understanding Nephron Structure**:
- The nephron is the structural and functional unit of the kidney. Each kidney contains about 1 to 1.5 million nephrons.
- Nephrons consist of several parts: the renal corpuscle (Bowman's capsule and glomerulus), proximal convoluted tubule (PCT), loop of Henle (which has a descending and ascending limb), distal convoluted tubule (DCT), and collecting duct.
2. **Function of Nephron**:
- The nephron is responsible for filtration, reabsorption, and secretion.
- Filtration occurs in the glomerulus, where blood plasma is filtered into the Bowman's capsule.
- Reabsorption of water, ions, and nutrients primarily occurs in the PCT, and further adjustments occur in the loop of Henle, DCT, and collecting duct.
3. **Analyzing the Options**:
- **Option 1**: Conditional reabsorption of water occurs in the proximal convoluted tubule (PCT).
- This statement is incorrect because while some water is reabsorbed in the PCT, the majority of conditional reabsorption occurs in the distal convoluted tubule (DCT) and collecting duct, influenced by hormones like ADH.
- **Option 2**: The concentrated filtrate when passing upward in the ascending loop of Henle dilutes due to the passage of electrolytes into the medullary fluid.
- This statement is correct. The ascending limb of the loop of Henle is impermeable to water but allows for the active transport of ions (like sodium and chloride) out of the filtrate, leading to dilution of the filtrate as it ascends.
- **Option 3**: More glucose is reabsorbed in the distal convoluted tubule (DCT) than in the proximal convoluted tubule (PCT).
- This statement is incorrect. The majority of glucose reabsorption occurs in the PCT, not the DCT.
- **Option 4**: There is no hormonal influence on the reabsorption of the filtration load in the collecting duct.
- This statement is incorrect. The collecting duct is influenced by hormones such as antidiuretic hormone (ADH), which regulates water reabsorption.
4. **Conclusion**:
- After analyzing all options, the correct statement regarding the functioning of the nephron is **Option 2**: The concentrated filtrate when passing upward in the ascending loop of Henle dilutes due to the passage of electrolytes into the medullary fluid.
