Which determines the abiltiy of a mammal to concentrate its urine

Options

A. Number of nephrons
B. Length of proximal convoluted tubules
C. Length of collecting ducts
D. Size of glomerulus

Answer

To determine the ability of a mammal to concentrate its urine, we need to analyze the structures involved in urine formation and concentration. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand Urine Concentration
- **Definition**: Concentration of urine refers to the amount of water present in the urine. When urine is concentrated, it has less water, indicating that the body is conserving water.

### Step 2: Identify Key Structures in the Nephron
- **Nephron Components**: The nephron is the functional unit of the kidney and consists of several parts, including:
- Glomerulus
- Proximal Convoluted Tubule (PCT)
- Loop of Henle
- Distal Convoluted Tubule (DCT)
- Collecting Duct

### Step 3: Role of Each Structure
- **Glomerulus**: Primarily involved in filtration of blood, not in urine concentration.
- **Proximal Convoluted Tubule (PCT)**: Responsible for reabsorbing about 65% of water and other solutes but does not play a major role in concentrating urine.
- **Collecting Duct**: Plays a crucial role in the final concentration of urine. It is where facultative reabsorption of water occurs, depending on the body’s hydration status and the action of hormones like ADH (antidiuretic hormone).

### Step 4: Conclusion
- The ability of a mammal to concentrate its urine is primarily determined by the **length of the collecting ducts**. Longer collecting ducts allow for more water reabsorption, leading to more concentrated urine.

### Final Answer
- The correct answer is **C: Length of the collecting ducts**.

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