In which part of excretory system of mammals can you first use the term "urine" for contained fluid?
(a) Urinary bladder
(b) Collecting tubule
(c) Bowman's capsule
(d) Loop of Henle

Options

A. Urinary bladder
B. Collecting tubule
C. Bowman's capsule
D. Loop of Henle

Answer

To determine the part of the excretory system of mammals where the term "urine" can first be used for the contained fluid, we can analyze the options provided:

1. **Understanding the Excretory System**: The excretory system in mammals consists of various structures including the kidneys, ureters, urinary bladder, and urethra. The kidneys play a crucial role in filtering blood and producing urine.

2. **Analyzing the Options**:
- **(a) Urinary Bladder**: This is a storage organ for urine, but the fluid contained here is already referred to as urine, not the first instance of the term being used.
- **(b) Collecting Tubule**: This is where the filtrate from the nephron is collected. As the filtrate passes through the collecting tubule, it undergoes further concentration and is first termed "urine" due to its concentrated nature.
- **(c) Bowman's Capsule**: This is the site of ultrafiltration where the initial filtrate is formed, but it is not yet referred to as urine; it is called glomerular filtrate.
- **(d) Loop of Henle**: This structure is involved in the reabsorption of water and salts, but the fluid here is still considered filtrate and not yet urine.

3. **Conclusion**: The first instance where the term "urine" is used for the contained fluid is in the **Collecting Tubule** (option B). This is where the filtrate becomes more concentrated and is officially termed urine.

**Final Answer**: (b) Collecting tubule

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