Which one of the following is correct for a normal human?

Options

A. pH of urine is around 8
B. On an average, 75-80 mg of urea is excreted via urine per day.
C. Presence of ketone bodies in urine is an indicator of diabetes mellitus
D. Relaxation of smooth muscles of bladder and simultaneous contraction of urethral sphincter causes release of urine.

Explanation

To solve the question, we need to evaluate each of the four statements provided about normal human physiology and excretion.

### Step-by-Step Solution:

1. **Evaluate the first statement**: "The pH of urine is 8."
- The normal pH of human urine is slightly acidic, typically around 6. Therefore, this statement is incorrect.

2. **Evaluate the second statement**: "On average, 75-80 mg of urea is excreted by urine per day."
- In reality, a normal human excretes approximately 25 to 30 grams of urea in urine daily, not 75-80 mg. Thus, this statement is also incorrect.

3. **Evaluate the third statement**: "Presence of ketone bodies in urine is an indicator of diabetes mellitus."
- This statement is correct. In diabetes mellitus, the body may break down fat for energy, leading to the production of ketone bodies. These ketone bodies can be excreted in urine, a condition known as ketonuria.

4. **Evaluate the fourth statement**: "Relaxation of the smooth muscles of the bladder and simultaneous contraction of the urethral sphincter cause the release of urine."
- This statement is incorrect. During urination (micturition), the bladder muscles contract while the sphincter relaxes to allow urine to flow out.

### Conclusion:
The only correct statement among the options provided is the third one: "Presence of ketone bodies in urine is an indicator of diabetes mellitus."

### Final Answer:
The correct answer is the third statement.

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