**Core Concept**
Stress urinary incontinence (SUI) occurs when increased abdominal pressure, such as during coughing, sneezing, or heavy lifting, exceeds the urethral closure pressure, leading to involuntary urine leakage. This type of incontinence is often associated with weakened pelvic floor muscles or urethral sphincter dysfunction.

**Why the Correct Answer is Right**
The mechanism behind SUI involves the disruption of the normal urethral closure mechanism. During stress events, the increased intra-abdominal pressure is transmitted to the bladder and urethra, causing urine leakage. This is often due to weakened pelvic floor muscles or urethral sphincter incompetence, which fails to maintain adequate urethral closure pressure. Relevant anatomical structures include the urethral sphincter, pelvic floor muscles (such as the pubococcygeus and iliococcygeus), and the urethral mucosa.

**Why Each Wrong Option is Incorrect**
**Option A:** Urge incontinence occurs when there is an involuntary loss of urine accompanied by a sudden, intense desire to void, often due to overactive bladder or detrusor overactivity.
**Option B:** Overflow incontinence is characterized by the involuntary leakage of urine due to a full bladder that cannot be emptied, often seen in patients with bladder outlet obstruction or neurogenic bladder.
**Option C:** Functional incontinence refers to the inability to reach the toilet in time due to physical or mental disability, rather than a true loss of bladder control.

**Clinical Pearl / High-Yield Fact**
The key to diagnosing stress urinary incontinence is to identify the specific situations that trigger urine leakage, such as coughing, sneezing, or lifting heavy objects. A thorough history and physical examination, including a cough stress test, can help confirm the diagnosis.

**Correct Answer:** C. Overflow incontinence is characterized by the involuntary leakage of urine due to a full bladder that cannot be emptied, often seen in patients with bladder outlet obstruction or neurogenic bladder.