Final answer:
During intercourse, the urine is prevented from entering the urethra by the internal urinary sphincter and the anatomy of the urinary system.
Step-by-step explanation:
During intercourse, the urine is prevented from entering the urethra by two main mechanisms: the internal urinary sphincter and the anatomy of the urinary system.
The internal urinary sphincter is a smooth muscle located at the juncture of the bladder and urethra. It relaxes as the bladder fills with urine, allowing urine to enter the urethra. When the sphincter is not relaxed, it forms a barrier that prevents urine from flowing into the urethra.
In addition to the internal urinary sphincter, the anatomy of the urinary system also plays a role in preventing urine from entering the urethra. The walls of the urinary system structures, including the bladder, are designed to expand as they fill with urine and contract to release urine. The ureters, which connect the kidneys to the bladder, have a one-way valve mechanism that allows urine to enter the bladder but prevents reflux of urine back into the ureters.