The name trigone comes from the Latin word trigonum, meaning triangle. It is commonly used as a descriptor for parts of human anatomy that have a triangular shape, but is most commonly used for part of the urinary tract. It is also used to describe the space where three or four more plant cells meet.
In human anatomy, the word "trigone" is used to describe many things. It can refer to the shape of the cusps on some molars. The catoid trigone is a triangular area where many muscles meet at the base of the neck. The olfactory trigone is a triangular part of the brain connected with the sense of smell. Other types of trigones are spaces in the brain. Their enlargement or abnormality can be a sign of mental disease, such as dementia or schizophrenia.
Out of all of these, the area of the body most commonly referred to as trigone is located in the bladder. It is the area where two tubes from the kidneys, called ureters, meet with the urethra, which in turn leads to the bladder. This area is shaped like a triangle, hence the name, and is made entirely of smooth muscle.
This area is a very sensitive part of the anatomy. As the bladder fills, it stretches. This creates the sensation of "needing to go," which signals that it is time for the bladder to be emptied. One of the urinary sphincters, which either cuts off or allows urine to flow, is located nearby.
The sphincter located nearest to the trigone is involuntary, meaning it is not under conscious control. Another sphincter, located nearest to the genital opening, is the one that a person has conscious control over. If the trigone becomes overstretched, signaling that the bladder has become over-full, it will signal the involuntary sphincter to release the urine immediately.
Sometimes the trigone may become infected. This is called trigonitus. The walls of the trigone will take on a scaly appearance, making it extremely painful to urinate. Trigontius is different form a simple bladder infection in that it is much more difficult to treat, though it may have the exact same symptoms.
Trigonitis occurs more frequently in women than men, though the causes are unknown. Effective treatments are still being researched. A course of antibiotics may work for one person, but have no effect on another. Unlike usual urinary tract infections, trigonitus can be further irritated by drinking cranberry juice.