THORAX ABDOMEN AND PELVIS

Detailed explanation-1: -The trigone (a.k.a. vesical trigone) is a smooth triangular region of the internal urinary bladder formed by the two ureteric orifices and the internal urethral orifice.

Detailed explanation-2: -Cholinergic muscarinic (M2 and M3) receptors are distributed in the body of the bladder, trigone, bladder neck, and urethra. The M2 cholinergic muscarinic receptors structurally predominate in normal bladders, but the M3 receptors may be functionally more important for bladder contraction.

Detailed explanation-3: -Bladder. This triangle-shaped, hollow organ is located in the lower abdomen. It is held in place by ligaments that are attached to other organs and the pelvic bones. The bladder’s walls relax and expand to store urine, and contract and flatten to empty urine through the urethra.