Ostium of uterine tube

The ostium of the uterine tube (plural ostia) may refer to the proximal or distal opening of the tube also called the Fallopian tube.

The proximal tubal opening (ostium or os) is located within the uterus at the uterotubal junction and accessible via hysteroscopy. Occlusion at this opening is referred to as proximal tubal occlusion.

The distal tubal opening (or abdominal ostium) is the opening in the infundibulum of uterine tube into the abdominal cavity. In ovulation, the oocyte enters the Fallopian tube through this opening. It is surrounded by fimbriae, which help in the collection of the oocyte. Occlusion of this opening is referred to as distal tubal occlusion.