Isthmus of the Fallopian Tube

The isthmus of the fallopian tube (isthmus uteri tubarius, isthmi utri tubarii, isthmus of the tube of the vaginal uterus, also ureteric isthmus, urinary isthmus) is a narrow tube between the wide upper and narrow lower parts of the fallopian tube.

Normally, the isthmus is located in the muscular part of the fallopian tubes, which contributes to the contraction of its muscles. This makes it easier for the egg to move through the tube for fertilization. The fertilized egg enters the wall of the fallopian tubes, where there are still many special endocrine glands that secrete a special substance - lutein. Luteins (aka corpus luteum of the ovary) are descendants of endogenous fetal endocrine cells that form the follicle or embryonic circulation after implantation of the fertilized egg sac into the endometrium. Ultimately, the corpus luteum of the endocrine gland lasts for five to six months or longer in some women before it disappears on its own if the pregnant woman does not develop further.