In the whole midgut, activity rises from a baseline of approximately three enzyme units (EU) per midgut to a maximum of 12 EU at 30 hours after the blood meal, subsequently falling to baseline levels by 60 hours. A similar cycle of activity occurs in the posterior midgut and posterior midgut lumen, whereas aminopeptidase in the posterior midgut epithelium decreases in activity during digestion. Aminopeptidase in the anterior midgut is maintained at a constant, low level, showing no significant variation with time after feeding. Alpha-glucosidase is active in anterior and posterior midguts before and at all times after feeding. In whole midgut homogenates, alpha-glucosidase activity increases slowly up to 18 hours after the blood meal, then rises rapidly to a maximum at 30 hours after the blood meal, whereas the subsequent decline in activity is less predictable. All posterior midgut activity is restricted to the posterior midgut lumen. Depending on the time after feeding, greater than 25% of the total midgut activity of alpha-glucosidase is located in the anterior midgut. After blood meal ingestion, proteases are active only in the posterior midgut. Trypsin is the major primary hydrolytic protease and is secreted into the posterior midgut lumen without activation in the posterior midgut epithelium. Aminopeptidase activity is also luminal in the posterior midgut, but cellular aminopeptidases are required for peptide processing in both anterior and posterior midguts.
The possible mechanisms by which vesicouterine fistulas occur following caesarean sections include undetected bladder injury during caesarean section, inadvertent placement of a suture through the bladder during the repair of the uterus and abnormal blood vessel connections following multiple caesarean sections.It may also present following use of obstetric forceps, manual placenta removal, external cephalic version, morbidly adherent placenta, surgical removal of fibroids, rupture of the uterus, perforation of the uterus and radiation therapy in the treatment of cervical cancer.Vesicouterine fistula can also occur as a birth defect in conjunction with vaginal atresia. Diagnosis
The diagnosis of a vesicouterine fistula is made by demonstrating an abnormal connection between the cavities of the bladder and uterus. It can be diagnosed using hysterosalpingography, hysterography, cystography, magnetic resonance imaging (MRI) and computerised tomography. MRI has been found to have 100% accuracy in the diagnosis of vesicouterine fistula. It is also less invasive than other modalities and is considered the gold standard for diagnosis. Treatment
The options of treatment include watchful waiting for spontaneous resolution of the fistula, use of medications that can stop menstrual periods such as oral contraceptive pills, progesterone and gonadotropin releasing hormone analogs. Surgery can be carried out through the vagina, bladder or peritoneum and can be done via laparoscopic or robotic surgery.Watchful waiting is the treatment of choice in case of small fistulas. The bladder is catheterised for a period of 4 to 8 weeks in order to allow spontaneous closure of the vesicouterine fistula.