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Embryology, Anatomy, and Physiology of the Bladder
Published in Karl H. Pang, Nadir I. Osman, James W.F. Catto, Christopher R. Chapple, Basic Urological Sciences, 2021
Allan Johnston, Tarik Amer, Omar Aboumarzouk, Hashim Hashim
The Allantois develops at ~day 16 as a small diverticulum (Figure 10.1).It extends from the yolk sac caudal wall into the connecting stalk.It is involved in early blood formation.It is associated with the development of the urinary bladder.
Sonoembryology
Published in Arianna D'Angelo, Nazar N. Amso, Ultrasound in Assisted Reproduction and Early Pregnancy, 2020
At 5 weeks and 0 days, the gestational sac measures 5 or 6 mm in diameter [18]. At the beginning of the fifth week, a small secondary yolk sac is visible as the earliest sign of the developing embryo [19,22]. At the end of the fifth week, an embryo measuring 2–3 mm in length can be seen as a small straight line adjacent to the yolk sac [18,19,22]. As the connecting stalk is short, the embryonic pole is found near the wall of the gestational sac. Even though the embryo is so small, heartbeats at a rate of about 100 bpm can frequently be detected within the embryonic pole [18,26] (Video 14.1).
Ultrasound in the First Trimester
Published in Asim Kurjak, CRC Handbook of Ultrasound in Obstetrics and Gynecology, 2019
Asim Kurjak, Vincenzo D’Addario
As the embryo grows, the amniotic sac enlarges and gradually obliterates the chorionic cavity, so that the embryo floats freely in the amniotic fluid, connected to the chorion by the umbilical cord. This derives from the above-mentioned connecting stalk, which in the meantime has grown longer and has been sheathed by the expanding amnion. The umbilical cord may be imaged starting from the 8th week of menstrual age as a trunk-like structure running from the ventral surface of the embryo to the chorion (Figures 20 and 21).
The Allantois and Urachus: Histological Study Using Human Embryo and Fetuses
Published in Fetal and Pediatric Pathology, 2022
Xuelai Liu, Xianghui Xie, Zhe-Wu Jin, Huan Wang, Yanbiao Song, Peng Zhao, Long Li
Histologic analysis of mid-sagittal sections of embryos of GA 6–7th weeks showed a connection between the abdominal wall and the umbilical cord (Fig. 1A and B). The umbilical cord was linked to the embryo via a connecting stalk of extraembryonic mesoderm, within which the umbilical vessels, omphalomesenteric duct, and primitive allantois were located (Fig. 1C, asterisk). The omphalomesenteric duct occupied the ventral position, whereas one of the umbilical arteries was located in the dorsal position, with the primitive allantois between these two structures. The primitive allantois was an enlarged tube at this embryonic stage, with its extraembryonic part in the umbilical cord and its intraembryonic part (the proximal end of the allantois) being a blind pouch extending inferoposteriorly to the urogenital ridge (Fig. 1D, arrowhead).
Prenatal Detection of Vesico-Allantoic Cyst: Ultrasound and Autopsy Findings
Published in Fetal and Pediatric Pathology, 2023
Maria Paola Bonasoni, Giuseppina Comitini, Ottavia Cavicchioni, Veronica Barbieri, Giulia Dalla Dea, Andrea Palicelli, Lorenzo Aguzzoli
The allantois appears on post-conceptional day 16 arising from the lower wall of the yolk sac. It extends into the connecting stalk and is continuous with the cloaca on one side, and to the abdominal wall (umbilicus) on the other. The intra-abdominal part connects the umbilicus to the urogenital sinus, from which the bladder and urethra originate. As long as the bladder grows and migrates into the pelvis, the intra-abdominal component of the allantois regresses and forms the urachus. Around the 16th to 18th week of gestation, the urachus involutes leaving a fibrotic ligament between the bladder dome and the umbilicus [4,6,7]. If the urachus remains patent, there is a persistence communication between the allantois and the fetal bladder, resulting into the vesico-allantoic cyst.