|Year : 2019 | Volume
| Issue : 1 | Page : 6-10
Morphogenesis of urinary bladder in human fetuses
Yanglem Elizabeth Devi1, N Saratchandra Singh1, Ch Rajendra Singh1, Laishram Ayingbi Devi2, Leon R Guria1
1 Department of Anatomy, Regional Institute of Medical Sciences, Imphal, Manipur, India
2 Department of Obstetrics and Gynaecology, Regional Institute of Medical Sciences, Imphal, Manipur, India
|Date of Web Publication||14-Oct-2019|
Yanglem Elizabeth Devi
Department of Anatomy, Regional Institute of Medical Sciences, Imphal, Manipur
Source of Support: None, Conflict of Interest: None
Introduction: The urinary bladder is a temporary reservoir for urine brought from the kidneys by the ureters. It develops from the upper expanded part of urogenital sinus. There is paucity of literature regarding development of urinary bladder during various stages of fetal life. Hence, this study was done to observe the changes taking place in the development of normal urinary bladder during various stages of fetal life.
Materials and Methods: The study was conducted in the Department of Anatomy, Regional Institute of Medical Sciences (RIMS), Imphal for 2 years from 2011 to 2013 after taking approval from the ethical committee of the institute. Fifty fetuses of different gestational age ranging from 15 weeks to term which were products of medical termination of pregnancy were collected from Department of Obstetrics and Gynaecology, RIMS.
Results: Three shapes of bladder were visible during the fetal life, i.e., round, ellipsoid, and pyramidal. Round and ellipsoid shape were visible during the early fetal period, and bladder assumed more pyramidal shape during later fetal life.
Conclusion: Urinary bladder assumed almost adult shape from 33 weeks onward with presence of four surfaces, i.e., one superior, two inferolateral, and one posterior surface or base.
Keywords: Morphogenesis, shapes of urinary bladder, umbilical artery, urachus
|How to cite this article:|
Devi YE, Singh N S, Singh CR, Devi LA, Guria LR. Morphogenesis of urinary bladder in human fetuses. J Med Soc 2019;33:6-10
| Introduction|| |
The urinary bladder is a temporary reservoir for urine brought from the kidneys by the ureters. When empty, it is somewhat tetrahedral in shape and has a fundus, neck, apex, a superior, and two inferolateral surfaces. The fundus or base is triangular and posteroinferior.
In adults, an empty bladder lies behind the pubic symphysis and the superior pubic rami as a completely pelvic organ. However, when distended, it rises into the abdomen to become abdominopelvic in position. In children up to 8–9 years, it is abdominopelvic even when empty because the capacity of the pelvis is small. The bladder neck, which is the most dependent part of the organ, lies at the level of the upper border of symphysis pubis at birth. It descends very rapidly during the first 3 years of life, and then, the rate of descent slows down until it reaches the adult position, i.e., the level just above the lower border of symphysis pubis. This descent of the neck is negligible after 9 years of age. When the bladder is full, the summit of the bladder reaches a level about 7.5 cm above the symphysis pubis just behind the anterior abdominal wall.
The embryonic hindgut of males and females ends in a large expanded region called cloaca. During the 4th to 7th weeks of development, the cloaca divides into the urogenital sinus anteriorly and the anal canal posteriorly. The urorectal septum is a layer of mesoderm between the primitive anal canal and the urogenital sinus. The tip of the septum will form the perineal body. Three portions of the urogenital sinus can be distinguished. The upper and the largest part forms the urinary bladder. Initially, it is continuous with the allantois. When the lumen of allantois is obliterated, a thick fibrous cord, the urachus, remains and connects the apex of the bladder with the umbilicus. In adults, it is known as the median umbilical ligament. The next part is a narrow canal, the pelvic part of the urogenital sinus, which in the male gives rise to the prostatic and membranous parts of the urethra. The last part is phallic part of the urogenital sinus. However, there is still paucity of literature regarding development of urinary bladder during later weeks of fetal life. Hence, this study was done to observe the changes taking place in the development of urinary bladder during various stages of fetal life.
| Materials and Methods|| |
The study was conducted in the Department of Anatomy, Regional Institute of Medical Sciences (RIMS), Imphal. Fifty fetuses of different gestational ages ranging from 15 to 40 weeks were collected from the Department of Obstetrics and Gynaecology, RIMS, Imphal. The fetuses were products of terminated pregnancies under Medical Termination of Pregnancy Act of India, 1971 and stillbirths. A formal permission for the study on fetuses was obtained from the Ethical Committee of RIMS, Imphal. Only those fetuses which were free from any gross anatomical abnormality were selected for the present study. The age of the fetuses were assessed from the obstetrical history, crown rump length, and gross features before fixation. The fetuses were preserved in 10% formol saline for 10–15 days.
After proper fixation in formol saline (for about 2 weeks), the fetuses were dissected. The abdomen was opened by giving a left paramedian incision, the incision was extended inferiorly to cut through the cartilage of the hip joint. After removing anterior abdominal wall, the urinary bladder was identified. Appearance of the urinary bladder to the naked eye, its position, and relation with surrounding visceras were identified. The urinary bladder was finally removed and was studied for the growth and development and its changing size, shape, and volume. As filling of the bladder can alter its shape, observation of its shape and measurement of its dimensions are done after the bladder has been removed and emptied of its contents. The length of the urinary bladder was measured from the apex to the midpoint of posterior border, breadth was measured at the site of maximum transverse diameter and after opening the bladder, and the distance between two ureteric orifices was measured as the interureteric distance which also forms the base of the bladder trigone. The lengths and breadths of the urinary bladder of different age groups were presented in the tables [Table 1] and [Table 2]. These measured lengths and breadths of individual urinary bladder were also plotted against their gestational age to analyze the result [Table 3].
|Table 1: Mean length of the urinary bladder at different fetal age groups|
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|Table 2: Mean breadth of the urinary bladder at different fetal age groups|
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|Table 3: Mean dimensions (Length and Breadth) at different gestational ages|
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As remarkable changes take place at every 4-week interval, the fetuses were categorized into six groups according to their gestational age as follows for easier study and observation:
- Group I: Up to 15 weeks
- Group II: 16–20 weeks
- Group III: 21–25 weeks
- Group IV: 26–30 weeks
- Group V: 31–35 weeks
- Group VI: 36–40 weeks.
| Results and Observation|| |
The appearance of the urinary bladder to the naked eye from the earliest available age of 15 weeks to full term was studied in detail. Growth and development at different age groups are described as below:
Group I: 15 weeks
In the earliest specimen of this series (15 weeks old fetus), the developing urinary bladder is seen as jelly-like, round-shaped bulge in the upper part of the urogenital sinus. It lies entirely in the abdominal cavity. Only the two lateral borders are well defined, thereby dividing the bladder into anterior and posterior surface. Anterior surface lies closely opposed to the anterior abdominal wall while its posterior surface rests on rectum and coils of small intestine in case of male fetus and to uterus and anterior vaginal wall in case of female fetuses. Both of these surfaces are covered with peritoneum, which is reflected from the anterior abdominal wall. The cranioventral end of the bladder opens into the allantois at the level of umbilicus; thus, the bladder initially extends all the way to the umbilicus. The two umbilical arteries run one on each side of the apex going toward the umbilicus [Figure 1]. The urinary bladder by this time measures in length of 13 mm and breadth of 6 mm [Figure 1].
Group II: 16–20 weeks
The urinary bladder at 20-week-old fetus is ellipsoid in shape with length of 14 mm and breadth of 6 mm, weighs about 800 mg. The apex of the developing urinary bladder is connected to the umbilicus through urachus, i.e., the fibromuscular remnant of the allantois with two umbilical arteries running one on each side of it. Bladder is still an abdominal organ.
Group III: 21–25 weeks
Bladder in this group is significantly bigger in size and more firm in consistency than that of the previous group. Urinary bladder in 22-week-old fetus is pyramidal in shape with length of 16 mm and breadth of 7 mm. It is still abdominal in position. In urinary bladder of 22-week-old female fetus, peritoneum covers the superior surface and upper part of the base and is reflected on anterior surface of uterus to form uterovesical pouch. Its apical portion progressively narrows to a small epithelized fibromuscular strand, the urachus which is the remnant of the allantois, and connects urinary bladder to the umbilicus. Two umbilical arteries run one on each side of urachus toward the umbilicus.
By 25 weeks, bladder is ellipsoid in shape and two lateral borders are well demarcated, but posterior border remain ill defined. Two inferolateral surfaces are well defined, superior surface and base looks like one continuous surface. Apex of the bladder is connected to the umbilicus through urachus and is broad near attachment on the bladder and tapers toward umbilicus. Lumen is still present in the urachus. The undescended right and left testis along with epididymis are seen lying one each side of the bladder [Figure 2]. The two ureters are seen entering the bladder at the two superolateral corners of the base of the bladder. They are crossed by vas deferens as they descend further to enter urethra at a lower level. In a 25 week old fetus, urinary bladder's length is 20 mm and breadth is 12 mm [Figure 2].
|Figure 2: Relationship of urinary bladder to the neighboring visceras in a 25-week-old male fetus|
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Group IV: 26–30 weeks
The urinary bladder continues to increase in size with more growth lengthwise and less growth along the breadth. Bladder of a 27-week-old fetus is pyramidal in shape with length of 22 mm and breadth of 16 mm. It is still connected to the umbilicus by urachus, and the two umbilical arteries are visible going one each side of urachus.
Group V: 31–35 weeks
In this series, bladders still continue to grow as it is evident from increased length, breadth, and thickness as compared to the previous group. In a 33-week-old fetus, bladder is pyramidal in shape. All the four surfaces, i.e., superior surface, two inferolateral surfaces, and base are well defined. Length measures 40 mm and breadth is 26 mm.
Group VI: 36–40 weeks
Bladder in this series assumed more adult form with further increased in size and wall thickness. Bladder of a 40-week-old fetus is pyramidal in shape with length of 55 mm, breadth of 32 mm, and weighs 6.25 gm. Interureteric distance measures 8 mm.
| Discussion|| |
Sulak et al. opined that during the fetal period, the urinary bladder was located above the transverse plane between the highest point of pubic symphysis and the sacral promontory in most of the cases (83%) and in the median sagittal plane in every case. It was determined that the angle of bladder did not change, and the mean value of the angle was 151° during the fetal period. Bladder was categorized into four different shapes (ellipsoid, round, cuboid, and triangular), and the most common shape found during the fetal period was cuboid. The vesical trigone was an isosceles triangle during the fetal period.
In the present study, urinary bladder was located above the transverse plane defined between the highest point of pubic symphysis and sacral promontory in almost all cases and was situated in the median sagittal plane in all the cases. In our study, three shapes of bladder were visible during the fetal period, i.e., round, ellipsoid, and pyramidal. Round and ellipsoid shape were visible during the earlier fetal period, and the bladder assumed more pyramidal shape during later fetal life [Figure 3].
|Figure 3: Anterior view of the urinary bladders at different weeks (numbers given in the figure indicate age in number of weeks)|
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According to Yu et al., the allantois appears on about day 16 as a tiny, finger-like outpouching from the caudal wall of the yolk sac. The bladder develops from the ventral portion of the expanded terminal part of the hindgut, the cloaca, which is contiguous with the allantois ventrally. The cranioventral end of the bladder opens into the allantois at the level of the umbilicus; thus, the bladder initially extends all the way to the umbilicus. By the 4th or 5th month of gestation, the bladder descends into the pelvis and its apical portion progressively narrows to a small, epithelialized fibromuscular strand, the urachus.
In the present study, urachus was visible from the earliest available fetus of 18-week-old. It has a board base toward the apex of the bladder and gradually tapers as it goes toward umbilicus.
Bruska and Woźniak stated that the interureteric distance at the level of the trigone of the urinary bladder was from 0.3 mm during 10th week to 1.2 mm at the end of the 12th week. There was no correlation with sex of fetuses.
In our present study, measurement of the interureteric distance was done at later weeks, it measures 4 mm at 21 weeks, 4.4 mm at 22 weeks, 5 mm by 25 weeks, 5.4 mm at 29 weeks, 5.6 mm at 33 weeks, 6 mm by 35 weeks of fetal age, and measures 8 mm by term. There was no correlation with sex of fetuses.
| Conclusion|| |
During fetal life, urinary bladder lies entirely in the abdomen proper close to the anterior abdominal wall. Urinary bladder assumed almost adult shape from 33-week-old onward with the presence of four surfaces, i.e., one superior, two inferolateral, and one posterior surface or base. In almost all the cases of the present study, urinary bladder was situated above the transverse plane between the highest point of pubic symphysis and sacral promontory, and in all the cases, it was situated in the median sagittal plane. During the fetal period, three shapes of bladder were visible, namely round, ellipsoid, and pyramidal shape of which round and ellipsoid shape were visible during the early fetal life while pyramidal shape was visible during the later fetal life. This knowledge of anatomy of fetal bladder might be useful while performing fetal surgery for bladder outlet obstruction like fetal vesicoamniotic shunting or in the placement of a vesicostomy.
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Conflicts of interest
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3]