Which embryologic structure primarily forms the urinary bladder during development?
Solution
Correct Answer: Option A
- The urinary bladder develops primarily from the upper part of the embryologic urogenital sinus, which is itself derived from the allantois.
- The allantois is an extension of the embryonic hindgut that extends into the umbilical cord. During development, the allantois forms a canal called the urogenital sinus, and the upper portion of this structure expands to become the urinary bladder.
To clarify the other options:
- The mesonephric duct (Wolffian duct) primarily contributes to the formation of the male reproductive tract and plays a role in connecting the kidneys to the bladder via the ureters but does not form the bladder itself.
- The ureteric bud arises from the mesonephric duct and induces the formation of the metanephric blastema to develop the definitive kidney; it forms the ureters, renal pelvis, calyces, and collecting ducts, but not the bladder.
- The metanephric blastema is the embryonic tissue that differentiates into the nephrons of the definitive kidney and has no direct role in bladder formation.
In summary, the allantois forms the urogenital sinus, from which the urinary bladder arises, making it the primary embryologic structure responsible for bladder development.
Reference: Larsen’s Human Embryology, 5th Edition, Chapter 9: The Urogenital System / Page 212
- The allantois is an extension of the embryonic hindgut that extends into the umbilical cord. During development, the allantois forms a canal called the urogenital sinus, and the upper portion of this structure expands to become the urinary bladder.
To clarify the other options:
- The mesonephric duct (Wolffian duct) primarily contributes to the formation of the male reproductive tract and plays a role in connecting the kidneys to the bladder via the ureters but does not form the bladder itself.
- The ureteric bud arises from the mesonephric duct and induces the formation of the metanephric blastema to develop the definitive kidney; it forms the ureters, renal pelvis, calyces, and collecting ducts, but not the bladder.
- The metanephric blastema is the embryonic tissue that differentiates into the nephrons of the definitive kidney and has no direct role in bladder formation.
In summary, the allantois forms the urogenital sinus, from which the urinary bladder arises, making it the primary embryologic structure responsible for bladder development.
Reference: Larsen’s Human Embryology, 5th Edition, Chapter 9: The Urogenital System / Page 212
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