Large intestine - Rectum - ontogenesis (including the embryogenesis) Flashcards
(15 cards)
From which embryonic part does the rectum develop?
The rectum develops from the hindgut, the last portion of the primitive gut tube.
What is the cloaca during embryonic development?
The cloaca is a common cavity for digestive, urinary, and reproductive tracts in the early embryo, where waste from both intestines and kidneys initially empties.
What structure separates the digestive and urinary tracts during development?
The urorectal septum, a wedge of mesoderm that grows downward to divide the cloaca into two parts.
What are the two parts formed by the urorectal septum?
Anorectal canal → becomes the rectum and upper anal canal
Urogenital sinus → becomes the bladder and urethra
At which week does the urorectal septum completely divide the cloaca?
By about week 7 of development, the urorectal septum reaches the cloacal membrane and completes the division.
From which germ layer does the rectum and upper anal canal develop?
From the endoderm, the innermost embryonic germ layer.
From which germ layer does the lower anal canal (below the pectinate line) develop?
From the ectoderm, the outer embryonic germ layer, forming from the proctodeum (anal pit).
What is the proctodeum?
An invagination of ectodermal tissue around the anal area that forms the lower anal canal.
What is the pectinate line?
The pectinate line marks the junction between the endodermal (upper) and ectodermal (lower) parts of the anal canal.
What is the clinical importance of the pectinate line?
It represents a transition zone with differences in epithelium, nerve supply, blood supply, and lymph drainage above and below the line.
By the end of embryogenesis, what major developmental event is completed for the rectum?
The rectum is fully separated from the urinary tract and connected to the anal canal.
What tissue layer forms the urorectal septum?
The urorectal septum forms from mesoderm, the middle germ layer of the embryo.
When does the cloacal membrane break down to form openings?
Around week 8, the cloacal membrane breaks down, creating the openings of the anus and urogenital tract.
What happens if the urorectal septum fails to develop properly?
Failure leads to fistulas (abnormal connections) between the rectum and urinary or reproductive tracts (e.g., rectovaginal or rectourethral fistulas).
What is the relationship between the rectum and peritoneum at birth?
The upper rectum is partially covered by peritoneum (anterior and lateral sides), while the lower rectum is below the peritoneal reflection (extraperitoneal).
