The urachus forms from the distal end of the allantois in the

embryo An embryo ( ) is the initial stage of development for a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sp ...

, and develops into a closed cord between the base of the

bladder The bladder () is a hollow organ in humans and other vertebrates that stores urine from the kidneys. In placental mammals, urine enters the bladder via the ureters and exits via the urethra during urination. In humans, the bladder is a distens ...

, and the

navel The navel (clinically known as the umbilicus; : umbilici or umbilicuses; also known as the belly button or tummy button) is a protruding, flat, or hollowed area on the abdomen at the attachment site of the umbilical cord. Structure The u ...

. It drains the bladder of the

fetus A fetus or foetus (; : fetuses, foetuses, rarely feti or foeti) is the unborn offspring of a viviparous animal that develops from an embryo. Following the embryonic development, embryonic stage, the fetal stage of development takes place. Pren ...

that joins and runs within the

umbilical cord In Placentalia, placental mammals, the umbilical cord (also called the navel string, birth cord or ''funiculus umbilicalis'') is a conduit between the developing embryo or fetus and the placenta. During prenatal development, the umbilical cord i ...

. The fibrous remnant lies in the

space of Retzius Retropubic space is a potential avascular space located between the pubic symphysis and the urinary bladder. The retropubic space is a preperitoneal space, located behind the transversalis fascia and in front of peritoneum. Other names for the r ...

, between the

transverse fascia The transversalis fascia (or transverse fascia) is the fascial lining of the anterolateral abdominal wall situated between the inner surface of the transverse abdominal muscle, and the preperitoneal fascia. It is directly continuous with the ilia ...

anteriorly and the

peritoneum The peritoneum is the serous membrane forming the lining of the abdominal cavity or coelom in amniotes and some invertebrates, such as annelids. It covers most of the intra-abdominal (or coelomic) organs, and is composed of a layer of mesotheli ...

posteriorly. At birth, the urachus develops into the

median umbilical ligament In human anatomy, the median umbilical ligament is an unpaired midline ligamentous structure upon the lower inner surface of the anterior abdominal wall. It is covered by the median umbilical fold. The median umbilical ligament represents the re ...

Development

The part of the

urogenital sinus The urogenital sinus is a body part of a human or other Placentalia, placental only present in the development of the urinary system, development of the urinary and development of the reproductive organs, reproductive organs. It is the ventral p ...

related to the bladder and urethra absorbs the ends of the Wolffian ducts and the associated ends of the

renal diverticula The renal Calyx (anatomy), calyces ( calyx) are conduits in the kidney through which urine passes. The minor calyces form a cup-shaped drain around the apex of the renal pyramids. Urine formed in the kidney passes through a renal papilla at the ...

. This gives rise to the trigone of the bladder and part of the prostatic urethra. The remainder of this part of the urogenital sinus forms the body of the bladder and part of the prostatic urethra. The apex of the bladder stretches and is connected to the umbilicus as a narrow canal. This canal is initially open, but later closes as the urachus goes on to definitively form the

Clinical significance

Failure of the inside of the urachus to be filled in leaves the urachus open. The telltale sign is leakage of urine through the umbilicus. This is often managed surgically. There are four anatomical causes: * Urachal cyst: there is no longer a connection between the bladder and the umbilicus, however a fluid filled cavity with uroepithelium lining persists between these two structures. * Urachal fistula: there is free communication between the bladder and umbilicus * Urachal diverticulum (vesicourachal diverticulum): the bladder exhibits outpouching * Urachal sinus: the pouch opens toward the umbilicus The urachus is also subject to neoplasia. Urachal adenocarcinoma is histologically similar to adenocarcinoma of the bowel. Rarely, urachus carcinomas can metastasise to other regions of the body, including pelvic bones and the lung. One urachal mass has been reported that was found to be a manifestation of IgG4-related disease.

Additional images

File:Inguinal fossae.PNG, Inguinal fossae File:Urachusrest im CT sagittal - 44Jahre - Zufallsbefund.jpg, Midsagittal CT scan of a man's abdomen showing the urachus File:Normal fully developed bladder with urachus and four of the most common urachal anomaly subtypes including patent urachus, vesicourachal diverticulum, urachal cyst, and umbilical-urachal.png, The normal urachus and its anomalous variants File:Urachal carcinoma - high mag.jpg, High magnification micrograph of a urachal carcinoma.

H&E stain Hematoxylin and eosin stain ( or haematoxylin and eosin stain or hematoxylin–eosin stain; often abbreviated as H&E stain or HE stain) is one of the principal tissue stains used in histology. It is the most widely used stain in medical diag ...

References

External links

*
"Persistent urachus" at Moorabbin Veterinary Hospital

{{Portal bar, Anatomy Embryology of urogenital system