| Urachus | |
|---|---|
 Vertical section of bladder, penis, and urethra. Urachus is seen at top | |
 Urachus is #1 | |
| Identifiers | |
| MeSH | D014497 |
| Anatomical terminology | |
The urachus is a fibrous remnant of the allantois, a canal that drains the urinary bladder of the fetus that joins and runs within the umbilical cord. [1] The fibrous remnant lies in the space of Retzius, between the transverse fascia anteriorly and the peritoneum posteriorly.
The part of the urogenital sinus related to the bladder and urethra absorbs the ends of the Wolffian ducts and the associated ends of the renal diverticula. 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 median umbilical ligament.
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:
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. [4]
One urachal mass has been reported that was found to be a manifestation of IgG4-related disease. [5]
The urethra is the tube that connects the urinary bladder to the urinary meatus, through which placental mammals urinate and ejaculate. In non-mammalian vertebrates, the urethra also transports semen but is separate from the urinary tract.
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 distensible organ that sits on the pelvic floor. The typical adult human bladder will hold between 300 and 500 ml before the urge to empty occurs, but can hold considerably more.
The prostate is an accessory gland of the male reproductive system and a muscle-driven mechanical switch between urination and ejaculation. It is found in all male mammals. It differs between species anatomically, chemically, and physiologically. Anatomically, the prostate is found below the bladder, with the urethra passing through it. It is described in gross anatomy as consisting of lobes and in microanatomy by zone. It is surrounded by an elastic, fibromuscular capsule and contains glandular tissue, as well as connective tissue.
The navel is a protruding, flat, or hollowed area on the abdomen at the attachment site of the umbilical cord. All placental mammals have a navel, although it is generally more conspicuous in humans.
The seminal vesicles are a pair of convoluted tubular accessory glands that lie behind the urinary bladder of male mammals. They secrete fluid that largely composes the semen.
The urogenital sinus is a body part of a human or other placental only present in the development of the urinary and reproductive organs. It is the ventral part of the cloaca, formed after the cloaca separates from the anal canal during the fourth to seventh weeks of development.
A Meckel's diverticulum, a true congenital diverticulum, is a slight bulge in the small intestine present at birth and a vestigial remnant of the vitelline duct. It is the most common malformation of the gastrointestinal tract and is present in approximately 2% of the population, with males more frequently experiencing symptoms.
The allantois is a hollow sac-like structure filled with clear fluid that forms part of a developing amniote's conceptus. It helps the embryo exchange gases and handle liquid waste.
The development of the urinary system begins during prenatal development, and relates to the development of the urogenital system – both the organs of the urinary system and the sex organs of the reproductive system. The development continues as a part of sexual differentiation.
The male reproductive system consists of a number of sex organs that play a role in the process of human reproduction. These organs are located on the outside of the body, and within the pelvis.
The external sphincter muscle of the male urethra, also sphincter urethrae membranaceae, sphincter urethrae externus, surrounds the whole length of the membranous urethra, and is enclosed in the fascia of the urogenital diaphragm.
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.
A urachal cyst is a sinus remaining from the allantois during embryogenesis. It is a cyst which occurs in the remnants between the umbilicus and bladder. This is a type of cyst occurring in a persistent portion of the urachus, presenting as an extraperitoneal mass in the umbilical region. It is characterized by abdominal pain, and fever if infected. It may rupture, leading to peritonitis, or it may drain through the umbilicus. Urachal cysts are usually silent clinically until infection, calculi or adenocarcinoma develop.
The seminal colliculus, or verumontanum, of the prostatic urethra is a landmark distal to the entrance of the ejaculatory ducts. Verumontanum is translated from Latin to mean 'mountain ridge', a reference to the distinctive median elevation of urothelium that characterizes the landmark on magnified views.
The development of the reproductive system is the part of embryonic growth that results in the sex organs and contributes to sexual differentiation. Due to its large overlap with development of the urinary system, the two systems are typically described together as the genitourinary system.
Urachal cancer is a very rare type of cancer arising from the urachus or its remnants. The disease might arise from metaplastic glandular epithelium or embryonic epithelial remnants originating from the cloaca region.
Diphallia, penile duplication (PD), diphallic terata, or diphallasparatus is an extremely rare developmental abnormality in which a male is born with two penises. The first reported case was by Johannes Jacob Wecker in 1609. Its occurrence is 1 in 5.5 million boys in the United States.
A urethral diverticulum is a condition where the urethra or the periurethral glands push into the connective tissue layers (fascia) that surround it.
A urachal fistula is a congenital disorder caused by the persistence of the allantois, the structure that connects an embryo's bladder to the yolk sac. Normally, the urachus closes off to become the median umbilical ligament; however, if it remains open, urine can drain from the bladder to an opening by the umbilicus.
Umbilical-urachal sinus is a congenital disorder of the urinary bladder caused by failure of obliteration of proximal or distal part of the allantois, and the presentation of this anomaly is more common in children and rarer in adults.
This article incorporates text in the public domain from page 1213 of the 20th edition of Gray's Anatomy (1918)
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