The transverse folds of rectum (or Houston's valves or the valves of Houston) are semi-lunar transverse folds of the
rectal
The rectum is the final straight portion of the large intestine in humans and some other mammals, and the gut in others. The adult human rectum is about long, and begins at the rectosigmoid junction (the end of the sigmoid colon) at the le ...
wall that protrude into the rectum, not the
anal canal
The anal canal is the part that connects the rectum to the anus, located below the level of the pelvic diaphragm. It is located within the anal triangle of the perineum, between the right and left ischioanal fossa. As the final functional seg ...
as that lies below the rectum. Their use seems to be to support the weight of
fecal matter
Feces ( or faeces), known colloquially and in slang as poo and poop, are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the large intestine. Feces contain a relati ...
, and prevent its urging toward the
anus, which would produce a strong urge to
defecate
Defecation (or defaecation) follows digestion, and is a necessary process by which organisms eliminate a solid, semisolid, or liquid waste material known as feces from the digestive tract via the anus. The act has a variety of names ranging fro ...
. Although the term rectum means straight, these transverse folds overlap each other during the empty state of the intestine to such an extent that, as Houston remarked, they require considerable maneuvering to conduct an instrument along the canal, as often occurs in
sigmoidoscopy
Sigmoidoscopy (from the Greek term for letter " s/ς" + "eidos" + "scopy": namely, to look inside an "s"/"ς"-like object) is the minimally invasive medical examination of the large intestine from the rectum through to the nearest part of the co ...
and
colonoscopy.
These folds are about 12 mm. in width and are composed of the circular muscle coat of the rectum. They are usually three in number; sometimes a fourth is found, and occasionally only two are present.
* One is situated near the commencement of the rectum, on the right side.
* A second extends inward from the left side of the tube, opposite the middle of the
sacrum.
* A third, the largest and most constant, projects backward from the forepart of the rectum, opposite the fundus of the
urinary bladder
The urinary bladder, or simply bladder, is a hollow organ in humans and other vertebrates that stores urine from the kidneys before disposal by urination. In humans the bladder is a distensible organ that sits on the pelvic floor. Urine ente ...
.
* When a fourth is present, it is situated nearly 2.5 cm above the anus on the left and posterior wall of the tube.
Transverse folds were first described by Irish–British anatomist
John Houston, curator of the
Royal College of Surgeons in Ireland Museum, in 1830. They appear to be peculiar to human physiology: Baur (1863) looked for Houston's valves in a number of mammals, including wolf, bear, rhinoceros, and several Old World primates, but found no evidence. They are formed very early during human development, and may be visible in embryos of as little as 55 mm in length (10 weeks of gestational age.)
External links
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References
{{Authority control
Digestive system
Rectum