Rectum

Schematic structure of the rectum (view from anterior )

The rectum , in northern German also cinders , ( Latin [intestinum] rectum , "the straight intestine", Germanized rectum , adjective rectal ) is a part of the rectum and thus the large intestine and is used to store the feces temporarily . H. the indigestible and intolerable food residues. Due to the defecation reflex , it is emptied via the anus (in Latin: the anus ). The rectum itself has no pain receptors , but its sphincter muscles do .

Word origin

The old and Middle High German word arsdarm ("arsehole") was later replaced by the concealing expression masdarm and became New High German for rectum .

Anatomy and physiology

The human large intestine:
1. Ascending colon ( ascending colon )
2. Transverse colon ( transverse colon )
3. Descending colon ( descending colon )
4. Sigma ( sigmoid colon )
5. End or rectum ( rectum ), no part of the colon

Scheme of the human digestive tract

The rectum in humans is about 15-18 cm long. The length varies from person to person and also depending on the measurement method. The bottom 4 cm are, however, assigned to the anus . The distinction is made here on the basis of piercing the pelvic floor . In addition, the end of the anal canal is already lined with a multilayered squamous epithelium and no longer with an intestinal mucosa . Together with the anus, the rectum forms the anorectum .

Its position in the body is in the so-called small pelvis between the urinary bladder (in men also the prostate , in women the uterus and vagina ) and the sacrum .

Characteristically, at the transition from the sigmoid to the rectum, the typical features of the colon, namely the appendices epiploicae , Haustren , taenien and the plicae semilunares are lost . Instead of the semilunar plicae, there are three folds in the rectum, of which the middle one is also known as the Kohlrausch fold and is just palpable anally. By definition, it is also the beginning of the ampulla recti, which continues aborally to the transition ( junction anorectalis ) into the anal canal ( canalis rectalis ).

Histologically, the rectum shows the typical structure of a membranous, muscular tube. The intestinal mucous membrane is followed by a muscle layer ( tunica muscularis ) made of smooth muscles , which consists of an inner ring ( stratum circulare ) and an outer longitudinal muscle layer ( stratum longitudinal ). A tunica serosa forms the outer end of the rectal wall . Fibers radiate from the longitudinal muscle layer of the rectum to the coccyx vertebrae ( musculus rectococcygeus ) and the urinary bladder ( musculus rectovesicalis ).

sphincter

The lower limit of the rectum is formed by an inner and an outer sphincter muscle ( muscles sphincteres ani internus et externus ). The internal sphincter consists of smooth muscles and cannot be influenced arbitrarily. The external sphincter consists of striated muscles that can be tensed or relaxed at will. Both sphincters work together via the defecation reflex and thus regulate bowel movements . Another important sphincter muscle is the puborectalis muscle , which forms a loop around the rectum and pulls it anteriorly.

Blood vessel supply

The arterial supply of the rectum is provided by the superior rectalis artery , the middle rectalis artery and the inferior rectalis artery . The superior rectal artery , a branch of the inferior mesenteric artery , divides at the level of the second sacral vertebra into two descending branches on each side of the rectum. The right branch divides again so that three branches take over the supply of the upper rectum. These branches anastomose with those of the arteria rectalis media (from the arteria iliaca interna ) and the arteria rectalis inferior (from the arteria pudenda interna ). The arteria rectalis media supplies the middle section of the rectum and the arteria rectalis inferior the lower section of the rectum.

The corresponding veins have a different drainage. While the superior rectal vein flows into the portal vein , the blood from the median rectales vein and the inferior rectalis vein flows into the inferior vena cava via the iliac vein . This is of importance in the hematogenous spread of metastases from rectal tumors. Since the lower levels do not drain through the portal vein, drugs introduced into the rectum (often in the form of suppositories ) go directly into the blood , bypassing the liver .

function

The basic task of the rectum, like all parts of the large intestine, is to remove fluid from the chyme. It is important for the ability to hold feces (continence, stool continence).

literature

Alexander Neiger (Ed.): Diseases of the anus and the rectum. Basel 1973 (= gastroenterological advanced training courses for practice. Volume 3).

Web links

Rectum images in the endoscopy atlas

swell

↑ Duden dictionary of origin 1963
↑ G. Salerno et al .: Defining the rectum: surgically, radiologically and anatomically . In: Colorectal Disease 8 Suppl 3, 2006, pp. 5-9.
↑ L. Richard Drake et al .: Gray's Anatomy for Students with Studentconsult Access . Elsevier, Urban & Fischer Verlag 2007, ISBN 978-3-437-41231-8 , p. 308.
↑ Ernst Stein: Proctology: Textbook and Atlas . 4th edition, Springer, 2002, ISBN 9783540430339 , p. 3.

[1] Duden dictionary of origin 1963

[2] G. Salerno et al .: Defining the rectum: surgically, radiologically and anatomically . In: Colorectal Disease 8 Suppl 3, 2006, pp. 5-9.

[3] L. Richard Drake et al .: Gray's Anatomy for Students with Studentconsult Access . Elsevier, Urban & Fischer Verlag 2007, ISBN 978-3-437-41231-8 , p. 308.

[4] Ernst Stein: Proctology: Textbook and Atlas . 4th edition, Springer, 2002, ISBN 9783540430339 , p. 3.