Anatomy

The colon and rectum together measure between 125 and 140 cm in the adult. The colon is divided into the caecum (10 cm), ascending (15 cm), transverse (40 cm), descending (25 cm) and sigmoid (25-40 cm) colons. The rectum measures approximately 13-15cm (Figure 5.1). The main function of the colon is absorption of water and electrolytes and the storage of faecal material until it can be excreted. The caecum is that part that lies below the ileocaecal valve and receives the opening of the appendix. It is completely surrounded by peritoneum allowing it to be mobile in the right iliac fossa. The base of the appendix is attached to the posteromedial surface of the caecum. The ascending colon extends upwards from the caecum to the inferior surface of the right lobe of liver. Here it becomes continuous with the transverse colon by turning sharply

Figure 5.1. Colorectum. Reproduced with permission from Hermanek P, Hutter RVP, Sobin, LH, Wagner, G, Wittekind, Ch. (Eds). TNM Atlas: Illustrated guide to the TNM/pTNM classification of malignant tumours, 4th edition. Springer-Verlag: Berlin and Heidelberg, 1997.

to the left, forming the right colic or hepatic flexure. The ascending colon is bound to the posterior abdominal wall by peritoneum covering its front and sides. The transverse colon extends from the hepatic flexure to the left, hanging downwards and then ascending to the inferior surface of the spleen where it turns sharply downwards to form the left colic or splenic flexure. The transverse colon is completely surrounded by peritoneum with the transverse mesocolon being attached to its superior border (the length of the transverse mesocolon accounts for the variability in the position of the transverse colon) and the greater omentum to its lower border. The descending colon extends downwards from the splenic flexure to the left side of the pelvic brim. It is bound to the posterior abdominal wall by peritoneum covering its sides and front. The sigmoid colon is continuous with the descending colon and hangs as a loop into the pelvic cavity. It is completely surrounded by peritoneum and a fan-shaped piece of mesentery attaches it to the posterior abdominal wall, thus allowing mobility. The rectum begins as a continuation of the sigmoid colon in front of the third sacral vertebra and follows the curvature of the sacrum and coccyx to where it pierces the pelvic floor to become continuous with the anal canal. Peritoneum covers the anterior and lateral surfaces of the upper third and the anterior surface of the middle third, the lower third being devoid of a peritoneal covering. At the junction of the middle and lower third the peritoneum is reflected onto the posterior surface of the upper vagina in the female to form the rectovaginal pouch (pouch of Douglas) (Figure 5.2) and onto the upper part of the posterior bladder in the male forming the rectovesical pouch. The extent of serosal covering in the colorectum in illustrated in Figure 5.3. The rectum is surrounded by a bi-lobed encapsulated fatty structure which is bulkier posterolaterally than anteriorly - the mesorectum. The small and large intestines differ in their appearance in a number of ways:

• The longitudinal muscle in the small intestine forms a continuous layer whereas in the colon it comprises three bands called taeniae coli. However, in the rectum the taeniae coli come together to form a broad band on the anterior and posterior surfaces.

• The wall of the colon is sacculated whereas the small intestine is smooth.

• The colon has "fatty tags" called appendices epiploicae.

• The permanent mucous membrane folds (plicae circulares) in the small intestine are not present in the colon.

Bladder

Bladder

Rectum

Vagina

Figure 5.2. Rectosigmoid and peritoneal reflection (lateral view). Reproduced with permission from Hermanek P, Hutter RVP, Sobin, LH, Wagner, G, Wittekind, Ch. (Eds). TNM Atlas: Illustrated guide to the TNM/pTNM classification of malignant tumours, 4th edition. Springer-Verlag: Berlin and Heidelberg, 1997.

Vagina

Rectum

Rectosigmoid junction

Figure 5.2. Rectosigmoid and peritoneal reflection (lateral view). Reproduced with permission from Hermanek P, Hutter RVP, Sobin, LH, Wagner, G, Wittekind, Ch. (Eds). TNM Atlas: Illustrated guide to the TNM/pTNM classification of malignant tumours, 4th edition. Springer-Verlag: Berlin and Heidelberg, 1997.

A Retroperitoneal (posterior) surface

A

A Retroperitoneal (posterior) surface

>> Peritoneal reflection

Serosal surface

>> Peritoneal reflection

Serosal surface

'Bare"area

Sigmo mesen

'Bare"area

Sigmo mesen

Figure 5.3. Extent of serosal covering of the large intestine. Arrows indicate the "bare" non-peritonealised areas of different levels. A. The ascending and descending colon are devoid of peritoneum on their posterior surface. B. The sigmoid colon is completely covered with peritoneum, which extends over the mesentery. C. The lower rectum lies beneath the pelvic peritoneal reflection. The asterisks in A indicate the sites where serosal involvement by tumour is likely to occur. Reproduced with permission from Burroughs SH, Williams GT.ACP best practice no. 159. Examination of large-intestine resection specimens. J Clin Pathol 2000;53:344-349.

Figure 5.3. Extent of serosal covering of the large intestine. Arrows indicate the "bare" non-peritonealised areas of different levels. A. The ascending and descending colon are devoid of peritoneum on their posterior surface. B. The sigmoid colon is completely covered with peritoneum, which extends over the mesentery. C. The lower rectum lies beneath the pelvic peritoneal reflection. The asterisks in A indicate the sites where serosal involvement by tumour is likely to occur. Reproduced with permission from Burroughs SH, Williams GT.ACP best practice no. 159. Examination of large-intestine resection specimens. J Clin Pathol 2000;53:344-349.

Microscopically, the colonic mucosa is made up of tubular crypts lined by columnar epithelium with mucin-secreting goblet cells and endocrine cells also being present.

Baby Sleeping

Baby Sleeping

Everything You Need To Know About Baby Sleeping. Your baby is going to be sleeping a lot. During the first few months, your baby will sleep for most of theday. You may not get any real interaction, or reactions other than sleep and crying.

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