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8

NCCN Guidelines for Patients

®

:

Rectal Cancer, Version 1.2017

You’ve learned that you have rectal

cancer. It’s common to feel shocked and

confused. Part 1 reviews some basics that

may help you learn about rectal cancer.

The rectum

Before learning about rectal cancer, it is helpful to

know about the rectum. The rectum is part of the

digestive system. This system breaks down food for

the body to use.

Digestive tract

After being swallowed, food moves through four

organs known as the digestive tract.

See Figure 1

.

First, food passes through the esophagus and into

the stomach.

In the stomach, food is turned into a liquid. From

the stomach, food enters the small intestine. In the

small intestine, food is broken down into very small

parts. This allows nutrients to be absorbed into the

bloodstream.

From the small intestine, food moves into the large

intestine. The large intestine changes unused food

from a liquid into a solid by absorbing water. This

solid, unused food is called feces or stool. The large

intestine also expels stool from the body through the

anus.

The rectum is part of the large intestine. It holds stool

until the stool is expelled from the body. The rectum

also triggers nerves that make you feel the urge to

have a bowel movement.

The rectum is almost 5 inches long. It is in the back

of your pelvis in front of your spine. It often contains

three folds that are shaped like a half moon.

See

Figure 2

.

Rectal wall

Layers of tissue make up the rectal wall. The inner

layer that has contact with stool is called the mucosa.

The mucosa consists of three sublayers. They are

the epithelium, lamina propria, and muscularis

mucosae.

The epithelium makes mucus to help move stool

along. The lamina propria is a thin layer of support

(connective) tissue. The muscularis mucosae is a

thin strip of muscle.

The second layer of the rectal wall is called the

submucosa. It consists of connective tissue, blood

and lymph vessels, and nerve cells. Lymph is a clear

fluid that gives cells water and nutrients. It also has

white blood cells that fight germs. Blood and lymph

drain from rectal tissue into vessels that are in the

submucosa and then travel to other sites.

The third layer of the rectal wall is called the

muscularis propria. It is mostly made of muscle

fibers. These muscles help move stool through the

rectum.

The last layer is a thin layer of connective tissue. It

has a single row of cells that make fluid. This fluid

allows the rectum to move smoothly against other

organs. This layer is called either subserosa or

adventia.

The upper part and front of the mid rectal wall is

covered in serosa. The serosa, also called the

visceral peritoneum, is a membrane. It also covers

the front part of 1) the left and right sides of the colon

and 2) the kidneys.

Most of the rectum that isn’t covered in serosa is

covered in fat. The fat is thick in the middle of the

rectum. It thins out the closer it gets to the anus. This

fat is covered by connective tissue called the fascia

propria.

1

Rectal cancer basics

The rectum