The Colon

Question 1

What is the colon?

Answer 1

The colon (large intestine) is the distal part of the gastrointestinal tract, extending from the cecum to the anal canal

Question 2

Primary function of the colon

Answer 2

It receives digested food from the small intestine, from which it absorbs water and electrolytes to form faeces

Question 3

Parts of the colon

Answer 3

Ascending
Transverse
Descending
Sigmoid.

Question 4

Average length of the colon

Answer 4

150cm

Question 5

Ascending colon - Intra or retroperitoneal?

Answer 5

Retroperitoneal

Question 6

Direction of the ascending colon

Answer 6

Ascends superiorly from the cecum.

When it meets the right lobe of the liver, it turns 90 degrees to move horizontally.

This turn is known as the right colic flexure (or hepatic flexure), and marks the start of the transverse colon.

Question 7

Another name for right colic flexure

Answer 7

Hepatic flexure

Question 8

What is the hepatic flexure?

Answer 8

The point at which the ascending colon meets the right lobe of the liver. It marks the beginning of the transverse colon.

Question 9

Direction of the transverse colon

Answer 9

It extends from the right colic flexure to the spleen, where it turns another 90 degrees to point inferiorly at the left colic (splenic) flexure

Question 10

What is the Left colic flexure (or splenic flexure)?

Answer 10

It is the point at which the transverse colon meets the spleen and turns inferiorly at a 90 degrees angle to become the descending colon

Question 11

What attaches the transverse colon to the diaphragm?

Answer 11

The phrenicocolic ligament.

Question 12

What is the least fixed part of the colon? Why?

Answer 12

The transverse colon

Because it is variable in position, sometimes dipping to the pelvis in tall, thin people

Question 13

Transverse colon - Retro or intraperitoneal?

Answer 13

Intraperitoneal

Question 14

What encloses the transverse colon?

Answer 14

The transverse mesocolon

Question 15

Direction of the descending colon

Answer 15

After the left colic flexure, the colon moves inferiorly towards the pelvis -€“ and is called the descending colon.

Question 16

Descending colon - Retro or Intraperitoneal?

Answer 16

It is retroperitoneal in the majority of individuals

Question 17

Location of the descending colon

Answer 17

It is located anteriorly to the left kidney, passing over its lateral border.

Question 18

Length of the sigmoid colon

Answer 18

40cm

Question 19

Location of the sigmoid colon

Answer 19

It is located in the left lower quadrant of the abdomen, extending from the left iliac fossa to the level of the S3 vertebra.

Question 20

What attaches the sigmoid colon to the posterior pelvic wall?

Answer 20

A mesentery -€“ the sigmoid mesocolon

Question 21

Why is the sigmoid mesocolon long?

Answer 21

The long length of the mesentery permits this part of the colon to be particularly mobile.

Question 22

What are paracolic gutters?

Answer 22

The paracolic gutters are two spaces between the ascending/descending colon and the posterolateral abdominal wall.

Question 23

Why are paracolic gutters clinically relevant?

Answer 23

They allow material that has been released from inflamed or infected abdominal organs to accumulate elsewhere in the abdomen.

Question 24

Anatomical features of the colon

Answer 24

Omental appendices
Teniae coli
Haustra
Larger diameter

Question 25

Omental appendices

Answer 25

Attached to the surface of the large intestine, they are small pouches of peritoneum, filled with fat.

Question 26

Teniae coli

Answer 26

Three strips of muscle running longitudinally along the surface of the large bowel They are called the mesocolic, free and omental coli.

Question 27

Haustra

Answer 27

The teniae coli contract to shorten the wall of the bowel, producing sacculations known as haustra.

Question 28

Where do the features of the colon cease?

Answer 28

They cease at the rectosigmoid junction, where the smooth muscle of the teniae coli broaden to form a complete layer within the rectum.

Question 29

What are the midgut derived structures of the colon?

Answer 29

Ascending colon and proximal 2/3 of the transverse colon

Question 30

What are the hindgut derived structures of the colon?

Answer 30

Distal 1/3 of the transverse colon, descending colon and sigmoid colon

Question 31

Arterial supply - Ascending Colon

Answer 31

Two branches of the superior mesenteric artery; the ileocolic and right colic arteries.

Question 32

Arterial supply - Transverse Colon

Answer 32

Branches of the superior mesenteric artery and inferior mesenteric artery - Right, middle and left colic arteries

Question 33

Arterial supply - Descending Colon

Answer 33

Single branch of the inferior mesenteric artery; the left colic artery

Question 34

Arterial supply - Sigmoid Colon

Answer 34

Sigmoid arteries (branches of the inferior mesenteric artery).

Question 35

Innervation of midgut structures

Answer 35

Superior mesenteric plexus

Question 36

Innervation of hindgut structures

Answer 36

inferior mesenteric plexus

Question 37

Rectosigmoid junction

Answer 37

The point after the sigmoid colon where taenia spread out and unite to form longitudinal muscle layer

Question 38

Epiploic appendages

Answer 38

Deposits of fatty adipose tissue along haustra

Question 39

Difference between left and right colic flexures

Answer 39

Left is more mobile, more acute, higher