Colon

Question 1

What is the length of the colon and in which sex is it longer?

Answer 1

100-180cm

Females

Question 2

What muscular arrangement distinguishes the colon?

Answer 2

3 longitudinal bands of muscle
Form taenia coli
Converge at the base of the appendix

Question 3

What is the appearance of the colon lumen and what structures cause this appearance?
Where is this most apparent?

Answer 3

Triangular
Taenia coli
Transverse colon

Question 4

What causes haustrations/sacculations?

Answer 4

Taenia coli are shorter than the colon

Causes a segmental appearance where the colon bulges (haustrations/sacculations)

Question 5

What part of the GI tract does the appendix project from?

Answer 5

Caecum

Question 6

What name is given to the start of the large intestine? What landmark denotes the start of the large intestine?

Answer 6

Ileocaecal junction

Ileocaecal valve

Question 7

What forms the ileocaecal valve?

Answer 7

Oblique entrance and partial invagination of the ileum into the caecum

Question 8

What complications can arise in the caecum during late bowel obstruction?

Answer 8

The caecum may dilate to the point of necrosis or perforation
Ileocaecal valve prevents back flow of excess air and colonic contents (no transit past the blockage distally or back proximal my through the valve

Question 9

Where is the caecum located?

Answer 9

Right iliac fossa

Question 10

What percentage of colonic rumours occur in the caecum and right side of the colon?
What presentations arise with a colonic tumour?

Answer 10

20%

Mass, change in bowel habits, iron deficiency anaemia, pain

Question 11

Where does the appendix project from?

Answer 11

Postero-medial aspect of the caecum

~3cm below the ileocaecal valve

Question 12

Describe the embryonic origin of the appendix and it’s movement during development.

Answer 12

Projection from the lateral side of caecum

Caecal wall overgrowth displaces the appendix medically and inferiorly

Question 13

How commonly does appendicitis occur?

Answer 13

40,000 cases per year

Question 14

Where does the ascending colon begin and end?

Answer 14

Begin - caecum

End - hepatic flexure

Question 15

Where does the transverse colon begin and end?

Answer 15

Begin - hepatic flexure

End - splenic fixture

Question 16

Why is the transverse colon difficult to navigate endoscopically?
In which sex do difficulties more commonly occur?

Answer 16

It is highly mobile

More common in females (70%)

Question 17

At what level does the transverse colon lie at most commonly?

Answer 17

Umbilicus (L3-L4)

Question 18

How long is the descending colon?

Answer 18

22-30cm

Question 19

The sigmoid colon is very variable in length, what’s the average length and the upper limit?

Answer 19

37cm - 70cm

Question 20

What are the appendices epiploicae (epiploic appendices) and what section of the large colon has the most of these?

Answer 20

Fat-filled pouches of peritoneum

Sigmoid colon

Question 21

What is sigmoid volvulous and why is the sigmoid colon prone to it?

Answer 21

Closed loop obstruction of sigmoid colon due to twisting
Large length
Loose mesenteric attachment

Question 22

What percentage of colon cancers occur in the sigmoid colon?

Answer 22

25%

Question 23

What are colonic diverticulum? And in what section of the colon are they most common in Western society?

Answer 23

Out pouchings of bowel wall

Sigmoid colon

Question 24

What makes a bowel wall susceptible to colonic diverticulums?

Answer 24

Where the artery pierces the muscular wall causing weakness

Question 25

Where does the rectum begin and end?

Answer 25

Begin - anterior to S3 | End - anal canal

Question 26

What differs between the human rectum and other mammalian rectums?

Answer 26

Human rectums are not straight

Question 27

Describe the shape of the human rectum

Answer 27

Curves anteriorly following the sacrum | Turns ~90 degrees through the pelvic diaphragm

Question 28

What are the valves of Houston?

Answer 28

3 transverse folds in the rectum which correspond with mucosal folds

Question 29

Why does the rectal lumen appear circular not triangular?

Answer 29

The thick circular muscle layer is stronger than the taeniae coli

Question 30

What percentage of colon cancers are found in the rectum?

Answer 30

50%

Question 31

How long is the anal canal?

Answer 31

~4cm

Question 32

What epithelium is found at the upper anal canal? | What is its embryonic origin?

Answer 32

Simple columnar epithelium | Hindgut

Question 33

The mid anal canal is the transition between what two embryonically derived tissues?

Answer 33

Endoderm of the hindgut (upper) | Ectoderm of proctodaeum invagination from skin

Question 34

What landmarks denote the mid anal canal? From where do they arise? What is the name of the line formed by the landmarks?

Answer 34

Valves of Ball Arise from vertical columns of Morgagni Dentate/pectineal line

Question 35

Below which landmark does the anal canal become stratified squamous epithelium?

Answer 35

Dentate/pectineal line

Question 36

What are the arterial supplies to the upper and lower rectum?

Answer 36

Upper rectum - superior rectal branch from inferior mesenteric artery Lower rectum - inferior rectal branch from internal iliac artery

Question 37

What are the differences in pain perceived in the areas of rectum and why?

Answer 37

Upper rectum - dull pain and poorly located Visceral Pelvic Splanchnic nerves Lower rectum - sharp pain and well defined Pudendal nerve

Question 38

What are the venous drains of the rectum and what do we therefore call the recall venous drainage?

Answer 38

Upper rectum - portal system via the inferior mesenteric vein Lower rectum - systemic circulation via the internal iliac vein A Porto-systemic anastomosis

Question 39

To which lymph nodes is lymph drained to from rectum?

Answer 39

Upper rectum - mesenteric nodes | Lower rectum - inguinal and iliac nodes

Question 40

What are haemorrhoids? | What determines whether they are painful or not?

Answer 40

Dilatations of the superior rectal veins | Whether they are above (painless) or below (painful) the dentate/pectineal line

Question 41

What kind of tumour will form in the rectum above the dentate line and what kind will form below the dentate line?

Answer 41

Above - adenocarcinoma | Below - squamous cell carcinoma