Large intestine

Question 1

What are the 3 parts of the large intestine?

Answer 1

1. Caecum (to which the appendix is attached)
2. Colon (ascending, transverse, descending, sigmoid)
3. Rectum

Question 2

Which feature prevents the reflux of chyme from the large intestine into the small intestine during peristalsis?

Answer 2

ileocecal valve

Question 3

Where is the ileocecal valve located?

Answer 3

In the ileocecal junction in the right iliac fossa. Located at the junction between the caecum and ascending colon.

Question 4

Where is the caecum located?

Answer 4

In the right iliac fossa between the ileum (distal small intestine) and the ascending colon. It is inferior to the ileocecal junction.

Question 5

When can the caecum be palpated?

Answer 5

When it is enlarged enough from faeces, inflammation or a malignancy

Question 6

Which parts of the large intestine are retroperitoneal (behind peritoneum)?

Answer 6

Ascending and descending colon

Question 7

Which parts of the large intestine are intraperitoneal (completely wrapped in visceral peritoneum)?

Answer 7

Caecum, transverse colon and sigmoid colon

Question 8

Which part of the large intestine is the least fixed and can therefore dip down into the pelvis in tall, thin individuals?

Answer 8

Transverse colon

Question 9

Between which flexures does the transverse colon lie?

Answer 9

The right colic / hepatic flexure and the left colic / splenic flexure

Question 10

How long is the colon?

Answer 10

About 1.5m

Question 11

Which structures meet at the hepatic / right colic flexure?

Answer 11

Ascending colon turns 90 degrees when it meets the right lobe of the liver to move horizontally as the transverse colon.

Question 12

Which structures meet at the splenic / left colic flexure?

Answer 12

Transverse colon turns 90 degrees to point inferiorly which becomes the descending colon.

Question 13

Which section of the abdomen is the spleen located in?

Answer 13

Left hypochondrium

Question 14

Which 3 structures are used to differentiate between the small and large intestine?

Answer 14

The large intestine contains taenia coli, haustra / haustrations and appendices epiploicae / omental appendices

Question 15

What is the taenia coli?

Answer 15

3 longitudinal bands of smooth muscle on the outside of the ascending, transverse, descending and sigmoid colon. Taenia coli contract to shorten the large intestine walls, propelling the faecal matter within by peristalsis.

Question 16

What are haustra / haustrations?

Answer 16

Pouches / sacculations created by semilunar folds on the internal surface of the large intestine. They aid the circumferential contraction of the muscular layer of colon.

Question 17

What are appendices epiploicae / omental appendices?

Answer 17

Fat filled pouches of the peritoneum attached externally to the walls of the colon (not the rectum). Function is unclear.

Question 18

Which is the most proximal part of the large intestine?

Answer 18

Caecum

Question 19

Which is the most distal part of the large intestine?

Answer 19

Rectum

Question 20

How is the rectum macroscopically distinct from the large intestine?

Answer 20

Absence of taenia coli, haustra and appendices epiploicae / omental appendices

Question 21

Structure of the rectum and anus

Answer 21

The rectum is continuous with the sigmoid colon and contains rectal valves. The rectum terminates into the anal canal which contains the internal hemorrhoidal plexus, rectal sinus and sphincters. Terminates at the anus.

Question 22

Function of the rectum

Answer 22

Temporary store of faeces

Question 23

Function of rectal valves

Answer 23

Support the weight of the faeces and slows the movement into the anal canal

Question 24

What are rectal valves made of?

Answer 24

Inner circular muscle

Question 25

Features of the anal canal

Answer 25

Internal hemorrhoidal plexus, rectal sinus, internal and external sphincters

Question 26

What is the internal hemorrhoidal plexus?

Answer 26

A venus plexus (collection of veins) that surrounds the rectum.

Question 27

Why are drugs given rectally faster acting than orally?

Answer 27

The drug enters the internal hemorrhoidal plexus which drains into the portal and systemic venus system (towards liver and heart) bypassing the the gut (oesophagus, stomach, small intestine).

Question 28

Causes of haemorrhoids

Answer 28

Dilation of internal hemorrhoidal plexus

Question 29

Which sphincter in the anal canal is smooth muscle?

Answer 29

Internal sphincters - involuntary control by ANS

Question 30

Which sphincter in the anal canal is striated muscle?

Answer 30

External sphincters - voluntary control gained about age 2.

Question 31

How would you diagnose disorders of the large intestine, rectum and anal canal?

Answer 31

Barium enema - liquid containing barium is injected into the rectum and coats the colon lining. X-rays are taken.

Question 32

Examples of disorders of the large intestine, rectum and anal canal that can be investigated by barium enema

Answer 32

Colonic tumours, polyps, diverticula (out-pouches), anatomical abnormalities

Question 33

What forms the ileocaecal valve?

Answer 33

A fold of mucosa

Question 34

Where is the vermiform (worm-like) appendix found?

Answer 34

Attached to the caecum

Question 35

Similarities in the basic structure of the small and large intestine

Answer 35

Both have simple columnar epithelium with goblet cells, intestinal crypts of Leiberkuhn, and mucosal glands (mucous secretions)

Question 36

Differences in the structure of the small and large intestine

Answer 36

The large intestine doesn't contain villi, has an incomplete layer of longitudinal muscle (taenia coli), has a ring-like arrangement of circular muscle (haustra) and has appendices epiploicae.

Question 37

Which 2 types of epithelial cells line crypts and intestinal villi?

Answer 37

Goblet cells (secrete mucus) and enterocytes (secrete water and electrolytes - doesn't stain)

Question 38

What are enterocytes?

Answer 38

Simple columnar epithelial cells lining the small and large intestine. Secrete water and electrolytes and absorb nutrients.

Question 39

Where is the anal canal located?

Answer 39

Extraperitoneal between the recto-anal junction and anus

Question 40

What is the change in epithelium at the recto-anal junction?

Answer 40

In the rectum / large intestine the epithelium is simple columnar which changes to stratified squamous epithelium in the external anal canal.

Question 41

What are the 3 zones of the anal canal?

Answer 41

Colorectal (columnar) zone - anal columns, anal valves, sinuses, crypts of Morgagni, pectinate line Intermediate zone - anoderm Squamous / cutaneous zone - perianal skin

Question 42

How is the anal column divided?

Answer 42

The superior 2/3 is divided from the inferior 1/3 by the pectinate / dentate line which lies inferior to the crypts of Morgagni.

Question 43

Blood supply above the pectinate line (upper 2/3 of anal canal

Answer 43

Superior rectal artery

Question 44

Blood supply below pectinate line (inferior 1/3 anal canal)

Answer 44

Middle and inferior rectal arteries

Question 45

Venous drainage above pectinate line (superior 2/3 anal canal)

Answer 45

Superior rectal vein followed by hepatic portal circulation

Question 46

Venous drainage below pectinate line (inferior 1/3 anal canal)

Answer 46

Middle and inferior rectal veins followed by vena cava circulation

Question 47

Innervation above the pectinate line (superior 1/3 anal canal)

Answer 47

inferior mesenteric plexus, pelvic splanchnic nerves, inferior hypogastric plexus

Question 48

Innervation below the pectinate line (inferior 1/3 anal canal)

Answer 48

Pudendal nerve

Question 49

Epithelium in the colorectal zone of the anal canal

Answer 49

Simple columnar epithelium

Question 50

Epithelium in the transitional zone of the anal canal

Answer 50

Simple columnar and stratified squamous epithelium

Question 51

Epithelium in the anoderm zone of the anal canal

Answer 51

Stratified squamous non-keratinised epithelium

Question 52

Epithelium in the cutaneous / squamous zone of the anal canal

Answer 52

stratified squamous keratinised epithelium

Question 53

Function of anal canal

Answer 53

Fecal continence and defecation

Question 54

Function of colon

Answer 54

Absorb fluid and electrolytes from chyme, mixing chyme, peristalsis, mass movements

Question 55

Illness caused by the colon failing to reabsorb water

Answer 55

Diarrhoea

Question 56

What are intestinal / bacterial flora?

Answer 56

Resident microbial populations in the large intestine

Question 57

Functions of intestinal flora in the large intestine

Answer 57

Ferment dietary fibre (cellulose) and lipid, produce gases (flatus), synthesis vitamins (vit B complex and vit K)

Question 58

Which vitamins are synthesised in the large intestine by intestinal flora?

Answer 58

Vitamin B complex and vitamin K

Question 59

Function of vitamin B complex

Answer 59

Impact energy levels, brain function, cell metabolism, RBC growth, nerve function, preventing infections, cell health

Question 60

Function of Vitamin K

Answer 60

Important for blood clotting and wound healing. It is fat-soluble.

Question 61

Two aspects of motility function of large intestine

Answer 61

Mixing/squeezing chyme via circular muscles contraction to break down large faecal material for defaecation. Propulsive movements

Question 62

Two aspects of propulsive movements of the large intestine

Answer 62

Peristalsis and mass movements

Question 63

Function of peristalsis in large intestine

Answer 63

propels semi-solid faecal matter towards rectum. Is short range in the transverse and descending colon.

Question 64

What are mass movements?

Answer 64

Infrequent, more sustained contractions usually after meals (gastro-colic reflex). Moves chyme/faeces from proximal colon to distal colon

Question 65

What triggers the desire to defaecate?

Answer 65

Rectal distension

Question 66

What is defaecation?

Answer 66

An involuntary reflex that ejects faecal matter from the rectum via the anal canal.

Question 67

What is an ileostomy?

Answer 67

The ileum (proximal end of small intestine) is brought out through the abdominal wall. The opening is called a stoma and the faecal matter is collected in a bag.

Question 68

Name of procedure in which the proximal end of the colon is diverted through an opening in the abdominal wall to an external bag

Answer 68

Colostomy

Question 69

Why would an ileostomy or colostomy be carried out?

Answer 69

As a temporary or permanent measure after bowel cancer, to relieve inflammation or due to inflammatory bowel disease e.g. ulcerative colitis.

Question 70

What is diarrhoea?

Answer 70

Excessively watery stools 3 or more times a day

Question 71

Causes of diarrhoea

Answer 71

Mainly GIT infections. Results in failure of fluid absorption and reduced colonic motility

Question 72

Results of diarrhoea

Answer 72

Dehydration, electrolyte imbalance (need electrolyte replacement - cause of 1 in 9 children deaths worldwide)

Question 73

What is constipation?

Answer 73

Not defaecating at least 3 times a week. Hard, dry faeces that is difficult to pass.

Question 74

Cause of constipation

Answer 74

Increased fluid absorption, GIT spasm, drug side effect e.g. opiates (morphine), lack of dietary fibre.