L46: Large Intestine

Question 1

What are the three components of the large intestine?

Answer 1

• Caecum;
• Colon;
• Rectum.

Question 2

What are the two colic flexures (curvatures)?

Answer 2

• Hepatic (right);

- Splenic (left).

Question 3

What are haustrae?

Answer 3

Sacculation of the large intestine- give rise to segmented appearance

Question 4

What are appendices epiploicae?

Answer 4

Fatty tags

Question 5

What are the two sphincters of the anal canal?

Answer 5

• Internal (involuntary);

- External (voluntary).

Question 6

Where does the caecum end and colon begin?

Answer 6

Ileo-caecal junction

Question 7

Where does chyme pass through into the large intestine?

Answer 7

Ileo-caecal valve

Question 8

What prevents back flow from L.I. to S.I.?

Answer 8

A fold of mucosa

Question 9

Where is the appendix located?

Answer 9

Off of the caecum

Question 10

What epithelium lines the large intestine?

Answer 10

Simple, columnar with goblet cells

Question 11

What are intestinal crypts (of Leiberkuhn)?

Answer 11

Intestinal glands found along the epithelium lining (invaginations), secrete intestinal juice

Question 12

What are the main differences of structure between the S.I. and L.I.?

Answer 12

• Villi in small intestine ONLY;
• In L.I., incomplete layer of longitudinal muscle (taenia coli);
• In circular muscle, ring-like arrangement of circular muscle (haustrae);
• Fatty tags.

Question 13

Why is the recto-anal junction at higher risk of cancer?

Answer 13

Change of epithelium from simple columnar to stratified squamous

Question 14

What is the primary function of the large intestine?

Answer 14

Fluid and electrolyte absorption

Question 15

What is the primary site of absorption in the large intestine?

Answer 15

Colon

Question 16

How is the colon subdivided?

Answer 16

• Ascending;
• Transverse;
• Descending;
• Sigmoid.

Question 17

What are the roles of intestinal flora?

Answer 17

• Ferment dietary fibre (cellulose) and lipid;
• Gas production (‘flatus’);
• Synthesis some vitamins;
• Vitamin B complex (cell metabolism);
• Vitamin K (blood clotting).

Question 18

Describe the motility of the large intestine.

Answer 18

Caecum and ascending colon:

• Mixing movements;
• Similar segmentation to S.I.;
• Contraction of circular muscles, shortening of longitudinal muscles.

Transverse and descending colon:

• Local peristalsis (faecal matter towards rectum);
• Mass movements (moves chyme/faeces from proximal to distal colon).

Question 19

What movements of the large intestine are infrequent?

Answer 19

Mass movements

Question 20

What type of muscle is in the internal anal sphincter?

Answer 20

Smooth (controlled by ANS)

Question 21

What type of muscle is in the external anal sphincter?

Answer 21

Skeletal (striated)

Question 22

What is diarrhoea?

Answer 22

• Excessively watery stools;
• Failure of fluid absorption
• Leads to dehydration and electrolyte imbalance.

Question 23

What is constipation?

Answer 23

• Hard faeces, difficult to pass;
• Due to increased fluid absorption;
• Side effect of some drugs, excess fibre (>70g).