Large intestine structure and function

Question 1

How does the ileum ultimately connect to the colon?

Answer 1

ileum - ileocaecal valve - caecum - vermiform appendix

Question 2

How long is the colon?

Answer 2

1.5-1.8m

Question 3

Name the 4 parts of the colon

Answer 3

ascending, transverse, descending and sigmoid

Question 4

Is the circular or longitudinal muscle layer incomplete in the colon?

Answer 4

longitudinal

Question 5

What are teniae coli?

Answer 5

3 bands spanning the entire length of the colon which is why the longitudinal muscle is disrupted

Question 6

What are haustra and how are they formed?

Answer 6

pouches of the large intestine due to the contractions of the teniae coli

Question 7

What epithelium is found in the mucosa of the large intestine?

Answer 7

simple columnar

Question 8

Describe the crypts of the large intestine

Answer 8

large and straight

large amount of goblet cells to secrete mucus to help with lubrication for the movement of faeces

Question 9

Where is the rectum anatomically?

Answer 9

Between the sigmoid colon and the anal canal

Question 10

Describe the rectum

Answer 10

straight muscular tube with simple columnar epithelium and a thick muscularis externa

Question 11

Where is the anal canal anatomically?

Answer 11

2-3cm between the distal rectum and anus

Question 12

What epithelium makes up the anal canal?

Answer 12

stratified squamous epithelium

Question 13

How many anal sphincters are there?

Answer 13

2 - internal and external which is comprised of skeletal muscle

Question 14

What is the primary role of the colon?

Answer 14

dehydrate chyme

Question 15

How does the colon dehydrate the chyme?

Answer 15

active transport of sodium and the water follows

Question 16

What are the 2 reasons for the transmit time of the colon being relatively long?

Answer 16

bacterial colonisation

ferment undigested carbohydrate

Question 17

What are the 3 products after fermentation of undigested carbohydrates

Answer 17

vitamin K
short chain fatty acids
Gas

Question 18

Explain the difference in muscle between the internal and external anal sphincters

Answer 18

internal - smooth under autonomic control

external - skeletal under voluntary control

Question 19

Explain how the defaecation reflex comes about

Answer 19

following a meal the faeces travels from the colon to the rectum which distends the wall of the rectum which is sensed by mechanoreceptors

Question 20

How is the defaecation reflex controlled by the nervous system?

Answer 20

parasympathetically by pelvic splanchnic nerve

Question 21

After the defaecation reflex has begun explain how this leads to faces being expelled

Answer 21

MMC in colon increases pressure on external sphincter which you voluntarily relax and pass faeces

Question 22

How can you put off the expulsion of faeces?

Answer 22

descending neural pathways

Question 23

Is there absorption of toxins from faecal material due to long retention times in the colon in constipation?

Answer 23

NO

Question 24

What are the symptoms of constipation and what are these due to?

Answer 24

headache, nausea, abdominal distension and loss of appetite caused by distension of rectum

Question 25

How can constipation be treated?

Answer 25

laxatives

Question 26

What is the definition of diarrhoea?

Answer 26

Too frequent passage of faeces which are too liquid

Question 27

What are some causes of diarrhoea?

Answer 27

pathogenic bacteria, toxins, viruses, food, nerves, protozoans

Question 28

What do enterotoxigenic bacteria do? plus examples

Answer 28

vibrio cholera, E coli

Produce protein enterotoxins to turn on chloride secretion and therefore promote extreme water loss

Question 29

What do enterotoxigenic bacteria do to intracellular 2nd messengers?

Answer 29

turn them on eg cAMP, cGMP and calcium

Question 30

How is diarrhoea by enterotoxigenic bacteria now treated in developing countries to prevent children dying?

Answer 30

sodium-glucose solution as the villi are not damaged so this will promote rehydration and the washing away of bacteria