Physiology and pharmacology of the large intestine

Question 1

How long is the Large intestine?

Answer 1

1.7m

Question 2

What are the 4 parts of the large intestine?

Answer 2

Caecum and appendix
Colon
Rectum
Anal canal and anus

Question 3

What are the four sections of the colon?

Answer 3

Ascending
Transverse
Descending
Sigmoid

Question 4

What are the three smooth muscle layers in the caecum and colon?

Answer 4

Teniae Coli
Internal anal sphincter
External anal sphyincter

Question 5

Do the caecum and appendix have a function in humans?

Answer 5

No

Question 6

How many litres of fluid does the caecum normally receive from the ileum per day?

Answer 6

1-2L

Question 7

How is entry from ileum to the caecum regulated?

Answer 7

The gastroileal reflex in response to gastrin and CCK through the ileocaecal valve

Question 8

What is the appendix?

Answer 8

A blind ended tube with extensive lymphoid tissue connected to the distal caecum via the appendiceal orifice that may be obstructed by faecalith.

Question 9

What are the 5 primary functions of the colon?

Answer 9

Absorption of Na+, Cl- and H20
Absorption of short fatty acid chains
Secretion of K+, HC03 and mucus
Reservoir of colonic contents
Periodic elimination of faeces

Question 10

Are there Villi in the mucosa of the colon?

Answer 10

No

Question 11

What is present in the mucosa of the colon?

Answer 11

Colonic folds
Crypts
Microvilli

Question 12

What do colonocytes mediate?

Answer 12

Electrolyte absorption by osmosis

Question 13

What do crypt cells mediate?

Answer 13

Ion secretion

Question 14

What do goblet cells secrete?

Answer 14

Copious mucus containing glycosaminoglycans

Trefoil proteins involved in host defense

Question 15

What are Na+ absorption and K+ secretion mediated by?

Answer 15

Aldosterone

Question 16

What might cause signifigant loss of K+ in the faeces?

Answer 16

Secretory diarrhoea

Question 17

How much ileocaecal material is absorbed by the colon each day?

Answer 17

0.1L

Question 18

What is Haustration?

Answer 18

Non-propulsive segmentation

Question 19

What is Peristaltic propulsive movements?

Answer 19

Mass movement

Question 20

What is Defaecation?

Answer 20

Periodic egestion

Question 21

What are Haurstra?

Answer 21

Saccules caused by alternating contraction of the circular muscle

Question 22

Where does haustration occur?

Answer 22

The proximal colon

Question 23

What generates haustration?

Answer 23

Slow wave activity

Question 24

Describe mass movement

Answer 24

simultaneous contraction of large sections (about 20 cm) of the circular muscle of the ascending and transverse colon (haustra disappear) - drives faeces into distal regions

Question 25

When does mass movement occur and what triggers it?

Answer 25

occurs about one to three times daily typically triggered by a meal (often breakfast) via the gastrocolic response involving gastrin extrinsic nerve plexuses

Question 26

Describe the process of motility in the large intestine

Answer 26

Mass movement > Rectum fills with feacal matter > Activation of rectal stretch receptors and afferents to brain > Activation of parasympathetic efferents > Contraction of smooth muscle of sigmoid colon and rectum

Question 27

How would a beneficial resident bacteria in the gut be described?

Answer 27

Commensal

Question 28

What is the function of commensal bacteria?

Answer 28

increase intestinal immunity by competition with pathogenic microbes promote motility and help maintain mucosal integrity synthesise vitamin K2 and free fatty acids (from carbohydrate) that are absorbed activate some drugs (e.g. used in treatment of IBD)

Question 29

How do gases in the large intestine arise?

Answer 29

swallowing air

Question 30

What is constipation and what causes it?

Answer 30

Presence of hard dried faeces within the colon (results from delay in defaecation and enhanced absorption of H2O)

Question 31

What are the causes of constipation?

Answer 31

ignoring, or suppressing, the urge to defaecate decreased colonic motility (e.g. improper diet, drugs, metabolic disorders, old age) obstruction of faecal movement paralytic ileus following abdominal surgery impairment of motility/defaecation reflex (e.g. Hirschprung disease, involving absence of a section of the enteric nervous system)

Question 32

What are the symptoms of constipation?

Answer 32

Abdominal discomfort Headache Loss of appetit General malaise

Question 33

what drugs are used to treat constipation?

Answer 33

Laxatives

Question 34

What are Purgatives?

Answer 34

Agents that cause purging or cleansing of the bowel by promoting evacuation

Question 35

When should laxatives and purgatives not be used?

Answer 35

When there is a physical obstruction of the bowel

Question 36

What do laxatives do?

Answer 36

increase peristalsis and/or soften faeces causing, or assisting, evacuation