PHYSIOLOGY AND PHARMACOLOGY OF THE GI TRACT

Question 1

what are the 2 muscle movements in the large intestine?

Answer 1

peristalsis

segmentation

Question 2

whats the difference between peristalsis and segmentation?

Answer 2

Segmentation involves contractions of the circular muscles in the digestive tract, while peristalsis involves rhythmic contractions of the longitudinal muscles in the gastrointestinal tract.

Question 3

what assists in preventing defecation?

Answer 3

anal rectal angle
puborectalis muscle
anal sphincters closed

Question 4

whats the first stage of defecation?

Answer 4

mass movements in the large intestine by peristalsis, puborectalis muscle relaxes allowing the anal rectal angle to be straightened, external anal sphincter relaxes, levator ani/diaphragm/rectal muscles contract

Question 5

whats the second stage of defecation?

Answer 5

internal anal sphincter relaxes and rectal contraction occurs allowing the drive for faecal material to come out.

Question 6

which nerve causes peristalsis in the colon?

Answer 6

myenteric plexus and pelvic nerves

Question 7

what causes the external anal sphincter to relax?

Answer 7

inferior rectal branch of pudendal nerve

S2,3,4 keeps the poo off the floor

Question 8

what is faecal matter comprised of?

Answer 8

water
dead bacteria
fat
inorganic matter
protein 
undigested roughage

Question 9

whats the first line antidiarrhoeal?

Answer 9

loperamide

Question 10

what is loparamides moa?

Answer 10

It acts on mu-opioid receptors on the nueral plexus of intestines. This causes decreased perstalsis and increase transit time which will increse water absorption and stool firmness.

Question 11

what is a potential side effect of loperamide?

Answer 11

drowsiness

Question 12

what are the risks of taking loperamide if you have ulcerative colitis?

Answer 12

It may increase chance of megacolon and bowel perforation

Question 13

what are the second line choices antidiarrhoeals?

Answer 13

codeine

co-phenotrope

Question 14

how does codeine work as an anti diarrhoeal?

Answer 14

Acts on mu-opioid receptors on neural plexus of intestines, decreasing peristalsis and increasing transit time. This will increase water absorption and stool firmness, alleviating diarrhoea.

Question 15

what are some issues with using codeine as an anti diarrhoeal?

Answer 15

also has potential issues for dependance and opioid toxicity.

Question 16

what is co-phenotropes moa?

Answer 16

It causes a decrease in peristalsis and increased contact of contents with mucosa.
It can cross the blood brain barrier and so there is a risk of dependancy.

Question 17

what is kaolins moa as an antidiarrhoeal?

Answer 17

This is hydrated aluminum silicate.
It is effective at absorbing water and as such has been used as an anti-diarrhoea agent. It can also absorb toxins and bacteria. The overall effect is to increase the firmness of the stool, alleviating fluid loss from diarrhoea.

Question 18

what is morphines effect on the bowel?

Answer 18

can decrease perstalsis and increase transit time which will increse water absorption and stool firmness.

Question 19

what are bulk-forming laxatives?

Answer 19

substances which are not digested but absorb liquid in the intestines and swell to form a bulky stool

Question 20

what are stimulant laxatives?

Answer 20

They irritate the intestinal cells causing the intestine to contract, which is responsible for the laxative action. Stimulant laxatives also promote water influx to the intestine, which in turn promotes bowel movement

Question 21

what are faecal softeners?

Answer 21

used on a short-term basis to relieve constipation by people who should avoid straining during bowel movements because of heart conditions, hemorrhoids, and other problems. They work by softening stools to make them easier to pass.

Question 22

what are osmotic laxatives?

Answer 22

draw water from the rest of the body into your bowel to soften poo and make it easier to pass

Question 23

what are examples of bulk forming laxatives?

Answer 23

Isaphgula husk and methylcellulose

Question 24

whats an example of an osmotic laxative?

Answer 24

lactulose

Question 25

what are examples of stimulant laxatives?

Answer 25

Senna, Bisacodyl, sodium pico sulphate, decussate sodium

Question 26

whats an example of a faecal softener?

Answer 26

decussate sodium

Question 27

what is the moa of Isaphgula husk and methylcellulose?

Answer 27

It works by increasing the bulk of stools as it is undigestible and can absorb excess water so it can more effectively stimulate stretch receptors in the mucosa

Question 28

when are bulk forming laxatives given?

Answer 28

when fibre content in the diet cannot be increased

Question 29

what is the moa of lactulose?

Answer 29

Its a synthetic disaccharide broken down by gut bacteria into lactic acid. The result is an increase in osmotic pressure and slight acidification of the colonic contents causing an increase in stool water content, softening the stool.

Question 30

why can lactulose also be used in liver failure?

Answer 30

also used to reduce the amount of ammonia in the blood of patients with liver disease. It works by drawing ammonia from the blood into the colon where it is removed from the body - can be important in hepatic encephalopathy

Question 31

whats the moa of Senna?

Answer 31

Stimulates nerve endings in the small bowel and activates the myenteric plexus. This icnreases bowel movements and secretion of water/electrolytes from colonic mucosa. This decreases time for water absorption and soften faeces.

Question 32

what is biascodyl and sodium pico sulphates moa?

Answer 32

This is hydrolyzed by intestinal brush border enzymes and colonic bacteria to form an active metabolite that acts directly on the colonic mucosa to produce colonic peristalsis.

Question 33

what is decussate sodium used to treat?

Answer 33

to relieve occasional constipation. It can also be used to help prevent straining to have bowel movements in patients who have just had a MI or surgery.

Question 34

what is decussate sodiums moa?

Answer 34

Its mode of action is either by stimulating the secretion of water/electrolytes on contact with mucosa or lowering the surface tension of the stool to permit water and lipids to enter more readily and thus soften the faeces.

Question 35

what is Dyssynergic defecation?

Answer 35

is a condition when the pelvic floor muscles are unable to coordinate with the surrounding muscles and nerves to produce a normal bowel movement.

Question 36

what can excessive use of laxatives cause?

Answer 36

melanosis coli tolerance electrolyte distubrnaes, mineral deficiencies and dehydration chronic constipation damage to nerves and muscles of the colon

Question 37

what is melanosis coli?

Answer 37

condition caused by the release of lipofuscin (pigment molecules) into the mucus membranes of the large intestine. This can be reversed if the laxative is removed but there are papers suggesting a potential link to cancer