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GI > Physiology and Pharmacology of the large intestine (laxatives and purgatives) > Flashcards

Physiology and Pharmacology of the large intestine (laxatives and purgatives) Flashcards

1
Q

what makes up the large intestine

A

caecum and appendix, colon, rectum, anal canal, anus

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2
Q

what are the parts of the colon

A

ascending, transverse, descending, sigmoid

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3
Q

describe the smooth muscle of the large intestine

A

Longitudinal smooth muscle layer in caecum and colon is divided into three strands – the taeniae coli, but encircles the rectum and anal canal

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4
Q

describe the muscles of the anal sphincter

A

smooth muscle is thickened at the internal anal sphincter, which is surrounded by the skeletal muscle of the external anal sphincter

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5
Q

what does the taeniae coli and circular muscle layers create

A

haustra- sac like bulges

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6
Q

what are the functions of the caecum and appendix

A

none in human- used to metabolise cellulose in other species

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7
Q

what permits the entry of food into the caecum and from where

A

entry from terminal ileum permitted by the gastroilea reflex in response to gastrin and CCK through the ileac valve

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8
Q

what is the function of the ileocaecal valve

A

maintaining a positive resting pressure

relaxing in response to distension of the duodenum

contracting in response to distension of the ascending colon

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9
Q

what controls the ileocaecal valve

A

vagus nerve, sympathetic nerve, enteric neurones and hormonal signals

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10
Q

where does the appendix attach to

A

the distal caecum

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11
Q

describe the absorptive functions of the colon

A

removes sodium and chloride (and water follows) from the lumen and transports it to the blood- starts to form solid stool

also absorbs products of bacteria metabolism; short chain fatty acid generated by bacteria

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12
Q

describe the secretory function of the colon

A

produces acidic enzymes, but neutralised by secretory functions of large intestine

net movement of K and HCO3 from blood to lumen

secretes mucous with a protective function- forms gel over epithelium and lubricates

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13
Q

what are the other functions of the colon

A

a reservoir and periodic expulsion of faeces

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14
Q

describe the mucosa of the colon

A

lacks villi but possesses colonic folds, crypts and microvilli that increase SA

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15
Q

what mediates electrolyte absorption in the colon

A

surface epithelial cells

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16
Q

what does electolyte absorption drive

A

absorption of H2O

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17
Q

what mediates ion secretion

A

crypts

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18
Q

what do goblet cells secrete

A

lots of mucous (when hydrated forms slippery gel)

trefoil proteins involved in host defence

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19
Q

what hormone enhances Na+ absorption and K+ secretion

A

aldosterone

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20
Q

what does a significant loss of K+ in faeces result in

A

hypokalaeia, secretory diarrhoea

21
Q

what are the patterns of motility in the large intestine

A

haustration (non-propulsive segmentation)

peristaltic propulsive movements (mass movement)

defaecation (periodic egestion)

22
Q

describe haustrationn

A

very slow mixing of contents- allows time for absorption, occurs in proximal colon, causes orad (towards the mouth) movement) but is overcome by mass movement sweep

23
Q

describe mass movement

A

simultaneous contraction of large sections of circular muscle of the ascending and transverse smooth muscle- drives faeces into distal regions

in distal colon it drives faeces to the rectum

24
Q

what triggers mass and how often does it happen

A

1-3 times a day

gastrocolic response (gastrin and extrinsic nerve plexuses)

25
Q

what triggers the defecation response

A

stretching of the distal colon in mass movement- rectal sphincteric relfex (relaxation) and active contraction of rectal smooth muscle

26
Q

what nerves are involved in defaecation

A

pelvic nerve (spinal chord- parasympathetic efferents) and pudenal nerve (to brain)

27
Q

how is defaecation assisted

A

straightening of the anorectal angle (squatting position), abdomental skeletal muscle contraction, expiration against closed glottis

28
Q

how is defaecation delayed

A

contraction of skeletal muscle of external anal sphincter, rectal wall gradually relaxes

29
Q

what is the role of commensals

A

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)

30
Q

what is eructation

A

burping

31
Q

was causes gas

A

swallowing air, food that bacteria cant digest

32
Q

where do we get vit k1

A

diet

33
Q

was causes constipation

A

delay in defaecation, decreased colonic motility, obstruction, enhanced water absorption

34
Q

what are the symptoms of constipation and what causes them

A

abdominal discomfort, headache, malaise, loss of appetite- cause by prolonged distention of the large intestine

35
Q

name a metabolic disorder that can cause reduced colonic motility

A

hypokalaemia

36
Q

what is hirschprung disease

A

a condition that prevents bowel movements (stool) to pass through the intestines due to missing nerve cells in the lower part of the colon

37
Q

why should laxatives and purgatives not be given when there is a physical obstruction to the bowl

A

as it causes a massive increases in pressure and possible perforation of the bowl

38
Q

what are purgatives

A

agents that cause purging or cleansing of the bowels by promoting evacuation (both large and small intestine)

39
Q

how do laxatives work

A

increase peristalsis and/or soften faeces causes/assisting evacuation

40
Q

what are the medically sound uses of laxatives and purgatives

A 
painful poos
predisposed to constipation 
straining potentially damaging
to clear bowl before surgery/ endoscopy 
to treat drug induced (opiate)/ bed ridden or elderly constipation
41
Q

how do bulk laxatives work

A

stimulate peristalsis by causing stretching, improve stool consistency

42
Q

how do osmotic laxatives work

A

increase peristalsis by retaining H2O and increasing volume- stretching

43
Q

how do stimulant purgatives work

A

causes enteric nervous system to cause smooth muscle contraction and peristalsis- increase H2O and electrolyte secretion and peristalsis

44
Q

how do faecal softeners work

A

detergent like action

45
Q

what is the treatment for IBS

A

symptomatic- diet, anti-diarrhoeals, anti-spasmodics, laxatives

46
Q

what do anti spasmodics do and what is a negative sie efffect

A

prevent spams of involuntary muscle, help relieve muscle cramping, cause constipation

47
Q

what is used for acute attacks of IBD

A

corticosteroids

48
Q

how is maintance of mild UC achieved

A

aminosalicylates (5-ASA: mesalazine, Olsalazine, Balsalazide)

GI (64 decks)

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