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Gastrointestinal > Physiology and Pharmacology of the Large Intestine > Flashcards

Physiology and Pharmacology of the Large Intestine Flashcards

1
Q

When does stuff enter the caecum?

A

After the gastroileal reflex (in response to gastrin and CCK).

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2
Q

What signals is the ileocaecal valve controlled by?

A

The vagus nerve, sympathetic nerves, enteric neurones and hormonal signals.

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3
Q

What is the opening to the appendix called?

A

The appendiceal orifice.

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4
Q

What is absorbed in the large intestine?

A

Sodium, chloride, water, short chain fatty acids (from carbohydrate fermented by colonic flora).

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5
Q

What is secreted in the large intestine?

A

Potassium, bicarbonate and mucus.

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6
Q

What are the main functions of the ascending and transverse colon?

A

Fluid reabsorption and bacterial fermentation.

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7
Q

What are the main functions of the descending and sigmoid colon?

A

Final drying and storage.

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8
Q

What are present in the colon to increase surface area?

A

Colonic folds, crypts and microvilli (no villi).

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9
Q

What cells mediate electrolyte absorption?

A

Colonocytes.

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10
Q

What cells mediate ion secretion?

A

Crypt cells.

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11
Q

What do goblet cells do in the large intestine?

A

Secrete lots of mucus containing glycosaminoglycans (hydrated to form a slippery gel), trefoil proteins involved in host defence.

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12
Q

What is enhanced by aldosterone?

A

Sodium absorption and potassium secretion.

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13
Q

What are the 3 patterns of motility in the large intestine?

A

Haustration (non-propulsive segmentation), peristaltic propulsive movements (mass movement), defecation (periodic egestion).

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14
Q

What are haustra?

A

Saccules cause by alternating contraction of the circular muscle.

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15
Q

What is the main difference between segmentation and haustration?

A

Haustration has a much lower frequency.

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16
Q

What are the functions of haustration and what is it generated by?

A

It causes oral movement, allows time for fluid and electrolyte reabsorption, mixes content. It is generated by slow wave activity.

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17
Q

What is mass movement?

A

Simultaneous contraction of large sections of the circular muscle of the ascending and transverse colon (haustra disappear) which drives faeces into distal regions.

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18
Q

How often does mass movement occur and what is it triggered by?

A

About 1 to 3 times daily, triggered by a meal via the gastrocolic response.

19
Q

What mediators does the gastrocolic reponse involve?

A

Gastrin and extrinsic nerve plexuses.

20
Q

What happens when mass movement occurs in the distal colon?

A

It propels faeces into the rectum triggering the defecation reflex in response to stretch.

21
Q

What happens when rectal stretch receptors are activated?

A

Causes contraction of smooth muscle of sigmoid colon and rectum - internal anal sphincter relaxes.

22
Q

Once the sigmoid colon and rectum have contracted, what are the 2 options?

A
  1. Relaxation of skeletal muscle of external anal sphincter.
  2. Contraction of skeletal muscle of external anal sphincter.
23
Q

What is defection assisted by?

A

Straightening of the anorectal angle (squatting), abdominal skeletal muscle contraction and expiration against a closed glottis.

24
Q

What do gut bacteria synthesise?

A

Vitamin K2 and free fatty acids (from carbohydrate).

25
Q

What are all the causes of conspitation?

A

Ignoring/suppressing the urge to defecate, decreased colonic motility, obstruction of faecal movement, paralytic ileus following abdominal surgery, impairment of motility/defecation reflex (Hirshprung disease).

26
Q

What symptoms can constipation cause?

A

Abdominal discomfort, headache, loss of appetite and general malaise.

27
Q

What are the symptoms of constipation caused by and what are they not caused by?

A

Cause by prolonged distention of the large intestine, not toxins absorbed from retained faecal matter.

28
Q

Name a metabolic disease causing decreased motility.

A

Hypokalaemia.

29
Q

When should laxatives or purgatives not be used?

A

When there is physical obstruction to the bowel.

30
Q

What do laxatives do?

A

Increase peristalsis and/or soften faeces causing, or assisting evacuation.

31
Q

What can cause laxative dependency?

A

Using laxatives too regularly where you develop an atonic colon.

32
Q

What are clinical indications of laxatives/purgatives?

A

When straining is potentially damaging to health e.g. angina or defecation is painful e.g. haemorrhoids, to clear the bowel before surgery or endoscopy, to tread drug-induced constipation or constipation in bedridden or elderly patients.

33
Q

What are the 4 classes of laxative?

A

Bulk, osmotic, stimulant, faecal softeners.

34
Q

What are bulk laxatives and are they fast or slow acting?

A

Indigestible polysaccharide polymers. Slow acting.

35
Q

Give an example of a bulk laxative.

A

Methylcellulose.

36
Q

What are osmotic laxatives and are they fast or slow acting?

A

Poorly absorbed solutes, fast acting.

37
Q

Give 3 examples of osmotic laxatives and how they are taken.

A

Magnesium sulphate or hydroxide orally, sodium citrate rectally, lactulose orally.

38
Q

What is the function of stimulant purgatives?

A

They cause increased water and electrolyte secretion and increased peristalsis.

39
Q

Give 3 examples of stimulant purgatives.

A

Bisacodyl, sodium picosulphate, senna.

40
Q

What is a common side effect of stimulant purgatives?

A

Abdominal cramps.

41
Q

How do faecal softeners work?

A

They have a detergent-like action.

42
Q

Give 3 examples of faecal softeners and how they are taken.

A

Docusate sodium orally, arachis oil as an enema.

43
Q

What is the treatment for IBS?

A

Adjustment of diet, anti-diarrhoeals, anti-spasmodics or laxatives as required.

Gastrointestinal (26 decks)

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