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Block 1: Physiology > Large intestine > Flashcards

Large intestine Flashcards

1
Q

What are the functions of the large intestine?

A
  1. Reabsorption of sodium and water
  2. Make and store faeces
  3. To move faeces towards rectum
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2
Q

How is sodium reabsorbed in the large intestine?

A

Enters cell via electrogenic channels or sodium-hydrogen ion exchangers
Pumped out of cell by Na+/K+ ATPase

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3
Q

How is water reabsorbed in the large intestine?

A

Movement of sodium ions creates concentration gradient for water to move through cells.
Generally take transcellular route due to tight junctions between colonic epithelial cells.

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4
Q

What are the two movements of the colon?

A

Mixing (haustral contractions)

Propulsion

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5
Q

What is the function of haustral contractions?

A

Mix the contents of the proximal colon to aid water reabsorption

[Nb. Mixing does not move contents along colon]

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6
Q

What is the function of propulsion?

A

Mass movement of luminal contents from the transverse to the sigmoid colon for expulsion.

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7
Q

What is peristalsis?

A

Alternating contractions and relaxations of the smooth muscle layers that mix and squeeze luminal contents through colon (and other areas of GI tract)

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8
Q

What is the gastrocolic reflex?

A

Mass movement in the colon initiated by food entering the stomach (which increases gastrin secretion and stimulation of ANS nerves).

Pushes contents of colon towards the rectum to initiate the defecation reflex.

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9
Q

Which of the 2 anal sphincters is voluntary?

A

External anal sphincter

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10
Q

What is the defecation reflex?

A
  1. Contraction of rectum
  2. Relaxation of internal anal sphincter
  3. Initial contraction of external anal sphincter
  4. Increased peristaltic activity in the sigmoid colon
  5. Relaxation of external anal sphincter
  6. Expulsion of faeces
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11
Q

What is the Valsalva manoeuvre?

A
  1. Full inspiration followed by forced expiration against a closed glottis causes the diaphragm to flatten
  2. Contraction of abdominal and thoracic muscles
  3. Increased pressure in abdominal cavity forces faeces towards rectum
  4. Defecation reflex initiated
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12
Q

What are the functions of anaerobic bacteria in the large intestine?

A
  1. Immunity
  2. Conversion of bilirubin to urobilinogens
  3. Formation of secondary bile acids
  4. Degradation of digestive enzymes
  5. Digestion of mucus
  6. Vitamin synthesis (e.g. Vitamin K)
  7. Metabolism of undigested polysaccharides
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13
Q

What disrupts the actions of anaerobic bacteria in the gut?

A

Oral antibiotics

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14
Q

What are the common purgatives used in treatment of constipation?

A

Bulk laxatives
Osmotic laxatives
Faecal softeners
Stimulant purgatives

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15
Q

How do bulk laxatives work?

A

Retain water in the GI lumen to soften and increase faecal bulk and to promote increased motility

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16
Q

What are bulk laxatives?

A

Polysaccharide polymers that are not broken down in the normal digestion process

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17
Q

Give 2 examples of bulk laxatives

A 
Methylcellulose (e.g. Citrucel) 
Ispaghula Husk (e.g. Fybogel)
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18
Q

How long do bulk laxatives generally take to act?

A

1-3 days

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19
Q

What are osmotic laxatives?

A

Made up of poorly absorbed solutes (e.g. saline purgatives, macragols and lactulose)

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20
Q

How do osmotic laxatives work?

A

Maintain an increased volume of fluid in the GI tract by osmosis which results in an abnormally large volume of fluid entering the colon (as transit through the small intestine is accelerated)

21
Q

Give an example of a saline purgative

A

Magnesium sulphate + Magnesium hydroxide

22
Q

How fast do saline purgatives act?

A

Approx. 1-2 hours

23
Q

What are saline purgatives used for?

A

Bowel prep (e.g. to empty bowels prior to procedure)

24
Q

What are Macragols?

A

Inert polymers of ethylene glycol

25
Q

What are macragols used for?

A

Treatment of faecal impaction in children

Long term management of chronic constipation

26
Q

How does lactulose work?

A

Bacteria in the colon converts it (a disaccharide) to two component monosaccharides which are poorly absorbed

27
Q

How fast does lactulose act?

A

1-3 days

28
Q

What is lactulose generally used for?

A

Chronic constipation
Hepatic encephalopathy
Treating constipation effects of opioids

29
Q

Name 2 examples of faecal softeners

A

Docusate

Arachis Oil

30
Q

How do faecal softeners work?

A

Anionoic surfactants that lower surface tension at oil-water interface allowing water or fats to enter the stool (thus softening stool)

31
Q

How long do faecal softeners take to act?

A

3-5 days

32
Q

What are faecal softeners generally used for?

A

Constipation with fissures/ piles

33
Q

Name 2 stimulant purgatives

A

Bisacodyl

Senna

34
Q

How is Bisacodyl usually administered?

A

Suppository

35
Q

How does Bisacodyl work?

A

Stimulate rectal mucosa resulting in mass movements and defecation in 15-30 minutes

36
Q

How does Senna work?

A

Release of anthracene derivatives has direct effect on myenteric plexus which increases colonic motility

37
Q

What are the four types of diarrhoea?

A

Motility-related
Osmotic
Inflammatory
Secretory

38
Q

What is secretory diarrhoea?

A

Increased active secretion or inhibition of absorption

39
Q

What type of diarrhoea is caused by Cholera?

A

Secretory

40
Q

What is osmotic diarrhoea?

A

Loss of water due to a heavy osmotic load where nutrients remain in lumen (causing water to be pulled into the lumen)

41
Q

What disease can cause osmotic diarrhoea?

A

Coeliac disease

42
Q

What is motility-related diarrhoea?

A

Abnormally high GI motility which decreases time for absorption of water and nutrients

43
Q

What can cause motility-related diarrhoea?

A

Diabetic neuropathy

44
Q

What is inflammatory diarrhoea?

A

Damage to mucosal lining leads to loss of protein-rich fluids and decreased ability to absorb lost fluids

45
Q

What can cause inflammatory diarrhoea?

A 
Infections (bacterial, viral, parasitic) 
Autoimmune problems (e.g. IBD)
46
Q

What ingredients are used in oral rehydration therapy?

A

Isotonic/ Hypotonic solution of Glucose and NaCl

47
Q

How do oral rehydration therapies work?

A

Glucose enhances ability to absorb Na+ and water follows Na+

48
Q

Name an anti-motility agent

A

Loperamide

49
Q

How do anti-motility agents work?

A

Act on mu-opioid receptors in the myenteric plexus to increase tone and contractions of colon but diminishes propulsive activity.
Contraction of pyloric, ileocaecal and anal sphincters.

Block 1: Physiology (15 decks)

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