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Y1 GI > Physiology and pharmacology of the large intestine > Flashcards

Physiology and pharmacology of the large intestine Flashcards

1
Q

What is the length and diameter of the large intestine

A

1.7 m long, 6 cm diameter

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2
Q

What makes up the large intestine

A 
Caecum 
Appendix 
Ascending colon 
Transverse colon 
descending colon 
Sigmoid colon 
Rectum 
Anal canal 
Anus
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3
Q

what are haustra

A

sac like pouches caused by the activity of the taeniae coli

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4
Q

What are the taeniae coli

A

Strands of longitudinal smooth muscle in caecum and colon

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5
Q

Where in the large intestine is smooth muscle thickened

A

At the internal anal sphincter which is surrounded by the skeletal muscle of the external sphincter

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6
Q

What is the function of the appendix

A

no specialised function in humans

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7
Q

What material does the caecum receive

A

indigestible residues
unabsorbed biliary components
unabsorbed fluids

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8
Q

What reflex permits entre into the caecum

A

The gastroilial reflex which is in respone to gastrin and CCK allowing passage of material through the ileocaecal valve

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9
Q

How does the ileocaecal valve act

A

Maintains a positive resting pressure
relaxes in response to duodenal distension
contracts in response to distension of the ascending colon
controlled by vagus nerve, sympathetic nerves, enteric neurons and hormones

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10
Q

What connects the caecum and appendix

A

The appendiceal orifice which if blocked by faecalith (hard faeces) can cause appendicitis

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11
Q

What are the primary functions of the colon

A 
Absorption of Na+, Cl-, and H2O 
Absorption of short chain fatty acids 
Secretion of K+, HCO3-, and mucus 
Reservoir storing colonic contents 
Periodic elimination of faeces
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12
Q

What happens to carbohydrates not absorbed by the small intestine

A

Carbs not absorbed by the small intestine are fermented by colonic flora into short chain fatty acids

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13
Q

What are faeces composed of and how much are excreted per day

A

150g per day
composed of H2O (100g)
solid material (50g)
cellulose, bacteria, bilirubin, salt

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14
Q

What structures increase absorption of the large intestine

A

Colonic folds
Crypts
Microvili

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15
Q

What are colonocytes

A

surface epithelial cells which mediate electrolyte absorption

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16
Q

Which cells mediate ion secretion

A

Crypt cells

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17
Q

What do goblet cells secrete

A

Mucus containing glycosominoglycans - hydrated to form a slippery surface gel
trefoil proteins involved in host defence

18
Q

What substance enhances K+ secretion and Na+ absorption

A

Aldosterone

19
Q

K+ is maintained in secretory diarrhoea true/false

A

false, there is significant loss of K+ in the faeces

20
Q

What is haustration

A

non-propulsive segmentation

21
Q

What is the name for mas movement through the large intestine

A

peristaltic propulsive propulsive movements

22
Q

What is defaecation

A

periodic egestion

23
Q

What causes haustra

A

alternating contraction of circular muscle generated by slow wave activity

24
Q

What is the purpose of haustra

A

mixes contents and allows time for fluid and electrolyte reabsorption

25
Q

How many times a day does mass movement occur

A

One to three times a day, typically triggered by a meal via the gastrocolic response involving gastrin and extrinsic nerve plexus

26
Q

Describe how defaecation occurs

A

Mass movement - the rectum fills with faecal matter
Rectal stretch receptors send afferents to the spinal cord and brain
brain causes urge to defaecate
Spinal cord activated parasympathetic efferents which cause contraction of the sigmoid colon and rectum and relaxation of internal anal spinchter
If skeletal muscle externam anal spinchter is relaxed defaecation occurs and if not it is delayed

27
Q

What role do commensal bacteria in the large intestine play

A

increase intestinal immunity by competing with pathogenic microbes
promote motility and help maintain mucosal integrity
synthesise vitamin K2 and free fatty acids from carbohydrates
Activate certain drugs

28
Q

Where does intestinal gas arise from

A 
Swallowed air (eructation 'burped up') 
Bacteria in the colon which attacks indigestible carbohydrates
29
Q

What is constipation

A

presence of hard dried faeces in the colon

30
Q

What causes constipation

A 
ignoring or supressing the urge to defaecate 
decreased colonic motility 
Obstruction of faecal movement
Paralytic ileus following abdominal surgery 
Impairment of motility/defaecation reflex
Hischprung disease (absence of secretion from enteric nervous system)
31
Q

What drugs treat constipation

A

Laxatives

purgatives

32
Q

What are purgatives

A

drugs that induce purging or cleaning of the bowels by promoting evacuation

33
Q

How do laxatives work

A

Increase peristalsis and/or soften faeces

34
Q

What are medically sound uses of laxatives/purgatives

A

when ‘straining’ is potentially damaging to health (angina) or when defecation is painful (haemorrhoids)
to clear bowels before surgery or endoscopy
To treat drug induced constipation or in bedridden or elderly patients

35
Q

What are four types of laxative

A

Bulk laxatives
Stimulant purgatives
Osmotic laxatives
Faecal softners

36
Q

How do bulk laxatives work

A 
They are indigestible polysaccharide polymers which improve stool consistency 
slow acting 
increase bulk and peristalsis 
retain H20 
METHYLCELLULOSE
37
Q

How do stimulant purgatives work

A 
increase H20 and electrolyte secretion 
increase peristalsis
faecal softening 
rapidly acting  
BISACODYL
38
Q

How do osmotic laxatives work

A 
Rapidly acting 
retain H20 
increase bulk 
increase peristalsis 
MAGBESIUM SULPHATE
39
Q

How to faecal softeners work

A

Detergent like action
increase H20 and electrolyte secretion
increase peristalsis
faecal softening

40
Q

What drugs are used to treat IBS and IBD

A

Glucocorticoids for acute attacks

Aminosalicylates (more for UC) for maintenance

Y1 GI (41 decks)

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