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S2 Case 2 - Diarrhoea > Large Intestine, Constipation, Diarrhoea + Lactose Intolerance > Flashcards

Large Intestine, Constipation, Diarrhoea + Lactose Intolerance Flashcards

1
Q

What does the longitudinal muscle do?

A

Lumen becomes shorter + fatter
= facilitate movement of food

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2
Q

What does the circular muscle do?

A

Narrower + longer

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3
Q

What does the muscularis mucosae do?

A

Change in absorptive + secretory area of mucosa

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4
Q

What are the 2 plexuses in enteric nervous system?

A

Myenteric
Submucosa

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5
Q

What is the enteric nervous system comprised of?

A

Sensory neurons then interneurons then effector neurons

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6
Q

What are the sensory neurons?

A

Mechanoreceptors, chemoreceptors + thermoreceptors

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7
Q

What are the interneurons?

A

Co-ordinate reflexes + motor programs

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8
Q

What are the effector neurons?

A

Excitatory + inhibitory motor neurons

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9
Q

What is involved in autonomic innervation of GI?

A

Parasympathetic + sympathetic

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10
Q

What are the excitatory influences of parasympathetic?

A

Increase gastric secretion, blood flow + smooth muscle contraction

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11
Q

What are the inhibitory influences of parasympathetic?

A

Relaxation of sphincters
Receptive relaxation of stomach

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12
Q

What does the parasympathetic not have?

A

Discrete ganglia = found on target organ

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13
Q

What does the sympathetic do?

A

Inhibitory influences
= decrease motility, secretion + blood flow

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14
Q

What is functionally more important parasympathetic or sympathetic?

A

Parasympathetic

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15
Q

What is smooth muscle in GI tract capable of + why?

A

Spontaneous contraction
= contract as one big cell
= joined by gap junctions

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16
Q

What is spontaneous activity of smooth muscle in GI tract modulated by?

A

Intrinsic (enteric) + extrinsic (autonomic) nervous system
Hormones

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17
Q

What does spontaneous electrical activity occur as?

A

Slow waves

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18
Q

What are slow waves driven by?

A

Interstitial cells of Cajal (ICCs)
= pacemaker cells

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19
Q

Where are ICCs located?

A

Between longitudinal + circular muscle layers in submucosa

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20
Q

What do slow waves determine?

A

Basic electrical rhythm

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21
Q

What does it depend on that slow waves reach threshold?

A

Neuronal stimuli
Hormonal stimuli
Mechanical stimuli

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22
Q

What is peristalsis?

A

Series of wave-like muscle contractions that move food through digestive-tract triggered by distention of gut wall
Involves longitudinal muscle layers

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23
Q

What is segmentation?

A

Rhythmic contraction of circular muscle layer that mix + divide luminal contents

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24
Q

What do circular muscle do?

A

Make lumen smaller = squeeze food = break large bits apart

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25
Q

What is the absorption of water driven by?

A

Transport of Na+
Passive process

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26
Q

What is diarrhoea defined as in terms of water loss?

A

Excess of 500 ml per day

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27
Q

How may water move?

A

Paracellularly = through tight junction
Transcellularly = through cell

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28
Q

Describe Na+/glucose co-transport mechanism for H2O movement

A

Electrogenic
Small intestine

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29
Q

Describe Na+/amino acid co-transport mechanism for H2O movement

A

Electrogenic
Small intestine

30
Q

Describe Na+/H+ co-transport mechanism for H2O movement

A

Electroneutral (powered by presence of bicarbonate)
Duodenum + jejunum

31
Q

Describe parallel Na+/H+ + Cl-/HCO3- co-transport mechanism for H2O movement

A

Electroneutral
Ileum + colon

32
Q

Describe epithelial Na+ channel mechanism for H2O movement

A

Electrogenic
Distal colon

33
Q

Why is something electrogenic?

A

Na+ goes to blood
= makes blood more positive
= creates electrical charge

34
Q

What is something electroneutral?

A

Na+ goes in
H+ comes out
= NO change in electrical charge

35
Q

When is Cl- also reabsorbed?

A

IN ALL OF THEM

36
Q

Describe Cl- secretion

A

Occurs at basal rate
From crypt cells
Important in diarrhoea

37
Q

What happens in basolateral membrane mechanism of Cl- secretion?

A

Na+, K+ + Cl- enter by co-transport
Cl- enters lumen through CFTR channel
Na+ reabsorbed
Cl- attracts Na+ via paracellular = H2O follows

38
Q

What are CRTF channels normally?

A

Closed

39
Q

What are CFTR activated by?

A

Bacterial enterotoxins
Hormones + neurotransmitters
Immune cell products
Laxatives

40
Q

What is the role of CFTR in diarrhoea?

A

Activation = generation of 2nd messengers

41
Q

What are the 2nd messengers?

A

cAMP
cGMP
Ca2+

42
Q

What is secretory diarrhoea?

A

Secretion of Na+, Cl- + H2O

43
Q

What is the 1st cause of secretory diarrhoea?

A

Excessive secretion
= caused by E.coli

44
Q

How does cholera cause secretory diarrhoea (excessive secretion)?

A

GDP goes to GTP
= subunit dissociates
Cholera toxin inhibits activity of GTPase activity of subunit

45
Q

What may also cause secretory diarrhoea (excessive secretion)?

A

Increased activity in adenylate cyclase
Increased conc of cAMP
cAMP stimulates CFTR
Hypersecretion of Cl-, Na+ + H2O

46
Q

What is the 2nd cause of secretory diarrhoea?

A

Impaired absorbance of NaCl
= caused by congenital defects

47
Q

What is 3rd cause of secretory diarrhoea?

A

Non-absorbable/ poorly absorbable solutes
= lactose intolerance

48
Q

What is 4th cause of secretory diarrhoea?

A

Hypermotility
= excessive peristalsis of GI

49
Q

What are the consequences of diarrhoea?

A

Dehydration
Metabolic acidosis
Hypokalaemia

50
Q

What is the treatment process for diarrhoea?

A

Maintain fluid balance (1st)
Anti-infective agents (if appropriate)
Anti-motility agents

51
Q

How does rehydration therapy work?

A

2 Na+ bind
Affinity for glucose increases
Na+ + glucose translocate to intracellular
2 Na+ dissociate, affinity for glucose falls
Glucose dissociates
Cycle repeated

52
Q

What do anti-motility drugs do?

A

Decrease motility in gut

53
Q

What can opiates do?

A

Anti-diarrhoeal activity
= inhibit enteric neurons
= decrease peristalsis, increase segmentation

54
Q

What are the major opioids used in diarrhoea?

A

Codeine
Diphenoxylate
Loperamide - 1st choice
Atropine

55
Q

What are problems with codeine?

A

NOT very selective
= CNS activation

56
Q

What are the problems with atropine?

A

Anti-muscarinic
= decrease parasympathetic activity
= decrease motility
BUT not selective

57
Q

Why is loperamide 1st choice?

A

Relatively selective to GI tract
Increases segmentation, decreases peristalsis

58
Q

What is lactose intolerance?

A

Lactase deficiency

59
Q

What is primary lactase deficiency?

A

Lack of lactase persistence allele

60
Q

What is secondary lactase deficiency?

A

Damage to proximal small intestine

61
Q

What is congenital lactase deficiency?

A

Rare autosomal recessive disease
= from birth

62
Q

When does hypolactasia cause a problem?

A

Lactose-containing food is consumed

63
Q

Describe process of lactose intolerance

A

NOT digested in small intestine
= goes to large intestine
= bacteria convert it to H gas + fatty acids
= attract H2O

64
Q

How is diagnosis done for lactose intolerance?

A

Diet observation

65
Q

How is lactose intolerance treated?

A

Reduction or elimination in lactose-containing food

66
Q

What are the causes of constipation?

A

Neurogenic disorders of large intestine
Abdominal muscle weakness
Diet poor of fibre
Aging

67
Q

Why do neurogenic disorders of large intestine cause constipation?

A

Reduce peristalsis
eg. IBD, cancer

68
Q

How do you treat constipation?
Changes in lifestyle

A

More H2O, less alcohol
Increase activity
Improve toilet routine = keep tp regular time

69
Q

What drugs can be used to treat constipation?

A

Laxatives
Antiemetics

70
Q

What laxatives can be used to treat constipation?

A

Bulk laxatives
Osmotic laxatives
Faecal softeners
Stimulant laxatives

71
Q

Why can antiemtics be used to treat constipation?

A

Increase motility + gastric emptying

S2 Case 2 - Diarrhoea (12 decks)

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