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Digestion and Excretion > Colonic Motility and Defacation > Flashcards

Colonic Motility and Defacation Flashcards

1
Q

What are two histological features of the colom?

A

Folds - outer longitudinal muscle, arrangement of mucosa highly adapted to its function
Colonic crypts - absorption

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2
Q

What does the colon absorb?

A

Water and electrolytes (Na+)

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3
Q

What does the colon secrete?

A

Mucous, Cl-

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4
Q

What are the absorptive cells of the colon?

A

Colonocytes

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5
Q

What is the boundary between the large and small intestine called?

A

Ileo caecal junction - high pressure zone

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6
Q

How is tone increased and decreased?

A

Increased by sympathetic nerve supply
Decreased by gastrin

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7
Q

What does the high pressure zone respond to?

A

Both ileal and colonic distension

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8
Q

What is the function of the ileocaecal valve?

A

Prevents backflow of material (bacteria) into small intestine

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9
Q

What is valve opening controlled by?

A

Both small and large intestine - facilitates unidirectional movement

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10
Q

What is the function of the ascending colon?

A

Half of the chyme is cleared within 90 mins

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11
Q

What is the function of the transverse colon?

A

Removal of water and electrolytes
Material retained for ~24 hrs

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12
Q

What is the function of the descending colon?

A

Storage of material

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13
Q

What is the function of the recto-sigmoid region?

A

Reservoirs for faeces
36-48 hrs

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14
Q

What are taenia coli?

A

Aggregation of longitudinal muscle into 3 bands resulting in haustra (pouches)

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15
Q

What is diverticulosis?

A

haustra bulge outwards and become infected

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16
Q

What is haustral shuttling?

A

Short distances in both directions
kneading of faecal mass - extracts as much water as possible

17
Q

What is segmental propulsion?

A

Peristalsis
both directions

18
Q

What is multihaustral propulsion?

A

Infrequent propulsions
Produced reflexively by gastrocolic reflex (fatty meals)
Moves faecal mass over large distances
Very regularly after meals

19
Q

What are the 5 triggers for mass movement in the colon?

A

Gastroileal reflex
Gastrocolic reflex
Irritation
Intense parasympathetic stimulation
Over-distension of a segment

20
Q

What are the 4 controls of colonic motility?

A

Basal electrical rhythm
Intrinsic nerves
extrinsic nerves
Endocrine/paracrine control

21
Q

What are ICCs increased by?

A

Stretcg
ACh
Histamine
Substance P
5-HT

22
Q

What are ICCS decreased by?

A

Noradrenaline
Adrenaline

23
Q

What is the intrinsic nerves for colon motility?

A

Myenteric plexus

24
Q

What is Hirschprung’s disease?

A

Congenital absence of ganglia
Tonic contraction of affected segment
Megacolon
Abdominal distension
Constipation

25
Q

What is Chaga’s disease?

A

Infection with Trypanosoma cruzi
damage to myenteric plexus
Megacolon and megaoesophagus
weight loss

26
Q

What is the effect of ACh?

A

Excitatory action on colonic smooth muscle

27
Q

What is the effect of adrenaline and noradrenaline?

A

Inhibitory action on colonic smooth muscle

28
Q

What is the role of the internal and smooth muscle sphincter?

A

Resting tone of anal canal
Usually contracted (sympathetic)
Relaxed by VIP/NO and presynaptic inhibition of sympathetic nerves
Uncontrolled contraction

29
Q

What is the function of the external anal striated sphincter?

A

Squeeze pressure
Motor drive from Onuf’s nucleus of the pudendal nerve
Increase in contraction from abdominal pressure rise
Consciously choose to contract

30
Q

What is the function of the puborectalis?

A

Forms a sling around anal canal
Changes the angle between rectum and anal canal

31
Q

What is defaecation?

A

Faeces enters and distends terminal segment after mass movement

32
Q

How is the rectum contracted?

A

By +ve feedback

33
Q

How is the internal anal sphincter relaxed?

A

Recto anal inhibitory reflex - role of NO

34
Q

What gives rise to sensation of urge?

A

Distension

35
Q

What is defaecation controlled by?

A

External anal sphincter and pelvic floor

36
Q

What causes faecal incontinence?

A

Obstetric injury
Damage to pudendal nerve

Digestion and Excretion (22 decks)

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