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MD3002 - GI Physiology > GI Tract Motility > Flashcards

GI Tract Motility Flashcards

1
Q

What is required for optimum functioning of the GI Tract?

A
  • timing of mixing
  • appropraite mixing
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2
Q

What is the function of incisor teeth?

A

cutting

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3
Q

What is the function of molar teeth?

A

grinding

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4
Q

What nerve is the majority of chewing innervated by?

A

5th cranial nerve

trigeminal

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5
Q

How does the brain stem nuclei control chewing?

A
  • reticular areas for rhythmical chewing
  • additional involvement from hypothalamus/amygdala and cerebral cortex
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6
Q

What are the main functions of chewing

A
  • mixes food with saliva
  • reduces sizes of food particles to facilitate swallowing
  • mixes food components with digestive enzymes
    • amylase and lipases
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7
Q

What acts as the main lubricant in the mouth?

A

mucin (glycoprotein) acts as a lubricant

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8
Q

What is required of the pharynx for swallowing?

A

requires pharynx to be a tract for propulsion of food; ensure food goes into the oesophagus not the lungs (respiration should not be compromised)

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9
Q

What are the 3 stages of swallowing?

A
  1. voluntary stage: initiates swallowing process
  2. pharyngeal stage: passage of food through pharynx into the oesophagus
  3. oesophgeal stage: involuntary transport of food from the pharynx to the stomach
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10
Q

What are the 4 main steps in swallowing?

A
  1. When ready for swallowing, food is voluntarily moved posteriorly into the pharynx

Next steps are almost automatic:

  1. The trachea is closed
  2. oesophagus is opened
  3. Fast-peristaltic wave intiiated by the nervous system of the pharnyx forces the bolus of food into the upper oesophagus

All in < 2 seconds

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11
Q

What intiates the pharyngeal stage of swallowing?

A
  • primarily a reflex act
  • voluntary movement of food to the back of the mouth
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12
Q

What elicits the swallowing reflex?

A

involuntary pharyngeal sensory receptors

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13
Q

What occurs following the activation of the involuntary pharyngeal sensory receptors in the swallowing reflex?

A
  • next stages are initiated by neuronal areas of the reticular substance of the medulla and lower portion of the pons (deglutition centre)
  • motor impulses from the swallowing center to the pharynx and upper oesophagus that cause swallowing are transmitted successively by the 5th, 9th, 10th, 12th cranial nerves (+ few superior cervical nerves)
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14
Q

What is the time frame of the pharyngeal stage of swallowing? And what is the implication of this?

A

occurs in < 6 seconds

interrupts respiration for a fraction on the usual respiratory cycle

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15
Q

What is the action of the swallowing centre on the respiration centre during eating?

A

Swallowing center specifically inhibits the respiratory center of the medulla during this time ie halts respiration

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16
Q

What is 1º peristalsis

A
  • Simple continuation of peristaltic wave that begins in the pharynx and spreads into the esophagus during the pharyngeal stage of swallowing.
  • Wave passes from pharynx to stomach in ~ 8-10s.
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17
Q

What is 2º peristalsis?

A
  • Result from distention of the oesophagus by retained food.
  • Waves continue until all food has emptied into the stomach.
  • Are initiated partly:
    • by intrinsic neural circuits in myenteric nervous system
    • by reflexes that begin in pharynx
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18
Q

What controls the peristaltic waves in upper/striated regions?

(upper 1/3)

A

controlled by skeletal nerve impulses from glossopharyngeal and vagus nerves

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19
Q

What controls the peristaltic waves in smooth muscle regions?

(lower 2/3)

A

controlled by vagus nerve that acts through connections with the oesophgeal myenteric nervous system

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20
Q

What does the relaxation wave precede?

A

peristalsis

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21
Q

What intiates the relaxation wave?

A

transmitted by myenteric inhibitory neurons

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22
Q

What occurs as a result of the relaxation wave?

A

Entire stomach becomes relaxed in preparation for food arrival

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23
Q

What functions as the oesophgeal sphincter?

A

last 3cm of oesophgeal circular muscle (gastroeophgeal sphincter)

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24
Q

What is the normal state of the oesophgeal sphincter?

A

tonically constricted

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25
Q

What is the functipn of ‘receptive relaxation’?

A

allows easy propulsion of food into the stomach

26
Q

What are the 3 motor functions of the stomach?

A
  1. Storage of large quantities of food until it can be processed in the stomach, duodenum and lower intestinal tract;
  2. Mixing of food with gastric secretions until it forms a semifluid mixture (ie chyme);
  3. (Slow) emptying of chyme from stomach into the small intestine at a rate suitable for proper digestion and absorption by the small intestine.
27
Q

How does food entering the stomach behave?

A
  • forms concentric circles in orad portion of the stomach
    • newest food lying cloestes to oesophgeal opening
    • oldest food lying nearest the outer wall of the stomach
28
Q

What is the chain reaction following food stretching the stomach

A

Food stretches stomach–> “vagovagal
refex” (stomach->brain stem-> back to the stomach)èêtone in stomach body muscular wall –> wall bulges progressively outward –> greater quantities food accommodated (up to a limit: ~0.8-1.5 litres.

29
Q

Where do mixing waves begin and how often do they occur?

A

begin in the mid/upper portions of the stomach walls, move toward antrum every ~15-20s

Initiated by gut basic electrical rhythm

30
Q

What happens to mixing waves are you move through the stomach?

A

body –> antrum

waves become more intense and force the antral contents under higher and higher pressure towards the pylorus

31
Q

Explain how the peristaltic waves are responsible for mixing stomach contents

A

antral contents are squeezed upstream through the peristaltic ring, towards body of stomach, not through pylorus

retropulsion = Important mixing mechanism

32
Q

What is emptying of the stomach promoted by?

A

promoted by intense persitaltic contractions in stomach antrum

33
Q

What is emptying of the stomach opposed by?

A

pylorus

degree of constriction is under the influence of the nervous system and hormonal signals from stomach and duodenum

34
Q

Explain the gastric and duodenal regulating factors of the stomach

A
  • increased stomach volume = increased gastric emptying
  • Enterogastric inhibitory reflexes:
  1. Distention of duodenum
  2. Presence of any irritation of the duodenal mucosa
  3. Acidity/osmolality of duodenal chyme
  4. Presence of certain digestion products in chyme eg from proteins/fats
35
Q

What are the hormonal regulating factors that contorl empyting the stomach?

A

– Stimulus mainly fats.
– CCK most potent hormone.

36
Q

What are the 2 main movements of the small intestine?

A
  • Mixing contractions – segmentation contractions
  • Propulsive movements - peristalsis
37
Q

Describe segmentatation contractions of the small intestine

A

chyme induced extension of GI wall → stretch → localised concentric contacted (spaced along intestine, short lasting) → segmentation

38
Q

What is the frequency of segmentation determined by?

A

frequency of slow waves

39
Q

When do segmentation contractions become weak?

A

when the excitatory activity of the enteric nervous system is blocked by atropine

40
Q

Where do propulsive movements occurs?

A

any part of the small intestine

41
Q

What is the rate of peristalsis?

A

move towards anus at 0.5-2cm/s

Faster in proximal SI; slower in terminal SI

42
Q

How quickly do propulsive movements die out?

A

Weak and die out after 3-5cm. Rarely >10cm

43
Q

Describe the net movement of chyme

A

SLOW (1cm/min)

Chyme pylorus to ileocecal valve = 3-5hr

44
Q

What occurs to peristalsis activity after we eat a meal?

A
  • Activity increased after a meal:
    • Entry of chyme into duodemum → stretch of duodenum wall
    • Gastroenteric reflex (from stomach distension via myenteric plexus)
    • Gastrin, CCK, insulin, motolin, serotonin
      • (Secretin, glucagon decrease motility)
45
Q

What can cause a peristaltic rush? - powerful, rapid peristalsis

A
  • mucosal irritation by infectious diarrhoea
  • initiated by nervous reflexes
    • autonomic/brain stem + intrinsic myenteric plexus reflexes
46
Q

Describe the location and action of the ileocecal valve

A

Valve protrudes into lumen of cecum, is forcefully closed when excess pressure builds up in cecum and tries to push cecal contents backward against the valve lips.

47
Q

What pressure can the ileocecal valve resist?

A

Usually can resist reverse pressure of 50-60cm water.

48
Q

What is the normal contraction of the ileocecal sphincter

A

remains mildly constricted and slows emptying of ileal contents into the cecum.

49
Q

What occurs at the ileocecal sphincter immediately after a meal?

A

Immediately after a meal, gastroileal reflex intensifies peristalsis in ileum ⇒ emptying of ileal contents into cecum.

50
Q

What do reflexes from the caecum control?

A

– degree of contraction of ileocecal sphincter
– the intensity of peristalsis in the terminal ileum

51
Q

What is the result of a distended caecum?

A

contraction of ileocecal sphincter intensified, ileal peristalsis is inhibited

=> greatly delay emptying of additional chyme into cecum from ileum.

52
Q

What delays emptying of the caecum?

A

Irritant(s) in the cecum

eg inflamed appendix can cause intense spasm of the ileocecal sphincter and partial paralysis of the ileum ⇒ block emptying of ileum into cecum.

53
Q

What are Cecum-to-ileocecal sphincter and cecum-ileum reflexes mediated by?

A

myenteric plexus and extrinsic autonomic nerves.

54
Q

What are the mixing movements in the colon?

A

“Haustrations” ie bag-like bulges

Similar to small intestine segmentation
+
Longitudinal muscle strips contraction contract

55
Q

How are the propulsive movements of the colon described?

A

mass movements

56
Q

Give the 6 steps of modified peristalsis in the colon

A
  1. First, a constrictive ring occurs (usually in transverse colon) in response to distension.
  2. The ~20+cm of colon distal to constrictive ring lose haustrations and contract as a unit.
  3. Fecal material moves en masse down the colon.
  4. Contraction develops progressively more force for ~30s
  5. Relaxation occurs during next 2-3 mins.
  6. Another mass movement occurs, perhaps farther along the colon.
57
Q

How long does a series of mass movements persist for?

A

~10-30mins

58
Q

What is the function of gastrocolic and duodencolonic reflexes? and when do they occur?

A

Facilitate mass movements after meals.

  • Result from distention of the stomach and duodenum.
  • Occur either not at all or hardly at all when extrinsic autonomic nerves to the colon have been removed;

– . ̇. almost certainly are transmitted via autonomic nervous system.

• Irritation in the colon can also initiate intense mass movements.

– eg with ulcerated condition of colon mucosa (ulcerative colitis), mass movements that persist almost all the time can occur.

59
Q

What is the intrinsic defecation reflex?

A

Mediated by rectal enteric NS

60
Q

What is the action of the PSNS defecation reflex>

A

– “Fortifies” intrinsic reflex
– Involves sacral segments of spinal cord.

61
Q

What is the normal content of faces in the rectum?

A

empty of faces

62
Q

What prevents the loss of feacal matter?

A

constricted internal-external sphincter

MD3002 - GI Physiology (4 decks)

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