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MD3002 Physiology > GI tract motility > Flashcards

GI tract motility Flashcards

1
Q

What is the primary purpose of incisor teeth?

A

Cutting

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2
Q

What is the primary purpose of the molar teeth?

A

Grinding

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3
Q

What is the majority of chewing muscle innervated by?

A

5th cranial nerve

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4
Q

What part of the brain controls mastication?

A

Brain stem nuclei

  • Reticular areas for rhythmical chewing
  • Additional involvement from hypothalamus/amygdala/cerebral cortex
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5
Q

What acts as a lubricant in the mouth?

A

Mucin (glycoprotein)

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6
Q

What digestive enzymes is food mixed with?

A
  • Carbohydrate with salivary amylase for carbohydrate digestion
  • Fat with lipases for lipid digestion
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7
Q

Describe the 3 stages of swallowing/deglutition

A
  1. Has a voluntary stage: initiates the swallowing process;
  2. A pharyngeal stag: is involuntary passage of food through the pharynx into the oesophagus
  3. An oesophageal stage; is involuntary transport of food from the pharynx to the stomach
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8
Q

Desribe the 4 swallowing steps

A
  1. When ready for swallowing, food is voluntarily moved posteriorly into the pharynx
  2. Trachea is closed
  3. Oesophagus is opened
  4. A fast peristaltic wave initiated by the NS of the pharynx forces the bolus of food into the upper oesophagus
    - All in < 2 seconds
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9
Q

How is the pharyngeal stage initiated?

A

Almost always voluntary movement of food into the back of the mouth
- Detected in ring area around the pharyngeal opening, excitation of involuntary pharyngeal sensory receptors to elicit the swallowing reflex

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10
Q

What nerves stimulate motor impulses from the swallowing centre to the pharynx and upper oesophagus?

A

5th, 9th, 10th, 12th cranial nerves (+ few superior cervical nerves)

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11
Q

How long is the pharyngeal stage?

A

< 6 seconds
- Interrupts respiration for fraction of usual respiratory cycle (swallowing centre specifically inhibits respiratory centre of medulla)

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12
Q

What are the 2 types of peristalsis?

A
  • Primary
    Continuation of peristaltic wave that begins in the pharynx and spreads into the oesophagus during the pharyngeal stage of swallowing
  • Secondary
  • result from distention of the oesophagus by retained food
  • Waves continue until all food has emptied into the stomach
  • Are initiated partly by:
  • Intrincic neural circuits in myenteric nervous system
  • By reflexes that begin in pharynx
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13
Q

What is the upper oesophagus innervated by?

A
  • Skeletal nerve impulses from the:

Glossopharyngeal, vagus nerve

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14
Q

What is the lower 2/3 of the oesophagus innervated by?

A

VAgus nerves that act through connections with the oesophageal myenteric nervous sytem

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15
Q

What wave precedes peristalsis and what is it transmitted via?

A
  • Relaxation wave
    Transmitted via myenteric inhibitory neurons
    Relaxes gastroesophageal sphincter and entire stomach
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16
Q

What part of the oesophageal circular muscle acts as a sphincter?

A

Last 3cm

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17
Q

What are the motor functions of the stomach?

A
  1. Storage of large quantities of food
  2. Mixing foos with gastric secretions until it forms a semifluid mixture (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
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18
Q

What does the food entering the stomach form in the orad portion of the stomach?

A
  • Concentric circles
  • Newest food lying closest to oesophageal opening
  • Oldest food lying nearest to the outer wall of stomach
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19
Q

What is the ‘vagovagal’ reflex?

A

Food stretches stomach -> Stomach -> brain stem -> back to stomach ->

  • Decreased tone in stomach body muscular wall
  • Wall bulges progressively outward
  • Greater quantities food accomodated (up to a limit ~0.8-1.5 litres)
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20
Q

What are mixing waves?

A
  • Weak peristaltic constrictor waves
  • Begin in the mid/upper portions of the stomach wall
  • Move towards antrum every ~15-20s
  • Initiated by gut wall basic electrical rhythm
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21
Q

Where are the mixing waves strongest?

A
  • More intense in antrum

- Force the antral contents under higher and higher pressure towards pylorus

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22
Q

What triggers emptying of the stomach?

A

Stretching of stomach walls

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23
Q

What are the enterogastric inhibitory reflexes?

A
  1. Distention of duodenum
  2. Presence of any irritation of the duodenal mucosa
  3. Acidity/osmolarity of duodenal chyme
  4. Presence of certain digestion products in chyme eg from proteins/fats
24
Q

What is the effect of increased stomach volume on gasric emptying?

A

Increased gastric emptying

25
Q

What are the hormonal regulating factors ?

A
  • Stimulus mainly fats

- CCK most potent hormone

26
Q

What does chyme induce on the GI wall?

A

Induces extension of GI wall -> stretch -> localised concenteric contractions (spaced along intestine, short lasting) -> segmentation

27
Q

What is the frequency of segmentation determined by?

A

Frequency of slow waves

28
Q

When do segmental contractions become weak?

A
  • When excitatory activity of the enteric nervous system is blocked by atropine
29
Q

What is the main source of background excitation that cause segmental contractions?

A

The myenteric nerve plexus

30
Q

What is the highest slow wave frequency?

A

~ 12 per min

31
Q

What is the speed of peristalsis in the small intestine?

A

0.5-2cm/s

Becomes slower as it moves down SI

32
Q

How long does it take usually for chyme to pass from the pyloris to ileocecal valve?

A

3-5 hrs

33
Q

What is the net movement of chyme in the SI?

A

1cm/min

34
Q

Why is peristalsis increased after a meal?

A
  • Entry of chyme into duodenum -> stretch of duodenum wall
  • Gastroenteric reflex (from stomach distension via myenteric plexxus)
  • Gastrin, CCK, insulin, motolin, serotonin
    Secretin, glucagon decrease motility
35
Q

What can cause peristaltic rush?

A
  • Mucosal irritation with infectious diarrhea
  • Initiated by nervous reflexes
    Autonomic/brainstem + intrinsic myenteric plexus reflexes
36
Q

How is the ileocecal valve closed?

A

When excess pressure builds up in cecu and tries to push cecal contents backwards against the valve lips

37
Q

Immediately after a meal what happens to the gastroileal reflex?

A

Intensifies peristalsis in ileum -> emptying of ileal contents into cecum

38
Q

What does pressure and chemical irritation do to the ileocecal sphincter?

A

Relaxes it and excites peristalsis

39
Q

How much chyme enters the caecum after absorption each day?

A

1.5 - 2 L each day

40
Q

What do reflexes from the cecum control?

A
  • Degree of contraction of ileocecal sphincter

- Intensity of peristalsis in the terminal ileum

41
Q

What does a distended cecum lead to?

A

Contraction of ileocecal sphincter intensified, ileal peristalsis is inhibited
- Greatly delay emptying of additional chyme into cecum from ileum

42
Q

What effect can irrant(s) in the cecum have to emptying?

A
  • Delays emptying
  • Inflammed appendix can cause intense spasm of the ileocecal sphincter and partial paralysis of the ileum -> block emptying of ileum into cecum
43
Q

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

A

Myenteric plexus and extrinsic autonomic nerves

44
Q

What si the intrinsic defecation reflex mediated by?

A

Rectal enteric NS

45
Q

What are the 2 defecation reflexes?

A 
- Intrinsic 
Mediated by rectal enteric NS 
- Parasympathetic defecation reflex 
Fortifies intrinsic reflex 
Involves sacral segments of spinal cord
46
Q

What reflexes facilitate mass movements after meals?

A
  • Gastrocolic and duodenocolic reflexes

- Result from distention of the stomach and duodenum

47
Q

What happens to the gastrocolic and duodenocolic reflexes when extrinsic autonomic nerves to the colon are removed?

A
  • They occur not at all or hardly at all

- Almost certainly are transmitted via autonomic nervous system

48
Q

Waht can irritation of the colon initiate?

A

Mass movements

49
Q

What does a distended caecum result in?

A

Contractions of ileocecal sphincter becoming intensified, ileal peristalsis inhibited

50
Q

What are the main functions of the colon?

A
  • To absorb water and electrolytes from chyme

- Store fecal matter unti lit is ready to be expelled

51
Q

What are Haustrations?

A
  • Mixing movements in the colon (bag-like buldges)
  • Similar to smal intestine segmenttion contractions can restrict colon to occlusion
  • Longitudinal muscle strips can also contract
52
Q

How much water is lost in the feces?

A

80 - 200 ml

53
Q

What are propulsive ‘mass movements’ 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
54
Q

How long do the series of mass movements persist for?

A

~10-30 min then caese but return

55
Q

When is the desire for defecation felt?

A

When faeces enters into the rectum

MD3002 Physiology (24 decks)

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