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Physiology I > W13 - GI system I (5.2, 5.3) > Flashcards

W13 - GI system I (5.2, 5.3) Flashcards

1
Q

List the mechanical functions of motility.

A
  • grinding = increasing surface area
  • storage = slows down propulsion for optimized digestion/absorption
  • mixing = renewal of surface
  • propulsion
  • reflux inhibition
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2
Q

What are slow waves?

Function?

A

continuous fluctuation of membrane potential generated by interstitial cells of Cajal to propagate electric activity via gap junctions to nearby long./circ. muscle layer

⇒ constitute tonic/basal contractivity of GI tract

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3
Q

Describe the generation of slow waves.

(7 steps)

A
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4
Q

How are APs generated in the GI tract?

Function?

A

if temporal summation of slow waves occurs and threshold is reached → depolarization due to opening of Na+ and Ca2+ channels

⇒ constitues phasic contraction of GI tract for propulsion

<u>NOTE:</u> force of contraction incr. with incr. AP frequency

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5
Q

What are the main functions of the oral cavity?

A
  • mastication
  • swallowing
  • lubrication of food
  • sampling of food for pathogen’s (Waldeyer’s lymphatic ring)
  • vocalization
  • taste
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6
Q

What are the 2 types of teeth which mainly contribute to mastication?

Function.

A
  • incisors → cutting
  • molars → grinding

⇒ increase surface area of ingested food, facilitated swallowing

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7
Q

Explain the reflex mechanism of mastication.

BUT… ?

A

cycles of reflex inhibition of muscles → jaw drops
and
stretch reflex → contraction

​BUT: can also be initiated voluntarily

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8
Q

How is swallowing done?

A

in 3 phases, only first phase is voluntary

  • oral phase
  • pharyngeal phase
  • esophageal phase
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9
Q

What happens in the oral phase of swallowing?

A

tongue pushes bolus back against soft palate/back of mouth containing somatosensory receptors

⇒ trigger swallowing reflex

NOTE: only voluntary phase of swallowing

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10
Q

What happens in the pharyngeal phase of swallowing?

A
  • upper esophageal sphincter relaxes while airways are closed to keep swallowed material out
  • stimulation of epithelial swallowing receptor area cause autonomic contractions of pharyngeal muscle

⇒ preciously timed

<u>also:</u> vocal cords approximate, palatopharyngeal folds pulled med. so only small food particles can pass

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11
Q

What happens in the esophageal phase of swallowing?

A

food moves downward into the esophagus, propelled by peristaltic waves + aided by gravity

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12
Q

Differentiate btw primary and secondary peristalsis.

Where can it be seen?

A

during esophageal phase of swallowing

  • primary peristalsis: continuation of peristaltic wave originating in pharynx
  • secondary peristalsis: results from distension of esophagus
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13
Q

How is swallowing terminated?

A

receptive relaxation of lower esophageal sphincter + proximal stomach

= wave of relaxation transmitted by myenteric inh. neurons (VIP) + vagovagal reflex

NOTE: precedes peristalsis (obv)

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14
Q

How does the pressure during swallowing change in the upper GI tract?

A

stimulation of the pharynx in the presence of a bolus initiates

  • ↓P (= opening) of the upper esophageal sphincter
  • ↓P of the lower esophageal sphincter to prepare for entry of food

peristaltic wave of contraction along the esophagus
(progressively incr. P)

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15
Q

Describe the symptoms of achalasia.

How is it treated?

A

= lower esophageal sphincter fails to relax

consequences:

  • enlargement of esophagus → infections
  • reflux = regurgitation → esophagitis

can be resolved surgically

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16
Q

What are the 3 main functions of gastric motility?

A
  • storage of ingested food - 1.5l
  • grinding and mixing of the food w/ gastric secretion
  • slow/controlled emptying of chyme into duodenum
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17
Q

What are the functions of the fundus and proximal stomach?

A

reservoir function

stable membrane potential → no phasic contractions

  • receptive relaxation before filling
  • adapative relaxation during filling

⇒ tonic activity reestabilished after meal

18
Q

What are the functions of the distal stomach?

A

grinding, mixing, fractional propulsion

slow waves begin spontaneously in the middle of the stomach → constrictive rings pass down to antrum

19
Q

Which substances incr., resp. decrease the contractive force of gastric propulsions?

A
  • incr.: gastrin, vagal activity (parasymp.)
  • decr.: CCK, NE (symp.)
20
Q

Describe the function of the pyloric pump.

A
  1. propulsion: progressively stronger propulsive contractions push bolus towards pylorus
  2. grinding: antrum grinds trapped material
  3. retropulsion: pyloric sphincter allows passage of fluids/particles < 2mm, bigger particles pushed back into proximal stomach
21
Q

Which factors can slow the rate of gastric emptying?

Mechanism?

A
  • acidity
  • high fat content → CKK, GIP
  • hypertonicity ​

⇒ cause entero-gastric reflex via chemoreceptors: directly ↓ gastric emptying or via ↑ symp. output

22
Q

Which factors increase the rate of gastric emptying?

A
  • incr. food volume → distension of stomach wall
  • release of gastrin from antral mucosa
23
Q

Explain the physiology of vomiting.

A
  1. retching
    • ​​antiperistalsis: contraction of stomach/duodenum
    • contraction of diaphragm/abs → ↑↑ intragrastric P, “inverted” swallowing, LES relaxes, UES closed
  2. expulsion: ​​after several retching cycles UES relaxes → expulsion
24
Q

What are the 2 types of movement of the GI tract?

A
  • segmental contraction
  • peristaltic contraction
25
Q

Describe the mechanism of segmental contraction.

Function?

A

distension of wall → stretching + contractions of circular muscle layer spaced at intervals

⇒ mixing of chyme

26
Q

Describe the mechanism of propulsive contraction.

Function?

A

contraction right behind bolus while muscle in front of bolus relaxes ⇒ peristaltic waves (1cm/sec)

→ propels chyme

27
Q

What does the law of the intestine state?

Mechanism.

A

= peristaltic reflex
⇒ contraction above and relaxation below a stimulated point in the intestine

  1. distension → EC cells to secrete 5-HT
  2. behind bolus: exc. transmitters released → contraction of circ. muscle, rel. of long. muscle
    in front of bolus: inh. transmitters released → contraction of long. muscle., rel. of circ. muscle

​describes the mechanism of propulsive contraction

28
Q

How is propulsive movement in the small intestine regulated?

A
  • enhanced by:
    • gastroenteric reflex (myenteric plexus)
    • gastrin, CCK, insulin
    • serotonin
    • motilin
  • decreased by:
    • ​secretin, glucagon
29
Q

What is important to mention when we talk about the 2 muscle layers of the GI tract?

A

reciprocally innervated

→ contract independently

30
Q

As a summary..

Which transmitters act excitatory, resp. inhibitory on GI muscle layers?

A
  • excitatory:
  • *ACh, substance P**
  • inhibitory:
  • *NO, ATP, VIP, PACAP**
31
Q

What are MMCs?

When and where do they occur?

A

migrating myoelectric complexes

motor activity of stomach/small intestine, faciliated by motilin ⇒ transportation of indigestible substances into the colon

every 90-120 min. during the interdigestive phase → responsible for the rumbling when hungry

32
Q

How is the ileocecal valve regulated?

Function?

A
  • closed in resp. to:
    • ​distension/irritation of cecum
    • reflexes (myenteric plexus, prevert. sympathetic ganglia)
  • opened in resp. to:
    • ​gastroileal reflex, gastrin
    • fluidity of contents (diarrhea)

​⇒ prevention of reflux + colonisation of small int. by bacteria

33
Q

What are the 2 main functions of the colon?

A
  • absorption of water/electrolytes
  • storage of fecal matter
34
Q

Which movements can be observed in the colon?

Where?

A
  • haustration: ascending - descending colon
  • antiperistalsis: ascending colon
  • mass peristalsis: transverse colon - sigmoid
35
Q

Define haustration.

Where does it occur?

Function?

A

in ascending - descending colon

  • slow segmenting, uncoordinated movements that occur ∽ every 25 minutes
  • done by circular muscle + taeniae coli

⇒ contributes to peristalsis (from haustrum to haustrum)

36
Q

What is antiperistalsis?

Where does it occur?

A

in ascending colon

peristalsis in upward direction

and during vomiting

37
Q

Where can mass peristalsis be seen?

How often does it happen daily?

A

in transverse colon - sigmoid

  • 1 - 3/day
  • tonic contraction of long (20cm) segments followed by relaxation for 2-3 min.
38
Q

Which reflexes can be seen in the colon?

Function?

A
  • gastrocolic/duodenocolic reflex:
    distension of stomach/duodenum → facilitate mass movements
  • colonocolic reflex:
    propells stool caudally by proximal muscle contraction and distal dilatation

both transmitted by ANS

39
Q

Describe the mechanism of the defecation.

A
  1. mass movement forces feces into rectum
  2. distension of rectal wall → rectocolic reflex: peristaltic wave in distal colon
  3. relaxation of int. anal sphincter
  4. vol. relaxation of ext. anal sphincter

⇒ rectal smooth muscle wall contracts, intra-abdominal pressure can be created with valsalva maneuver

40
Q

As a summary..

In which segments of the GI tract can tonic and propulsive contractions be observed?

A
  • tonic:
    in all sphincters, upper third of stomach
  • propulsive:
    esophagus, lower 2 thirds of stomach, small int., rectum
41
Q

What is the peristaltic rush?

Mechanism.

A

very powerful peristaltic movement which occurs when the intestinal mucosa is irritated intensely (e.g. by antigens, stress)

⇒ diarrhea

42
Q

What is a megacolon?

Causes?

A

severe constipation → enlargement of colon

e.g. due to

  • Hirschsprung’s disease (lack of myenteric plexus in a segment of sigmoid)
  • Chagas disease

Physiology I (10 decks)

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