W13 - GI system I (5.2, 5.3) Flashcards Preview

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Flashcards in W13 - GI system I (5.2, 5.3) Deck (42):
1

List the mechanical functions of motility.

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

2

What are slow waves?

Function?

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

3

Describe the generation of slow waves.
(7 steps)

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4

How are APs generated in the GI tract?

Function?

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

NOTE: force of contraction incr. with incr. AP frequency

 

5

What are the main functions of the oral cavity?

  • mastication
  • swallowing
  • lubrication of food
  • sampling of food for pathogen's (Waldeyer's lymphatic ring)
  • vocalization
  • taste

6

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

Function.

  • incisors → cutting
  • molars → grinding

⇒ increase surface area of ingested food, facilitated swallowing

7

Explain the reflex mechanism of mastication.

BUT... ?

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

BUT: can also be initiated voluntarily

8

How is swallowing done?

 

in 3 phases, only first phase is voluntary

  • oral phase
  • pharyngeal phase
  • esophageal phase

 

9

What happens in the oral phase of swallowing?

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

⇒ trigger swallowing reflex

NOTE: only voluntary phase of swallowing

10

What happens in the pharyngeal phase of swallowing?

  • 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

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

A image thumb
11

What happens in the esophageal phase of swallowing?

 

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

 

12

Differentiate btw primary and secondary peristalsis.

Where can it be seen?

during esophageal phase of swallowing

  • primary peristalsis: continuation of peristaltic wave originating in pharynx

  • secondary peristalsis: results from distension of esophagus

13

How is swallowing terminated?

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

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

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)

15

Describe the symptoms of achalasia.

How is it treated?

 

= lower esophageal sphincter fails to relax

consequences:

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

can be resolved surgically

16

What are the 3 main functions of gastric motility?

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

17

What are the functions of the fundus and proximal stomach?

reservoir function

stable membrane potential → no phasic contractions

  • receptive relaxation before filling
  • adapative relaxation during filling

⇒ tonic activity reestabilished after meal

18

What are the functions of the distal stomach?

grinding, mixing, fractional propulsion

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

19

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

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

20

Describe the function of the pyloric pump.

  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

Which factors can slow the rate of gastric emptying?

Mechanism?

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

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

22

Which factors increase the rate of gastric emptying?

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

23

Explain the physiology of vomiting.

  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

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

  • segmental contraction
  • peristaltic contraction

25

Describe the mechanism of segmental contraction.

Function?

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

⇒ mixing of chyme

26

Describe the mechanism of propulsive contraction.

Function?

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

→ propels chyme 

27

What does the law of the intestine state?

Mechanism.

= 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

How is propulsive movement in the small intestine regulated?

  • enhanced by: 
    • gastroenteric reflex (myenteric plexus)
    • gastrin, CCKinsulin
    • serotonin
    • motilin
  • decreased by:
    • secretin, glucagon

29

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

reciprocally innervated

 contract independently

 

30

As a summary..

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

  • excitatory:
    ACh, substance P
  • inhibitory:
    NO, ATP, VIP, PACAP

31

What are MMCs?

When and where do they occur?

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

How is the ileocecal valve regulated?

Function?

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

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

33

What are the 2 main functions of the colon?

  • absorption of water/electrolytes
  • storage of fecal matter

34

Which movements can be observed in the colon?

Where?

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

35

Define haustration.

Where does it occur?

Function?

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

What is antiperistalsis?

Where does it occur?

in ascending colon

peristalsis in upward direction

and during vomiting

37

Where can mass peristalsis be seen?

How often does it happen daily?

in transverse colon - sigmoid 

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

38

Which reflexes can be seen in the colon?

Function?

  • 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

Describe the mechanism of the defecation.

  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

As a summary..

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

  • tonic:
    in all sphinctersupper third of stomach
  • propulsive:
    esophagus, lower 2 thirds of stomach, small int., rectum

41

What is the peristaltic rush?

Mechanism.

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

⇒ diarrhea

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42

What is a megacolon?

Causes?

severe constipation → enlargement of colon

e.g. due to

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