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Physiology Exam 3 - GI > Lecture 22 - Intro to GI System + Motility > Flashcards

Lecture 22 - Intro to GI System + Motility Flashcards

1
Q

Mastication

A
  • invoking the rhythmic movement of jaw, tongue, lips when food is int he mouth
  • increases the total surface area of food exposed to secretions
  • initially voluntary control - reflexly maintained through mouth tactile stimuli
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2
Q

Deglutation

A

= process by which bolus of liquid/masticated food is transported from mouth to stomach

  • involved: tongue, soft palate, pharyngeal wall, epiglottis, esophagus, etc.
  • extrinsic innervation from facial cranial nerves (VII), glossopharyngeal cranial nerve (IX), medial pterygoial nerve, vagus cranial nerve (X), hypoglossal cranial nerve (XII), lingual nerve
  • 3 phases
    1) oral phase
    2) pharyngeal phase
    3) esophageal phage
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3
Q

Oral phase of deglutation

A
  • voluntary elevation of tongue against hard palate of mouth
  • soft palate then raised - reflexly closing off nasopharynx (prevents passed of food into nose)
  • initiation of swilling = voluntary control –> once initiated = reflexly controlled
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4
Q

Pharyengeal phase of deglutation

A

= coordinated contraction of pharyngeal muscles + opening of UES –> food enters esophagus
- 3 mechanisms to block food entry into airways
A) elevation of larynx + close of glottis
B) downward tilt of epiglottis
C) cessation fo respiration
- UES constricts after food passed to prevent regurgitation

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5
Q

Esophageal phase of deglutation

A
  • peristalsis propels food toward LES + stomach funds
  • 2 types of peristalsis
    1) primary esophageal peristalsis = wave of contraction directly associated with the swallow
    2) secondary peristalsis = results from the dissension by residual bolus in the esophagus after 1st wave (can also be do to flux of gas or gastric contents
  • during peristaltic wave (before bolus arrival) at LES –> it opens to allow food to enter stomach + contraction after prevents reflux
  • liquids can move towards stomach by gravity ahead of the wave
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6
Q

Chyme

A

= liquified, partially digested food

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7
Q

Peristalsis

A

= coordinated wave of contraction over relatively long distance

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8
Q

characteristics of esophageal peristaltic wave

A
  • veloctiy = 3-5cm/sec
  • reaches LES in 5-10 seconds after swallowing
  • Esophageal pressures can range from 30–>120mmHg
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9
Q

Three mechanisms that prevent food from entering into airway

A

1) elevation fo larynx + closure of glottis
2) downward tilt of esophagus
3) cessation of respiration

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10
Q

Control/Innervation of deglutination

A

= reflex process coordinated by swallowing center in medulla following voluntary initiation of swallowing

  • sensory afferent inputs = CN IX, CN X (glossopharyngeal + vagal)
  • main efferents = vagal nerve fibers –> directly innervate skeletal muscle in ICL + OLL of upper 1/3 of esophagus
  • -> stimulation here initiates peristalsis
  • rest of GI through colon has smooth muscle in the ICL + OLL
  • Vagus innervates myenteric plexus (Auerbach’s plexus) in between those smooth muscle layers (not the smooth muscle directly)
  • here it influences the coordination and force of the wave
  • the propagation of the wave is principally dependent on the plexus ( if plexus is damaged and w/o innervation - an initiated wave can proceed but it occurs in uncorrelated contractions + is not effective in food propulsion
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11
Q

Control of LES opening/closing

A
  • LES has basic myogenic tone under neural + possible hormonal control (tonic pressure is higher than that of the stomach fundus)
  • following swallow - peristalsis at any level of esophagus is sufficient to cause inhibition of myogenic tone + opening of LES
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12
Q

Neural control of LES

A

+) Vagal Excitatory influence on postganglionic neurons in myenteric plexus

  • via nicotinic receptors
  • post ganglionic fibers release Ach –> muscarinic receptors
  • ) Vagal inhibitory influence on postganlionic neurons in myenteric plexus
  • via nicotinic receptors
  • postganglionic fibers release VIP + NO
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13
Q

Hormones affecting LES

A
  • increased progesterone (during pregnancy) –> decrease LES tone –> causing “heartburn”
  • sympa nerves stimulation –> causes contraction of LES - but have little effect of LES tone - may participate in reflex reactions
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14
Q

What are the 5 functions associated with gastric motility

A

1) Receptive relaxation
2) Stress relaxation
3) Gastric peristalsis
4) Gastric emptying
5) Migrating Myoelectric complex

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15
Q

1) Receptive relaxation

A

= neurally mediated receptive relaxation allow stomach to fill

  • immediately after relaxation of LES - fundus + body of stomach relax
  • coupled to LES relaxation
  • controlled by myenteric plexus + vagus
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16
Q

2) Stress relaxation

A
  • smooth muscle fibers lengthen under mechanical stress
  • receptive + stress relaxation –> minimize large increase in internal gastric pressure
  • allow proximal stomach to accept large volumes of food
17
Q

3) Gastric peristalsis

A
  • stomach antrum displays periodic peristaltic contractions when distended by food (drives chyme towards pylorus)
  • when empty it does contract occasionally but vigorous activity doesn’t occur
18
Q

4) Gastric emptying

A
  • time depends on meal, emotional state, etc.
  • average is 3% emptying per minute
  • governed by size of food particles relative GI pressures - which are controlled by mechano, chemo-receptors, hormones, reflex arcs –> long (vago-vagal) + short (myenteric)
  • duodenum distension –> decreases stomach emptying = entero-gastric reflex
19
Q

entero-gastric reflex

A

= duodenal distension inhibits stomach emptying

20
Q

Control of gastric peristalsis

A

= distension + vagal activity –> increase the spike activity - don’t effect the BER frequency
- Gastrin –> triggers Ach release from nerve endings in stomach –> increases the spike frequency

21
Q

5) Migrating myoelectric complex

A

= occasional intense peristaltic contractions every 75-90min during inter-digestional periods

  • propagated from stomach to small intestines + along entire length of small intestine
  • serve “house-keeping” role sweeping residual food particles, secretions bacteria out of GI tract
  • contractions = associated with abdominal gurgling = borborygmi (associated with ulcers too)
  • coupling here between MMC in stomach + intestine vs. slow waves of gastric peristalsis (are not transmitted to small intestine
  • motility in fed state is not coupled
  • motilin - has a role initiating the MMC
22
Q

Borborygmi

A

= gurgling sound associated with with the contractions of the MMC during and inter-digestional period

23
Q

Motilin

A

= AA peptide hormone - produced in proximal small intestine

- has role in initiating the MMC

24
Q

BER of the stomach

A

+ basal electrical rhythm of stomach due to pacemaker activity of interstitial cells of Cajal in the OLL smooth muscle layer
- Pacemaker firing = 3-4/min –> initiates slow wave depolarization that are propagated toward the pyloric sphincter along smooth muscle
- occurs in body + strum of stomach (not in esophagus or fundus)
- conducted to + propagated by cells in smooth muscle layers (not by myenteric plexus or neurons)
- defines the frequency + direction of stomach contractions
= slow wave depolarizations that are sub threshold –> necessary but not sufficiency for contraction (gastric antral peristalsis)

During fed state

  • AP “spikes” (due to distension/neuro/hormonal stimulation) –> bring the slow wave depolarizations to threshold
  • -> initiate a contraction
  • they are phase locked to BER frequency - only occur during depolarized phase of slow wave potentials
  • Both the SWDs and AP spikes are required for contractility associated with gastric peristalsis

As peristaltic wave moves along atrium toward pyloric sphincter

  • pressure on chyme bolus incerases
  • pyloric sphincter tone = very high (only a mslal amount of food goes through - rest stays in stomach)
  • increase the pressure onf chyme during contraction –> resulting in retropulsino towards anterior stomach = shearing forces
  • -> the mechanical chyme homogenization (through this forward and retrograde movements in contracting part of antrum)
25
Q

Segmentation contractions

A

= occur due to small intestine filling with food
= locall, short-lived contractions –> divide the intestine into short segments
- homogenization of chyme
- results in backwards and foreword movements of chyme –> mixing it with secretions + exposing it to absorptive surface of intestinal mucosa

26
Q

BER of small intestine

A

= has a distinctly different frequency from the stomach

  • 12/min in duodenum
  • 8/min in ileum
  • SWDs = sub threshold but dissension from food + neuro/hormonal action –> cause the threshold due to AP spikes –> increase tension development
  • spike are phase lock to intestinal BER (intestinal BER determines MAX contractile frequency)
  • incerase in BER frequency = decrease in contractile frequency along the intestine length
  • frequency of duodenal BER > frequency of antral BER (therefore the two cannot be directly coupled - intestine has its own pacemakers)
  • max frequency of segmentation contractions in duodenum > than that in ileum
  • -> presure gradient tending to move food arboreally
  • muscle thickness proximally > muscle thickness distally ==> more forceful contractions proximally
27
Q

ileocecal valve

A

= sphincter between large + small intestine

  • under control of myenteric plexus
  • normally closed
  • contraction of ileum near sphincter –> relaxes it
  • increased gastric activity relaxes it (gastro-ileal reflex)
  • distension of cecum –> contracts the sphincter
28
Q

gastro-ileal reflex

A

= increased gastric activity relaxes the ileocecal valve

29
Q

2 dominant types of contractions in the large intestine

A

1) haustra contractions
= annual constrictions leading to sacculations known as haustra
- slice through fecal material - exposing new surface areas for residual water + electrolytes absorption
- accomplishes most of movement of feces through colon
2) peristalsis
- propels fecal material towards sigmoid colon
- segmentatal contractions of rectum tend to propel any contents retrograde into colon (hence rectum = usually empty)

30
Q

gastro-colic relex

A

= in infants –> after feeding - urge to defecate

31
Q

sweeping contractions along sigmoid colon

A
  • occurs four times per day –> fills rectum –> defecation urge

Physiology Exam 3 - GI (1 decks)

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