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GIGU test! > Motillity of the Gastrointestinal Tract > Flashcards

Motillity of the Gastrointestinal Tract Flashcards

1
Q

What are the functional layers that make up the majority of the GI tract

A

Mucosal Layer

  • muscularis mucosae, consists of SM, its contractions change the shape and surface area of the epithelium
  • epithelium
  • Lamina propria

Submucosa

Muscle Layers (muscularis propria)

  • SM layers that provide motility to the GI tract
  • circular muscle
  • longitudinal muscle
  • myenteric plexus

Serosa
-near the blood

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2
Q

What are the two plexus in the GI tract that have control over the functional layers

A

Submucosal plexus

Myenteric Plexus

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3
Q

what are the functions of the circular and longitudindal muscle in the GI tract

A

Circular muscle: decreases the diameter of the segment

Longitudinal muscle: decreases the length of the segment

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4
Q

what are the two types of contractions that are key for motility in the GI tract

A

Phasic contractions: periodic contractions followed by relaxation

  • i.e. esophagus, stomach (antrum), SI and all tissues involved in mixing and propulsion
  • wave of muscle tension

Tonic contractions: maintain a constant level of contraction without regular periods of relaxation
-i.e. stomach (orad), lower esophageal, iliocecal, internal anal sphincters

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5
Q

What is the relationship between the slow waves, APs, and contractions in the smooth muscle

A

as a slow wave increase there is some muscle tension

as a action potential goes, there is much more muscle contraction

the more number of APs on a slow wave increase the size of contraction

however if their is no AP but there are some slow wave still will have muscle tension

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6
Q

what increases the number of APs in the GI tract?

A

1) stretch
2) Acetylcholine
3) Parasympathetics

all lead to depolarization

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7
Q

what decreases the number of APs in the GI tract

A

1) Norepinephrine
2) Sympathetics

all lead to hyperpolarization

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8
Q

what are the two plexus that make up the Enteric Nervous system and what do they each control

A

Submucosal Plexus

  • In the submucosa
  • mainly control GI secretions and local blood flow

Myenteric Plexus (Auerbachs)

  • between the circular and longitudinal SM layers
  • mainly control GI movements
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9
Q

What creates the pacemaker like slow wave activity in the GI smooth muscle

A

Pacemaker regions in the myenteric plexus generate spontaneous slow wave activity

these cells are the Interstitial cells of Cajal (ICC)

  • create the slow wave that spreads rapidly in the SM via the gap junctions
  • drives the frequency of contraction
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10
Q

What is important about mastication and what are the nerves that control this?

A

Important for breaking down the food with teeth and saliva

muscles of mastication are innervated are innervated by the motor branch of the 5th cranial nerve

Both voluntary and involuntary

controlled by nuclei in the brainstem

Mastication is caused by a chewing reflex

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11
Q

what are the three phases of swallowing

A 
Oral phase (voluntary
-initiates swallowing process

Pharyngeal phase (involuntary)

  • soft palate is pulled upward
  • epiglottis moves to cover trachea
  • UES relaxes
  • peristaltic wave of contraction is initiated in the pharynx
  • food is propelled through the UES

Esophageal phase (involuntary)

  • Controls by the swallowing reflex and the ENS
  • Primary peristalic wave
  • Secondary peristalic wave
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12
Q

What is the Involuntary swallowing reflex controlled by?

A

medulla

Afferent: sensory input of vagus/glossopharyngeal
-goes to swallowing center in medulla

then goes to brainstem nuclei

Efferent is in put to the pharynx

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13
Q

WHat are the two types of Peristalic waves?

A

Primary Peristalic wave:

  • Continuation of the pharyngeal peristalsis
  • controlled by the medulla
  • cannot occur after vagotomy

Secondary Peristalic wave:

  • occurs if primary wave fails to empty the esophagus or if gastric contents reflux into esophagus
  • Medulla and ENS are involved
  • Can occur in the absence of the oral and pharyngeal phases
  • Occurs even after vagotomy
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14
Q

What is significant about the pressure change of muscle as the bolus travels down the esophagus

A

the pressure will increase subsuquenty as a wave as the bolus moves down the esophagus until reach the LES and the fundus where the pressure will decrease since these need muscle relaxation to open the sphincter and expand the stomach to allow for food to enter

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15
Q

What are the two problems that the intrathoracic location of the esophagus runs into and how are they solved?

A
  • Keeping the air out of the esophagus at the upper end
  • keeping acidic gastric contents out of the lower end

these are solved by the UES and LES being closed unless a food bolus is passing

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16
Q

What is achalasia of the esophagus?

A

Impaired peristalis

  • Incomplete LES relaxation during swallowing
  • Elevation of LES resting pressure

this is due to decreased number of ganglion cells in the myenteric plexuses
-degeneration preferentially involves inhibitory neurons that produce NO/VIP

results in backflow of food int the throat (regurgitation)
also difficulty in swallowing liquids and solids (dysphagia)

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17
Q

How is the esophagus physiologically affected in Gastroesophageal reflux disease (GERD)

A

Changes in the barrier between the esophagus and stomach LES becomes weakens

  • abnormally low pressures in the LES
  • caused by pregnancy, largemeal, heavy lifting, due to iincrease intragastric pressures

Persistent reflux leads to inflammation and GERD

  • hearburn, acid regurgitation
  • gastrointestinal bleeding
  • esophagitis
  • scar tissue
  • Barretts esophagus
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18
Q

What are the functional divisions of the stomach

and what are the extrinsic and intrinsic innervation?

A

Two regions: orad and caudad

Extrinsic innervations: Parasympathetic and sympathetic

Intrinsic innervations: Myenteric and submucosal plexuses (ENS)

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19
Q

What occurs in the Orad region of the stomach, and how does it happen?

A

Receptive relaxation:

  • decrease pressure and increase volume of the orad region
  • Vagovagal reflex
  • CCK decreases the contractions and increases gastric distensibillity

Orad exhibits minimal contractile activity

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20
Q

What occurs in the Caudad region of the stomach?

A

Mix and Digestion

Primary contractile event is peristalitic contraction (mid stomach to pylorus)

  • contraction increase in force and velocity as it approaches the pylorus (decrease lag time)
  • max frequency is 3-5 min
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21
Q

If particles cant fit through the pyloric sphincter what happens

A

Retropulsion of the contents back to the mid stomach where the process repeats again

22
Q

What increases gastric contractions?

A

Parasympathetic stimulation

Gastrin and Motlin

all increase AP and the foce of contraction

23
Q

what slows down gastric contractions?

A

Sympathetic stimulation

Secretin and GIP

all decrease AP and force of contractions

24
Q

How does gastric emptying process increase via contractile activity of the stomach?

A
  • Decrease distensibillity of the orad stomach
  • increase force of peristalitic contractions of the caudad stomach
  • decrease tone of the pylurus
  • increase diameter and inhibition of segmenting contractions of the proximal duodenum
25
Q

How does gastric emptying process decrease via contractile activity of the stomach?

A
  • relaxation of orad (increase in distensibility)
  • decrease force of peristaltic contractions
  • increase tone of pyloric sphincter
  • Segmentation contractions in intestine
26
Q

What is the Entero-Gastric reflex?

A

Negative feedback from duodenum will slow down rate of gastric emptying

  • acid in duodenum stimulates secretin release to inhibit stomach motility via gastrin inhibition
  • fats in duodenum stimulate CCK and GIP to inhibit stomach motility
  • hypertonicity in duodenum will inhibit gastric emptying
27
Q

What is the slow gastric emptying and some of the causes?

A

also known as Gastroparesis
-slow emptying of the stomach leading to fullness, loss of appetite, nausea, and sometimes vomiting

causes: gastric ulcer, physical obstruction, eating disorders, vagotomy
Diabetes Mellitus

28
Q

what is the migrating Myoelectric complex/migrating mortor complex

A
  • Periodic bursting peristaltic contractions
  • Occur at 90 min intervals, during fasting
  • Help empy large undigested residue left in the stomach
  • inhibited during feeding
  • Motilin plays a significant role in the complex
  • Important at getting rid of small intestinal bacterial overgrowth (SIBO)
29
Q

How is motility important in the small intestine for digestive and absorptive functions?

A
  • Mix the chyme with digestive enzyme and pancreatic secretions
  • expose nutrients to the intestinal mucosa for absorption
  • Propel the unabsorbed chyme along the small intestine to the large intestine
30
Q

How does segmentation contractions affect the motility

A

Generates back and forward movements

Produces no forward propulsive movements along the small intestine

31
Q

how does peristaltic contractions affect the motility

A

Circular and longitudinal muscles works in opposition to complement each others actions
-are recipriocally innervated

help push things down the tract

32
Q

how do the slow waves in the Small intestine SM differ from slow waves in the stomach SM

A

Small intestine the slow wave activity does not generate muscle tone
-needs an AP on the top of a slow wave to generate muscle tension

33
Q

how does the slow wave frequency change throughout the small intestine?

A

overall decrease

Duodenum: 12 cycles a min
Jejunum: 10 cycles a min
ileum: 8 cycles a min

34
Q

what is the Hormonal control of the activities of the smooth muscle cells?

A

Contraction:

  • serotonin
  • prostaglandins
  • CCK
  • Motlin
  • Gastrin
  • insulin

INhibit contraction:

  • Epinephrine
  • secretin
  • glucagon
35
Q

What is the vomiting reflex and the events

A

Coordinated by medulla, nerve impulses are transmitted by vgus and sympathetic afferents to multiple brain stem nuclei

Events:

  • reverse peristalsis in small intestine
  • Stomach and pylorus relaxation
  • Forced inspiration to increase abdominal pressure
  • movement of the larynx
  • LES relaxation
  • Glottis closes
  • Forceful expulsion of gastric contents
36
Q

how does the flow of contents from the small intestine to the large intestine regulated by the ileocecal junction?

A

distention of the ileum causes relaxation of the sphincter and allows flow of contents from the ileum to the colon

Distention of the colon causes contraction of the sphincter and precents passage of contents from the colon to the ileum

37
Q

what innervates the internal anal sphincter?

what innervates the external anal sphincter?

A

internal = Pelvic splanchnic n (parasympathetic)

external = Pudenal N
-somatic motor fibers (voluntary)

38
Q

what are the 4 types of innervation of the Large intestine

A
  • ENS
  • Parasympathetic Nervous system
  • Sympathetic Nervous system
  • Somatic pudendal nerves
39
Q

what is the Parasympathetic innervation distribution on the large intestine?

A

Vagus nerve: Cecum, ascending and transverse colon

Pelvic Nerves (S2-S4): Descending and sigmoid colon, rectum

40
Q

what are the sympathetic nervous system innervation of the large intestine

A

T10-L2

Superior mesenteric ganglion: proximal regions

inferior mesenteric ganglion: Distal regions

hypogastric plexus: Distal rectum and anal canal

41
Q

what are the somatic pudendal nerves innervation distribution of the large intestine?

A

External Anal sphincter

42
Q

Motility in the large intestine is done in what way? and how does it affect absorption in both poor and excess motility?

A

Mass movements

occur in the colon over larger distances
-1-3 times a day

stimulate defecation reflex

A final mass movement propels the fecal content into the rectum

motility is key for absorption of water and vitamins and the conversion of digested food into feces

  • poor motillity causes greater absorption and lead to constipation
  • excess motillity leads to less absorption and diarrhea
43
Q

Motility of the rectum and the anal canal

A

Rectum fills intermittently

  • mass movements
  • segmentation contractions

as it fills with feces, SM wall of the rectum contracts and internal anal sphincter relaxes
-rectosphincteric reflex

the external anal sphincter is tonically closed (and is under voluntary control)

44
Q

Rectosphincteric reflex and what nerves is it under?

A

Under neural control

  • controlled by the ENS
  • reflex is reinforced by activity of neurons within the spinal cord

Sensation of rectal distention and voluntary control of the external anal sphincter are mediated by pathways within the spinal cord to the cerebral cortex
-destruction of these pathways causes loss of voluntary control of defecation

45
Q

what is Hirschsprung disease?

A

Cause: Ganglion cells absent from segment of the colon

result: VIP levels low and smooth muscle constriction and loss of coordinated movement therefore colon contents will accumulate
- colon equivalent to achalasia

present at birth and leads to congenital mega colon

  • failure to pass meconium
  • poor feeding, jaundice, vomitting, constipation
  • swollen bell, and malnutrition

treatment: surgical resection of colon segment lacking the ganglia

46
Q

Summary of reflexes: Vago-vagal reflex

A

long reflex, generally stimulatory that increases motility, secretomotor, vasodilatory activities
-vagus carries both afferents 75% and efferents 25%

47
Q

Summary of reflexes: Intestino-intestinal reflex

A

depends on the extrinsic neural connections

  • inhibitory if an area of the bowel is grossly distended
  • contractile activity in the rest of the bowel is inhibited
48
Q

Summary of reflexes: Enterogastric reflex

A

Negative feedback from duodenum will slow down the rate of gastric emptying

49
Q

Summary of reflexes: gastroileal reflex

A

gastric distension relaxes the ileocecal sphincter

50
Q

Summary of reflexes: gastro and duodeno-colic reflex

A

distention of stomach/duodenum initiates movements

-transmitted by way of the ANS

51
Q

Summary of reflexes: Defecation reflex

A

rectosphinteric

rectal distention initiates defecation

when the rectum is distended by feces, the internal sphincter relaxes

GIGU test! (40 decks)

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