Motility of the GI System

Question 1

Peristalsis in the GI tracts

Answer 1

Rhythmic contraction of the circular and longitudinal smooth muscle based on direction of movement.
Circular constricts behind, longitudinal constricts in front.

Question 2

Control of peristalsis by the ENS; example using the circular muscle

Answer 2

Baroreceptors, chemical sensory neurons activated, stimulating interneurons that synapse on motor neurons.
Behind - stimulatory (ACh, substance P)
In front - inhibitory (NO, ATP)

Question 3

Segmentation contractions

Answer 3

Section of the SI contracts to propel chyme in two directs, then relaxing so that it moves back together. Mix without net movement, incoprporating digestive enzymes and facilitating contact with epithelial cells.

Question 4

3 cells involved in GI motility patterns

Answer 4

Smooth muscle cells
Interstitial cells
Enteric motor neurons
- All electrically coupled, act as a functional unit. modulated by hormones and paracrine factors.

Question 5

Interstitial cell functions

Answer 5

Pacemakers that coordinate and time contractions into rhythmic patterns

Question 6

Enteric motor neurons function

Answer 6

Exc/inh motoneurons that innervate smooth muscle cells by interacting with ICC and modulating their activity and smooth muscle contractability.

Question 7

Tissues in the GI that are skeletal and under voluntary control (4)

Answer 7

Pharynx, UES, upper esophagus, external anal sphincter.

Question 8

GI smooth muscle is _________ contracted.

Answer 8

Tonically!

Question 9

Slow waves in muscle contraction

Answer 9

Spontaneous cyclic variations in the smooth muscle Vm with a specific frequency.

Question 10

SW frequency in the stomach

Answer 10

3/min

Question 11

SW frequency in the duodenum

Answer 11

12/min

Question 12

SW frequency in the terminal ileum

Answer 12

8/min

Question 13

Small slow waves vs large slow waves

Answer 13

slow - coordinate contractions
large - only act when they coordinate with the crest of slow waves

Question 14

Neural or hormonal stimulate can modulate the _________ of slow waves, but has no effect on _________.

Answer 14

Amplitude; frequency

Question 15

ICC-IM
ICC-MY
ICC-DMP

Answer 15

IM - in smooth muscle cells
MY - myenteric plexus between lsm and csm, regulate rhythm
DMP - specific to small intestine at inner surface of circular muscle layer.

Question 16

3 pathophysiologies of ICC loss of function

Answer 16

• Chronic constipation
• Achalasia
• Pyloric stenosis

Question 17

Achalasia

Answer 17

Inability to relax certain sphincters

Question 18

Pyloric stenosis

Answer 18

Infants having an obstruction of small intestine, characterised by thickening muscle and failure of pylorus to relax - causing regurgitation and vomiting.

Question 19

Mastication as a reflex or voluntary action

Answer 19

Food in mouth -> oral and periodontal mechanoreceptors activate -> jaw opening -> jaw-closer stretch receptors activate (masseter spindles) -> rebound contraction by stretch reflex.
Repeat through subsequent compression.

Question 20

3 phases of swallowing

Answer 20

1. Oral (V) - tongue pushes food back.
2. Pharyngeal (InV)- protective reflexes triggered by afferent fibres in the pharynx (no choking zone).
3. Esophageal (InV) - sequence involving peristalsis.

Question 21

Esophageal phase sequence

Answer 21

1-2: food enters, UES closes to prevent back flow.
3-4: peristaltic contraction propels downwards.
5: LES is relaxed and open, food enters stomach.

Question 22

Esophageal peristalsis happens _______.

Answer 22

Twice! Primary to push down bolts, and secondary to clear any remaining debris.

Question 23

LES reflex relaxation

Answer 23

Starts early on in the process of swallowing and stays open til the end.

Question 24

Dysphagia

Answer 24

Difficulty swallowing from either structural or neuromuscular issues.
Associated with stroke, ALS, parkinson’s.
Increases risk of malnutrition, aspiration, choking.

Question 25

GERD

Answer 25

Back flow of acidic contents into esophagus as the LES is open. Drug treatment: H2 blockers, proton pump inhibitors.

Question 26

Function of orad and caudate regions

Answer 26

Reception, storage Mixing, propulsion. Both have an inner oblique muscle layer responsible for churning movement, thicker in the antrum.

Question 27

Vasovagal reflex

Answer 27

Gastric stretch receptors send afferents to the medulla via the vagus nerve. Vagal efferent synapse onto the ENS interneurons, then inhibitory motor neurons to cause relaxation in anticipation of more food arriving.

Question 28

4 stomach movements

Answer 28

Propulsion towards pylorus Grind and mixing Retropulsion Emptying as antrum contracts in intermittent spurts to propel chyme to the duodenum.

Question 29

Duodenal inhibitory factors

Answer 29

Distension, acidity, increased osmolarity, presence of protein and fat digestive products. Allow sufficient time for chyme neutralisation and effective digestion of fats.

Question 30

Migrating myoelectric complex

Answer 30

Occurs during fasting, bursts of muscle contractions every 1.5-2 hours. Loud. Pylorus stays open “House-keeping role”, absence linked to gastroparesis, obstruction, IBS, bacteria growth.

Question 31

Gastroparesis

Answer 31

Impaired gastric emptying but no obstruction May be caused by impaired NM functioning, diabetes, medications, vagal nerve injuries.

Question 32

Gastroileal reflex

Answer 32

Occurs immediately after a meal, inducing ileocecal valve relaxation. Cecum distention causes the valve to close to prevent any backflow to the ileum.

Question 33

Proximal colon function

Answer 33

Fluid and electrolyte absorption

Question 34

Taeniae coli

Answer 34

Three longitudinal ribbons of smooth muscle that run along the outer surface of the colon

Question 35

Haustrations (pockets known as haustra)

Answer 35

Result from ring-like contractions for he circular muslcles and simultaneous relaxation fo the longitudinal muscle (taeniae coli).

Question 36

Movement from one haustrum to the next

Answer 36

Is slow! facilitates contact with the epithelial cells to absorb water and electrolytes.

Question 37

Mass movements of the colon

Answer 37

1-3 times a day, resemble enduring, intense peristaltic contractions.

Question 38

Triggers for mass movements

Answer 38

Gastro colic reflex colon distention irritants parasites, enterotoxins

Question 39

Enteric defecation reflexes

Answer 39

Stretch receptor activation *Local reflex in ENS by sensory fibers *Activation of motor neurons Activation of descending and sigmoid colon and rectum smooth muscles.

Question 40

Parasympathetic defecation reflex arc

Answer 40

Stretch receptor activation *Signals sen to sacral region of the SC *Pelvic PS motor fibres activated Activation of descending and sigmoid colon and rectum smooth muscles.

Question 41

Somatic motor control of defecation

Answer 41

Initiated by combination of reflexes, IAS relaxed, EAS contracted until convenient; - Glottis closes, pelvic floor muscles, diaphragm, and abdominal muscles contract. - external anal sphincter relaxes through pure al nerve. Closing reflex engages, contracts both.

Question 42

Stimulants of the defecation reflex.

Answer 42

Food in stomach (gastrocolic reflex) Chyme in the ileum (ileocecal reflex).

Question 43

Sequence of events for vomiting

Answer 43

1. Hypersalivation, deep inhalation 2. Fundus relaxes, antrum and proximal duodenum contract strongly. 3. Protective reflexes (palate rises, glottis closes, larynx forward, dilate esophagus. LES relaxes and moves upwards. 4. Contraction of diaphragm and abdominal muscles causes gastric contents upward.

Question 44

Leaky BBB (medulla) in vomiting

Answer 44

Affected by circulating chemical, and irritants. All vomiting is controlled by the vomiting center in the medulla.

Question 45

Interstitial cells of Cajal (ICCs)

Answer 45

Pacemakers, innervation by enteric nerve cells and generate electrical slow wave activity that is delivered to smooth muscle cells through gap junctions.