Gi Physiology - Motility

Front 1

Unitary smooth muscle

Back 1

Contains gap junctions to permit rapid spread of action potentials and subsequent, coordinated contraction of muscle tissue.

Front 2

Slow waves

Back 2

Oscillating smooth muscle membrane potentials that set frequency of contractions; alone produce weak tonic contractions; depolarizing portion caused by cyclic opening of Ca2+ channels.

Front 3

Interstitial cells of Cajal

Back 3

Pacemaker cells in myenteric plexus; contain cyclically opening Ca2+ channels.

Front 4

Chewing reflex

Back 4

Involuntary; sensory info from mechanoreceptors in the mouth sent to brainstem which directs reflex oscillatory motor activity.

Front 5

Swallowing reflex

Back 5

Includes the oral, pharyngeal and esophageal phases. Mechanoreceptor afferents project to swallowing center in the medulla via the vagus and glossopharyngeal nerves; swallowing center detects sensory information and mediates motor response; efferents project to skeletal muscle in the pharynx and upper esophagus via vagus.

Front 6

Oral phase

Back 6

Voluntarily initiated; tongue forces back bolus into pharynx which contains high number of mechanoreceptors; project via vagus and glossopharyngeal nerves to swallowing center; activation initiates the pharyngeal phase.

Front 7

Pharyngeal phase

Back 7

Propels bolus through pharynx into esophagus; phase includes numerous events such as, elevation of the soft palate, closure of the epiglottis, relaxation of the upper esophageal sphincter, initiation in the pharynx of a primary peristaltic wave, and inhibition of breathing.

Front 8

Esophageal phase

Back 8

The esophageal phase pushes the bolus into the orad of the stomach

Front 9

Primary peristalsis

Back 9

Upper esophageal sphincter closes; peristaltic waves initiated by swallowing reflex continues as mechanoreceptors trigger local reflexes

Front 10

Secondary peristalsis

Back 10

Initiated by distension if food not cleared from esophagus; local reflex mediated by enteric nervous system.

Front 11

Receptive relaxation

Back 11

Lower esophageal sphincter and orad stomach relaxes in anticipation of approaching bolus.

Front 12

Mixing waves and retropulsion

Back 12

Gastric mixing in the thick caudad breaks food up and combines it with secretions. Strong contractions, increase distally toward the antrum, most of the chyme is initially deflected back from pylorus (retropulsion).

Front 13

Migrating myoelectric complexes

Back 13

Periodic contractions occurring during fasting (about every 90 min) to clear the stomach of remaining chyme; promoted by motilin. Also occur about every 90 min in the small intestine to clear residual chyme.

Front 14

Segmentation contractions

Back 14

Contracting segment occurs within chyme followed by relaxation; this mixes the chyme with secretions (e.g., pancreatic) and digestive enzymes.

Front 15

Peristaltic contractions

Back 15

Functions to propel chyme forward; initiated when enterochromaffin cells detect bolus and release serotonin; serotonin stimulates primary afferents.

Front 16

Vomiting reflex

Back 16

Afferents from many sources, such as vestibular system, back of the throat, the GI tract, and the trigger zone in the 4th ventricle; project to vomiting center in the medulla; autonomic efferents project to small intestine and upper GI tract.

Front 17

Segmentation contractions

Back 17

Occur in cecum and proximal colon to mix feces; associated with the sac-like haustra; can take 8 – 15 hours to move feces through colon.

Front 18

Mass movements

Back 18

Can move feces relatively long distances in just a few minutes; occur 1 – 3/day often after a meal; contraction of several segments at once; water absorption occurs along colon, making feces becomes harder to move.

Front 19

Gastrocolic reflex

Back 19

Distention of stomach produces mass movements in colon; requires extrinsic nerve activity (parasympathetic); motility produced by CCK and gastrin.

Front 20

Defecation reflex

Back 20

Include both local afferents/efferents within the GI wall and those that project to and from the sacral spine (parasympathetic via pelvic nerves); local reflex is weak; defecation usually requires parasympathetic stimulation.