Motility: Johnson Flashcards
Describe the pressures in the esophagus and oral stomach at rest and during a swallow.
At the upper eso. sph., as the bolus arrives, pressure drops to allow passage of the bolus, then rises above baseline to propel it. Down the length of the eso., the muscles will contract (pressure rises) after the bolus passes them to propel the bolus. At the lower eso. sph., as the bolus arrives at the level of the diaphragm, muscle relaxes (pressure drops) to allow passage, and then returns to baseline tone.
Explain the regulation of pharyngeal events, peristalsis and gastric receptive relaxation during a swallow
Regulated centrally by swallowing center. Vagal nerve then carries signals to myenteric plexus (btwn longitudinal and circular muscle layers). Afferent vagal pathways send sensory information back to swallowing center to take autonomic control in times of lodged food, etc.
Understand gastric esophageal reflux disease (GERD)
Acid reflux from stomach causes “heart burn”. Can be caused by hiatal hernia, pregnancy, and failure of secondary peristalsis.
Tx: omeprazole (Prilosec) to inhibit acid secretion
Explain the regulation of the contractile activity of the stomach and the role of slow waves
Vagal-vagal reflex regulates SM relaxation of stomach smooth muscle to accommodate entry of food bolus. This allows for a minimal rise of pressure (~10mmHg) in stomach as food continues to fill it.
Peristalsis pushes bolus towards pylorus. Small amounts of food are “squirted” through pylorus into duodenum and the bulk is retropulsed back into the stomach. This strong pyloric contraction is largely responsible for mashing up the food into smaller particles. Contractions occur 3-5 times/min. Cells of Cajal are responsible for depolarization leading to contractions. More food mass = greater depolarizations. Amplitude of depolarizations increases as bolus moves towards pylorus, but frequency remains constant.
Describe the regulation of gastric emptying.
Discuss causes and effects of impaired gastric emptying- failure to empty and increased emptying.
:: More liquid in stomach = faster emptying.
:: Solids have to be reduced in size to ~1mm3 before they are suitable for emptying into to duodenum.
:: As acid enters the duodenum, it triggers an intrinsic reflex that inhibits emptying of the stomach.
:: Gastric emptying regulated by 4 types of motility: contractions/pressure in orad (upper 1/2) portion of stomach, gastric peristalsis, pyloric relaxation, duodenal peristalsis.
:: More fat in meal = slower rate of gastric emptying
:: Hypotonic and hypertonic solutions both empty at slower rates than isotonic solutions.
::Impaired gastric emptying::
Failure due to: obstruction, ulcer, cancer. vagotomy (loss of innervation of stomach by vagus nerve).
Effects: fullness, loss of appetite, nausea.
Increase due to: Inadequate regulation
Effects: Diarrhea, duodenal ulcer (decr. pH)
Describe the functions of slow waves and spike potentials in regulating the contractions of the small intestine.
What is segmentation?
How does peristalsis of the SI differ from that of the stomach?
What is the migrating motility complex (MMC)?
Can’t have greater freq. of contractions than slow wave frequency.
S.I. contractions are brief and irregular, in occurrence.
In the SI, the only time you get a contraction is if you get a spike potential (high AP) during a slow wave. Freq. of spiking is determined by digestive state of individual. More food = more spiking. Moving distally down GI tract, freq. of contractions decreases. Cells of Cajal are responsible for slow wave depolarizations.
::Segmentation is contraction that results in splitting of the bolus and churning of the material so that it is all exposed to the wall of the intestine for absorption.
::Peristalsis of the gut is propagated for
Explain the function of the ileocecal reflex
Sphincter is tonically contracted. As bolus nears sphincter, it relaxes to allow passage, then contracts to prevent retrograde flow from colon.
Understand the rectosphincteric reflex and the control of defecation
1-2 times/day, the haustra disappear, giving rise to peristaltic contractions that move feces through colon in a bolus.
RS reflex: rise in pressure in rectum due to presence of bolus results in relaxation of internal anal sphincter by pelvic nerve. External anal sphincter is somatically controlled by pudendal n. and determines if bolus will actually be excreted, given the appropriate social circumstances.
