47. Motor functions of the stomach – hunger contractions, storage function, mixing and propulsion of food. Emptying of the stomach; control of its motor activity. Vomiting.

stomach movement

Stomach movement:

Hunger Contractions

• Occur when the stomach is empty

• Rhythmical basic contractions; can become strong enough to cause tetanic contractions (lasting 2–3 minutes)

• Can cause hunger pangs (painful sensations), especially during starvation

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Storage Function

• Bolus entry causes stomach distension

• Stretch receptors activate the vagovagal reflex → relaxation of stomach wall muscles

• New food remains near the oesophageal opening, older contents move toward pylorus

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Mixing Waves

• Gentle, non-propulsive contractions

• Occur every ~20 seconds

• Mix food with gastric juices

• Soften and liquefy food into chyme

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Propulsive Peristaltic Contractions

• Push chyme toward the pyloric sphincter

• Some chyme enters duodenum; some is pushed back into the stomach body

• Backflow is called retropulsion, aiding further mixing and digestion

emptying of stomach + regulation

Gastric Emptying

• Driven by intense peristaltic contractions in the antrum of the stomach

• Only small particles can pass through the pyloric sphincter

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Effect of Food Type on Emptying Time

• Carbohydrate-rich foods → fastest gastric emptying

• Fat-rich foods → slowest gastric emptying

• Protein-rich foods → intermediate, but can slow emptying if unprocessed

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Regulation of Gastric Emptying

• Enterogastric reflex is triggered when:

  • Excessive chyme enters the small intestine

  • Chyme is too acidic

  • Chyme contains too much fat or protein (unprocessed)

• Effects of the enterogastric reflex:

  • Constriction of pyloric sphincter

  • Inhibition of gastric peristalsis

  • Slows further emptying into the small intestine

MOTILITY REGULATION: +Parasympathetic à increase (via Ach binding to m3 receptors) motility -Sympathetic à decrease motility (via NA binding to a2 receptors)

regulation of gastric motility:

Regulation of stomach motility:

Enteric nervous system

1. Myenteric plexus (plexus of Auerbach)- ---

2. Submucosal plexus - in submucosa---of intestine wall

Myenteric plexus controls gastric activity

When this plexus is stimulated, its causes:

1) increased tonic contractions

2) increased intensity of the rhythmical contractions

3) increased rate of rhythm of contraction

4) increased velocity of conduction of excitatory waves.

Some neurons of the myenteric plexus are also inhibitory, their nerve endings secrete inhibitory transmitters.

vomiting

Vomiting (Emesis)

• Forceful expulsion of stomach & proximal small intestine contents via mouth

• Triggered by irritation or overdistension

• Controlled by vomiting center in the medulla oblongata

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Phases of Vomiting:

1. Nausea (pre-ejection):

   • ↓ Gastric motility

   • ↑ Small intestine tone

2. Retching (pre-ejection):

   • Retro-peristalsis (reverse contractions of stomach & esophagus)

   • No expulsion

3. Vomiting (ejection):

   • Larynx rises, UES opens

   • Glottis closes, soft palate elevates (blocks nasal passage)

   • Diaphragm & abdominal muscles contract → ↑ intragastric pressure → expulsion