47 - - Gastric motility – hunger contractions, storage functions, mixing and propulsion of food. Emptying of the stomach. Control of gastric motility. Vomiting.

sections

• stomach movement

• hunger contraction

• regulation of stomach motility

• autonomic nervous system effect on gastric movement

• hormonal control

• vomiting

• stomach movement

• Stomach movement:

  1. Peristalsis- wave like contraction of the stomach wall for mixing of food—(propulsive movements)

  2. Receptive relaxation of the stomach- the brain sends signals to the walls of the stomach

  3. Retro pulsation- reverse waves – big particle are broken down- occurs from the pyloric part to the antrum of stomach

• The motor functions can be divided into three parts:

  1. storage of large quantities of food

  2. mixing of this food with gastric secretions → producing chyme

  3. emptying of the chyme from the stomach → duodenum

• hunger contraction

• No food in the stomach

• contractions are rhythmical peristaltic contractions in the body of the stomach

• Sometimes become as strong to cause tetanic contractions.

• Due strength of the contractions the person sometimes feels pain, especially in the state of starvation.

• Food enters stomach, tone of stomach wall decreases to expand- about 1.5-2 L storage but can increase

• regulation of stomach motility

• Enteric nervous system

  • Myenteric plexus (plexus of Auerbach)

  • 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.

• autonomic nervous system effect on gastric movement

• Parasympathetic nervous sysem:

  • stimulation causes increase of enteric nervous system → increased gastric motility

  • increase saliva secretion

  • increase vasodilation

  • decrease muscle tone of sphincters so chyme can move to next section

• Sympathetic: opposite effects

• In general, Afferent sensory nerve fibres can be stimulated by:

  1. irritation of the stomach wall by food

  2. distention of the stomach

  3. presence of specific chemical substances → signals transmitted through those fibers can then cause excitation or inhibition

• hormonal control

• Motilin → secreted by the stomach and upper duodenum during fasting and increases gastrointestinal motility

• secretin inhibits

• CCK- inhibits stomach motility

• GIP- gastric inhibitory polypeptide- inhibits gastric movem

• vomiting

• Vomiting: forcible voluntary or involuntary emptying ("throwing up") of stomach contents through the mouth.

• caused by:

  • motion sickness, pregnancy

  • infection, poison

  • overdose, alcohol

  • smell, watching someone vomit, strong pain