Gastric Motility and Gastric Emptying

• What are the three main roles of the stomach?

  Storage, digestion, and motility
• What is the function of the stomach as a reservoir?

  The stomach acts as a reservoir to store food
• How does the stomach mix food?

  The stomach mixes food with acid to create chyme
• What is chyme?

  Chyme is the mixture of food and acid created in the stomach
• What happens during the emptying phase of the stomach?

  Nutrients are delivered to the small intestine
• Is absorption a normal function of the stomach?

  No, absorption is not a normal function of the stomach
• What is receptive relaxation of the stomach?

  Receptive relaxation is a process that allows the stomach to accommodate food with little increase in pressure
• What triggers receptive relaxation in the stomach?

  It is triggered by a vagally-mediated process upon feeding
• What role do mechanoreceptors play in receptive relaxation?

  Mechanoreceptors detect distension in the stomach and send information to the brain
• What neurotransmitters are involved in the relaxation of smooth muscle in the stomach?

  Nitric oxide and vasoactive intestinal polypeptide
• What is the resting membrane potential of smooth muscle cells in the stomach?

  The resting membrane potential fluctuates with depolarization and repolarization
• How does the resting membrane potential differ in the upper and lower portions of the stomach?

  The upper portions are less negative and electrically quiescent, while the lower portions are more negative and exhibit a basal electrical rhythm
• Where do peristaltic waves in the stomach originate?

  They originate from the gastric pacemaker located at the junction between the stomach body and the antrum
• What is the function of the gastric pacemaker?

  It generates slow waves that propagate across the stomach wall, causing coordinated muscle contractions
• How do peristaltic waves facilitate digestion in the stomach?

  They facilitate mixing and churning of the stomach contents before emptying into the duodenum
• How does the frequency of peristaltic waves change with the volume of gastric contents?

  The frequency is altered by the volume of gastric contents
• What effect does osmolarity have on gastric emptying?

  Hypertonic and hypotonic solutions empty slower than isotonic solutions
• How does fat content in a meal affect gastric emptying?

  Meals higher in fat take longer to be digested and emptied from the stomach
• Which macronutrient empties the fastest from the stomach?

  Glucose empties faster than proteins, which empty faster than fats
• What happens when acid passes from the stomach into the small intestine?

  It triggers the release of secretin, which slows down the rate of gastric emptying
• How does particle size affect gastric emptying?

  Smaller particles empty faster than larger particles
• What is the relationship between liquid and solid food in terms of gastric emptying?

  Liquids will empty faster than solids, which empty faster than indigestible material
• How does the volume of food affect gastric emptying?

  The stomach will empty in proportion to the volume of its contents
• What are the four classes of luminal stimuli that trigger GI reflexes?

  Distension, chemical irritation, osmolarity changes, and nutrient composition
• How does distension trigger GI reflexes?

  It activates mechanoreceptors in the gut wall, promoting peristalsis
• What is the effect of chemical irritation in the intestinal lumen?

  It can alter the pH and stimulate chemoreceptors, leading to increased mucous secretion or inhibition of gastric emptying
• How do osmolarity changes affect GI reflexes?

  They activate osmoreceptors, initiating reflexes to regulate fluid absorption and secretion
• How does nutrient composition trigger GI reflexes?

  Specific nutrients can trigger chemoreceptors, stimulating the secretion of digestive enzymes or hormones
• What roles does the stomach have?

  Storage, mixing, nutrient absorption
• Define receptive relaxation of the stomach.

  Receptive relaxation is a reflex that occurs when the stomach's upper portion relaxes and dilates as food enters the stomach.
• How does the stomach accomplish receptive relaxation?

  The stomach accomplishes this by controlling gastric motility. Upon feeding, the stomach undergoes a vagally-mediated process known as receptive relaxation which allows an increase in intragastric volume with little increase in pressure.