O1ii / 18B08 / 14B24: Describe gastric emptying (40 marks) + Outline its regulation (60 marks)
18B08: Exam Report
Describe gastric emptying (40% of marks) and outline its regulation (60% of marks).
24% of candidates passed this question.
Candidates were required to provide a description of gastric emptying (40% marks). Although the question showed the allocation of marks, many candidates did not provide sufficient detail for this section. This required some description of what gastric emptying is (the co-ordinated emptying of chyme from the stomach into the duodenum).
Better answers provided detail regarding the process of gastric emptying in the fed and fasted state and differentiated between liquids, solids, carbohydrate, protein and fats. Factors regulating emptying included an outline of peristaltic waves, the basal electrical rhythm and its modulation, the migratory motor complex (MMC) and its modulation, neural input, stretch and hormonal control.
Many candidates erred by answering the question “the regulation of gastric secretions” rather than the question (the regulation of gastric emptying). Although they scored well for hormonal control, they missed out on marks for the other factors relevant to the regulation of gastric emptying.
14B24: Exam Report
Describe the control of gastric emptying.
23% of candidates passed this question.
An understanding of the physiology of gastric emptying has direct relevance to intensive care practice as it influences enteral feed tolerance, helps inform regarding risk of aspiration and has important pharmacologic implications.
Candidates’ answers were superficial and the role of intrinsic reflexes and local hormonal responses poorly understood and described. A simple and clear coverage is provided in Principles of Physiology for the Anaesthetist / P. Kam, I. Power – 3rd Ed.
Oii / 18B08 / 14B24: Describe gastric emptying (40 marks) and outline its regulation (60 marks)
Definition
Gastric emptying = the coordinated emptying of chyme from the stomach to the duodenum
Mechanism
Occurs when pressure in Antrum > Pyloric Resistance
- Food intake
- Fundus & upper stomach relax to accommodate food
- ↑gastric volume with minimal ∆ gastric pressure
- KA VAGOVAGAL REFLEX (stomach can accommodate 1.5L)
- Mixing & crushing mechanisms activate to form chyme
- Antral contractions mix solid food with gastric juices
- Pyloric + antral contractions move food into duodenum
- Duodenum contracts → moves nutrients for absorption
- After cessation of digestive processes, gastric motility continues by MMC (during fasting)
Migratory Motor Complex
- Occur in 100 min cycles
- Trigger peristaltic waves
- Allows emptying of gastric contents that were not transformed into chyme
Regulation
Promoting Gastric Emptying
- Vagal Excitation
- Due to ↑volume in stomach
- ↑Antral pump activity
- Gastrin
- Released by G cells in antrum & duodenum
- Release stimulated by ↑Antral distention & vagal excitation
- ↑gastric motility (but also constricts Pyloric Sphincter & ↓gastric emptying)
- Food Content
- Liquids empty faster than solids
- CHO faster than fats & protein
- Motilin
- Associated with MMC
- Released by proximal SI cells
- ↑motility & gastric emptying
Delaying Gastric Emptying
- Sympathetic stimulation
- Via Coeliac plexus
- Inhibits gastric emptying
- Pain, fear, anxiety
- Duodenal filling
- Inhibits vagus activity
- Delays gastric emptying
- KA ENTERO-GASTRIC REFLEX
- Regulates delivery of chyme for maximal nutrient absorption
- Hypertonic chyme
- Including hyperglycaemia
- Detected by duodenal osmoreceptors
- ↓gastric emptying
- Acid
- Secretes SECRETIN
- ↓gastric emptying
- ↓acid production
- ↑alkaline pancreatic juice production
- ↑ Fat
- Secretes CCK
- ↓gastric emptying
- Contraction of GB
- Bile salts emulsify fats
- ↑ α-acids
- Secretes GASTRIN
- Pyloric sphincter contraction
- Delays gastric emptying
- Pathological ↓ in gastric emptying
- Alcohol
- Opioids
- Pyloric stenosis
- Vagotomy
- Author: Krisoula Zahariou