Regulation of gastric emptying flow chart MBBS physiology
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Regulation of Gastric Emptying - MBBS Physiology
Here is a complete structured breakdown to go with the flowchart above.
Normal Gastric Emptying - Key Facts
- After a mixed meal (~1.5 L), emptying takes approximately 3 hours
- Liquids empty faster than solids
- Isotonic contents empty faster than hypotonic or hypertonic
- Only particles <2 mm pass through the pylorus; larger particles are retained and ground (retropulsion)
- During fasting, the migrating myoelectric complex (MMC) sweeps residue every 90 minutes
FACTORS THAT ACCELERATE Gastric Emptying
| Factor | Mechanism |
|---|---|
| Gastric distension | Stretch receptors in stomach wall trigger antral peristalsis (vagovagal reflex) |
| Gastrin | Released by G-cells in response to food; stimulates antral contractions |
| Motilin | Released during fasting; drives MMC Phase III ("housekeeper wave") |
| Parasympathetic (vagus) | Increases antral motor activity |
| Liquid meals | Follow first-order kinetics; ~200 mL emptied per 12 min for water |
| Small particle size | Particles <2 mm pass pylorus without resistance |
FACTORS THAT DELAY Gastric Emptying
These are the most exam-important. All arise from duodenal feedback (enterogastric inhibition):
Hormonal (Duodenal-Enterogastric Reflex)
| Stimulus in Duodenum | Hormone Released | Effect on Stomach |
|---|---|---|
| Fat / fatty acids | CCK (from I-cells, duodenum/jejunum) | Inhibits antral motility, contracts pyloric sphincter, delays emptying |
| Acid (low pH) | Secretin (from S-cells) | Inhibits gastric motility, contracts pylorus, stimulates pancreatic HCO3- |
| Hyper/hypotonic solutions | GIP (from K-cells) | Inhibits gastric emptying, stimulates insulin |
| Amino acids / peptides | CCK (also) | Same as fat effect |
| Fat in ileum | Peptide YY (ileal brake) | Delays gastric emptying further |
Neural (Enterogastric Reflex)
- Chemoreceptors and mechanoreceptors in the duodenal mucosa detect low pH, fat, high osmolarity
- Relay signals via interneurons in the myenteric plexus to inhibit antral contractions and contract the pylorus
- Delayed emptying involves: (1) fundic relaxation, (2) inhibition of antral motor activity, (3) isolated phasic pyloric contractions, (4) altered intestinal motor activity
Other Inhibitory Factors
- Sympathetic stimulation (splanchnic nerves) - inhibits GI motility
- Pain, stress, fear - via corticotrophin-releasing factor (CRF) and central dopaminergic pathways
- Duodenal distension
- Leptin (acts via same pathway as CCK)
- Supine position (delays liquid emptying)
Gastric Emptying Rate by Meal Type (from Medical Physiology graph)
Saline (red) empties fastest, acid meal (green) intermediate, oleate/fat meal (blue) slowest - illustrating CCK-mediated inhibition by fat. (Costanzo Physiology 7th Ed, Fig. 8)
Pyloric Sphincter Role
- Acts as a gatekeeper - allows particles <2 mm to pass
- Relaxes with: nitric oxide, VIP, serotonin, prostaglandin E1
- Contracts with: CCK, secretin, histamine (slows delivery to duodenum)
Quick Memory Trick for MBBS Exams
"FAT ACID HYPER STOP" = the 3 main duodenal brakes:
- Fat → CCK → slows emptying
- Acid → Secretin → slows emptying
- Hypertonic solution → GIP → slows emptying
All three act via the enterogastric reflex (neural) + hormonal pathways in parallel.
Sources: Costanzo Physiology 7th Ed; Boron & Boulpaep Medical Physiology; Ganong's Review of Medical Physiology 26th Ed; Schwartz's Principles of Surgery 11th Ed
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