O1ii: Explain the factors that prevent gastro-oesophageal reflux
Definition
Gastro-oesophageal Reflux = backward flow of the contents of stomach into the oesophagus that is due to malfunctioning of the Lower Oesophageal Sphincter
Factors that Maintain Les Integrity
- LES is formed by the lowest 2 – 4cm of the oesophagus → acts as a physiologic sphincter by tonic contraction of muscle fibres
- Anatomical
- Pressure
- Hormones
- Physiology
1) Anatomical
- Intrinsic Sphincter
- Smooth m. of the oesophagus
- Neural control (Vagus n.)
- ACh – sphinter contracts
- NO, VIP-sphincter relaxation (just after swallowing)
- Extrinsic sphincter
- Skeletal m. fibres of diaphragm
- Neural control (Phrenic n.)
- Actions coordinated with resp
- Fibres surround oesophagus & exert ‘pinchcock-like” action
- Gastro-oesophageal angle
- Oblique “sling” fibres of stomach
- Creates a flap valve to help close off gastro-oesophageal junction when ↑intra-gastric P
2) Pressure
- At rest, LOS pressure is 15 – 25mmHg greater than gastric P
- Prevents G-O reflux
3) Hormones
- ↑TONE: gastrin, motilin, α-adrenergic stimulation
- ↓TONE: glucagon, VIP, progesterone
4) Physiology
- 1 – 2 secs after swallowing LES relaxes
- Remains relaxed for ~10 secs then contracts
- After passage of food bolus, LES tone rises ~10mmHg above resting tone for 15 secs, before returning to resting level
5) Drugs
- ↑LES: metoclopramide, anticholinesterases, α-adrenergic agonists, histamine, suxamethonium
- ↓LES: antimuscarinics (atropine), dopamine, ethanol, opioids, β-adrenergic agents
Measurement
- Intraluminal manometry
- Continuously infused catheter probes are withdrawn from the stomach in small increments
- Pressure being measured the whole time