Physiology
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Gastrointestinal
A patient presents to ED complaining of difficulties with swallowing. Which of the following cranial nerves is most important for controlling the oesophageal phase of swallowing:
Answer:
The oesophageal phase involves transport of the bolus along the oesophagus to the stomach by peristalsis. A coordinated wave of relaxation in front of the food bolus and contraction behind the bolus of the circular and longitudinal muscles of the oesophagus propels the food bolus along. Gravity accelerates the movement. The lower oesophageal sphincter relaxes as the food bolus approaches the lower end of the oeosphagus, opening and allowing the bolus to pass into the stomach. The sphincters and the peristaltic waves are principally controlled by activity in the vagus nerve and aided by a high degree of coordination of the activity within the enteric nerve plexuses within the tract itself.Swallowing
Physiology / Gastrointestinal / Mouth and Oesophagus
Last Updated: 21st April 2019
Swallowing is the controlled transport of a food bolus from mouth to stomach, involving a sequential reflex, which is coordinated by the swallowing centre in the medulla and pons and consists of three phases: the buccal, pharyngeal and oesophageal phases. Fibres in the vagus and glossopharyngeal nerves carry information between the gastrointestinal tract and the brainstem.
Buccal Phase (voluntary)
During the buccal phase, food is chewed and mixed with saliva to form a food bolus. Tongue movements then push this food bolus upwards and backwards against the hard palate, forcing it into the pharynx.
Pharyngeal Phase (involuntary)
The pharyngeal phase lasts about 1 second and is initiated by the food bolus stimulating mechanoreceptors in the pharynx and firing impulses via the glossopharyngeal nerve (CN IX) and the vagus nerve (CN X) to the swallowing centre.
In the pharyngeal phase:
- The soft palate elevates, closing off the nasopharynx
- The base of the tongue retracts, pushing the bolus against the pharyngeal walls
- Laryngeal muscles contract to close the glottis and elevate the larynx, closing off the airway
- Breathing is inhibited
- The tip of the epiglottis moves over the tracheal opening, closing off the airway
- The pharyngeal constrictor muscles contract sequentially from top to bottom, squeezing the bolus downwards
- The upper oesophageal sphincter relaxes to permit the food bolus to enter the oesophagus
As the bolus enters the oesophagus, these changes reverse, the larynx opens and breathing continues.
Oesophageal Phase (involuntary)
The oesophageal phase involves transport of the bolus along the oesophagus to the stomach by peristalsis. A coordinated wave of relaxation in front of the food bolus and contraction behind the bolus of the circular and longitudinal muscles of the oesophagus propels the food bolus along. Gravity accelerates the movement.
The lower oesophageal sphincter relaxes as the food bolus approaches the lower end of the oeosphagus, opening and allowing the bolus to pass into the stomach.
The sphincters and the peristaltic waves are principally controlled by activity in the vagus nerve and aided by a high degree of coordination of the activity within the enteric nerve plexuses within the tract itself.
Phases of Swallowing. (Image by Boumphreyfr [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)])
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
