Oesophagus and Swallowing Flashcards
Which cells is the oesophagus composed of?
Fibromuscular tube (25cm) of striated squamous epithelium
Where in the body is the oesophagus located?
Lies posterior to the trachea
Begins at end of laryngopharynx and joins stomach a few cm from diaphragm (at the cardiac orifice of the stomach)
What is the role of the oesophagus?
Transports food to stomach (eating gullet)
Secretes mucus
What promotes the transport of ingested food into the stomach?
Highly coordinated muscular process;
contraction & relaxation of oesophagus to move food through GIT
Relaxation of the sphincters (UOS and LOS)
Describe the muscular structure of the oesophagus
Skeletal muscles surround the oesophagus below the pharynx (the upper third)
Smooth muscles surround the lower ⅔
Name the 2 oesophagul sphincters?
Upper oesophageal sphincter (UOS): striated muscle;
Lower oesophageal sphincter (LOS): smooth muscle;
Describe the features of UOS
Musculo-cartilaginous structure
Constricted to avoid air entering the oesophagus
Describe the features of LOS
acts as a flap valve
LOS = area of high pressure zone where it merges with the stomach
LOS has intrinsic and extrinsic components
What are the intrinsic components of the LOS?
Intrinsic component: oesophageal muscles; under neurohormonal influence;
What are the extrinsic LOS components?
Extrinsic component: diaphragm muscle (adjunctive external sphincter)
What is the consequence of malfunctioning of the intrinsic/extrinsic LOS components?
Malfunction of intrinsic and extrinsic components of lower oesophagul sphincter → GORD
What is GORD?
GORD - gastro-oesophagul reflux disease
What are the 3 components of the LOS?
- Thick circular smooth muscle layers and longitudinal muscles
- Clasp-like semi-circular smooth muscle fibres on the
right side - Sling-like oblique gastric (angle of His) muscle fibres
on the left side
How are the semi circular smooth muscle fibres activated in the oesophagus?
Myogenic activity (some resting tone), but less ACh-responsive
Describe the functional features of the oblique gastric muscle fibres
Work in concert with clasp like-semi-circular smooth muscle fibres, help prevent regurgitation- responsive to cholinergic innervation
Explain how the Angle of His (oblique fibres) in infants may cause reflux
Angle of His is poorly developed in infants as it makes a vertical junction with stomach, hence why reflux is common in infants
What is the Angle of His (oblique angles)?
The acute angle created between stomach entrance (cardia), and oesophagus. It forms a valve, preventing reflux entering the oesophagus
What is the consequence of reflux into the oesophagus?
Reflux of duodenal bile, enzymes, gastric acid cause irritation of the oesophageal lining, inflammation and in extreme cases Barrett’s oesophagus
What are the components of the extrinsic LOS?
- Crural diaphragm
2. Pinchcock action of crural fibres
Describe the role of the crural diaphragm in the extrinsic LOS
Crural diaphragm encircles the LOS
Forms channel through which oesophagus enters the abdomen
Explain how the crural fibres produce the pinchcock action
Fibres of the crural portion of the diaphragm possess a “pinchcock-like” action => (extrinsic sphincter; diaphragmatic sphincter) - myogenic tone
What is the oesophagul innervation?
Involvement of cholinergic (i.e. via ACh) and non-cholinergic, NANC innervation in the control of tone of the lower oesophageal sphincter
Outline the neural control of the oesophagul sphincters
Acetylcholine, SP: contraction of intrinsic sphincters
NO and VIP: relax the intrinsic sphincters
Extrinsic / intrinsic sphincters work in concert to push food → stomach
Describe the muscular and neural structure of the upper part of the oesophagus
Striated muscle; supplied by somatic motor neurons of vagus nerve without interruption
- Vagus nerve
- Splanchnic nerves (thoracic sympathetic
trunks)
Describe the muscular and neural structure of the lower part of the oesophagus
smooth muscles;
Innervated by visceral motor neurons of vagus nerve with interruptions (-synapse with postganglionic neurons; cell bodies in oesophagus and splanchnic plexus)
Which nerves encircle the oesophagus>
encircled by nerves of the oesophageal plexus
What is the Dorsal vagal nucleus
cranial nerve nucleus for the vagus nerve in the medulla
Where is the DVN located?
It lies under the floor of the 4th ventricle
What is the role of the DVN?
Mostly serves parasympathetic vagal functions in the GIT, lungs and other thoracic and abdominal vagal innervations
What is the nucleus Ambiguus?
where the cell bodies for the preganglionic parasympathetic vagal neurons that innervate the heart reside
What is the role of the phrenic nerve?
Innervates the external & internal intercostal muscles and the diaphragm, it passing motor information to the diaphragm and receiving sensory information from it
Where is the phrenic nerve located?
originates in the neck (C3-C5) and passes down between the lung and heart to the diaphragm
How many phrenic nerves are there?
2, left and right
What innervates the phrenic nerve ?
The phrenic nerve receives innervation from parts of both the cervical plexus and the brachial plexus of nerves
What is the significance of the phrenic nerves?
Provide the only motor supply to the diaphragm as well as sensation to the central tendon. In the thorax, each phrenic nerve supplies the mediastinal pleura and pericardium
What controls the contraction of the crural diaphragm?
Contraction of the crural diaphragm is controlled by the inspiratory centre in the brain stem and the nucleus of the phrenic nerve
What innervates the crural diaphragm?
right and left phrenic nerves through ACh
What causes the swallow reflex?
Excitation of receptors in pharynx (oesophageal peristalsis and relaxation)
What is swallowing?
Swallowing is the coordinated opening and closing of the upper and lower oesophageal sphincters
Outline how the swallowing reflex takes place
- The afferent stimulus travels to the sensory nucleus
(nucleus solitarius, smaller upper inset). - Programmed events from DVN + nucleus ambiguus
mediate oesophageal peristalsis and sphincter
relaxation via NO /VIP - Efferent impulses pass to pharyngeal musculature and
tongue - Vagal efferent fibres communicate with myenteric
neurons that mediate relaxation of LOS (larger lower
inset).
What are the functions of the oesophagus?
Swallowing (deglutition)
Conveys food and fluids from pharynx to stomach
How is swallowing initiated?
Swallowing is triggered by afferent impulses in the trigeminal, glossopharyngeal and vagus nerves
What causes swallowing to take place?
Efferent impulses pass to the pharyngeal musculature and the tongue
- trigeminal, facial and hypoglossal nerves
(tongue muscles)
Which impulses are required to integrate for swallowing to occur?
DVN, NTS and NA
Describe how swallowing is voluntarily initiated?
Voluntary action – collect material on tongue and push it backwards into pharynx (skeletal muscle, mucus membrane)
Describe how swallowing is involuntarily initiated?
Waves of involuntary contractions push the material into oesophagus
Food moves from Mouth→oropharynx→laryngopharynx→oesophagus + stomach
What reflex responses occur during swallowing?
Inhibition of respiration - nasopharynx closed off
Closure of glottis (around the vocal cords) by epiglottis
Prevents food from entering the trachea
Ring of peristaltic waves (4cm/sec) behind the material moves it towards the stomach
What causes food to move along the GI tract?
Progressive muscular contractions and relaxations move the food towards the stomach and along the GIT
What is swallowing difficulty caused by?
Swallowing difficulty (oropharyngeal dysphagia) is caused by:
- UOS inability to open
- Timing discoordination between UOS opening and
pharyngeal push of ingested bolus
What is the purpose of secondary peristalsis?
allows any remnants of food to be moved on
Explain how secondary peristalsis occurs
Relaxation of upper oesophageal sphincter (UOS) – food passes
UOS closes as soon as food passes
Glottis opens
Breathing resumes
Explain how primary and secondary peristalsis occur to aid swallowing
Lower oesophageal sphincter opens + stays open throughout swallowing
LOS closes after material passed
A large food material does not reach the stomach after the first peristaltic wave
Stimulation of receptors upon distension of oesophagus lumen by the food → repeated waves of peristalsis (secondary peristalsis)
How is gastric reflex prevented ?
LOS – closes after material has passed
“Pinchcock” effect of the diaphragmatic sphincter on the lower oesophagus
Plug-like action of the mucosal folds in the cardia
What is the effect of the plug-like action of the mucosal folds?
Abdominal pressure acting on the intra-abdominal parts of the oesophagus
Valve-like effect of oblique entry of oesophagus into stomach – in adults only
Explain how the UOS and LOS prevent gastric reflux?
form an opening when relaxed and closing completely when contracted
there is an anti-reflux barrier in the region of gastro-oesophageal junction
