Oesophagus and its disorders Flashcards
Describe the anatomy of the oesophagus (3)
- Fibromuscular tube (25cm) of striated squamous epithelium
- 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 does the oesophagus secrete?
Mucus
What promotes the transport of ingested food into the stomach?
- This is a highly coordinated muscular process; involves contraction and relaxation of the oesophagus which transports the food through the GIT
- Relaxation of the sphincters (UOS and LOS)
What muscle surrounds the oesophagus and at what positions?
- Skeletal muscles surround the oesophagus below the pharynx (the upper third)
- Smooth muscles surround the lower two thirds
What are the two sphincters of the oesophagus?
Describe there structures
Give the intrinsic and extrinsic component oF the LOS
Upper oesophageal sphincter (UOS): striated muscle;
Musculo-cartilaginous structure
Constricted to avoid air entering the oesophagus
• Lower oesophageal sphincter (LOS): smooth muscle; acts as a flap valve
LOS = area of high pressure zone
LOS has intrinsic and extrinsic components
Intrinsic component: oesophageal muscles; under neurohormonal influence
Extrinsic component: diaphragm muscle (adjunctive external sphincter)
The lower oesophageal sphincter has intrinsic and extrinsic components.
What are the intrinsic components of the LOS?
- Thick circular smooth muscle layers and longitudinal muscles
- Clasp-like semi-circular smooth muscle fibres on the right side
Myogenic activity (some resting tone), but less ACh-responsive - Sling-like oblique gastric (angle of His) muscle fibres on the left side
Working in concert with the clasp like-semicircular smooth muscle fibres, help to prevent regurgitation- responsive to cholinergic innervation
Angle of His is poorly developed in infants as it makes a vertical junction with stomach, hence why reflux is common in infants
What are the extrinsic components of the LOS?
Crural diaphragm encircles the LOS
= Forms channel through which oesophagus enters the abdomen
Fibres of the crural portion of the diaphragm possess a “pinchcock-like” action (extrinsic sphincter; diaphragmatic sphincter)- myogenic tone
Describe the innervation of the oesophagus
Involvement of cholinergic (i.e. via ACh) and non-cholinergic, NANC innervation in the control of tone of the lower oesophageal sphincter
Neural control of the oesophageal sphincters
- Acetylcholine, SP: contraction of intrinsic sphincters
- NO and VIP: relax the intrinsic sphincters
- Extrinsic and intrinsic sphincters work in concert to push the food into the stomach
Describe other nerves of the oesophageal plexus
DVN: dorso vagal nucleus;
NA: nucleus ambiguus;
NTS: nucleus tractus solitarius
Describe Oesophageal motor innervation
What 2 post-ganglionic fibres in the myenteric plexus does ACh affect?
The striated muscle of the upper oesophagus is innervated directly by the somatic efferent cholinergic fibres of the vagus nerve originating from the nucleus ambiguus.
Smooth muscle of the distal oesophagus is innervated by the preganglionic vagus nerve fibres from the dorsal motor nucleus. ACh affects two types of post-ganglionic neurons in the myenteric plexus: excitatory cholinergic neurons and inhibitory nitrinergic neurons via NO, VIP
Describe the functions of the oesophagus?
- Swallowing (deglutition)
* Conveys food and fluids from pharynx to stomach
How is swallowing initiated?
- Voluntary action – collect material on tongue and push it backwards into pharynx (skeletal muscle, mucus membrane)
- Waves of involuntary contractions push the material into oesophagus
Where does food move?
Food moves from Mouth→oropharynx →laryngopharynx→oesophagus and stomach
What reflex responses are initiated to swallow?
- Reflex responses
- Inhibition of respiration (breathing)- nasopharynx is 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
- A second wave of peristalsis moves any food remnants along
What is swallowing difficulty caused by?
Swallowing difficulty (oropharyngeal dysphagia) is caused by the inability of the UOS to open or discoordination of the timing between the opening of UOS and the pharyngeal push of ingested bolus
When food passes through the oesophagus when does the UOS and LOS open and close?
What happens during secondary peristalsis
Relaxation of upper oesophageal sphincter (UOS) – food passes
- UOS closes as soon as food passes
- Glottis opens
- Breathing resumes
Lower oesophageal sphincter opens and stays open throughout swallowing
LOS closes after material has passed
A large food material does not reach the stomach after the first peristaltic wave
Stimulation of receptors upon distension of the lumen of the oesophagus by the food → repeated waves of peristalsis (secondary peristalsis)
Is secondary peristalsis of any benefit?