Oesophagus and its disorders Flashcards
What is the oesophagus?
- Fibromuscular tube (25cm) of striated squamous epithelium
Where does the oesophagus lie?
- Lies posterior to the trachea
Where does the oesophagus begin and join the stomach?
- Begins at end of laryngopharynx and joins stomach a few cm from diaphragm (at the cardiac orifice)
What is the oesophagus wall composed of?
- The oesophagus wall is composed of striated muscle in the upper part, smooth muscle in the lower part, and a mixture of the two in the middle.
What coexists at the LOS?
- At the LOS both squamous and columnar epithelium may coexist.
What are the functions of the oesophagus?
- Transports food to stomach (eating gullet)
* Secretes mucus
What promotes the transport of ingested food into the stomach?
– Relaxation of the sphincters (UOS and LOS)
What does relaxation of the sphincters involve?
involves contraction and relaxation of the oesophagus which transports the food through the GIT
Steps that occur down the oesophagus
it moves from the mouth to the throat (pharynx; 1). Just as the food approaches the upper oesophageal sphincter, it opens (2) so that food/bolus can enter the oesophagus. Then rhythmic waves of muscular contractions and relaxations, called peristalsis, propel the food downward (3). The food/bolus then passes through the lower oesophageal sphincter (4) and finally into the stomach (reservoir; 5)
What muscles surrond the oesophagus?
Skeletal and smooth muscle
Where does the skeletal muscle surround the oesophagus from?
• Skeletal muscles surround the oesophagus below the pharynx (the upper third)
Where does the skeletal muscle surround the oesophagus from?
• Smooth muscles surround the lower two thirds
How many sphincters does the oesophagus have?
2
What are the 2 sphincters known as?
- Upper oesophageal sphincter (UOS)
* Lower oesophageal sphincter (LOS)
What type of muscle is the UOS?
Striated muscle
What type of structure is the UOS?
• Musculo-cartilaginous structure
Why is the UOS constricited?
• Constricted to avoid air entering the oesophagus
What type of muscle is the LOS?
Smooth muscle
What is the LOS?
area of high pressure zone where the oesophagus merges with the stomach
What type of components does the LOS has?
• LOS has intrinsic and extrinsic components
What is the intrinsic component of the LOS and where is it located?
• Intrinsic component: oesophageal muscles; under neurohormonal influence
What is the extrinsic component of the LOS?
diaphragm muscle
What can the Malfunction of intrinsic and extrinsic components of LOS ?
Leads to GORD(oesophageal reflux disease)
What layers does the intrinsic components of LOS have?
- Thick circular smooth muscle layers
What fibres are located on the right hand side of the intrinsic component of the LOS?
- Clasp-like semicircular smooth muscle fibres on the right side
What type of activity does the intrinsic components of LOS have, and what is it less responsive of?
– Myogenic activity (some resting tone), but less ACh-responsive
What fibres are located on the left hand side of the intrinsic component of the LOS?
– Sling-like oblique gastric (angle of His) muscle fibres on the left side
How does the intrinsic components of LOS helps to prevent regurgitation?
Intrinsic components of LOS Work in concert with the clasp like-semicircular smooth muscle fibres, help to prevent regurgitation
Why is reflux common in infants?
– 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?
- Angle of His (oblique angle) is the acute angle created between the entrance to the stomach (cardia), and the oesophagus
What does the angle of His form and what can it cause?
It forms a valve, preventing reflux of duodenal bile, enzymes and gastric acid from entering the oesophagus, where they can cause irritation of the oesophageal lining, inflammation and in extreme cases Barrett’s oesophagus
What encircles the LOS and what does it form?
• Crural diaphragm encircles the LOS
– Forms channel through which oesophagus enters the abdomen
What do fibers of the crural portion of the diaphragm posess?
• Fibres of the crural portion of the diaphragm possess a “pinchcock-like” action
What does the anti-reflux barrier include and what are they known as?
- The anti-reflux barriers include two sphincters: LOS and the diaphragmatic sphincter
What does the extrinsic component of LOS consist of?
consists of the diaphragm muscle
What does the the diaphragm muscle function as?
functions as an adjunctive external sphincter that raises the pressure in the terminal oesophagus related to the movements of respiration.
What does the crural diaphragm form?
- Crural diaphragm forms the oesophageal hiatus
What does the oesophageal hiatus encircle?
it encircles the proximal 2-4 cm of the LOS
What does the oesophageal hiatus determine?
determines the inspiratory-spike-like increase in LOS pressure
What are involved in the control of tone of the lower oesophageal sphincter?
Involvement of cholinergic (i.e. via ACh) and non-cholinergic, NANC innervation in the control of tone of the lower oesophageal sphincter
What is involved in the neural control of the oesophageal sphincter?
- 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
How does NO cause relaxation of smooth muscle cells?
- NO interacts with AC which converts GTP to cGMP; cGMP activates PKG which acts on myosin phosphatase on smooth muscle cells and causes smooth muscle relaxation
- Myosin phosphatase is an enzyme which dephosphorylates the regulatory chain of myosin II. The dephosphorylation reaction occurs in smooth muscles which initiates the relaxation of smooth muscles. Thus, myosin phosphatase undoes the muscle contraction process initiated by initiated by myosin light-chain kinase
What type of muscle is the upper part of the oesophagus?
Striated muscles
What is the upper part of the oesophagus supplied by?
supplied by somatic motor neurons of vagus nerve without interruption
What type of muscle is the lower part of the oesophagus?
Smooth muscles
What is the lower part of the oesophagus innervated by?
– Innervated by visceral motor neurons of vagus nerve with interruptions
The oesophagus is encircled by nerves of what?
Oesophagus is also encircled by nerves of the oesophageal plexus
What is the dorsal vagal nucleus?
- Dorsal vagal nucleus (of the vagus nerve or posterior motor nucleus of vagus) is a cranial nerve nucleus for the vagus nerve in the medulla
Where does the dorsal vagal nucleus lie?
It lies under the floor of the 4th ventricle and mostly serves parasympathetic vagal functions in the GIT, lungs and other thoracic and abdominal vagal innervations.
What resides in the nucleus ambiguus?
- The cell bodies for the preganglionic parasympathetic vagal neurons that innervate the heart reside in the nucleus ambiguus
What is the phrenice nerve?
nerve that originates in the neck (C3-C5) and passes down between the lung and heart before it reaches the diaphragm
What is the phrenice nerve important for?
Important for breathing
What does the phrenice nerve innervate?
innervates the external; and internal intercostal muscles and the diaphragm; it passes motor information to the diaphragm and receives sensory information from it.
How many phrenic nerves are there?
2 phrenic nerves
Left and right
Where does the phrenic nerve originate mainly from but where does it also receive contributions from?
- The phrenic nerve originates mainly from the 4th cervical nerve, but also receives contributions from the 5th and 3rd cervical nerves (C3-C5) in humans
What fibres does the phrenic nerve contain?
- The phrenic nerves contain motor, sensory, and sympathetic nerve fibres
What is the only motor supply to the diaphragm as well as sensation to the central tendon?
Phrenic nerves?
What does each phrenic nerve supply in the thorax?
In the thorax, each phrenic nerve supplies the mediastinal pleura and pericardium.
What does the swallow reflex lead to?
Excitation of receptors in pharynx (oesophageal peristalsis and relaxation)
Name some postganglionic transmitters
NO, VIP
What is contraction of the crural diaphragm controlled by?
- Contraction of the crural diaphragm is controlled by the inspiratory centre in the brainstem and the nucleus of the phrenic nerve
What is the crural diaphragm innervated by?
The crural diaphragm is innervated by right and left phrenic nerves through ACh
What is the striated muscle of the upper oesophagus innervated by?
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
What is the smooth muscle of the distal oesophagus innervated by?
- Smooth muscle of the distal oesophagus is innervated by the preganglionic vagus nerve fibres from the dorsal motor nucleus
What two types of neruons does ACh affect?
ACh affects two types of post-ganglionic neurons in the myenteric plexus: excitatory cholinergic neurons and inhibitory nitrinergic neurons via NO, VIP
What triggers swallowing?
• Swallowing is triggered by afferent impulses in the trigeminal, glossopharyngeal and vagus nerves
What initiats swallowing?
- 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
What happens in the inhibition of respiration?
nasopharynx is closed off
What closes the glottis?
• Closure of glottis (around the vocal cords) by epiglottis
What does closure of glottis prevent?
– Prevents food from entering the trachea
What moves food towards the stomach?
• Ring of peristaltic waves (4cm/sec) behind the material move it towards the stomach
