Oesophagus and its disorders Flashcards
What does the oesophagus lie posterior to?
Lies posterior to the trachea
Where does the the esophagus begin and where does it join the stomach?
Begins at end of laryngopharynx and joins the stomach a few cm from
diaphragm (at the cardiac orifice of the stomach)
What muscles surround the upper third of the oesphagus?
Skeletal muscles surround the upper third of the oesophagus, below the
pharynx
What muscles surround the lower 2/3rds of the oesphagus?
Smooth muscles surround the lower two thirds
What muscle is the UOS made from?
Striated muscle
Why is the UOS constricted?
Constricted to avoid air entering the oesophagus
What muscle is the LOS made up of?
Smooth muscle
What is the intrinsic components of the LOS made up of and what is it under the influence of?
Intrinsic components of LOS: oesophageal muscles; under
neurohormonal influence
What is the extrinsic component of LOS made of?
Extrinsic components of LOS: diaphragm muscle
What muscle types is the intrinsic components of the LOS made up of?
Thick circular smooth muscle layers and longitudinal muscles
What are the muscle fibres like on the right side of the LOS? What activity keeps them running?
Clasp-like semi-circular smooth muscle fibres on the right side
– Myogenic activity (some resting tone initiated by the cells within), but
less ACh-responsive
What are the muscle fibres like on the left side of the LOS and how do they work and what do they prevent?
Sling-like oblique gastric (angle of His) muscle fibres on the left side
– Work in concert with the clasp like-semicircular smooth muscle fibres,
help to prevent regurgitation- responsive to cholinergic innervation
Why is reflux common in infants?
Angle of His is poorly developed in infants for it makes a vertical
junction with stomach, hence why reflux is common in infants
What part of the diaphragm encircles the LOS and what does this form?
Crural diaphragm encircles the LOS
-Forms channel through which oesophagus enters the abdomen
What type of action do the fibres of the crural portion of the diaphragm posses?
Fibres of the crural portion of the diaphragm possess a “pinchcock-like”
action (extrinsic sphincter; diaphragmatic sphincter)- myogenic tone
What is the upper part of the esophagus innervated by? What neurotransmitter is involved?
Striated muscle fibres in upper part:
-Nucleus ambiguus gives out somatic motor neurons from vagus nerve(splanchnic nerves)
-Ach
What is the lower part of the oesophagus innervated by? What neurotransmitter is involved?
Smooth muscles in lower part:
-Innervated by visceral motor neurons of the vagus nerve with interruptions
-synapse with postganglionic neurons; cell bodies in oesophagus and splanchnic plexus
What is the neural control of the oesophageal sphincters?
Oesophagus is encircled by nerves of the
oesophageal plexus
What neurotransmitters contract the intrinsic sphincters?
Acetylcholine & SP contract the intrinsic
sphincters
What neurotransmitters relax the intrinsic sphincters?
NO & VIP relax the intrinsic sphincters
What does gastrin do to intrinsic factors?
Gastrin contracts the intrinsic sphincters
What is the route of impulses during swallowing? BASIC
-Afferent impulses in the glossopharyngeal- vagal reflex
-Integration of impulses in the nucleus of tractus solitarius (NTS), nucleus
ambiguus (NA) and dorsal vagal nucleus
-Efferent impulses/motor pathways pass to the pharyngeal musculature, tongue, along the oesophagus; the LOS opens
Explain innervation of the oesophagus? DETAILED
-Afferent sensory pathways detect food in pharynx as well as oesophagus and crural part of diaphragm and transmit impulses which are integrated in the NTS
-This triggers phrenic nerve which has a motor innervation to the crural parts of diaphragm causing contraction
-Myenteric plexus is also innervated by vagus nerve which innervates the LOS
What is inhibited during swallowing?
Inhibition of respiration (breathing)- nasopharynx is closed off
What is closed during swallowing and what is this to prevent?
Closure of glottis (around the vocal cords) by epiglottis
– Prevents food from entering the trachea
What waves behind the food mass move the food towards the stomach and at what rate?
Ring of peristaltic waves (4cm/sec) behind the food mass moves it towards the stomach
What does the second wave of peristalsis do during swallowing?
A second wave of peristalsis moves any food remnants along the
oesophagus
What happens as soon as food passes the UOS and what does this cause?
– UOS closes as soon as food passes
– Glottis opens
– Breathing resumes
– Coordinated peristalsis moves the food towards the LOS
What triggers secondary peristalsis?
Distension of the lumen of the oesophageal body by food remnants
stimulates the receptors → repeated waves of peristalsis (secondary
peristalsis)
What does secondary peristalsis ensure?
Secondary peristalsis ensures that all of the ingested food reaches the
stomach. Do not forget the role of vagal innervation - cholinergic (ACh, SP)
and non-cholinergic innervation (NO, VIP)
Introduction
What are the 3 mechanisms that prevent gastro-oesophageal reflux?
- LOS – closes after the food mass has passed
- “Pinchcock” effect of the diaphragmatic sphincter on the lower
oesophagus (side-to-side compression between “2 pillars” of the crus) - Plug-like action of the mucosal folds in the cardia– occludes the lumen
of the gastro-oesophageal junction:
– Intrabdominal pressure compresses the intra-abdominal parts of the
oesophagus
– Valve-like effect of oblique entry of oesophagus into stomach
What type of muscles are the sphincter muscles of the UOS and LOS and what do they act as?
Sphincter muscles of UOS and LOS = strong circular muscles
– Act as valves; and the law of the gut promotes and controls the movement
of the food mass aborally (movement towards the anus)