PBL 1 Flashcards
What are the two plexuses of the ENS and where are they found?
Submucosal plexus (Meissner’s plexus) - lies in the submucosa layer
Myenteric plexus - lies in the muscularis externa layer
Describe the concept of the ‘Gut brain’
Neurons in the submucosal and myenteric plexuses have their own neuronal cell bodies, therefore are able to function on their own, independent of extrinsic nerve fibres from the CNS
What are pacesetter cells?
Cells found in the smooth muscle of the digestive tract, which set rhythmic cycles of activity in the muscle. They undergo spontaneous depolarisation, triggering waves of contraction that spread throughout the muscle
Which plexus of the ENS is responsible for controlling peristalsis waves?
Myenteric plexus in the muscularis externa
What is the difference between primary and secondary peristalsis?
Primary - coordinated by afferent and efferent fibres in glossopharngeal and vagus nerves
Secondary - local reflexes which are stimulated by the presence of ‘stuck bolus’ in the oesophageal walls
What are the various things that happen in the pharyngeal stage of swallowing?
Pharynx contracts
Upper oesophageal sphincter opens
Airways closes
Larynx is elevated - causes epiglottis to swing back
How does the type of muscle change down the oesophagus?
Upper 1/3rd - striated/skeletal
Middle 1/3rd - mixed skeletal and smooth
Lower 1/3rd - smooth muscle
What vertebral levels are the upper and lower oesophageal sphincters at?
UOS: C6
LOS: T11
What are the pressure levels at the upper and lower oesophageal sphincters?
Why are these pressures high?
UOS: 100mmHg
LOS: 20mmHg
Ensure that they remain closed apart from during swallowing
How is swallowing controlled by the brain?
- Sensory receptors in the oropharynx, larynx and oesophagus detect changes and send signals back to the brainstem
- The brainstem central program generator (CPG) in the medulla send signals through the motor neurons V, VII, XI, X, XII to control the muscles involved in swallowing
What are the two types of saliva and what do they contain?
Serous secretion - contains ptyalin (alpha amylase), good for digesting starches
Mucous secretion - contains mucin, used for lubricating
What are the four classes of salivary glands and what type of secretion do they have?
Parotid glands - serous secretion
Submandibular - serous/mucous secretion
Sublingual - mucous secretion
Buccal - mucous secretion
What are the two stages of saliva secretion?
1) Primary secretion by the acinis
2) Reabsorption on ions by the salivary ducts
How does the rate of saliva secretion effect the composition?
The faster the secretion, the more salty the secretion, as there is less time for reabsorption by the salivary ducts
What happens in primary secretion of saliva by acini?
Calcium activitied chloride channel allows Cl- efflux into the salivary duct lumen
The negative potential created by chloride causes Na+ to enter the lumen via tight junctions
Water follows via osmosis through aquaporin 5 channels
How is tight junction permability in epithelium determined?
By claudin family proteins:
- some claudin don’t have any pores - won’t let anything through
- some claudin have pores that are selective to sodium - will let sodium through
What happens during reabsorption in the salivary ducts?
Sodium and chloride ions are reabsorbed into epithelial cells and into the blood
- sodium enters passively through ENaC channel
- chloride is drawn in through channel through positive potential
- chloride is also exchanged for bicarbonate
What happens during parasympathetic innervation of salivary glands?
Ach is released which binds to muscarinic receptors on acini
This produces IP3, which in turn causes calcium release in epithelial cells
Calcium activates Cl- and K+ transporters to stimulate ion release from acini
What happens during sympathetic innervation of salivary glands?
There is a slight stimulation of salivary release, but much less so than parasympathetic stimulation
What are the 2 types of dysphagia?
Oropharyngeal dysphagia (high dysphagia) - problems with swallowing in the mouth or throat Oesophageal dysphagia (low dysphagia) - problems with swallowing in the oesophagus
What are the main causes of Oropharyngeal dysphagia?
Zenker’s Diverticulum (Anatomical) - decreased compliance of cricopharyngeus (UOS)
Stroke (Neurological) -
Myasthenia Gravis (Muscular) - weak pharyngeal contraction
How can stoke lead to aspiration Pneumonia?
Stroke can cause dysphagia
Inability to swallow food can lead to it going down wrong hole
Inhalation of stomach contents or secretions into the respiratory tract can lead to infection
What is videofluorscopy?
Patient swallows barium while in a fluoroscope (x ray)
You can then determine where the bolus is going
What is a fiberoptic endoscopic examination?
Where an endoscope is passed through the nose to get a view of the pharynx and larynx
Good at looking at anatomy but not for function
