Physiology -- Deglutition and Dysphagia Flashcards
3 functional activities of the GIT
- Propulsion
- Secretion & digestion
- Absorption
What do the pressure gradients of the GIT result from?
Coordinated contraction of muscular elements in the GI wall
Magnitude of the pressure gradient in the GIT
5 - 30 mm Hg
Stimulus to generate contractions in the GIT
Physiological distension
What does physiological distension cause?
- Stimulation of stress muscle fibres
- Neurotransmitter release (ENS)
What is the ENS modulated by?
ANS and hormones
2 types of contraction
Segmentation and Peristalsis
Define segmentation
Standing rings of contraction
Define peristalsis
Propagated contraction
5 sphincters in the GIT from top to bottom
- Upper esophageal
- Lower esophageal
- Pyloric
- Ileocecal
- Internal and external anal
3 requirements for flow
- Generate pressure
- Prevent dissipation of pressure
- Decrease resistance
3 phases of swallowing
- Oral
- Pharyngeal
- Esophageal
Alteration in the phases of swallowing can result in what?
Dysphagia
Define dysphagia
Difficulty or delay in passage of solid or liquid food bolus that is sensed by the patient within seconds of initiaiton of a swallow attempt
Prevalence of dysphagia in people over 65
15%
2 types of dysphagia
- Oropharyngeal
- Esophageal
Define esophageal dysphagia
Food stuck in the center of the chest
Define oropharyngeal dysphagia
Coughing or choking
2 mechanisms that can result in dysphagia
- Mechanical obstruction and/or structural abnormality
- Neuromotor
Type of control exhibited in the oral phase
Voluntary control
2 neural components of the oral phase
- Ability to initiate (voluntary –> cortex)
- Coordinated movements (reflex; involuntary –> medulla)
4 abnormalities in the oral phase
- Neuromuscular defect
- Congenital abnormalities
- Bucco-pharyngeal obstruction
- Trauma and inflammation
How do neuromuscular defects cause abnormalities in the oral phase
Prevent generation of pressure
How do congenital abnormalities cause abnormalities in the oral phase?
Promote dissipation of pressure
How can bucco-pharygneal obstruction cause abnormalities in the oral phase?
Increase resistance to flow
DIfferential diagnosis of dysphagia in the event of trauma and inflammation causing abnormalitites in the oral phase
Odynophagia
3 prerequisites for propulsion
- Generation of pressure
- Prevention of the dissipation of pressure
- Decrease resistance
Pharyngeal receptors bring afferent neurons to which part of the brain?
Deglutition center
Deglutition reflexes sent out from the deglutition center resulting from the information received from the pharyngeal receptors
- Protective reactions
- Deglutition apnea
- Relax UES
- Contract pharyngeal constrictors
Trigger areas for deglutition reflexes
- Soft palate
- Uvula
- Palatine tonsil
- Root of tongue
- Epiglottis
What does the deglutition center have a direct inhibitor influence on? What does this lead to?
Respiratory center –> deglutition apnea
6 steps in the pharyngeal phase
- Raise soft palate
- Raise base of tongue
- Vocal cords come together
- Forward and upward movement of larynx
- Propagated contraction of pharyngeal constrictors
- Relaxation of UES
Where do the impulses for the closure of the cricopharyngeus originate?
Centraly
What mediates the closure of the cricopharyngeus
Vagus releasing ACh at neuromuscular junction –> muscle contraction
How does the cricopharyngeus relax?
Cessation of impulses from vagus releasing ACh
4 characteristics of the pharyngeal phase
- Involuntary
- Rapid
- “Stereotyped”
- Temporospatial coordination
3 defects in the pharyngeal phase
- Failure of propulsion
- Obstruction to flow
- Psychological factors
2 effects caused by failure of propulsion in pharyngeal phase
- Generates less pressure
- Increases dissipation of pressure
4 parts that can be involved in the failure of propulsion in the pharyngeal phase
- Brain
- Cranial nerves
- Myoneural junction
- Muscle
Effect of obstruction to flow causing pharyngeal phase defects
Increased resistance
2 causes of obstruction to flow in pharyngeal phase
- Mass effect
- Incomplete sphincter relaxation
Psychological factor that can cause defective pharyngeal phase
Globus hystericus
3 esophageal forces
- Pharyngeal momentum
- Gravity
- Peristalsis
What force is generated each time that we swallow
A single primary peristaltic wave (part of the deglutition reflexes)
Time of propagation of one wave of primary peristalsis along the length of the esophagus
8 - 10 seconds
Describe the vagal innervation from the deglutition center to generate primary peristalsis (diagram)
Consequence of cutting the vagal fibres high up in the neck on primary peristalsis
Consequence of cutting vagal fibres transthoracically on primary peristalsis
Primary peristalsis continues because the distal esophagus has the enteric circuitry necessary for the propagation of the peristaltic wave (orange fibres in diagram)
Define “vago-vagal reflex”
Reflex produced due to the vagal afferent nerves sending information to the brain centers, which send out efferent vagal nerves
What is essential for initiating peristalsis in the proximal esophagus
Vagus
What is required for the continuation and propagation of peristalsis in the distal esophagus
Intactness of ENS
Stimulus for secondary peristalsis
Local distension (i.e. food lodged in esophagus)
Similarities between primary and secondary peristalsis
- Upper esophagus requires vagus
- Lower esophagus requires ENS
- Pressure generated is 30 - 60 mmHg
Differences between primary and secondary peristalsis
- Different stimuli
- Primary = pharyngeal receptors
- Secondary = local distension
- Different frequency
- Primary = only 1 contraction per swallow
- Secondary = many contractions until bolus is displaced
Define deglutitive inhibition
Central inhibition of primary peristaltic wave resulting from rapid, repeated stimulation of pharyngeal receptors (i.e. sipping fluid through a straw)
How are liquids brought through the esophagus?
Deglutitive inhibition –> cessation of stimulation of pharyngeal receptors –> single peristaltic wave sweeps over esophagus –> empty contents
3 facotrs influencing esophageal transport
- Viscosity of bolus
- Temperature of bolus
- Posture of subject
What type of control is exhibited in the closure of the LES
Myogenic
What type of control is exhibited in the relaxation of the LES?
Neurogenic –> local release of NANC
Compare the characteristics of the upper esophageal sphincter vs. the lower esophageal sphincter
When closed, what is the magnitude of the resistance to flow provided by the lower esophageal sphincter?
10 - 30 mm Hg
6 characteristics of the LES musculature (in vitro)
- More collagen fibres
- Lower RMP; partially contracted at RMP
- More resistant to stretch
- Sensitive to hypoxia
- Ca++ dependent
- More sensitive to transmitters and hormones
Does gastrin provide modulation of the LES?
ONLY in large (pharmacologic) doses!!
3 gut hormones that have an effect on LES
- Gastrin (increase tone)
- Secretin (decrease tone)
- CCK (decrease tone)
Special hormone that decreases LES tone and the specific period when it has an effect
Progesterone decreases sphincter tone during the last trimester of pregnancy (reason for reflux during this period)
6 external influences on the LES and their effects
- Cigarette smoking
- Alcohol (high doses)
- Morphine, valium
- Fat
- Chocolate
- Carminatives
All decrease LES tone
Factors that affect the LES (Venn diagram)
Define pyrosis
Heartburn: retrosternal burning sensation, radiating upwards from the xiphoid towards the neck
Rate of occurrence of reflux in healthy individuals + duration
1 - 4 instances per hour (usually <30 sec)
Define transient LES relaxation (TLESr)
Reflux occurring in healthy individuals
3 disordered functions associated with GERD
- Ineffective esophageal clearance of refluxate
- Less effective secondary peristalsis
- Defective epithelial resistance to damage by refluxate
Why does an increase in intraabdominal pressure cause a greater than expected increasei in LES pressure?
Reflex tightening of the LES (vago-vagal reflex)
3 ways to examine the esophagus
- Radiology
- Endoscope
- Intraluminal pressure recording (manometry)
Esophageal resting pressure
-5 mm Hg
UES resting pressure
+80 mm Hg
LES resting pressure
+20 mm Hg
Pharyngeal resting pressure
0 mm Hg
Stomach resting pressure
+5 mm Hg
Describe the normal manometric recordings in response to swallowing
- 8 - 10 sec for wave to reach distal esophagus
- Pressure complex = 30 - 80 mm Hg
- LES relaxes early
Describe the manometric findings of a patient with achalasia
- LES does not relax with wet swallows
- Wet swallows do not produce peristaltic pressure waves in the esophagus
- Instead, there are low-amplitude, simultaneous P waves with a nearly identical configuration (not sequential)
Define achalasia
Failure to relax:
- Aperistalsis
- Incomplete relaxation of LES with swallowing
- Increased resting tone of LES
Potential cause for achalasia
Dysfunction of inhibitory neurons in distal esophagus:
- NO
- VIP
3 categories of oropharyngeal dysphagia
- Structural
- Myogenic
- Nervous system
3 types of structural oropharyngeal dysphagia
- Poor dentition, xerostomia
- Intraluminal
- Extraluminal
3 intraluminal causes of oropharyngeal dysphagia
- Diverticulae
- Webs
- Oropharyngeal tumors
3 extraluminal causes for structural oropharyngeal dysphagia
- Osteophytes
- Thyromegaly
- Lymphadenopathy
5 causes for nervous system-related oropharyngeal dysphagia
- Head injury
- Brainstem tumors
- Stroke
- MS
- Parkinson’s
2 types of esophageal dysphagia
- Structural
- Motility abnormalities
4 intraluminal causes for esophageal dysphagia
- Stricture
- Schatzki’s ring
- Cancer
- Eosinophilic esophagitis
Extraluminal cause for esophageal dysphagia
Mediastinal tumors (lymphoma, lung cancer)
5 motility abnormalities that may cause esophageal dysphagia
- Achalasia
- Esophageal spasm
- Secondary achalasia from tumor infiltration
- Diabetes
- Collagen vascular disorders
