Physiology Of The Mouth, Pharynx And Oesophagus Flashcards
What are the functions of saliva?
- Lubricates/wets food for swallowing
- Helps with taste
- Begins digestion of starch + lipids
- Protects oral environment
How does saliva protect the oral environment?
- Washes away bacteria + food particles
- Keeps mucosa moist
- Cools hot foods
- Contents destroy bacteria
- Maintains alkaline environment -> neutralizes acid produced by bacteria preventing teeth damage
How much saliva is produced each day? What is its pH?
800-1500ml
6.2-8.0 pH (depends on whether its resting or stimulated)
What type of solution is saliva relative to plasma?
Hypotonic
What does saliva contain?
H2O
High [K+], [HCO3-] + [Ca2+] but low [Na+] + [Cl-] relative to plasma
Mucous
Digestive enzymes (e.g. salivary α-amylase + lingual lipase)
Antibacterial agents like thiocynate ions, proteolytic enzymes (e.g. lysozyme) + Abs
Why is calcium high in saliva?
To stop Ca2+ moving out of teeth by decreasing the concentration gradient
What do antibacterial agents do in the saliva?
Proteolytic enzymes attack bacteria + aid thiocynate ions in entering bacteria having a bactericide effect
Digest food particles that would provide metabolic support for bacteria
Where are the 3 pairs of salivary glands? What type of saliva do they produce?
- Parotid (on side of cheek): serous saliva, watery + rich in enzymes
- Sublingual (under tongue): mucous saliva with no enzymes
- Submandibular (under mandibular bone): mixed serous + mucous saliva
What type of glands are salivary glands?
Exocrine
What are the other salivary glands present?
Many tiny buccal glands inside of cheek + mouth
Von Ebner’s glands of tongue
Where are the 2 main digestive enzymes of saliva produced?
α-amylase - mostly in parotid salivary glands
Lingual lipase - Von Ebner’s glands of tongue
What is the structure of salivary glands? What does each part do?
‘Bunch of grapes’ appearance including:
- Acini lined by acinar cells; initially secrete saliva
- Ducts lined by ducts cells; modify secretion
- Myoepithelial cells; contract to eject saliva responding to NS signals
Does mucous stain a lighter or darker pink than serous acinus?
Lighter/paler
Explain the 1st step of saliva production.
- Isotonic ultrafiltrate diffuses from plasma through the acinar cells
- Mixes with enzymes e.g. α-amylase (serous cells) or mucins (mucous cells)
- Primary secretion drains into duct from acinar cells
Explain the 2nd step of saliva production.
Ductal modification in where there is absorption of Na+/Cl & secretion of K+/HCO3- via transporters (+ ATPase on basolateral membrane) = net absorption of solute
Ductal cells impermeable to H2O so H2O cannot follow the solute making the solution hypotonic + alkaline
What is resting saliva?
The lower flow rate of saliva due to it not being needed so there is more time for ductal modification making the solution more hypertonic relative to plasma as solutes have time to move more
What is stimulated saliva?
The higher flow rate of saliva when there is maximal salivation meaning there is less time for ductal modification so solution is more isotonic relative to plasma due to less solute movement
What is the exception to the resting vs stimulated saliva rule?
HCO3- because it is selectively stimulated when saliva production is stimulated so [HCO3-] increases with increases flow rate
What are the characteristic features of resting saliva?
Low volume Highly modified Very hypotonic Neutral pH/slightly acidic Few enzymes
What are the characteristic features of stimulated saliva?
High volume Less modification Less hypotonic More alkaline (lots of bicarb) Lots of enzymes
What are the hormonal factors involved in saliva secretion?
ADH + aldosterone: during dehydration/low vascular volume, Na+ & H2O reabsorption increases decreasing saliva volume
What does parasympathetic stimulation do to saliva secretion?
Increases it in response to:
- Stimulation of taste via taste receptors + mechanoreceptors in mouth
- Sight/smell of food
- Nausea
- Conditioned reflexes
Decreases it in response to:
- Sleep
- Fear
- Dehydration
What does sympathetic stimulation do to saliva secretion?
Initially stimulates release of preformed mucous saliva but after that, decreases saliva flow e.g. when you get xerostomia through stress
What neural control is there over saliva secretion?
Parasympathetic (most important)
Sympathetic
What are the signs and symptoms of dry mouth (xerostomia)?
Burning/scalding sensation in mouth Dry/painful throat Dry/rough tongue Dry/cracked lips Problems swallowing/speaking Altered taste Halitosis Dental caries + periodontal disease Oral infections e.g. candidiasis Difficulty keeping dentures in place
What are the potential causes of xerostomia?
Side effect of medication (e.g. TCA, antimuscarinic or β-blockers) Dehydration Anxiety Lifestyle (e.g. smoking) Radiation therapy for head + neck cancer Damage to salivary glands or innervation Sjogrens syndrome Medical conditions (e.g. poorly controlled diabetes, AD)
What is Sjogrens syndrome?
Autoimmune destruction of salivary + lacrimal glands causing xerostomia + dry eyes
Other glands can be involved causing dyspareunia, dry skin, dysphagia, otitis media + pulmonary infection
Where are receptors for taste found?
Tongue
Palate
Larynx
Pharynx
What are the 5 classifications of taste?
Sweet Sour Bitter Salty Umami
Where are the taste buds found?
Papillae:
- Fungiform (medial + anterior of tongue x 2)
- Foliate (more posterior + lateral of tongue x 2)
- Circumvallate (completely posterior + lateral to midline of tongue x 2)`
What do taste buds contain?
Taste receptor cells
Supporting cells
Basal cells
What does the umami receptor bind?
Glutamate (in protein-rich food + MSG)
What do basal cells in taste buds do?
Precursors to taste receptor cells + replace cells sloughed off the tongue
What are taste receptor cells?
Chemoreceptors (specialised epithelial cells) that transduce a chemical stimuli into an electrical signal
They respond to all taste types but may respond best to one type
How does the taste sensation work?
- CNs carry afferent info on taste
- Saliva needed as solvent
- Also requires olfaction (i.e. taste tells you jam is sweet, but smell tells you its strawberry jam)
- Signal carried to medulla + then to other regions of brain e.g. sensory cortex
What does chewing (mastication) involve?
Physical digestion i.e. breaking up food to increase SA for enzyme action
Teeth: cut (incisors) + crush (molars) food
What are the muscles of chewing (mastication)?
Masseter
Temporalis
Medial + lateral pterygoid
Suprahyoid of neck
What other facial features are involved in chewing (mastication)? What do they do?
Movement of mandible, tongue, lips + cheek help mix food with saliva creating a bolus for swallowing
What is the pharynx?
A muscular tube with 2 layers that interconnects the nasal cavity, oral cavity, larynx + oesophagus
It is the extension/top of the alimentary canal
What are the 3 parts of the pharynx and their boundaries?
Nasopharynx (behind nasal cavity): extends from skull base to soft palate
Oropharynx (posterior to oral cavity): from soft palate to epiglottis
Laryngopharynx (posterior to larynx): from epiglottis to cricoid cartilage
What are the 2 main muscular layers of the pharynx?
Inner longitudinal
External circular (made up of 3 pharyngeal constrictors; superior, middle + inferior)
What happens when the pharynx contracts?
Shortens + widens pharynx when swallowing
Elevates larynx when swallowing
Focuses bolus of food into oesophagus by peristalsis
What is special about the lower part of the inferior pharyngeal constrictor muscle?
Forms the UOS
What is the oesophagus?
Muscular tube that transports food by peristalsis, passing through the oesophageal hiatus in the diaphragm + ending at the cardiac opening of the stomach
What type of muscle is the oesophagus made up of?
Internal circular + external longitudinal muscle layers:
- Superior 1/3 = voluntary striated muscle
- Middle 1/3 - voluntary striated muscle + SM
- Inferior 1/3 = SM under autonomic control
What are the 4 points of compression/narrowing of the oesophagus?
- Junction between pharynx + oesophagus (UOS)
- Crossed by aortic arch in superior mediastinum
- Where it is posterior to L main bronchus in posterior mediastinum
- Where it passes through diaphragm at oesophageal hiatus
What is the lower oesophageal sphincter (LOS)? What does it do?
Physiological (NOT anatomical) sphincter at the gastro-oesophageal junction which allows food through + prevents reflux of gastric contents into the oesophagus
What oesophageal sphincter has the higher resting basal tone?
LOS
What are the additional components of the lower oesophageal sphincter (LOS) that help shut it?
R crus of diaphragm (contracts acting like a pinchcork)
Acute angle at which oesophagus enters stomach
Mucosal folds at gastro-oesophageal junction (acts like ‘cork in the bottle’)
+ve intra-abdominal pressure collapses oesophagus preventing reflux
What is gastro-oesophageal reflux disease (GORD)?
Reflux of acidic contents through LOS occurring when normal anti-reflux mechanisms are impaired
What is reflux oesophagitis?
Mucosa of oesophagus becomes damaged due to acidic irritation
How can normal anti-reflux mechanisms become impaired?
Increased frequency of transient lower oesophageal sphincter relaxations (TLESRs)
Increased intra-abdominal pressure e.g. pregnancy
Low LOS pressure
Hiatus hernia prevents normal functioning of LOS + disrupts diaphragmatic action on LOS
What are the signs and symptoms of gastro-oesophageal reflux disease (GORD)?
Heartburn: burning lower chest pain radiating upwards (related to meals, worse on bending/lying down + relieved by antacids)
Acid brash: acid in back of throat
Regurgitation of stomach contents
Water brash: increased salivation in response to acid presence
What is the correlation between symptoms and pathological severity in gastro-oesophageal reflux disease (GORD)?
Poor because a patient may not have many symptoms but severe oesophagitis in endoscopy or vice versa
What are the risk factors associated with gastro-oesophageal reflux disease (GORD)?
Pregnancy Obesity Fat Coffee Chocolate Alcohol Large meals Smoking Certain drugs e.g. antimuscarinics Systemic sclerosis Achalasia treatment Hiatus hernia
What is Barrett’s oesophagus?
Metaplasia of stratified squamous epithelium of oesophagus to columnar mucosa so there is proximal displacement of squamocolumnar junction between 2 cell types seen high up in the oesophagus
What are the causes of Barrett’s oesophagus?
Complication of GORD
Hiatus hernia
What do patients with Barrett’s oesophagus have an increased risk of?
Oesophageal adenocarcinoma
Explain the oral (voluntary) phase of swallowing.
- Tongue moves bolus from oral cavity back towards oropharynx
- Sensory receptors in soft palate + anterior pharynx detect bolus + send info via CNs to swallowing centre in medulla
- Swallowing reflex initiated
Duration = up to 1 second
Explain the pharyngeal (involuntary) phase of swallowing.
- Soft palate elevates blocking off nasopharynx
- Respiration inhibited, glottis closes, larynx elevates + epiglottis tilts to cover opening of larynx to protect respiratory tract
- UOS opens
- Peristaltic wave of contraction of pharyngeal constrictor muscles propels food through sphincter into oesophagus
Duration = 1 second
Explain the oesophageal phase of swallowing.
- UOS closes preventing reflux into pharynx
- Larynx falls, glottis opens + respiration commences
- Primary peristaltic wave (coordinated by swallowing reflex) propels food down oesophagus + stretch receptors detect bolus presence
- LOS relaxes to allow bolus into stomach
- Secondary peristaltic wave may occur (mediated by ENS - brain not needed as it is a localised system)
What are the stages of swallowing?
- Oral (voluntary)
- Pharyngeal (involuntary)
- Oesophageal
Why is it important to assess swallowing?
It is an important brainstem function that must be checked in head injury, post-surgery or stroke for e.g. because dysfunctional swallowing is associated with a high risk of aspiration which can cause pneumonia
How do you assess swallowing?
- History + examination
- Speech + language therapy (SLT):
- Clinical assessment
- Bedside swallow test
- Instrumental assessment - Barium swallow
- Manometry
What is achalasia?
Loss of coordination of peristalsis of lower oesophagus + spasm of LOS preventing food from moving easily through oesophagus into stomach -> dilation + hypertrophy of oesophagus superior to area of functional obstruction+ damage to Auerbach’s plexus
What are the symptoms of achalasia?
Intermittent dysphagia for solids/liquids
Regurgitation of food
Retrosternal chest pain
How would you be able to determine the difference between dysphagia associated with oesophageal carcinoma or achalasia?
Dysphagia tends to be more rapid with cancer but cannot rule it out on history so must do:
- CXR
- Barium swallow
- Endoscopy
- Manometry
What instrumental assessments can be done on swallowing?
Videofluoroscopic swallowing study
Fibreoptic endoscopic evaluation of swallowing
