Physiology of Mouth, Pharynx, Oesophagus Flashcards
State the functions of saliva
Lubricates food for swallowing
Helps with taste
Begins digestion of starch and lipids
Protects oral environment - cools hot food, washes away bacteria
Maintains alkaline environment - prevents teeth damage
List the 6 components of saliva
Water
High K+, HCO3-, Ca2+
Low Na+ Cl-
Mucous
Digestive enzymes - salivary a-amylase, lingual lipase
Antibacterial agents - thiocynate ions, proteolytic enzymes
What is the pH of saliva?
What type of solution is it?
6.2-8.0
Hypotonic solution (compared to plasma)
What is the purpose of proteolytic enzymes and thiocynate ions?
Proteolytic enzymes attack bacteria and aid thiocynate ions in entering the bacteria and have bactericide effect.
They also digest food particles that would provide metabolic support for the bacteria
Name the 3 pairs of salivary glands
Parotid
Sublingual
Submandibular
Which glands in the tongue produce lingual lipase?
Von Ebner’s glands
What type of glands are salivary glands?
Exocrine glands
What type of secretions does the parotid gland produce?
Serous saliva
Watery
Rich in enzymes
What type of secretions does the sublingual gland produce?
Mucous saliva
No enzymes
What type of secretions does the submandibular gland produce?
Mixed serous and mucous
Where is the main site of production of salivary a-amalyse?
Parotid gland
Describe the structure of salivary glands
Bunch of grapes appearance
Has acinus at the end of the ducts
What 3 type of cells are found in a salivary gland?
Where are they found?
What is their function?
Acinar cells - line the acini (endpieces) and produce the initial secretion
Duct cells - line the ducts of the glands, modify the secretion
Myoepithelial cells - contract to eject saliva
What are the 2 steps to saliva production
Primary secretion
Ductal modification
Outline primary salivary secretion
Isotonic filtrate from plasma diffuses through acinar cells
Mixes with enzymes (serous cells) or mucins (mucous cells)
Secretion drains into ducts
Outline ductal modification
Net absorption of Na+ and Cl-
Net secretion of K+ and HCO3-
Absorption outweighs secretion
Water is unable to follow Na+ - cells or impermeable
End up with hypotonic solution
What provides the energy or electrolyte transport across the duct cells of a salivary gland?
Na+/K+ ATPase on the basolateral membrane
Draw out a salivary ductal cell with its transporters
Slide 14
Describe some differences between resting and stimulated saliva
What is the ‘exception to the rule’?
Rest - saliva flow rate is lower, more time for ductal modification
Stimulated - flow rate is higher, less time for ductal modification, saliva is more similar to plasma
HCO3- is selectively stimulated when saliva production is stimulated - stimulated saliva is more alkaline
What hormonal factors can influence salivary production?
Antodiuretic hormone (ADH)
Aldosterone
In dehydration Na+ and water reabsorption increases, saliva volume decreases
Briefly describe the neural control of saliva secretion
Controlled by the ANS
Parasympathetic - increases saliva secretion in response to mechanoreceptors, sigh and smell of food, conditioned reflexes
Sympathetic - initially stimulates release of preformed mucous saliva, but then saliva flow decreases
What is the term given for ‘dry mouth?
Xerostomia
Give some symptoms of Xerostomia
Burning/scalding sensation in mouth
Dry and painful throat
Dry and rough tongue
Dry and cracked lips
Problems swallowing and speaking
Altered taste
Halitosis
Dental caries and periodontal disease
Oral infections, e.g. candidiasis
Difficulty with keeping dentures in place
List some potential causes of xerostomia
Side effect of medication, e.g. tricyclic antidepressants, antimuscarinic drugs, beta-blockers etc.
Dehydration
Anxiety
Lifestyle, e.g. smoking
Radiation therapy for head and neck cancer
Damage to salivary glands or their innervation
Sjögren’s syndrome
Medical conditions, e.g. poorly controlled diabetes, Alzheimer’s disease
What is Sjogren’s syndrome?
Autoimmune destruction of salivary and lacrimal glands
What are the two most common symptoms of Sjogren’s syndrome?
Dry mouth
Dry eyes
List the 4 places taste buds are found
Tongue
Palate
Larynx
Pharynx
What are the 5 taste classifications?
Sweet
Sour
Bitter
Salty
Umani
In what structures in the tongue are taste buds found?
Papillae
What 3 types of papillae are there?
Fungiform
Foliate
Circumvallate
What 3 cells types to taste buds contain?
Taste receptor cells
Supporting cells
Basal cells - replace taste receptor cells when they are sloughed off
What type of cells are taste receptor cells?
Chemoreceptors - specialised epithelial cells which transduce a chemical stimuli into electrical signals
They respond to all taste types, but usually response best to one
Where are taste signals sent to?
The medulla, then sensory cortex
What is the purpose of mastication?
Break food up to increase the surface area for enzymes to work
Name some important muscles of mastication
Which cranial nerve supplies them?
Masseter
Temporalis
Medial pterygoid
Lateral pterygoid
CN Vc
What are the 3 portions of the pharynx?
What are their borders?
Nasopharynx - skull base to soft palate
Oropharynx - soft palate to epiglottis
Laryngopharynx - epiglottis to cricoid cartilage, posterior to larynx
Name the 3 external circular muscles of the larynx
What is their purpose?
Superior constrictor
Middle constrictor
Inferior constrictor
Forces bolus into oesophagus by peristalsis
What 2 categories of muscle are found in the pharynx?
Inner longitudinal muscles
External circular muscles
What do the inner longitudinal muscles of the pharynx do?
Shortens/widens the pharynx when swallowing
Elevates larynx when swallowing
What is the cricopharyngeus?
Why is it important?
The lower portion of the inferior constrictor muscle of the pharynx
It forms the upper oesophageal sphincter
What forms the upper oesophageal sphincter?
The lower border of the inferior constrictor muscle
Where does the oesophagus end?
The cardiac opening of the stomach?
T10
Describe the distribution of muscle in the oesophagus and its control
Superior third - voluntary striated muscle (somatic control)
Middle third - voluntary striated muscle and smooth muscle
Inferior third - smooth muscle (autonomic control)
List the 4 points of compression/narrowing of the oesophagus
Junction between pharynx and oesophagus
Superior mediastinum where it is crossed by the arch of the aorta
Posterior mediastinum where it is posterior to the left main bronchus
Oesophageal hiatus
What is the function of the lower oesophageal sphincter (LOS)?
Prevent reflux of gastric contents into oesophagus
What components of the LOS prevent reflux?
Higher resting basal tone of muscles (not a true anatomical sphincter)
Right crus of diaphragm
Acute angle of entry to the stomach
Mucosal folds at gastro-oesophageal junction
Positive intra-abdominal pressure
List some symptoms of gastro-oesophageal reflux disease (GORD)
Heartburn
Acid brash
Regurgitation
Water brash
There is a poor correlation between symptoms and pathological severity
Why does pregnancy increase the likelihood of developing GORD?
Higher intra-abdominal pressure forces stomach contents upwards
What complication can occur due to GORD?
Reflux oesophagitis - damage to the mucosa
What is Barrett’s oesophagus?
Metaplasia of squamous epithelium of oesophagus to columnar mucosa
Proximal displacement of squamocolumnar junction - difference between simple squamous and columnar epithelium caused by acid being further up the oesophagus
What type of cells normally line the oesophagus?
What do these cells change to in Barrett’s oesophagus?
Simple squamous
Columnar epithelium
List the 3 phases of swallowing
Oral phase
Pharyngeal phase
Oesophageal phase
What happens during the oral phase of swallowing?
Tongue moves bolus to oropharynx
Sensory receptors in palate and anterior pharynx send info to swallowing centre in medulla
Swallowing reflex initiated
Voluntary
What happens during the pharyngeal phase of swallowing?
Soft palate elevates and blocks nasopharynx - respiration inhibited
Glottis closes
Larynx elevates
Epiglottis tilts to cover opening of larynx
Peristaltic wave pushes food through sphincter into oesophagus
Involuntary
What happens during the oesophageal phase of swallowing?
Upper oesophageal sphincter closes - prevents reflux into pharynx
Larynx falls
Glottis opens
Respiration recommences
Primary peristatic wave coordinated by swallowing reflex, propels food down oesophagus
Lower oesophageal sphincter relaxes
Secondary peristatic wave occurs mediated by the enteric nervous system
Involuntary
What controls the primary and secondary peristatic waves in swallowing?
Primary - swallowing reflex
Secondary - enteric nervous system
Where in the brainstem is swallowing coordinated?
Medulla
What is achalasia?
List some symptoms
Loss of coordination of peristalsis of lower oesophagus and spasm of LOS
Intermittent dysphagia for both solids and liquids
Regurgitation of food
Retrosternal chest pain
