Mouth & Swallowing Flashcards
What functions of the GI tract are applicable to the mouth?
- ingestion
- mechanical processing
- digestion
- secretion
- limited amounts of absorption and excretion
What substances are absorbed in the mouth?
The mucosa under the tongue is highly vascularised so some substances are absorbed here
Why may drugs be given ‘sub-lingually’?
The blood supply goes straight to the heart and does not travel to the liver
This prevents the drug being broken down in the liver allowing it to work more rapidly and have a greater effect
When is excretion performed via the mouth?
What may induce this?
Toxins and irritants in the stomach induce vomiting
An obstruction in the small bowel can also cause vomiting
What is meant by the hard palate providing an ‘anvil’?
The muscular tongue squashes food against the hard palate, forming it into boluses for swallowing
What is the role of the soft palate?
Along with the epiglottis, the soft palate ensures that food and air don’t end up in the wrong places
What is the role of the lips?
They act as a guard
They are opened to allow food to enter the mouth, but closed to prevent it exiting while it is being processed
What is the role of the teeth?
The rig of teeth is present for mechanical processing
There are different teeth which are suited to processing different types of food
where are the incisors found and what is their role?
They are present at the front of the mouth
They act like blades, designed to cut off a piece of food
Where are the cuspids (canines) and what is their role?
They are the pointed teeth behind the incisors
They spike into foods allowing them to be teared
why do the cuspids have their name?
they have a single root
Where are the premolars (bicuspids) and molars found?
How many roots do they have?
The premolars are behind the cuspids (canines) and have 2 roots
The molars are behind the premolars and have 3 - 4 roots
What are the roles of the premolars and molars?
They crush and grind food, especially as the jaw moves laterally as this grinds food between the upper and lower teeth
What are the 3 functions of the muscles of mastication (chewing)?
- closing the jaw
- sliding or rocking of the lower jaw from side to side
- chewing
The tongue and cheeks help to move food across the teeth
what are the 3 types of movement involved in chewing?
It involves mandibular:
- elevation and depression
- protraction and retraction
3, medial and lateral movement
What is the main role of saliva?
Why is this important?
It has a role in lubrication of both the mouth and the food
This allows things to move more easily and it helps to keep the mouth clean
What types of fluid are found within saliva?
Serous fluid which contains enzymes
Mucous which makes it ‘slippery’
How does saliva help in protection against acid and bacteria?
It contains antibacterial enzymes, such as lysozyme and IgA
It contains bicarbonate and calcium ions, which prevent the mouth from becoming too acidic
Calcium helps to stop the teeth from dissolving in acid
How does saliva have a role in digestion?
It contains enzymes:
- salivary amylase (ptyalin) breaks down carbohydrates
- lingual lipase begins to break down fats
How is saliva production regulated?
Almost entirely by neural control
How does sympathetic and parasympathetic activity modulate saliva production?
They BOTH increase saliva production
Parasympathetic activity produces more serous fluid which carries enzymes (fluid-like)
Sympathetic activity increases mucous secretion (thicker)
What is the difference in the reasons for the sympathetic and parasympathetic stimulation of saliva production?
Sympathetic stimulation of saliva is to facilitate respiration
Parasympathetic stimulation is to facilitate digestion
What is the parasympathetic system that controls saliva production controlled by?
The salivatory centre in the brainstem
What signals in the salivatory centre in the brainstem will increase saliva production?
- local stimuli, such as taste and touch in the mouth
the sensory input in the mouth triggers saliva secretion
- central stimuli, such as smell and sight of food
this is the cephalic phase that involves taking signals from other senses
- learned reflex, such as Pavlov’s dog or time of day
What is the first stage in parasympathetic stimulation of saliva production?
Parasympathetic stimulation leads to acetylcholine release onto the salivary acinar cells
what is the role of acetylcholine in saliva production?
ACh binds to muscarinic receptors
This leads to an increase in intracellular calcium concentration
This is achieved through the IP3/DAG second messenger system
How does raised intracellular calcium concentration contribute to salivation?
Increased intracellular Ca2+ causes vesicles to fuse with the apical membrane
This leads to secretion
How does sympathetic stimulation lead to saliva secretion?
- sympathetic stimulation leads to the release of noradrenaline
- noradrenaline binds to adrenergic receptors
- this leads to an increase in intracellular calcium levels
What is an acinus?
A balloon of epithelial cells which produces a primary secretion
What is the primary secretion that is produced by the acini?
It is an initial isotonic (neutral) fluid
It mainly contains NaCl, protein and/or mucous
How is the isotonic primary secretion made?
- Cl- is moved into acinar cells and exported across the apical face of the cell
- bicarbonate moves in the same direction
- this leads to movement of Na+
- this leads to a primary secretion that is mainly isotonic saline
Why are proteins part of the primary secretion?
Proteins are excreted by exocytosis due to a calcium stimulus
How is the secondary secretion formed?
As the primary secretion moves through the ducts, it is processed to form the secondary secretion
- Na+ is exchanged for protons
- Cl- is exchanged for bicarbonate
There is more bicarbonate than proton secretion
How does the secondary secretion vary from the primary secretion?
It becomes increasingly alkaline and more hypotonic (dilute)
Why is the flow rate through the ducts important?
If the flow rate is too high, there is not enough time for the primary secretion to be processed to the secondary secretion
This leads to the saliva in the mouth being more neutral
what are the 3 salivary glands?
- parotid gland
- submandibular gland
- sublingual gland
What is the role of the parotid gland?
it is the largest salivary gland
- it predominantly produces serous secretions (25% salivary volume)
- it is the main source of salivary amylase and proline-rich proteins
What are proline-rich proteins?
they seem to collate molecules and play a role in protecting the teeth from damage
what is the nervous supply to the parotid gland?
It receives parasympathetic supply via the glossopharyngeal nerve (CN IX)
It receives sympathetic supply via the superior cervical ganglion
What is the role of the submandibular gland?
- produces a mixture of serous and mucous secretion (70% salivary volume)
- main source of lysozyme and lactoperoxidase
What are the roles of lysozyme and lactoperoxidase in the mouth?
They are antibacterial so protect against bacterial infection
They prevent the teeth from decaying
What is the nervous supply to the submandibular gland?
Parasympathetic supply from facial nerve (CN VII)
Sympathetic supply from superior cervical ganglion
what is the role of the sublingual gland?
- predominantly produces a mucous secretion (5% salivary volume)
- main source of lingual lipase
What is the nerve supply to the sublingual gland?
- Parasympathetic supply from facial nerve (CN VII)
2. Sympathetic supply from superior cervical ganglion
What is the role of Ptyalin a-amylase?
It is involved in the initial digestion of polysaccharides
What type of linkages are starch and other large polysaccharides made up of?
a-1,4 and a-1,6 linkages
a-1,6 linkages cause branches
What are the molecules produced by ptyalin a-amylase and why?
a-amylases can only cut at a-1,4 sites and not adjacent to the a-1,6 sites
this leads to di- and trisaccharides and limit dextrins
What is the optimum pH of ptyalin and when is it denatured?
Optimum pH is around 7
It is denatured at pH 4 so it denatured immediately as it comes in contact with stomach acid
What is the role of lingual lipase?
It is involved in the initial digestion of triglycerides
It will cleave one fatty acid from the molecule
This leaves diacylglycerol and a free fatty acid
what is the optimum pH of lingual lipase and when is it denatured?
Optimum pH is around 4, so it is stable in the stomach and works together with gastric lipase
It is denatured by pancreatic proteases
How come lingual lipase is not very effective in the mouth?
The fat lumps need to be broken down into smaller units
Fats are not water-soluble so lingual lipase can only work on the outer edges of the molecules
what are the 3 types of papillae that contain taste buds?
- foliate
- circumvallate
- fungiform
What actually is contained within a papilla?
The clusters of cells embedded in them are taste buds themselves
They are specialised epithelial cells which have microvilli that sense the food in the mouth
What do the epithelial cells within a tastebud release?
Neurotransmitters which will communicate with nerve cells
what are the 2 types of taste bud?
- ion channel-based sensor
2. G protein-coupled receptor-based sensor
What will an ion channel-based sensor detect?
What type of stimulus is this?
It detects a salty or sour stimulus
It detects protons
The sour stimulus comes from the presence of acid
What does a salty stimulus lead to?
The opening of a sodium ion channel in the membrane
This leads to a sodium influx and depolarization of the membrane
What does a sour stimulus lead to?
Protons bind to sodium channels in the membrane
The sodium influx depolarises the membrane and leads to the opening of Ca2+ ion channels
Calcium influx triggers the release of neurotransmitters
What will a G protein-coupled receptor-based sensor detect?
Sweet, umami (savoury/glutamates) and bitter stimuli
How does a G protein-coupled receptor-based sensor work?
All 3 stimuli signal through the calcium cascade and calcium-induced calcium release
This causes membrane depolarisation and the release of neurotransmitters
What is the difference between odour receptors and taste sensors?
How are they linked?
Taste sensors are specialised epithelial cells
Odour receptors are nerve cells
Smell helps to fine-tune the response to the taste receptors
How do olfactory (odour receptors) cells work?
The receptor cilia of the olfactory cells have GPCRs
These signal through cAMP to cause depolarisaiton that will trigger the action potential
How does the food pass into the oesophagus?
Food passes from the oral cavity, through the oropharynx and laryngopharynx and to the oesophagus
How are the soft palate and the epiglottis involved in preventing food and air from going to the wrong places?
The soft palate seals off the nasopharynx
The epiglottis seals off the bottom part of the oropharynx and the trachea
How is the reflex involved in swallowing triggered?
The food bolus pushes against the soft palate
This initiates a reflex that causes the soft palate to rise and close off the nasopharynx
What happens to the epiglottis and the upper oesophageal sphincter as a result of the swallowing reflex?
The epiglottis moves downwards to seal the trachea
The UES relaxes to allow the bolus to enter the oesophagus
Immediately after, it contracts to open the airway
How is the food bolus carried to the stomach?
By peristalsis
What are the dimensions of the oesophagus?
How is it innervated and how does it reside in the absence of food?
It is 25 cm long and 2 cm wide
It is flattened/collapsed in the absence of food
It is innervated by fibres from the oesophageal plexus
What is the epithelium like in the oesophagus?
It has stratified squamous epithelium that is thrown into folds
Multi-layered epithelium means that, if a few cells are scraped off, they can easily be replaced
What is the role of the submucosal oesophageal glands?
They secrete mucus to facilitate the passage of the food bolus
what controls the behaviour of the epithelium in the oesophagus?
the lamina propria and the muscularis mucosae
What is meant by tension waves in swallowing?
During swallowing, a wave of tension spreads down the oesophagus
How is the tension wave created?
- the upper oesophageal sphincter is controlled by the swallowing reflex
- the reflex causes brief closure of the pharynx and opening of the UES
- a wave of tension forms behind the bolus which helps to push it down the oesophagus
What happens to the lower oesophageal sphincter on swallowing?
It opens upon swallowing
What is meant by the UES and LES having a degree of passive tone?
They sit closed by default
There is a specific action to open them when needed
What is meant by the cephalic phase of GI activity?
Some control of GI activity is initiated before food is eaten, as it is anticipated
This involves a combination of stimuli
What is the cephalic phase mediated by?
The parasympathetic nervous system
The vagus nerve carries signals both to and from the gut and can modify the cephalic phase
What actions are produced during the cephalic phase and what are they controlled by?
- salivary secretion via the facial and glossopharyngeal nerve (CV VII and IX)
- control of GI motility and secretion via the vagus nerve (CN X)