L4 - Chewing, Taste and Swallowing Flashcards
what is the function of chewing/mastication?
- mechanical digestion (allows for swallowing)
- mixing food with saliva (lubrication, dilution, neutralisation) - allows you to taste food
- tasting of food
- chemical digestion (alpha-amylase mostly from parotid gland to break down starch)
stimulus for the cephalic phase of gastric digestion
what are the three phases of control of gastric acid release?
3 clear phases of control of gastric acid release:
- cephalic (mouth) - starts gastric acid production
- gastric (stomach) - peak gastric acid amount
- intestinal (intestine) - decreasing gastric acid amount
describe the controls of mastication/chewing
control:
- voluntary (skeletal muscle)
- involuntary reflex (brainstem)
- initiation is the bolus in the mouth
- strength is dependent on the consistency of the bolus
- dependent on the occlusion/bite
stimulation of taste centres
what are the necessary cues to taste/know flavour?
- visual (colour)
- texture/shape
- taste
- flavour/odour (flavour is more than just taste, it is about smell, texture and temperature too as well as neural integration)
describe taste buds (how many and what diff types)
- up to 10,000 taste buds
- type I, II, III cells
what are the five different types of tastes and how are the tongue papillae distributed in the mouth?
types:
- sweet (energy, glucose, fructose)
- salty (blood pressure, sodium)
- sour (danger)
- bitter (danger, coffee, drugs)
- umami (translated as delicious, savour, glutamate taste, MSG)
myth about localisation of tastes, sensibility is equal in different parts of the tongue:
- circumvallate papillae
- foliate papillae
- fungiform papillae
what is the signal transduction pathway for sweet, bitter and umami? and what cells does this occur in?
Occurs in Type II cells and uses cell surface receptors: G-alpha-q associated and cell specific
- GPCR activated, phospholipase C does it’s thing and calcium gets released into the cytosol
- TRMP5 is temperature sensitive 15-35 degrees C, brings Na+ into cell
- depolarisation activates ATP channel (CALHM1)
- ATP creates depolarisation in associated afferent fibre
What is the signal transduction pathway for sour? and what cells does this occur in?
Occurs in Type III cells
- hydrogen ions from the sour stimulus enter through channels
- this decreases pH inside the cell, which blocks K+ leak channels
- cell depolarises, which opens voltage-gates Na+ channels
- depolarisation spreads to the synapse
- voltage gated Ca2+ channels open
- neurotransmitter is released into synapse
Salty: detected by sodium channel (ENaC) leading to cell depolarisation
describe the neural integration that occurs for taste signalling
- signals can converge on ganglion neurons or transmit with our convergence
- the presence of one taste can alter the reception of a different taste: mixture suppression eg. consider bitter and sweet combinations or salty and sweet
- main message here is that it is highly integrated
describe olfactory involvement for humans and dogs and what causes a loss of olfactory involvement
- humans have approx 5-10M olfactory receptor neurons, dogs ahem 20x that which makes them useful to detect drugs, food, and even cancer
Loss of olfactory involvement - flu or cold blocking the nose/olfactory bulb is why everything tastes the same when you are sick, you need olfactory involvement to differentiate between diff flavours
- COVID
- severe brain trauma after an accident
- Parkinson’s or Alzheimer’s disease
describe the function and process of swallowing
function:
- rapid transfer of food from the mouth to the stomach
- converts mouth and pharynx pathway from gas transfer function to food transfer funtion
- prevention of reflux
process:
- oral events: initiation of the swallowing reflex, cascade of sequential events in the pharynx
- oesophageal events
- receptive relaxation in the stomach
what are the specific oral and oesophageal processes of swallowing?
oral events:
initiation by stretch receptors:
- food forced into pharynx by tongue (only voluntary part of this)
- stretch receptors
- brain stem initiates swallowing
soft palate:
- soft palate pushes upwards
- prevents food from entering nasal passage
epiglottis:
- moves down to cover the entrance to the trachea
- prevents aspiration of food
esophageal events:
upper oesophageal sphincter:
- relaxes (opens)
- allows food to enter the esophagus
lower esophageal sphincter:
- opens (relaxes) at the start of swallowing
- food enters stomach
- closes after peristalsis wave
esophagus (peristalsis):
- smooth muscle contracts
- peristaltic wave pushes food to stomach stomach
- lasts about 9 seconds
describe the voluntary and involuntary parts of swallowing
voluntary:
- oral events are voluntary control
- activate stretch receptors
- activate the swallowing centre in brainstem
- sets off an involuntary response
involuntary (swalloing centre):
- pharyngeal muscles - striated
- oesophageal muscle - upper striated
- lower smooth muscle
striated muscle is controlled directly by swallowing centre, whilst smooth muscle is controlled indirectly
describe what happens in the oesophagus during swallowing
food in the esophagus:
- initiates a primary peristaltic wave
- sweeps food down esophagus
- if food is not cleared, a second peristaltic wave is initiated
- repeated until cleared
at the same time:
- relaxation of the upper and lower oesophageal sphincter allows passage of food
- relaxation of the proximal stomach (receptive relaxation)
describe what gastroesophageal reflux disease (GERD) is, causes and treatment of it
it is reflux of acidic chyme into esophagus which causes irritation to oesophageal mucosa (‘heartburn’)
causes:
- abnormal relaxation of lower oesophageal sphincter
- lack of receptive relaxation in the stomach
- excessive gastric secretion (due to stress)
- infection with H. pylori (an be treated with antibiotics now)
treatment:
- antacids
- H+/K+-ATPase inhibitors (omeprazol) - inhibits gastric acid from being made
- lifestyle changes (diet)
- surgery
