biology of taste Flashcards
role of taste
- survival
- stimulant to salivary flow
- oral hygiene
5 taste sensations and roles
- Salty:
- supplying vital minerals lost in sweat and urine
- Sour:
- stimulating salivary flow, maintain pH in neutral
- Sweet:
- supplying glucose for energy
- Bitter:
- avoiding toxic intake
- Umami:
- protein supplements
3 types of papilla
fungiform
foliate
vallate
where are fungiform papillae found
on dorsum of tongue,
contains the most taste buds
where are foliate papillae found
how many taste buds do they have
in interior part of tongue
contains around 1500 taste buds
where are vallate papillae found
how many taste buds
anterior and adjacent to sulcus terminalis
8-12 circumvallate papilla each containing 250-300 taste buds
what happens to taste buds with age
number of taste buds decrease in area anterior and adjacent to sulcus terminalis
about 100 in each papilla by age of 70
draw locations of papillae
where are taste buds found
on the lateral borders of the papilla
cellular composition of taste buds
one taste bud contains 50-100 taste cells
3 types of taste cells
- Type I (Dark cell)
- Type II (Light cell)
- Type III (Light cell)
- These 3 extend into taste pore (pit).
- Basal, less defined progenitor cells (type IV).
characteristics and roles of type I (dark) taste cells
- narrow and flattened
- separated from basement membrane
- secrete pit substance
- contanis GAGs, vitamin C, enzymes
characteristics and roles of type II and III (light) taste cells
- type II
- thick microvillus projects into taste pore
- directly involved in taste transduction
- type III
- does not have microvillus
- contains synaptic vesicles to synapse with adjacent nerve fibres
what are type IV taste cells
progenitor cells
can develop into type I, II or III taste cells
roles of nerve fibres in taste buds in
- are everywhere
- lose myelin sheaths
- adjacent to all cell types
- invaginations in type I
- coiled around type II
- form synaptic connections with type III
characteristics of taste cells
- 14-30 day life span
- high turnover
- neuron epithelia cells
- electrically excitable cells
- capable of generating action potentials
- contain voltage-dependant channels for Na+, K+ and Ca2+
molecular mechanicm of tasting salty food
- The amiloride-sensitive Na+ channel in taste cells serves as the salt receptor.
- The influx of Na + ions results in a direct depolarization of the taste cell and leads to the generation of action potential.
molecular mechanism of tasting sour foods
- Sourness is the measurement of proton (H+) concentration in solution.
- H+ blocks Na+/K+ channel to lead taste cell repolarized directly.
molecular mechanism of tasting sweet foods
- G protein couple receptors serve as sweet receptor.
- Sugars block K+ channel to depolarise taste cells, which is due to induce cyclic AMP
- Sweet binds to GPCR
- G protein recruited
- Adenylate cyclase activated
- Converts ATP to cAMP
- Activates PKA
- PKA phosphorylates potassium channel
- Blocks potassium channel
- Depolarisation
molecular mechanism of tasting bitter foods
- acts via G Protein couple receptors
- Ca ++ release from the mitochondrion of taste cells to lead the neuron-transmitter deportation.
- Bitter taste transmitted to brain
- cAMP phosphodiesterase (PDE) to decrease cAMP which leads to open K+ channel to result in cell repolarisation.
- Hyperpolarisation
molecular mechanism of tasting umami food
- Taste of amino acid (Glutamate)
- Recently recognized
- Unique taste, which can not be elicited by any combination of the other four taste types.
- Glutamate is present in a variety of protein-rich foods (aged cheese)
- Heterodimers of T1R1 and T1R3 proteins(GPCRs) form a receptor for glutamate
- Activation of this receptor decrease cAMP to repolarize/hyperpolarise taste cells.
factors affecting taste perception
- Taste adaptation
- individual thresholds exist.
- The different sensitive for certain taste is also due to the individual thresholds for taste cell depolarization.
- Oral cavity temperature
- cold foods/drinks reduce receptor ability.
- Combinations of taste factors
- e.g. adding sugar to acid foods, no change in H+, but reduced acid taste perception.
- Hormonal & cytokines influences
- alter taste thresholds.
- When sick - different taste perception
- Genetic influences
- phenylthiocarbamide (bitter) taste insensitivity in 30% Caucasians.
- Age
- sensitivity declines (higher salt & bitter thresholds).
- /Reduced circumvallate papillae.
- External factors -
- smoking, local anaesthetics.
effect of COVID-19 on taste
- loss of taste
- SARS-Cov-2 using ACE2 and TMPRSS2 entering epithelia cells
- Some taste cells are highly expressed ACE2 and TMPRSS2
- Particularly in type IV taste cell of foliate papillae and vallate papillae
- Virus replication in taste cells will slow the cell replacement in taste buds
- Above is served at least one of the many mechanisms of covid 19 infection
