biology of taste

Question 1

role of taste

Answer 1

• survival
• stimulant to salivary flow
• oral hygiene

Question 2

5 taste sensations and roles

Answer 2

• 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

Question 3

3 types of papilla

Answer 3

fungiform

foliate

vallate

Question 4

where are fungiform papillae found

Answer 4

on dorsum of tongue,

contains the most taste buds

Question 5

where are foliate papillae found

how many taste buds do they have

Answer 5

in interior part of tongue

contains around 1500 taste buds

Question 6

where are vallate papillae found

how many taste buds

Answer 6

anterior and adjacent to sulcus terminalis

8-12 circumvallate papilla each containing 250-300 taste buds

Question 7

what happens to taste buds with age

Answer 7

number of taste buds decrease in area anterior and adjacent to sulcus terminalis

about 100 in each papilla by age of 70

Question 8

draw locations of papillae

Answer 8

Question 9

where are taste buds found

Answer 9

on the lateral borders of the papilla

Question 10

cellular composition of taste buds

Answer 10

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).

Question 11

characteristics and roles of type I (dark) taste cells

Answer 11

• narrow and flattened
• separated from basement membrane
• secrete pit substance
  
  • contanis GAGs, vitamin C, enzymes

Question 12

characteristics and roles of type II and III (light) taste cells

Answer 12

• 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

Question 13

what are type IV taste cells

Answer 13

progenitor cells

can develop into type I, II or III taste cells

Question 14

roles of nerve fibres in taste buds in

Answer 14

• are everywhere
• lose myelin sheaths
• adjacent to all cell types
  
  • invaginations in type I
  • coiled around type II
  • form synaptic connections with type III

Question 15

characteristics of taste cells

Answer 15

• 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+

Question 16

molecular mechanicm of tasting salty food

Answer 16

• 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.

Question 17

molecular mechanism of tasting sour foods

Answer 17

• Sourness is the measurement of proton (H+) concentration in solution.
• H+ blocks Na+/K+ channel to lead taste cell repolarized directly.

Question 18

molecular mechanism of tasting sweet foods

Answer 18

• 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

Question 19

molecular mechanism of tasting bitter foods

Answer 19

• 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

Question 20

molecular mechanism of tasting umami food

Answer 20

• 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.

Question 21

factors affecting taste perception

Answer 21

• 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.

Question 22

effect of COVID-19 on taste

Answer 22

• 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