What Are Taste Buds?

Introduction 

Taste buds are sensory organs that form part of the gustatory (taste) system. The primary role of the gustatory system is to identify the taste of substances that enter our mouths. 

The secondary role of the gustatory system is to work with the olfactory (smell) system to allow us to experience flavours.¹ Gustation (taste) begins with our taste buds – the specialised cells that form our taste buds enable us to identify the five basic tastes: sweet, umami, sour, bitter, and salty. The ability to detect these five tastes helps us to eat a balanced diet containing all the nutrients necessary for life whilst avoiding potentially harmful substances.²

In this latter role, our taste buds essentially act as gatekeepers for the rest of our digestive system. These specialised sensory cells will send signals to the brain that tell us whether a substance is “good” and we should continue to eat it or whether a substance is “bad” and we should spit the substance out. 

Your sense of taste is fundamentally important; without it, you may experience a change in the types of foods you want to eat, or you may lose your appetite altogether.

The anatomy of our taste buds?

Where are the taste buds located?

The taste buds are located in the oral cavity (the mouth). They are mainly found on the surface of the tongue but are also present at the back of the mouth, on the roof of the mouth, on the pharynx (throat), larynx (voice box), and epiglottis (the piece of tissue that sits at the back of the throat, underneath and behind your tongue). 

There are tiny bumps on your tongue that make the surface of your tongue feel rough; these bumps are called papillae. The papillae house your taste buds – there are three types:

• Fungiform – located across the surface of the tongue
• Circumvallate – located mainly at the back of the tongue
• Foliate – located on the sides of the tongue

Inside the papillae, the taste buds are exposed to the contents of your oral cavity through a small opening known as a taste pore.³

What is the microscopic structure of taste buds?

Taste buds are oval in shape and are formed of clusters of 50 – 100 cells.³ There are two major types of cells in a taste bud:

• Taste receptor cells – detect specific chemicals within the substances (food or drink) that enter the oral cavity. In order to detect chemicals, taste cells have hair-like structures called microvilli that stick up out of the taste pore into the oral cavity. These protrusions in the cavity have receptors that can bind to specific chemicals. When a chemical binds to its corresponding receptor on the cell surface, the cell transmits a signal to your brain via a nerve fibre. The signal tells your brain what taste the chemical has – sweet, salty, sour, bitter, or umami.
• Basal cells – are immature taste cells. In humans, taste receptor cells get replaced every 10 to 11 days from this ‘reserve’²

What is the function of taste buds?

Our sense of taste has evolved over millions of years. The resulting 5 basic taste sensations help us to consume a balance of nutrients and avoid toxins.

What are the 5 basic tastes, and what do they mean to us?

• Sweet: if a substance tastes sweet, it often indicates the presence of sugars – an important source of energy. 
• Sour: we are programmed to not like really sour foods – it is often a sign that fruits are unripe or that foods have gone off due to uncontrolled fermentation (rotting). We can learn to appreciate lower levels of sourness. 
• Salty: a salty taste is associated with a high presence of sodium ions. Sodium levels need to be maintained at a constant level in our bodies in order to maintain electrolyte balance and sustain life. 
• Bitter: in a similar manner to sour, we only learn to appreciate bitter foods as we get older, such as coffee. This is because substances that are toxic to us often taste bitter.
• Umami (Savoury): substances that have an umami taste contain amino acids (the building blocks of proteins). The taste of umami is derived from three natural substances found in meat and vegetables: glutamate, guanylate, and inosinate. Amino acids are vital because they are not only our only source of nitrogen, which is needed for our metabolism but also for building proteins that help form the structure of tissues and the enzymes that govern all biochemical reactions in the body. Our body can make some amino acids; however, others (known as essential amino acids) can only be obtained from our diet. The umami flavour is usually found to be very pleasant, incentivising us to eat more foods rich in these vital amino acid nutrients.⁴

How do taste buds identify different flavours?

There is a myth that different parts of your tongue are responsible for identifying different tastes. However, this has since been proven to be untrue, and instead, all your taste buds have the capacity to detect all 5 of the basic tastes via receptors on the surface of the taste cells, which bind to specific chemicals in food sources. When the chemical binds, a signal is sent from the cell to the brain via sensory nerves, which tells us what taste the chemical identifies as.⁵

What factors influence our taste perception?

Many factors can contribute to an altered ability to perceive taste; these include:

• Genetic factors
  • Taste receptor gene variation: natural variation in the DNA sequences that encode our taste receptors can alter the way in which chemicals bind
  • Genetic disorders, such as Familial Dysautonomia which leads to the complete loss or severe depletion of your taste buds
• Biological factors
  • Sex: sex hormones may change the way in which we perceive taste
  • Ageing: as we get older, we experience a natural decline in the number of taste buds and papillae – so, generally, our sense of taste gets weaker as we age
  • Neurological disorders: neurological disorders that affect the areas of the   brain that receive and process the taste signals sent from the taste may cause alterations to taste perception
• Viral illnesses
  • Common cold: taste perception becomes altered due to inflammation in taste tissues
  • COVID-19: may alter taste through the direct infection of cells on the tongue or through inflammation affecting the cells of the mouth or the cranial nerves
• Nutritional factors
  • Zinc deficiency: zinc is an important component of the proteins involved in getting information from the taste receptor to the sensory nerve
• External factors
  • Drugs: drugs such as some antibiotics, anti-inflammatories, and immunosuppressants can cause changes in the production and secretion of your saliva, can cause damage to the cranial nerves, or can modify the sensory pathways, impairing our ability to taste
  • Trauma/surgical procedures: injury to the tongue or damage to the taste nerves can significantly impact taste perception
  • Smoking increases the likelihood of respiratory infections and, therefore, inflammation in the cells of the oral cavity
  • Alcohol consumption: alcohol changes taste receptor sensitivity
  • Radiation therapies for the head and neck: weaken the responsiveness of taste cells

If you experience changes in how you taste, you should speak to your healthcare provider, especially if it is affecting your appetite.

Summary

Taste buds play a critical role in our ability to taste the food and drink we eat. The 5 basic tastes that taste buds allow us to identify – sweet, umami, sour, bitter, and salty – ensure that we consume all the nutrients we need to survive. Also, the detection of bitter or sour chemicals also ensures that we avoid eating potentially harmful substances. 

The enjoyment we get from experiencing taste can be taken away by a wide range of factors that lead to taste impairment or a complete loss of the sense of taste. It is important that if you do notice a change in your sense of taste, you speak to your healthcare provider – they will work to identify a cause and recommend treatment if appropriate.