Ageusia . Inability to detect any flavor whether sweet, sour, salty or acidic.
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- 1 Physiology of the sense of taste
- 2 Types of ageusias
- 3 Evolution
- 4 Diagnosis
- 5 Treatment
- 6 Sense of taste
- 7 Capturing taste
- 8 Impaired sense of taste
- 1 Common causes:
- 9 Impaired sense of smell
- 10 Disorders of smell
- 11 Causes
- 12 Diseases that affect the sense of smell
- 1 The cause of rhinitis can be:
- 13 What can be done in this situation?
- 14 Sources
Physiology of the sense of taste
Like all sensory systems of the central nervous system, peripheral receptors and some central pathways are included in the taste system. Peripheral receptors are represented by the taste cells of the taste buds (some authors call these buds taste buds) that are found on the tongue, pharynx, and upper esophagus.
The gustatory corpuscles are supplied by the chord branch of the tympanum of the facial nerve (cranial nerve VII), the lingual branch of cranial nerve IX and the laryngeal branch of cranial nerve X (vagus), nerves that transmit taste information from the tongue , the palate, the epiglottis and the esophagus to the brain.
Food molecules that can be tasted are detected by taste cells in the taste buds . The groups of these corpuscles form the papillae of which three types are known: the fungiform papillae (which are distributed mainly in the anterior part of the tongue), the large goblet papillae located in the posterior third of the tongue) and the papillae that are located on the edge of the tongue. Other groupings of gustatory corpuscles are located on the palate and pharynx. Different types of papillae contain from 5 to several hundred taste corpuscles.
Each gustatory corpuscle is made up of four morphologically distinct cell types: basal cells, dark cells, light cells, and intermediate cells. The basal cells are small and rounded and are found at the base of the corpuscles and appear to be the precursors of the other three, which appear to be different stages of differentiation of the taste cells, the clear cells being the most mature.
Each gustatory corpuscle has a small opening in the epithelial surface called the gustatory pore and contains about 100 cells, which extend their microvilli towards the pore. Although taste cells are non-neuronal epithelial cells, they are excited by electrical currents and have voltage-sensitive sodium, calcium, and potassium channels capable of generating action potentials. Due to their basal pole, the taste cells are innervated by sensory neurons.
The taste system distinguishes four basic stimuli: bitter, salty, sour and sweet. Recently, a fifth stimulus, called unami, has been added, represented by the stimulus that sodium monoglutamate produces . Each of these stimuli works through a different mechanism, although two stimuli can cause the same taste sensation through different mechanisms. These mechanisms belong to two general categories: those in which ion channels intervene and block them, and a second type in which specific membrane receptors and second messengers intervene.
In general, taste substances act on specific ion channels or receptors located on the taste cell membrane, directly or indirectly causing depolarization of the cell. In turn, this depolarization induces calcium entry through voltage-operated Ca channels, with release of neurotransmitters at the synapses of the sensory fibers. The salty taste involves the penetration of sodium ions through its channels (a type of sodium channel sensitive to amiloride), while the bitter taste depends on the entry of H + (also through the sodium channel sensitive to amiloride ) at the same time as the potassium channel is closed, normally open at rest.
The bitter taste is due to the blockage of the K + channels, but there are also membrane receptors coupled to a specific G protein (gustducin), which when binding to the bitter taste substance (quinine), trigger a cascade of events in which the phospholipase, inositol triphosphate and calcium release from its intracellular deposits. Likewise, receptors that couple to gustducin or another G protein are involved in the sweet taste to stimulate the production of inositol triphosphate. Other sweet tasting receptors could bind to another G protein that interacts with adenylyl cyclase causing an increase in cyclic AMP that induces phosphorylation of K + channels by protein kinase A.
The taste of glutamate is considered by some to be a fifth stimulus category, which would have as its receptor the metabotropic glutamate receptor that is also expressed in certain regions of the brain.
The taste cells are innervated at their base by the peripheral branches of the taste fibers so that taste information is transmitted from the taste buds to the cerebral cortex through synapses in the brain stem, in particular in the solitary nucleus of the brain stem. and in the ventroposteromedial nucleus of the thalamus . The alterations in the sense of taste are due to conditions that interfere with the access of the taste substance to the receptors in the taste cells, to lesions in these cells or the lesions in the neuronal pathways responsible for transporting the nervous stimulus to the cerebral cortex.
The conditions that interfere with the arrival of the taste substance can be varied, from a xerostomia produced in turn by various causes (such as Sjögren’s syndrome ), radiation therapy, poisoning by heavy metals or other toxic substances, and bacterial colonization of the taste pore .
Loss of neural transmission capacity may be due to cancers, trauma of various kinds, infections, etc. In clinical practice, the most frequent cause of taste disturbances is medication, although the mechanism by which some drugs have this effect is unknown. The xerostomia , regardless of etiology adversely affects the oral mucous. If, in addition, antibiotics and corticosteroids are used concomitantly or the patient suffers from any immunodeficiency, Candida hyperproliferation may occur., with or without symptoms of infection. Respiratory infections and trauma to the head can cause dysfunction of taste and smell. Injuries to the tympanic branch of the facial nerve during middle ear surgery or extraction of the third molars are usually relatively frequent.
Finally, aging is also associated with a reduction in the sense of taste that can be limited to a single substance and of a mild nature.
Types of ageusias
The alterations of the sense of taste are categorized in the following modalities
- Total Ageusia: inability to detect any taste whether sweet, sour, salty or sour
- Partial ageusia: when the patient is able to distinguish the taste of some substances but not all.
- Specific Ageusia: when the patient is unable to recognize the taste of a certain substance
- Hypoageusia: when the perception of taste is decreased, and may be total or partial
- Dysgeusia: taste distortion, or perception of a taste in the absence of the substance that should have caused it
Many patients with loss of sense of taste also show a loss of the sense of smell and vice versa.
The development of the senses that man has undergone has been controlled by the evolutionary phenomenon and has been closely related to the physical and chemical conditions of the environment that has surrounded us in the course of time. In fact, the way our senses work is a consequence of adaptation to the environment.
The senses of taste and smell have also been developed to be able to adapt to avoid dangers in the ingestion of foods that are already decomposed and that present a danger when ingesting them, as well as poisonous foods that, in general, give off a number of chemical substances that upon reaching the nose we detect them; In this way it has been learned, in the course of the evolution of life, to reject them. There are also poisonous or rotten substances that do not smell. However, by testing them with the language, we have learned to know that they do not suit us because they cause us harm.
Having made this short introduction, we will now analyze the senses that are the subject of this work.
Patients with loss of sense of taste should be evaluated in terms of olfactory and taste functions , performing tests to determine the threshold of perception of different tastes and smells. It should be noted that the tests for the determination of taste function are less standardized than those for odors. The quality and intensity of perception of the four basic flavors is first determined, using sugar, citric or hydrochloric acid, caffeine or quinine sulfate and sodium chloride. Increasing dilutions of flavorings are applied to the quadrants of the tongue to quantify the intensity of perception.
Electrogustometry allows to accurately determine taste deficits in the different quadrants of the tongue. Once the loss of taste has been evaluated, it is important to establish the anatomical diagnosis. For example, loss of sense of taste in the two anterior nerves associated with facial paralysis is indicative of injury to the tympanic branch of the facial nerve, close to the junction of this branch with the facial nerve in the mastoid
There is no treatment to resolve loss of taste. When associated with a xerostomia, it can be treated with artificial saliva or pilocarpine. When associated with a bacterial or fungal infection, eradicating the infection aids in the recovery of taste sensations. Traumatic dysgeusia usually resolves spontaneously.
Sense of taste
This faculty of humans, among other animals, acts by contact of soluble substances with the tongue. The human being is capable of perceiving a wide range of flavors in response to the combination of various stimuli, including texture, temperature, smell and taste. Considered in isolation, the sense of taste only perceives four basic flavors: sweet, salty, sour and bitter; each of them is detected by a special type of taste buds.
The tongue has almost 10,000 taste buds that are unevenly distributed on the upper face of the tongue, where they form spots that are sensitive to certain classes of compounds that induce taste sensations. Typically, the sweet and salty taste-sensitive papillae are concentrated on the tip of the tongue, the acid-sensitive ones occupy the sides, and the bitter-sensitive ones are on the back.
Chemical compounds in food dissolve in the moisture of the mouth and penetrate the taste buds through the pores on the surface of the tongue, where they come into contact with sensory cells. When a receptor is stimulated by one of the dissolved substances, it sends nerve impulses to the brain. The frequency with which the impulses are repeated indicates the intensity of the flavor; the type of flavor is likely to be recorded by the type of cells that have responded to the stimulus.
The flavor can be: sweet, salty, bitter and acidic. Where are the receptors of the different flavors found?
- Sweet: on the tip of the tongue.
- Bitter: in the calciform papillae.
- Salty and acidic: at the tip and front of the edges of the tongue. There are also receptors that are sensitive to acidic flavors in the lining of the lips, and sensitive to all flavors in the soft palate.
There is no gustatory uptake in the sublingual region and on the underside of the tongue.
Impaired sense of taste
The deterioration of the gustatory sense varies from its distortion to its complete loss. It can manifest as a decrease in the sense of taste and smell; dysgeusia; deterioration of taste; loss of taste; metallic taste. The tongue can only “perceive the taste” sweet, salty, sour and bitter. Disorders of taste can be caused by any condition that interferes with the transmission of flavor stimuli to the brain or by conditions that affect how this organ interprets such stimuli. There are two kinds of taste disorders, and they are:
- The Hypogeusia: consisting of the loss of the ability to taste or distinguish between sweet, salty, sour, etc.
- The Ageusia, which is the almost total loss to detect flavors.
- In some cases this condition occurs from birth, but in most cases it develops after injury or illness.
- Common cold
- Nasal infection due to an infection (such as infections of the salivary glands), polyps, etc.
- Viral pharyngitis
- Dry mouth
- Aging (the number of taste buds decreases with age)
- Excessive smoking (especially pipe smoking) since it causes dry mouth
- Vitamin deficiency (vitamin B12) or minerals (zinc in the diet)
- Injury to the mouth, nose, or head
- Side effects of medications such as antithyroid drugs, captopril, griseofulvin, lithium, penicillamine, procarbazine, rifampin, vinblastine, or vincristine
- Bell’s palsy
- Sjogren’s syndrome
- Strep throat (strep throat infection)
There may be other causes for impaired taste, in addition to those mentioned. The possibility of their incidence is not determined by the order in which they occur. Causes of this symptom include rare diseases and medications. Furthermore, the causes may vary according to the person’s age and sex and the specific characteristics of the symptom, such as exact location, quality, duration, aggravating factors, mitigating factors, and associated diseases. Addictions (cigarette, alcohol and illegal drugs) alter the normal functioning of the sense of taste.
Impaired sense of smell
All the senses are important to lead a healthy and full life, and the sense of smell is a key to our safety, it alerts us when there is some kind of leak, some spill, some fire, when the food is in poor condition, etc. as well as allowing us to enjoy smells like the perfume of a flower, the smell of food and much more. Suffering loss in the sense of smell can also be a sign of other serious health conditions.
Disorders of smell
People who experience smell disorders lose the ability to smell or perceive odors differently. As a loss of the sense of smell some people have hyposmia, it is when the sense of smell is diminished. And anosmia, is when you cannot perceive smells in the least. As a result of odor perception, some people notice that familiar odors are distorted, or odors that were normally pleasant have become unpleasant, and in some cases people perceive odors that are not present.
- Smell disorders can have many causes. Most people who develop this condition have had some illness or injury, which are the triggers for upper respiratory infections and head damage.
- Some causes may be polyps in the nasal cavities, sinusitis, hormonal disorders, or dental problems.
- Exposure to certain chemicals like insecticides and solvents, and some medications.
- People with neck or head cancer who receive radiation treatments may also experience problems with their sense of smell.
Many people who have disorders of smell, can also have disorders in the sense of taste (the ones we saw when dealing with this sense at the beginning of the work.)
Diseases that affect the sense of smell
Rhinitis: Rhinitis is the inflammation of the nasal mucosa. It attacks both adults and children. It produces congestion, nasal respiratory failure, nasal itching, runny nose and in some cases sneezing. In children, depending on the intensity of their symptoms, it can decrease concentration, cause irritability and sleep disorders. Among the predisposing factors (those that do not cause rhinitis but favor the action of the causal agents) are extreme cold or heat, excess humidity and a low percentage of humidity, temperature changes, seasonal changes.
The cause of rhinitis can be:
Infectious (viral, bacterial, specific), can be acute (no more than three weeks in duration) or chronic (more than three weeks in duration).
- The acute one is caused by exposure to temperature changes, cold weather and recognizes viruses as the main cause. This is the most common cause in childhood and is estimated at 4-6 episodes per year, this frequency being increased in children under 5 years of age. Contact with patients in nurseries and schools is a very important contagion factor. You may experience a complication with bacteria (strep pneumoniae, haemophilus influenzae).
It is accepted that when symptoms last longer than a week, complication with sinusitis is possible. There are conditioning factors such as allergy, mucociliary dysfunction (produced by mucociliary dysfunction syndrome, high temperatures, low humidity), and immunodeficiencies.
Atopic predisposition is present in the family. Naso-ocular congestion and itching, runny nose, sneezing. Symptoms are triggered by the presence of an allergen (allergy-producing agent). Not only inhalational allergens can produce it, but also those found in food and medicines. The classic signs of the presence of this disease are: The characteristic horizontal nasal wrinkle in children produced by the repeated tendency to scrub it with the palm of the wrist from the bottom up. Denie’s line, which is a deep crease in the eye bag. Edematous and pale nasal mucosa (it is not pale in infectious, on the contrary it is rubeotic). Clear rhinorrhea like egg white, are strongly indicative of allergic rhinitis.
What can be done in this situation?
You experience a problem of taste or smell, you must try to identify and record the circumstances that surrounded him. When was the first time you noticed? Did you have a cold or flu at the time? A blow to the head? Were you exposed to air pollutants, pollen, dandruff, or dust that you might be allergic to? Is it a recurring problem? Does it appear at a special time of year?
All this information should be carried when visiting the doctor who deals with nose and throat problems. We must also tell him about our other health problems and what other medications we are taking.
Diagnosis can also lead to treatment of the underlying cause. Many of these disorders are reversible.