8 julio, 2024

Foliated papillae: what they are, characteristics, functions, histology

What are foliate papillae?

The foliate papillae, foliar or foliaceous, present as short, leaf-shaped vertical folds located parallel to the lateral edges on the back of the tongue. They are usually arranged bilaterally symmetrically. In the human there are four or five vertical folds, of variable size and shape.

The foliate papillae appear as a series of red, leaf-shaped mucosal ridges. They are covered with epithelium, lack keratin, and are therefore softer than the rest of the papillae.

They have a large number of taste buds. Sometimes they appear small and inconspicuous, and other times they are prominent.

These papillae can usually be seen with the naked eye on the posterior edges of the tongue, distinguished as several folds that lie close together.

The human has on average 20 foliate papillae, each of which has hundreds of taste buds embedded on the surface. These papillae are involved in the sensation of taste.

Characteristics of the foliate papillae

– The foliate papillae, as their name indicates (Porridge: small bump, folium: leaf) are structures with folds of the epithelium that give it a foliar appearance.

– They are located in two groups that are arranged on the posterior edges on both sides of the tongue, near the terminal groove, just in front of the circumvallate papillae.

– They are formed by up to 10 to 20 visible ridges on the surface of the tongue, covered by a non-keratinized epithelium. The lateral walls of the more central invaginations are filled with taste buds that open into these slits, into which saliva can penetrate. The ducts emanating from the lateral lingual salivary glands are in contact with the bottom of some clefts of the foliate papillae.

– In humans, the foliate papillae are well developed at birth, but it has been proposed that they revert to the rudimentary structure in adults. This situation has been suggested to be related to the need to mix the feed components using the groove of the leaf papillae at milk feeding ages.

– Beyond the age of 45, many taste buds degenerate, causing taste sensitivity to decrease in old age. While in humans the foliate papillae are rudimentary, in other mammals they are well developed and represent the sites of greatest aggregation of taste receptors.

Functions of the foliate papillae

The most important part of the foliate papilla is the presence of the taste buds. In addition to making eating enjoyable, the sensation of taste also has a protective role. The number of taste buds found in human foliate papillae varies widely between individuals from 15 to 1,500.

On average, about 1,300 taste buds are distributed on both sides of the tongue, particularly over the most posterior folds of the two foliate papillae. However, there is considerable individual variation in the distribution of taste buds in humans.

The lingual serous glands of von Ebner are located close to the foliate and circumvallate papillae. The saliva secreted by these glands provides the immediate moist environment for the taste buds, and it has been hypothesized that they act as modulators of taste perception.

Histology of the foliate papillae

The foliate papillae are covered by a nonkeratinized stratified squamous epithelium. Under the microscope, this surface epithelium lining the ridges of the foliate papillae is marked by numerous taste buds, the receptive sensory endings of which open into the intermediate grooves that separate an individual foliate papilla from its neighbor.

In the human, the foliate papillae of the tongue consist of 10 to 20 parallel folds located on the posterior margin of the tongue.

The structure of the papillae can be distinguished by several features:

The connective tissue core of the foliate papillae appears as ridges and grooves, with scattered small bumps on the surface of the ridge.
Toward the connective tissue side of the papillae are collagen fibers forming a lace-like junction, which are apparently connected to the basement membrane and basal mucosal layer by a series of anchoring fibrils.
The junction of connective tissue with epithelial tissue forms the ridges and grooves. The ridges may be narrow, and this is commonly associated with keratinization of connective tissue rather than nonkeratinizing epithelium. These folds make it possible to increase the surface area for contact with dissolved elements in saliva.
The increased surface area of ​​the intussusceptions allows prolonged contact with the chemicals introduced into the oral cavity, thus enhancing their ability to stimulate taste signals.
On the sides of the invaginations are located the taste buds, with a barrel appearance, which extend through the entire thickness of the epithelium and open on the surface through the taste pore.

Connective tissue papillae are sometimes called simple papillae and are present under the entire surface of the tongue, including the mucosal papillae. This arrangement serves to increase the anchorage of the epithelium to the underlying tissues.

The nuclei of the foliate papillae structure contain lymphoid tissue. Histological studies have identified the presence of a diffuse infiltration of lymphoid cells in the lamina propria below the foliate papillae.

This finding has been considered as a primitive form of lingual follicles found in the pharyngeal portion of the tongue.

The content of lymphoid tissue makes the foliate papillae easily inflamed, since this tissue responds with an increase in cell proliferation to certain external stimuli, such as infections, trauma, excessive smoking or irritating agents.

This reaction produces an increase in the size of the foliate papillae.

Possible diseases or disorders

Due to the position occupied by the foliate papillae on the posterior surface of the tongue, and due to the content of lymphoid tissue, they have a great tendency to swell, motivating concern in the person who comes for consultation.

This enlargement can be misdiagnosed as tumors.

Papillitis means inflammation of the papillae of the tongue. When talking about foliar papillitis, it refers to inflammation of the foliate papillae. In its normal condition its consistency is soft. With inflammation they appear swollen and red in color.

It is considered a fairly common inflammation in the population. The papillae take on an irritated appearance, and in addition to the enlargement, they present pain on contact. Usually, it does not mean any serious problem for the patient, just discomfort in chewing, swallowing and speaking.

The most frequent causes for enlarged papillae are smoking, gastrointestinal problems, infections and even stress.

References

dental science. (2017) Online. Available at: dental-science.com.
Gravina S., Yep G., Khan M. (2013) Human Biology of Taste. Annals of Saudi Medicine. 33:217-222

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