The papillae and their associated taste buds constitute the specialized mucosa of the oral cavity. Although filiform papillae do not have taste buds, the other three types, viz., foliate, fungiform, and circumvallate, contain taste buds in their epithelium. The fungiform (i.e., mushroom-shaped) papillae (see inset on Plate 49) are most numerous near the tip of the tongue. Taste buds are present in the epithelium on their dor-sal surface. The taste buds in the epithelium covering the circumvallate and foliate papillae are located in deep clefts that separate the papillae from adjacent mucosa or from each other, respectively. Ducts of lingual salivary glands (von Ebner’s glands; a component of the minor salivary glands) empty their serous secretions into the moat surrounding each circumvallate papilla. The secretions flush material from the moat to allow the taste buds to respond to new stimuli. Similarly, ducts of small serous glands empty into the clefts between foliate papillae. Taste buds in section appear as oval, pale-staining bodies that extend through the thickness of the epithelium. A small opening at the epithe-lial surface is called the taste pore. Taste buds react to only five stimuli: sweet, salty, bitter, sour, and umami. These modalities appear to be more concentrated in the specific areas of the tongue; taste buds at the tip of the tongue detect sweet stimuli, those immediately posterolat-eral to the tip detect salty stimuli, those on the circumvallate papillae detect bitter and umami stimuli.
Foliate papillae, tongue, human, H&E, ×50.
Foliate papillae consist of a series of parallel ridges that are separated by narrow, deep mucosal clefts (see orientation photograph, pg 75). They are aligned at right angles to the long axis of the tongue on its posterior lateral edge. In younger individuals, they are readily observed by gross inspection. However, with age, foliate papillae may not be recognized. This micrograph shows three papillae, each is separated from its neighbor by a narrow cleft (C). The surface of these papillae is covered by a thick stratified non keratinized epithelium (SE). The basal surface of the epithelium is extremely uneven due to the presence of deep, penetrating connective tissue papillae (CTP). In contrast, the epithelium lining the clefts (Ep) is relatively thin and uniform. It contains numerous taste buds. These are the light-staining objects seen in the cleft epithelium. Underlying the epithelium is a layer of loose connective tissue (LCT) and a central core of dense connective tissue. Within this core and between bundles of muscle fibers beneath the papillae are lingual serous glands (LSG). These glands, like the serous glands associated with the circumvalate papillae, have ducts (D) that empty into the base of the clefts between papillae.
Taste bud, tongue, human, H&E, ×1100.
This micrograph shows to advantage the taste pore (TP), the cells of the taste bud, and its associated nerve fibers (NF). The cells with the large, round nuclei are neuroepithelial sensory cells (NSC). They are the most numerous cells of the taste bud. At their apical surface, they possess microvilli that extend into the taste pore. At their basal surface, they form a synapse with the afferent sensory fibers that make up the underlying nerve. Among the sensory cells are supporting cells (SC). These cells contain microvilli on their apical surface. Also present in the taste bud at its base are small cells simply referred to as basal cells (BC), one of which is identified here. They are the stem cells for the supporting and neuroepithelial cells which have a turnover life of about 10 days.