Final answer:
The velvety texture of the tongue is due to keratinized tissue in the filiform papillae, which, along with other types of papillae, play a role in taste sensation and food manipulation.
Step-by-step explanation:
The tongue's keratinized tissue contributes to its velvety texture, playing a role in conditions such as geographic and hairy tongue. The tongue is covered in papillae, which are extensions of the lamina propria of the mucosa and covered in stratified squamous epithelium. Among these, filiform papillae are long and thin and do not contain taste buds but have touch receptors that assist in moving food around the mouth. Their keratinized surface gives the tongue a rougher texture, which is compared to a cat's tongue that is used for grooming. Meanwhile, the fungiform papillae contain taste buds and are mushroom-shaped, being more prominent towards the back of the tongue.
In addition to these, the lingual glands secrete mucus and serous fluid containing lingual lipase, an enzyme which begins aiding digestion in the stomach. The tongue's mobility is facilitated by the lingual frenulum, and conditions such as ankyloglossia, or 'tongue tie,' can restrict this movement and impair speech. These examples illustrate the complexity of the tongue's structure and functions, related both to its mechanical and sensory roles in the oral cavity.