Digestive system

Digestive system
I. LIPS
The lips control access to the oral cavity from the outside environment.
A. External Surface
The external surface is covered with thin skin and therefore possesses hair
follicles, sebaceous glands, and sweat glands.
B. Transitional Zone
The transitional zone (vermilion zone) is the pink area of the lip. Here
the connective tissue papillae extend deep into the epidermis. Hair
follicles and sweat glands are absent, whereas sebaceous glands are
occasionally present.
C. Mucous Membrane
The vestibular aspect of the lip is lined by a wet epithelium (stratified
squamous nonkeratinized) with numerous minor mixed salivary glands
in the subepithelial connective tissue.
D. Core of the Lip
The core of the lip contains skeletal muscle.
II. TONGUE
The tongue is a muscular organ whose oral region is freely moving; its root is attached to the floor of the pharynx. Skeletal muscle forms the core of the tongue, among which groups of serous and seromucous glands are interspersed.
A. Oral Region (Anterior Two-Thirds)
The mucosa of the dorsal surface of the anterior two thirds of the tongue is modified to form four types of lingual papillae.
1. Filiform Papillae
Filiform papillae are long and slender and are the most numerous. They form a roughened surface (especially in animals such as cats) and are distributed in parallel rows along the entire surface. They are covered by a parakeratinized stratified squamous epithelium (but bear
no taste buds) over a connective tissue core.
2. Fungiform Papillae
Fungiform papillae are mushroom-shaped, are scattered among the
filiform papillae, and may be recognized by their appearance as red dots. They contain taste buds along their dorsal aspect.
3. Foliate Papillae
Foliate papillae appear as longitudinal furrows along the side of the tongue near the posterior aspect of the anterior two-thirds. Their taste buds degenerate at an early age in humans. Serous glands of von Ebner are associated with these papillae.