Histology of the Mouth
Introduction
Major functions of GI tract: conveyence of bulk material, digestion of food, absorption of nutrients, electrolyte balance (secretion, absorption), immunological defense, exo-, endo-, and paracrine secretion
Histophysiology: ingestion (oral cavity); fragmentation (oral cavity, stomach); digestion (oral cavity, stomach, small intestine); absorption (stomach, small intestine, large intestine); elimination (anal canal)
Sphincters: hormonal and neural stimuli; between the esophogus and stomach, stomach and small intestine, small intestine and large intestine, end of anal canal (2 – voluntary and involuntary); top of esophagus
Actions on food bolus: ingestion, mastication, digestion, lubrication
Epithelial tissue: always stratified squamous non-keratinized epithelium (exceptions: gums and hard palate)
- house connective tissue papilla which contain capillaries and nerves
- the epithelium plus the lamina propria (dermis)
Þ mucosa; where the mucosa is loose, as on the soft palate and cheeks, there is a fat-containing submucosa of loose connective tissue
Between oral cavity and esophogus: palatine tonsil, lingual tonsil and pharyngeal tonsil Þ form 1st line of defense
The Lip and Cheek
Each made of 3 layers: outer skin layer, middle muscle layer (lip - orbicularis oris; cheek - buccinator), inner mucosa layer
- muscle layer of both lip and cheek are innervated by the facial nerve (VII)
Sensory nerve endings in papillae of both lip and cheek are terminals of the trigeminal nerve (V)
Lip and cheek help to push food into the space between the teeth and tongue
LIP: (2 faces)
Þ hair, sebaceous and sweat glands, papillae
mucosa (innermost) Þ strat squam epith; lies on loose connect tiss; highly sensitive; salivary glands (lubricates bolus)
differs from cheek by presence of a red area (transitional area between the skin and mucosa)
- has tall dermal papillae containing vascular network and nerve endings
- the covering epithelium contains eleidin making it translucent, allowing the red color of blood to show thru
CHEEK:
- similar to mucosa of lip except it contains a lot of fat and elastic bands (folded bands, closely packaged)
The Hard and Soft Palate
Separate the oral cavity from nasal cavity (permanently by hard palate; momentarily by soft palate during swallowing, phonation and fright)
On nasal side: both palates covered by pseudostratified ciliated columnar epithelium with goblet cells; glands are of mixed type (both mucous and serous)
On oral side: soft palate – non-keratinized stratified squamous epith; hard palate – keratinized stratified squamous epith; glands are purely mucous
Mucous membrane consists of epithelium and underlying lamina propria (thin layer of loose connective tissue)
- bound by a submucosa of dense connective tissue to the periosteum of bone in the hard palate
- bound by a submucosa of dense connective tissue to the perimysium of muscles of the soft palate
Anterior 1/3 of the hard palate, on oral side, consists of fat rather than glands Þ shock absorber
The Tongue
Most mobile organ in body Þ large mass of muscle fibers enclosed in an epithelial bag packed with connective tissue
Muscles of the Tongue:
Intrinsic Muscle Group: superior longitudinal, inferior longitudinal, transverse, horizontal lingual muscles
Extrinsic Muscle Group: connects the tongue to the mandible (genioglossus), to the hyoid bone (hyoglossus), to the styloid process (styloglossus), and to the soft palate (palatoglossus)
Muscles supplied by myomotor fibers of the hypoglossal nerve (XII); except the palatoglossus (accessory nerve - XI)
Sensory fibers to all muscles are from the trigeminal nerve (V)
Epithelium of the tongue:
Covered by non-keratinized (ventral side) stratified squamous epithelium
Foramen cecum and Sulcus terminalis Þ divide tongue into anterior and posterior parts
Posterior: root of tongue
Þ prominent aggregations of lymphoid tissue Þ lingual tonsils (first line of defense)
Palatine tonsils (bigger and more differentiated)
Anterior: body of tongue
Þ coated with 3 types of papillae (also folate papillae – ridges on side of tongue)
filiform papillae: most numerous, evenly distributed, projections of mucosa throwing epithelium into secondary projections
fungiform papillae: less numerous, larger with a bulging, flattened top which may contain taste buds
circumvallate papillae: 9 - 12, shaped like fungiform, but larger and surrounded by a trench, arranged in V-shape pointing posteriorly, taste buds (~250) found in the epithelium of the wall and trench
Taste Buds:
Also found in mucosa of soft palate, epiglottis and pharynx
Pale, oval bodies extending from basement memb up to a tiny opening at the surface, contain a short protruding "taste hair" and attach to branches of the VII (facial) or IX (glossopharyngeal) cranial nerves
Neuroepithelial cells of taste buds regenerate from basal cells
Sweet and salty Þ tip of tongue; sour Þ sides of tongue; bitter Þ base of tongue
Serous and mucous glands:
Scattered thru the tongue, on inner surface of lip, and throughout the mucosa of the mouth
Serous cells: pyramidal, with nucleus in basal part of cell, cell boundaries are indistinct, cytoplasm contains zymogen granules (precursors of the enzymes ptyalin and maltase)
Mucous cells: nucleus is situated flat against the base of the cell, produce a viscid fluid consisting mainly of mucin
Both cells contribute to the fluid secretion of the mouth Þ saliva
Saliva:
99.5% water, containing mucin and the enzymes ptyalin (salivary amylase) and maltase Þ digest starches
Produce one liter of saliva per day
Serves to keep mouth moist between meals and lubricates food Þ bolus for easy swallowing
Salivary Glands
Major salivary glands: parotids (anterior to ears), submandibular (near angle of mandibles), sublingual (beneath tongue)
Minor salivary glands: labial (in lip), anterior lingual, buccal (in cheek), palatine (in soft palate)
Structure:
Salivary glands may be encapsulated by connective tissue, which send septa into the interior of the organ, subdividing it into lobules (large blood vessels, large ducts, and nerves may be found within the interlobular septa)
All salivary glands are acinar, compound and composed of interlobular and intralobular ducts
- interlobular ducts
= excretory ducts
Þ columnar or stratified squamous epith Þ surrounded by connective tissue
intralobular ducts (inside the lobule) = striated/secretory and intercalated ducts Þ no connective tissue associated
- striated duct = simple tall columnar epith; round, central nuclei and many mito. close to a folded cellular memb
- intercalated duct = simple cuboidal epith
acini or alveolar cells = produce isotonic secretion that is modified as it passes thru the ducts Þ hypotonic secretion
- serous
(basophilic cytoplasm, orange-pink secretory granules)
- mucous
(larger, rather pale-staining and have dense, flattened, basally-placed nucleus)
ducts become smaller as they branch
Þ secretory duct (striated) Þ intercalated duct (abundant) Þ acini (mucous or serous)
2 capillaries exist: one around the alveolar/acinar cells and another around the ducts
Myoepithelial cells are often found between the glandular cells and the basement memb
- they are contractile, facilitating the movement of the secretion into the duct system
Innervation:
sympathetics come from superior cervical ganglion Þ vasoconstriction and scanty mucous secretion
parasympathetics come in with cranial nerve IX (glossopharyngeal) and the chorda tympani branch of VII (facial) and synapse within the gland Þ vasodilation and copious watery secretion
Parotid Gland:
Gland is encapsulated; characterized by numerous fat cells; Lymphatic nodules are occasionally present
Stenson’s duct = single terminal duct (lined with pseudostrat columnar epith) that empties into mouth at maxillary 2nd molar
As the duct penetrates deeper into the gland Þ interlobular or excretory ducts (simple, columnar epith surrounded by connective tissue) Þ branches into striated duct (reabsorb sodium from saliva and excrete potassium into it forming a hypotonic secretion) Þ intercalated ducts (relatively long)Þ terminal alveolus (SEROUS ONLY!!)
affected by aldosterone (sodium-saving hormone) and ADH (anti-diuretic hormone)
Submandibular or Submaxillary Gland:
Gland is encapsulated; Characterized by its pale staining; very eosinophilic and have a prominent lumen
Warton’s duct (excretory; opens into mouth beneath tongue) Þ striated (quite abundant)Þ intercalated (very short and hard to find)Þ acinar (MIXED!!: small pale groups of mucous cells interspersed among the predominate serous alveoli)
Frequently the mucous acini are "capped" by a crescent of serous cells Þ serous demilunes
Sublingual Gland:
Gland is unencapsulated! Þ not a single entity but a collection of glands surrounded by a connective tissue capsule
Several small ducts come from this gland Þ opens into the mouth under the tongue
Excretory duct (simple columnar epith) Þ striated duct and intercalated duct (rare and extremely short, or absent) Þ acinar cells (almost entirely mucous-secreting!!;a few serous cells)
von Ebner’s Salivary Glands of the Tongue:
The only pure serous minor salivary glands in the mouth
Located in relation to the circumvallate papillae of the tongue, main ducts open into the "moat" that surround each papilla
Wash and cleanse the taste buds constantly
Labial Salivary Glands:
Present on the inner side of the lip
Extremely abundant and pure mucous in nature