DIGESTIVE SYSTEM

consists of:

Muscular, hollow tube (= “digestive tract”)

+

Various accessory organs

Histological Organization

Tube made up of  four layers.

Modifications along its length as needed.

The 4 Layers of the Gut

1) Mucosa

Epithelium –            usually simple columnar with goblets; may be stratified squamous if protection needed

Lamina propria – connective tissue deep to epithelium

Muscularis mucosae -produces folds – plicae (small intestine) or rugae  (stomach)

2) Submucosa – made up of loose connective tissue contains submucosal plexus and blood vessels

3) Muscularis externa – smooth muscle, usually two layers (controlled by the myenteric plexus ) –

outer layer: longitudinal

inner layer: circular

4) Serosa

visceral layer of mesentery or adventitia depending on location

Oral cavity

•         Mouth & its structures i.e. tongue, teeth, gums, major & minor salivary glands & tonsils (Waldeyer’s ring)

Two parts

•         Vestibule

•         Oral cavity proper

Mucosal lining of oral cavity

1. Masticatory mucosa — gingiva & hard palate (keratinized & parakeratinized Ep)

•         Parakeratinized Ep.—superficial cells donot lose their nuclei (pyknotic)& cytoplasm does not stain intensely with eosin

•         Keratinized epithelium resembles skin but lack st. lucidum

•         Lamina propria has papillary & reticular layer

2. Lining mucosa

•         Found on lips, cheek, alveolar mucosal surface, floor of mouth,  inferior surfaces of tongue & soft palate

•         At these sites covers striated muscle, bone & glands

•         Fewer & shorter papillae so that it can adjust to movements of muscles

•         Epithelium is non keratinized or parakeratinized

•         Non keratinized lining ep. Is thicker than keratinized ep. & has three layers

•         St. basale, spinosum, superficial layer

•         Submucosa present except on inner surface of tongue

3. Specialized mucosa

•         Restricted to dorsal surface of tongue where it contains papillae & taste buds

LIP

Subdivided into three regions

1. External region (St Sq. keratinized ep.) epidermis beneath which is dermis
2. Transitional/Vermillion zone
3. Internal region (St Sq. non keratinized ep.) wet mucosa

External surface (Cutaneous area )
Epidermis
Dense irregular C.T (Sebaceous & Sweat glands & Hair follicles

Internal surfaceInner region (oral mucosa):
Epithelium
Lamina propria having minor labial salivary glands
Occasional non functiong sebaceous gland

Vermillion Zone (Red areaThe vermilion is composed of non keratinized squamous epithelium with thick st. lucidum and tall papillae of underlying dermis that covers numerous capillaries, which give the vermilion its characteristic color.
Hair follicles, sebaceous & sweat glands are located throughout the lip skin; however, these structures are absent in the vermilion

PALATE

Hard palate: oral aspect – St sq. parakeratinized to keratinized ep

•         Bony shelf to which bundles of collagen fibers are attached

•         In midline of hard palate —  No submucosa; Lamina propria merges with Periosteum

•         Where there is submucosa on hard palate adipose tissue & mucous glands are present

Soft palate: oral aspect – St sq. non keratinized ep

•         Core of skeletal m

•         Minor salivary glands

Dorsum of Tongue

Surface of tongue – Mucosa

Epithelium

•         Dorsal surface: St sq. parakeratinized to partly keratinized ep

•         Ventral surface: St sq. non keratinized ep

Lamina propria

Core

•         Submucosa: Dense irregular C.T

•         Striated Muscular core-transverse, longitudinal & vertical m

•         Minor salivary glands

DORSAL SURFACE OF TONGUE (ANT 2/3RD ) LINGUAL PAPILLAE

1. Filiform (thread Like) Papillae

•         Numerous & smallest

•         Covered by keratinized ep.

•         No taste buds

•         Distributed over entire surface

2.   Fungiform papillae

•         Mushroom shaped

•         Scattered singly among filiform

•         More abundant at tip

•         Covered by non keratinized ep.

•         Few taste buds are present

Foliate papillae

Present in rabbits

Circumvallate papillae

•         Infront of sulcus terminalis (8-12)

•         Large & round

•         Surrounded by a trench

•         Non keratinized ep.

•         Many taste buds present

Taste buds

•         Tongue, soft palate & laryngeal surface of epiglottis

•         Oval, pale staining (30-50um wide)

•         Long axis extend through full thickness of epithelium

•         Apex communicate with oral cavity through gustatory pore

•         Tongue, soft palate & laryngeal surface of epiglottis

•         Oval, pale staining (30-50um wide)

•         Long axis extend through full thickness of epithelium

•         Apex communicate with oral cavity through gustatory pore

•         3 types of cells

•         Neuroepithelial cells- tall columnar cells with sterocilia; function as sensory receptors & nerve fibers terminate here

•         Sustentacular cells- tall columnar cells with sterocilia & dense secretory granules in apical cytoplasm function as supporting cells

•         Basal cells– small (stem) cells located at periphery of taste buds close to basal lamina

Glands of tongue

•         Anterior lingual glands are mixed type (tip), embedded in muscle & ducts open on ventral surface

•         Von Ebner glands are pure serous type, ducts open in trenches of circumvallate  papillae

•         Mucous glands of root lie in posterior 1/3rd of tongue, ducts open into crypts of lingual tonsil

GUMS

•         St. sq keratinized ep to variable extent

•         Lamina propria bearing tall papillae having rich capillary plexus

•         Coarse collagen fibers that bind gums to alveolar bone

•         No submucosa or glands

For better understanding,

Stomach

Histological slides of lip

Histological slides of tongue

Histological slides of esophagus