Department of Anatomy &Histology
Dr.Raja Ali
Digestive System:
Taste buds: are present on fungiform, foliate, and circumvallate papillae.
In histologic sections, taste buds appear as oval, pale-staining bodies
that extend through the thickness of the epithelium . A small opening onto the
epithelial surface at the apex of the taste bud is called the taste pore, Fig.( 1 ).
Three principal cell types are found in taste buds:
• Neuroepithelial (sensory) cells are the most numerous cells in the taste bud.
These elongated cells extend from the basal lamina of the epithelium to the
taste pore, through which the tapered apical surface of each cell extends
microvilli . Near their apical surface they are connected to neighboring
neuroepithelial or supporting cells by tight junctions. At their base they form
a synapse with the processes of afferent sensory neurons of the facial (cranial
nerve VII), glossopharyngeal (cranial nerve IX), or vagus (cranial nerve X)
nerves.
• Supporting cells are less numerous. They are also elongated cells that extend
from the basal lamina to the taste pore. Like neuroepithelial cells, they contain
microvilli on their apical surface and possess tight junctions, but they do not
synapse with the nerve cells.
• Basal cells are small cells located in the basal portion of the taste bud, near the
basal lamina. They are the stem cells for the two other cell types. Taste buds
are also present on the glossopalatine arch, the soft palate, the posterior
surface of the epiglottis,
and the posterior wall of
the pharynx down to the
level of the cricoid
cartilage.
Fig.( 1 ):schematic
&histological section of taste
buds
Taste is a chemical sensation in which various chemicals elicit stimuli
from neuroepithelial cells of taste buds.
The lingual tonsil consists of accumulations of lymphatic tissue at the base of
the tongue.
The complex nerve supply of the tongue is provided by cranial nerves and
the autonomic nervous system.
Fig.(2): Tooth.
Esophagus: (Fig.3).
 The esophagus is a fixed muscular tube that delivers food and liquid
from the pharynx to the stomach.
 Courses through the neck and mediastinum , where it is attached to
adjacent structures by connective tissue.
 As it enters the abdominal cavity, it is free for a short distance,
approximately 1 to 2 cm.
 The overall length of the esophagus is about 25 cm.
 On cross section , the lumen in its normally collapsed state has a
branched appearance because of longitudinal folds.
 When a bolus of food passes through the esophagus, the lumen
expands without mucosal injury.
 The mucosa has a nonkeratinized stratified squamous epithelium .
 lamina propria is similar to the lamina propria throughout the
alimentary tract;
 The muscularis mucosae, is composed of longitudinally organized
smooth muscle that begins near the level of the cricoid cartilage.
 The submucosa dense irregular connective tissue that contains the
larger blood and lymphatic vessels, nerve fibers, and ganglion cells
(Meissner’s plexus).
 Glands are also present (sub –mucosal esophageal gland).
 The muscularis externa consists of two muscle layers, aninner
circular layer and an outer longitudinal layer (between them the
myenteric plexus (Auerbach’s plexus), is present).
 The esophagus is fixed to adjoining structures throughout most of its
length; thus, its outer layer is composed of adventitia.
 After entering the abdominal cavity, the short remainder of the tube is
covered by serosa, the visceral peritoneum.
 Mucosal and submucosal glands of the esophagus secrete mucus to
lubricate and protect the luminal wall.
 Glands: present in the wall of the esophagus are:
 Esophageal glands proper :
 Lie in the submucosa.
 Are scattered along the length of the esophagus , more concentrated in
the upper half.
 They are small, compound, tubuloalveolar glands (Fig.3).
 The excretory duct is composed of stratified squamous epithelium .
• Esophageal cardiac glands
 Are named for their similarity to the cardiac glands of the stomach .
 Found in the lamina propria of the mucosa.
 They are present in the terminal part of the esophagus.
 Those glands near the stomach tend to protect the esophagus from
regurgitated gastric contents.
Fig.(3):histological section through the esophagus.