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Digestive system
By
Dr. Sara Mohammed Naguib Lecturer of histology
Minia university
2017
Oral Cavity
The oral cavity is specialized for sensory
discrimination (taste), mechanical processing
(chewing), initial lubrication, enzymatic
digestion (salivary secretion), and immune
surveillance (tonsils), with a protective
stratified squamous epithelium throughout.
The entire oral cavity is lined by a
stratified squamous epithelium. The
epithelial lining is divided into two broad
types
Masticatory epithelium covers the surfaces involved in the processing of food (tongue, gingivae and hard palate). The epithelium is keratinized to different degrees depending on the extent of physical forces exerted on it.
Lining epithelium, i.e. non-keratinized stratified squamous epithelium, covers the remaining surfaces of the oral cavity
Lips
When we think of lips we usually only think of a small part, of the "anatomical" lips, which surrounding the oral orifice. The outside and inside of the lips are lined by skin and oral mucosa respectively. Between the two, we find labial vessels, nerves, the orbicularis oris muscle (striated), which shapes the lips, and labial salivary glands.
The vermilion border is the area of transition from the skin to the oral mucosa. The epithelium is somewhat thicker than in other parts of the facial skin. Connective tissue papilla extend deep into the epithelium and are heavily vascularized. It is the proximity of these vessels to the surface of the epithelium which gives the pro-labium its red appearance.
Tongue
The tongue provides excellent opportunities for
learning histology, with examples of all the
basic tissue types appearing in a variety of
forms.
-The bulk of the tongue consists of interlacing
striated muscle fibers in three different planes
→ complex movements, connective tissue and
bundles of myelinated nerve fibers within the
muscle. Also, the surface of the tongue is
covered by stratified squamous epithelium.
The dorsal surface of the tongue is divided by the
sulcus terminalis into
An oral part, the anterior two-thirds, and and a
pharyngeal part, the posterior one-third.
The mucosa covering the upper surface of the
tongue is thrown into numerous projections called the
lingual papillae which consist of a connective tissue
core covered with a stratified squamous epithelium.
On the basis of their appearance four types of
papillae can be distinguished:
filiform, fungiform, circumvallate and foliate papillae.
Taste bud: consists of:
Receptor cells: each has microvilli in the taste pore at its apical end. These allow contact with the external medium. At the basal end, each sensory cell makes synaptic contact with fibers of the facial nerve (VII) or glossopharyngeal nerve (IX).
Sustentacular cells: Those surround a tiny taste pore.
Basal cells: renew both of these types of cell.
Chemicals stimulate the receptors, and initiate impulses in the afferent nerve fibers
Digestive system:
1. Digestive tract
2. Associated glands
salivary gland
pancreas
liver
General Histology of the Alimentary Canal
Mucosa (tunica mucosa): innermost 3 layers surrounding
lumen
Epithelium: may be a wet surface epithelia stratified
squamous epithelium or simple columnar epithelium.
Lamina propria: loose CT that may contain glands as in
fundus, pylorus, and intestinal crypts.
Muscularis mucosa: thin layer smooth muscle → movement
in mucosa. It may run up into villi
Submucosa: loose CT, may contain glands (as esophagus & duodenum) and Meissner's nervous plexuses.
Musculosa: two or more muscle layers: inner circular may be modified in sphincters & outer longitudinal, Auerbach's plexus between muscle layers → independent peristaltic action.
Serosa (Adventitia): irregular dense CT surrounded by mesothelium (serosa) or bound to body wall (adventitia).
Digestive system:
1. Digestive tract
2. Associated glands
salivary gland
pancreas
liver
Types of salivary glands:-
Major salivary glands:
parotid, sublingual, and submandibular salivary glands.
Minor salivary glands:- they are scattered under oral
mucosa. Saliva is produced by secretory units and is
conducted to the oral cavity by short ducts. They include
buccal, labial, palatal and lingual glands.
Salivary glands
Compound tubuloalveolar glands
Saliva has many functions:
Dissolves foods to be tasted and swallowed.
Moistening and lubricating the oral mucosa.
It contains amylase that digest starch.
Has antibacterial activity.
Structure of salivary glands
Stroma
Parenchyma
Stroma is formed of :
Connective tissue capsule surrounds the whole gland. They
send septae.
Connective tissue septae ( trabeculae) that subdivide the
glands into lobes and lobules.
Reticular network form the background of the gland.
Parenchyma:- includes
Secretory acini ( serous, mucous and mixed
mucoserous acini)
Excretory ducts.
Difference between serous , mucous and mixed acini
Difference between serous , mucous and mixed acini
They exhibit the
secreting cells
They exhibit the characters of polarized protein
secreting cells
mucus-secreting cells criteria
Myoepithelial ( basket) cells They are thin and spindle-shaped and situated between
the basement membrane and epithelial cells of the acini
and the initial portion of the duct system. myoepithelial
cells can contract and press on the acinus, facilitating
release of the secretory product into the duct.
Duct system of salivary gland
Major salivary gland
Different between serous and mucous acini
serous mucous
Diameter
Lumen
Epithelial lining
Cell boundary
Nuclei
Cytoplasm
Secretion
Basket cells
Different between parotid, sublingual and submandibular
Site
Capsule
Acini
Opening of duct