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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